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Catálisis para el Medioambiente y la Energía

Grupos de Investigación:

  • Fotocatálisis Heterogénea: Aplicaciones
  • Materiales y Procesos Catalíticos de Interés Ambiental y Energético (web)
  • Química de Superficies y Catálisis

Catedráticos

Caballero Martínez, Alfonso

caballero@us.es

954 48 95 38

Grupo de Investigación:
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Navío Santos, José Antonio

navio@us.es

954 48 95 50

Grupo de Investigación:
Fotocatálisis Heterogénea: Aplicaciones

Odriozola Gordón, José Antonio

odrio@us.es

954 48 95 44

Grupo de Investigación:
Química de Superficies y Catálisis

Investigadores Científicos

Centeno Gallego, Miguel Angel

centeno@icmse.csic.es

954 48 95 43

Grupo de Investigación:
Química de Superficies y Catálisis

Colón Ibáñez, Gerardo

gcolon@icmse.csic.es

954 48 96 26

Grupo de Investigación:
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Científicos Titulares

Hidalgo López, María del Carmen

mchidalgo@icmse.csic.es

954 48 95 50

Grupo de Investigación:
Fotocatálisis Heterogénea: Aplicaciones

Holgado Vázquez, Juan Pedro

holgado@icmse.csic.es

954 48 95 36

Grupo de Investigación:
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Profesores Titulares

Domínguez Leal, María Isabel

mleal@icmse.csic.es

954 48 96 64

Grupo de Investigación:
Química de Superficies y Catálisis

Romero Sarria, Francisca

francisca@icmse.csic.es

954 48 96 64

Grupo de Investigación:
Química de Superficies y Catálisis

Investigadores/Doctores Contratados

Bobadilla Baladrón, Luis Francisco

bobadilla@icmse.csic.es

954 48 95 00 + ext. 90 92 18

Grupo de Investigación:
Química de Superficies y Catálisis

Ivanova Lyuvimirova, Svetlana

svetlana@icmse.csic.es

954 48 95 00 + ext. 90 92 18

Grupo de Investigación:
Química de Superficies y Catálisis

Laguna Espitia, Oscar

oscarh@icmse.csic.es

954 48 95 43

Grupo de Investigación:
Química de Superficies y Catálisis

Martínez Tejada, Leidy Marcela

leidy@icmse.csic.es

954 48 95 76

Grupo de Investigación:
Química de Superficies y Catálisis

Penkova, Anna Dimitrova

anna@icmse.csic.es

954 48 95 00 + ext. 90 92 18

Grupo de Investigación:
Química de Superficies y Catálisis

Pereñiguez Rodríguez, Rosa

rosa@icmse.csic.es

954 48 95 76

Grupo de Investigación:
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Becarios Predoctorales

Azancot Luque, Lola

lola.azancot@icmse.csic.es

954 48 95 00 + ext. 90 92 31

Grupo de Investigación:
Química de Superficies y Catálisis

Castillo Barrero, Rafael

r.castillo.b@icmse.csic.es

954 48 95 00 + ext. 90 92 22

Grupo de Investigación:
Química de Superficies y Catálisis

Jiménez Barrera, Elena


954 48 95 00 + ext. 90 92 22

Grupo de Investigación:
Química de Superficies y Catálisis

Navarro Jaén, Sara

sara.navarro@icmse.csic.es

954 48 95 00 + ext. 90 92 31

Grupo de Investigación:
Química de Superficies y Catálisis

Santos Muñoz, José Luis

josel.santos@icmse.csic.es

954 48 95 00 + ext. 90 92 30

Grupo de Investigación:
Química de Superficies y Catálisis

Personal Contratado

Blandón Évora, Laura

laura.blandon@icms.us-csic.es

954 48 95 00 + ext. 90 92 22

Grupo de Investigación:
Química de Superficies y Catálisis

López Martín, Ángeles María

angeles.lopez@icmse.csic.es

954 48 95 00 + ext. 90 92 25

Grupo de Investigación:
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Martín Gómez, Andrés Noel

andres.martin@icms.us-csic.es

Grupo de Investigación:
Fotocatálisis Heterogénea: Aplicaciones

Navarro De Miguel, Juan Carlos

jnavarro12@us.es

954 48 95 00 + ext. 90 92 22

Grupo de Investigación:
Química de Superficies y Catálisis

Platero Moreno, Francisco Jesús


954 48 95 00 + ext. 90 92 25

Grupo de Investigación:
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Diseño racional de fotocatalizadores altamente eficientes mediante control a nivel atómico



Investigador Principal: Gerardo Colón Ibañez
Periodo: 02-10-2007 / 01-10-2020
Organismo Financiador: Ministerio de Economía y Competitividad. Unión Europea
Código: RATOCAT (project4076)
Componentes: Alfonso Caballero Martínez, Angeles Martín

Resumen [+]

El uso de la energía solar para la generación de hidrógeno a partir de agua es probablemente uno de procesos más limpios y sostenibles para la obtención de energía. Sin embargo, los catalizadores que dan mejores rendimientos son demasiado caros para ser económicamente viables. El proyecto RATOCAT tiene como objetivo el desarrollo de materiales fotocatalíticos optimizados.    De esta forma las prestaciones fotocatalíticas de sistemas basados en TiO2 y gC3N4 podrían optimizarse mediante el diseño de su superficie con nanoestructuras de composición, nanoarquitectura, tamaño y estado químico altamente controladas. Se empleará para ello estudios de simulación teórica para proponer la nanoestructuras óptimas que serán depositadas de forma controlada y precisa mediante atomic layer deposition (ALD). Los test de actividad fotocatalítica tanto a escala de laboratorio como en planta piloto (Plataforma Solar de Almería).


Desarrollo de Materiales Foto-Funcionales para Aplicaciones Medioambientales



Investigador Principal: José Antonio Navío Santos
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: CTQ2015-64664-C2-2-P
Componentes: María del Carmen Hidalgo López, Manuel Macías Azaña

Resumen [+]

La fotocatálisis heterogénea es un proceso avanzado de oxidación que ha sido objeto de una enorme cantidad de estudios relacionados con la purificación de gases y del agua. La mayoría de estos estudios se han realizado para el tratamiento de aguas y utilizando el TiO2 o materiales basados en este óxido y más recientemente, aunque en una clara minoría, se han estudiado otros óxidos inorgánicos binarios, ternarios y cuaternarios, predominando en todo caso los estudios de estos últimos materiales para el tratamiento de aguas. En cuanto al catalizador (base del proceso fotocatalítico) que es el responsable de la eficacia o fracaso del proceso, en la última década se han desarrollado numerosos y variados métodos de síntesis que han sido principalmente probados en procesos de degradación fotocatalítica en fase acuosa. Sin embargo, pocos estudios se han realizado con óxidos mixtos ( binarios, binarios-acoplados, ternarios y cuaternarios) y menos en fase gasesosa.

En base a estas consideraciones y a la dilatada y reconocida experiencia que el grupo de este Subproyecto#2 tiene el campo de la síntesis y caracterización de materiales foto-funcionales (en el UV y UV/Vis), y debido al reducido número de estudios fotocatalíticos en fase gas, en su mayoría estudiando un sólo componente, se plantea en este Subproyecto#2, el desarrollo de materiales foto-funcionales que conduzcan a materiales basados no sólo en TiO2 con propiedades mejoradas sino a otros materiales basados en este óxido y a otros óxidos inorgánicos binarios, los obtenidos por acoplamientos de óxidos binarios y ternarios, que se obtengan por procedimientos de síntesis distintos (o modificados) a los ya recogidos en la bibliografía, y cuya fotoactividad sea evaluada por el grupo del Subproyecto#1, sin que se descarte ensayos previos de actividad fotocatalítica en agua por el grupo del Subproyecto#2.

Entre los materiales que se pretenden sintetizar en el Subproyecto#2 (empleando métodos no-hidrotermales, hidrotermales y sol-gel) se contemplan: óxidos binarios (TiO2, ZnO, ZnO2, Fe2O3, WO3, Bi2O3, Ta2O5 , La2O3), óxidos binarios acoplados (TiO2-WO3, TiO2-ZnO, TiO2-ZnO2; TiO2-Ta2O5, TiO2-La2O3, ZnO-Fe2O3 y ZnO2-Fe2O3), óxidos ternarios (Bi2WO6, Bi2WO6-ZnO, Bi2WO6-ZnO2, Bi2WO6-Fe2O3, Bi2Ti2O7, ZnWO4, La2Ti2O7), contemplando la foto-deposición de metales (Pt, Ag, Au) en los sistemas que muestren una actividad fotocatalítica considerable (Semiconductores/Metal).

Los mejores sistemas evaluados se remitirán al grupo del Subproyecto#1 para el estudio de la viabilidad fotocatalítica en la eliminación de NOx,COVs, CO, CO2 y SO2 presentes en emisiones gaseosas.


Sistemas Catalíticos Estructurados para la Producción de Biocombustible



Investigador Principal: José Antonio Odriozola Gordón
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: ENE2015-66975-C3-2-R
Componentes: María Isabel Domínguez Leal, Anna Dimitrova Penkova, Francisca Romero Sarria

Resumen [+]

La dependencia de nuestro actual sistema energético de las fuentes de combustibles fósiles y sus adversos efectos medioambientales están potenciando el desarrollo de fuentes de energía de origen renovable. Este es el caso de los biocombustibles de segunda generación. Los procesos de producción de combustibles a partir de biomasa lignocelulósica y residuos orgánicos son habitualmente catalíticos y se caracterizan por la necesidad de un intenso intercambio de calor asociado al elevado efecto térmico de las reacciones químicas implicadas, dificultad para minimizar simultáneamente las limitaciones difusionales y la caída de presión en los reactores convencionales de lecho fijo y, en ocasiones, por necesitar tiempos de contacto extremadamente cortos. Todo ello hace que las tecnologías catalíticas convencionales trabajen en condiciones no óptimas.

Los sistemas catalíticos estructurados, catalizadores estructurados y reactores de microcanales ofrecen excelentes oportunidades para superar estas limitaciones ya que permiten minimizar simultáneamente las limitaciones difusionales y la caída de presión, mejorar los flujos radiales de calor y materia y permitir tiempos de contacto muy cortos con elevadas eficiencias. Los monolitos de canales paralelos longitudinales, las espumas de porosidad abierta y las mallas metálicas son sustratos que pueden fabricarse a partir de numerosas aleaciones metálicas y con diferentes densidades de celda o poro. También pueden ser recubiertas de cualquier catalizador de interés, adaptándose así a los diferentes requerimientos de cada proceso. Por otro lado, los reactores de microcanales pueden proporcionar una intensificación del proceso sin igual que va acompañada de un excelente control de la temperatura, de la calidad de producto y con mejoras sustanciales en la seguridad del proceso.

El objetivo del proyecto es estudiar sistemas catalíticos estructurados para la producción de energía de origen renovable. En concreto, se estudiarán la síntesis de Fischer-Tropsch, la síntesis directa de dimetiléter y la producción del gas de síntesis que alimentará estos procesos mediante reformado de biogás y "producer gas".Además se estudiará la reacción de desplazamiento del gas de agua que resulta clave para el ajuste de la relación H2/CO en el gas de síntesis.

Se hará especial hincapié en la influencia de las características térmicas de los sistemas estructurados en su comportamiento catalítico. Para ello se estudiará el efecto de la densidad de celdas en monolitos, densidad de poros en espumas, luz de malla en mallas apiladas, tipo de aleación metálica, espesor del recubrimiento catalítico y geometría del sustrato (incluyendo en algunos casos reactores de microcanales).Se considerarán como fases activas catalizadores muy próximos al estado del arte.

El desarrollo de estos estudios se hará con el apoyo de tres tareas transversales lideradas por cada uno de los tres grupos participantes, pero en las que participarán todos ellos: la preparación de los sistemas catalíticos estructurados, la caracterización mediante técnicas avanzadas y los estudios de modelado y simulación. Mediante este proyecto se pretende generar un conocimiento que contribuya a expandir el actual campo de aplicación de los sistemas catalíticos estructurados hacia aplicaciones energéticas sostenibles que se verían beneficiadas por las ventajas que ofrecen estos sistemas en línea con el reto Energía segura, eficiente y limpia.


Desarrollo de procesos catalíticos y fotocatalíticos para la valorización del gas natural: activación y transformación de metano e hidrocarburos ligeros



Investigador Principal: Alfonso Caballero Martínez
Periodo: 1-01-2015 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: CTQ2014-60524-R
Componentes: Juan Pedro Holgado Vázquez, Gerardo Colon Ibáñez, Rosa María Pereñiguez Rodríguez, Alberto Rodríguez Gómez

Resumen [+]

  En el presente proyecto se pretenden realizar diversos estudios y desarrollos relacionados con distintos procesos de activación y transformación de metano en moléculas de más valor añadido. Con este fin se estudiarán tanto procesos bien establecidos de conversión indirecta, a través de reacciones de reformado (RM) para la obtención de gas de síntesis, como distintos procesos de conversión directa, en concreto la oxidación directa a metanol (DOM) y la aromatización de metano (DAM).

    En lo que respecta a la reacción de reformado, se plantea el desarrollo de sistemas catalíticos con resistencia mejorada a los procesos de desactivación. Para ello se prepararán y caracterizarán nuevos catalizadores bimetálicos nanoestructurados de niquel depositados en soportes como ceria, alumina y alumina/ceria, así como soportes mesoporosos de tipo SBA-15, dopados con ceria y alumina. Como segundo metal se utlizarán cobalto o hierro. Paralelamente, se realizará un estudio de la reacción de reformado por vía fotocatalítica utilizando sistemas de Cu, Pt y Ni depositados en soportes activos clásicos como titania o ceria, así como otros de más reciente desarrollo, como son Ga2O3, nitruro de carbono o grafeno. En este caso, se pretende igualmente explorar las posibilidades de la activación fotoquímica para la reacción de oxidación preferencial de CO (foto-PROX) en presencia de hidrógeno, de utilidad en los procesos de purificación de hidrógeno procedente del gas de síntesis. Se incidirá en la preparación de sistemas con una estructura de de bandas apropiada para el control de esta oxidación selectiva de CO.

     En cuanto a los procesos de conversion directa, se estudiará la reacción de DOM usando O2, H2O2 o N2O como activadores de la reacción, en combinación con sistemas basados en Au/Pd, Fe, Cu y/o Ni depositados en soportes como zeolitas ZSM-5, grafeno y TiO2. En este último caso, utilizando Au/Pd como fase metálica activa en presencia de H2O2 como especie oxidante se planteará la posibilidad de combinar la síntesis in situ de agua oxigenada con la posterior oxidación directa de metano. Igualmente, se explorará el proceso de oxidación fotocatalítica de metano a metanol como una alternativa novedosa y altamente atractiva. En este caso, el uso de nuevos fotocatalizadores de oxidación como el BiVO4 así como la presencia de mediadores redox permitirán controlar la oxidación selectiva a metanol.

    Algunos sistemas estrechamente relacionados con los anteriores, y en particular los basados en Mo soportados en zeolitas ZSM-5 y MCM-22, se utilizarán para el estudio de la reacción de aromatización de metano. La proporción de aluminio, el porcentaje de molibdeno y su activación en la estructura microporosa del soporte, así como la adición de promotores como Ga, Tl o Pb serán algunas de las variables a optimizar para esta reacción. De forma paralela se podrá estudiar el proceso de aromatización fotoinducido, recientemente descrito por algunos autores.


Desarrollo de catalizadores biomórficos obtenidos a partir de biomasa residual para producción de hidrógeno y refino de bio-oil



Investigador Principal: Miguel Angel Centeno Gallego
Periodo: 1-01-2014 / 31-12-2017
Organismo Financiador: Ministerio de Economía y Competitividad
Código: ENE2013-47880-C3-2-R
Componentes: María Isabel Dominguez Leal, Carlos López Cartes, Leidy Marcela Martínez Tejada, Svetlana Ivanova

Resumen [+]

El objetivo principal del presente proyecto coordinado entre las universidades de Zaragoza y el Instituto de Ciencias de Materiales de Sevilla es el desarrollo de catalizadores metálicos soportados en carbones biomórficos (CB), para su posterior aplicación a procesos de producción de hidrógeno y de refino de bio-oil. La técnica de Mineralización Biomórfica es una innovadora herramienta capaz de sintetizar materiales inorgánicos funcionales utilizando como plantilla diversas estructuras formadas en procesos biológicos. Así, a partir de materiales lignocelulósicos (biomasa) se puede preparar una gran variedad de materiales cerámicos microestructurados. No obstante, la replicación de los distintos niveles jerárquicos existentes en los tejidos biológicos sigue siendo un gran reto a día de hoy. Para avanzar en esta línea, en este proyecto se va a abordar el estudio de la síntesis, caracterización y aplicación de catalizadores metálicos soportados en carbón biomórfico (Me/CB), con distribuciones de tamaño homogénea y porosidad jerarquizada.
La preparación de estos materiales se realiza mediante descomposición térmica en atmósfera reductora (o inerte) a alta temperatura, y elevadas velocidades de calentamiento, de un material lignocelulósico (e.g. celulosa, lignina, papel) impregnado con los precursores metálicos catalíticos. De esta manera, en una sola etapa, se obtiene un soporte carbonoso biomórfico con nanopartículas de metal dispersas en su superficie. Este método de síntesis presenta una extraordinaria versatilidad, puesto que además de poder utilizar diferentes materias primas de partida, se pueden obtener catalizadores de muy distintas composiciones y contenidos metálicos, así como su estructuración en dispositivos monolíticos y espumas. Como materias primas, además de celulosa, lignina o papel, se van estudiar biomasas agrícolas residuales.
Los catalizadores tipo Me/CB se pretenden aplicar en procesos de producción de hidrógeno (descomposición de hidrocarburos ligeros, de amoniaco y deshidrogenación de ácido fórmico), en la reacción de Water-Gas-Shift (WGS), y en distintas reacciones test de refino de bio-oil (conversión de acético a acetona, hidrogenación de vainillina y ciclohexeno y conversión de m-cresol a fenol).
 


Aprovechamiento de CO2 para la obtención de gas de síntesis en catalizadores



Investigador Principal: Miguel Angel Centeno Gallego
Periodo: 01-02-2013 / 31-01-2017
Organismo Financiador: Junta de Andalucía
Código: P11-TEP-8196 (Proyecto de Excelencia)
Componentes: Svetlana Ivanova, Maria Isabel Domínguez Leal, José Antonio Odriozola Gordón, Tomás Ramírez Reina, Francisca Romero Sarria

Resumen [+]

Hoy en día no existen dudas acerca de que la concentración de gases de efecto invernadero, en particular la de CO2, está aumentando de manera considerable en la atmósfera terrestre. Para evitar este aumento continuado se debe aumentar la eficiencia en la producción de energía, disminuir la intensidad del uso de las fuentes fósiles y, finalmente, potenciar la captura y secuestro del CO2. Todo esto debe conseguirse manteniendo el crecimiento económico y la calidad de vida. En consecuencia, si tenemos en cuenta el desarrollo de las naciones menos industrializadas y el intensivo consumo energético necesario para aumentar su nivel de vida, la captura y secuestro de CO2 parece la alternativa más favorable.
En el presente proyecto se propone la utilización del CO2 como materia prima para el reformado de gas natural como paso previo a la obtención de combustibles líquidos sintéticos. Usando tecnologías convencionales, esta propuesta sólo es económicamente viable asociada a grandes reservas de gas natural. Sin embargo, la tecnología de microcanales permite abordar la síntesis de combustibles sintéticos de forma discontinua y con capacidad de producción flexible de modo económicamente viable. Para ello, es necesario el diseño, caracterización y ensayo de catalizadores activos, selectivos y estables en la reacción de reformado de metano con vapor y CO2:

CO2 + 3CH4 + 2H2O  → 4CO + 8H2

La selección de estos catalizadores culminará con la estructuración de los mismos utilizando soportes metálicos con microcanales paralelos (micromonolitos) a fin de establecer las condiciones necesarias para, en un futuro, la construcción de reactores de microcanales.


Aprovechamiento de gas no convencional: Reactores de microcanales en GTL



Investigador Principal: José Antonio Odriozola Gordón
Periodo: 01-01-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: ENE2012-37431-C03-01
Componentes: Svetlana Ivanova, Anna Dimitrova Penkova, Tomás Ramírez Reina, Sandra Palma del Valle, Ara Muñoz Murillo, María Isabel Domínguez Leal, Francisca Romero Sarria

Resumen [+]

Existen en la actualidad fuentes de gas que podríamos agrupar bajo el calificativo de no-convencional que incluyen el que se encuentra confinado en formaciones geológicas de baja permeabilidad, el gas asociado al crudo, los pequeños yaciemientos en lugares remotos, el biogas producido en la digestión anaerobia de residuos y los denominados product gas generados en la gasificación de biomasa y en la combustión de alquitran. La composición de todas estas fuentes de gas es similar estando constituidas por una mezcla de metano y dióxido de carbono con cantidades inferiores de otros gases permanentes. La concentración de CO2 puede llegar a ser de hasta el 40% en volumen como ocurre con el gas asociado de algunos campos off-shore y el biogas producido por fermentación de residuos agrícolas. La valorización de este gas mediante el proceso GTL (Gas to Liquid) es una alternativa cuando su localización remota o distante de los gaseoductos no permite ser agregado a las fuentes convencionales o no puede ser consumido in situ, ya que los combustibles líquidos son más fáciles de almacenar y transportar y tienen aplicación directa en el transporte.
La tecnología GTL convencional no es aplicable ya que su viabilidad económica exige instalaciones y suministros a una escala elevadísima. Por ello, se está desarrollando esa misma tecnología en reactores de microcanales de pared catalítica que consiguen incrementar de forma notable el rendimiento de las unidades de producción de gas de síntesis y síntesis de Fischer-Tropsch (SFT), al poder trabajar con elevadas velocidades espaciales, mejorando el control de la temperatura y con ello de la selectividad y la seguridad del proceso; además, la naturaleza modular basada en la replicación de unidades simplifica de forma considerable el escalado del proceso, adaptándose bien a unidades de producción de gas no convencional que, por lo general, no son grandes.
En el presente proyecto se pretende desarrollar la tecnología de microcanales para el proceso GTL utilizando mezclas metano-dióxido de carbono para simular las fuentes de gas no convencional. Los estudios que hemos venido realizando sobre reactores de microcanales deberán ampliarse a condiciones de presión y temperatura más drásticas, lo que debe permitir validar y mejorar la selección de materiales para la construcción y las técnicas de unión.
La aplicación de esta tecnología requiere el desarrollo de nuevos catalizadores activos, selectivos y estables que se adapten a los procesos GTL en reactores de microcanales. Se diseñarán catalizadores para el reformado al vapor, el reformado seco y la oxidación parcial de metano para la producción de gas de síntesis, así como catalizadores SFT. Se construirán reactores de microcanales para el ensayo de dichos catalizadores, se obtendrán las ecuaciones cinéticas de los catalizadores seleccionados y se modelarán y simularán los reactores construidos.
 


Desarrollo de sistemas catalíticos nanoestructurados preparados mediante métodos sol-gel y de deposición fotoquímica para aplicaciones energéticas y medioambientales (NanoFotoCat)



Investigador Principal: Alfonso Caballero Martínez
Periodo: 01-01-2012 / 31-12-2014
Organismo Financiador: Ministerio de Ciencie e Innovación
Código: ENE2011-24412
Componentes: Gerardo Colón Ibáñez, Juan Pedro Holgado Vázquez, Sergio Obregón Alfaro, Rosa María Pereñiguez Rodríguez, Fátima Ternero Fernández

Resumen [+]

En el presente proyecto se plantea el desarrollo de una serie de catalizadores nanoestructurados basados en metales de transición tales como Ni, Cu, Au o Pd, y depositados en soportes activos (TiO2, CeO2, WO3, Fe2O3 y soportes mesoporosos como SBA-15 dopado con titania y ceria). Se utilizarán métodos de preparación convencionales (impregnación, deposición-precipitación, etc.), junto con procedimientos de síntesis de desarrollo más reciente, como métodos sol-gel y, muy especialmente, el denominado Fotodeposición Asistida Fotoquímicamente (Photochemical Assisted Deposition, PAD). De esta forma, esperamos controlar de manera rigurosa a la escala nanométrica tanto el tamaño de la partícula metálica y/o bimetálica, como la interacción metal-soporte. En el caso concreto del método PAD, uno de los objetivos principales del proyecto es el estudio y la optimización de las variables del proceso de deposición de manera que, además de controlar el tamaño de la partícula metálica desde diámetros en torno a 15nm hasta sistemas atómicamente dispersos sobre soportes activos como ceria o titania, nos permita diseñar la distribución de los metales en la partícula metálica, haciendo uso de procesos controlados de fotodeposición consecutivos y/o simultáneos de los metales. Esta metodología debe permitir la obtención de distribuciones metálicas de tipo core-shell o aleadas, lo que como es conocido, puede llegar a afectar de manera fundamental a las prestaciones catalíticas. Estas prestaciones serán comprobadas en diferentes reacciones de interés energético y/o medioambiental, tanto en fase gas como en fase líquida. Así, los sistemas basados en niquel y oro se utilizarán en las reacciones de reformado húmedo y seco de metano (Steam and Dry Methane Reforming, SRM/DRM) y la oxidación selectiva de CO (Preferential Oxidation of CO, PROX), respectivamente. Los sistemas mono y bimetálicos basados en paladio y paladio-oro serán utilizados para la optimización de la reacción de síntesis directa de agua oxigenada a partir de hidrógeno y oxígeno, realizada en fase líquida a alta presión. La correlación entre el estado físico-químico y la reactividad de los sistemas catalíticos nos permitirá aclarar aspectos fundamentales de los mecanismos de las reacciones heterogéneas propuestas.


Materiales Foto-Activos para el desarrollo de la Energía Solar en Procesos Fotocatalíticos de Interés Medioambiental



Investigador Principal: José Antonio Navío Santos
Periodo: 1-01-2012 / 31-12-2012
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: CTQ2011-26617-C03-02
Componentes: Mª del Carmen Hidalgo López, Manuel Macías Azaña, Julie J. Murcia Mesa; Sebastián Murcia López

Resumen [+]

La fotocatálisis heterogenea ha mostrado sobradamente su potencial para destoxificación y desinfección de medios acuosos y gaseosos. Sin embargo, su desarrollo tecnológico ha sido muy limitado debido a una serie de dificultades que pueden agruparse en dos grupos principales:

1. Dificultades para separar el catalizador del medio al finalizar el proceso, para su reactivación y reutilización.

2. Bajo rendimiento del proceso, que sólo aprovecha un porcentaje muy pequeño de los fotones útiles, siendo estos además una pequeña parte del espectro natural.

En nuestra propuesta se coordinan tres subproyectos liderados por tres grupos que aunan amplia experiencia en: Síntesis, modificación y caracterización de materiales fotocatalíticos (principalmente el grupo de la Universidad de Sevilla), Preparación y caracterización de óxidos metálicos en lámina delgada sobre diferentes substratos(principalmente el grupo del CIEMAT) y Modificación, caracterización espectroscópica de centros activos y estudios de fotorreactividad en fase acuosa y gaseosa (principalmente el grupo de la ULPGC).

 

Sobre la base de esta experiencia acumulada y de las principales tendencias en el desarrollo de la fotocatálisisheterogénea, nuestro consorcio se plantea como objetivo central de este proyecto: Sintetizar materiales basados en TiO2, SnO2, ZnO y materiales ternarios tipo titanato de bismuto (BITs),  en forma de polvo con tamaño manométrico con alta actividad fotocatalítica y su fijación sobre sustratos adecuados (vidrio, membranas, láminas metálicas, etc.) recubiertos con películas delgadas de diferentes óxidos metálicos que faciliten el anclaje de estas partículas y/o actúen como semilla para la formación o cristalización de estas partículas, para poder utilizar estos sistemas de forma eficiente en procesos de descontaminación fotocatalítica en fase acuosa y gaseosa.


Desarrollo de nuevos procesos industriales basados en sistemas catalíticos para la obtención sostenible de ingredientes base en fragancias y aromas



Investigador Principal: Juan Pedro Holgado Vázquez
Periodo: 04-05-2011 / 31-12-2014
Organismo Financiador: Ministerio de Economía y Competitividad
Código: IPT-2011-1553-420000
Componentes: Alfonso Caballero Martínez, Víctor Manuel González de la Cruz, Rosa Pereñíguez Rodríguez, Gerardo Colón Ibáñez

Resumen [+]

En la actualidad, los procesos industriales utilizados para la transformación de muchos compuestos utilizados en el campo de las fragancias y los aromas ofrecen bajos rendimientos y generan una enorme cantidad de residuos peligrosos, que requieren varias etapas de segregación y tratamiento de los mismos durante el proceso. La mayor parte de estos procesos se basan en reacciones de oxidación/reducción de compuestos estequiometricos, o están basados en sistemas de catálisis homogénea, los cuales presentan inconvenientes asociados con la corrosión, la recuperación del catalizador de la mezcla de reacción y su regeneración para su posible reutilización. En este contexto “eco-amigable”, existe un interés creciente para el uso de oxidantes menos contaminantes, tales como el peróxido de hidrógeno o el oxígeno molecular, y la integración de dichos oxidantes en sistemas de catálisis heterogénea. Obviamente uno de los mayores retos que presentan las reacciones basadas en sistemas catalíticos es lograr el máximo rendimiento (producto de conversión por selectividad) con objeto de reducir el consumo de reactivos (materias primas), y minimizar los procesos de separación y eliminación de subproductos no deseados fruto de la ineficacia del proceso. En este tipo de reacciones (con compuestos principalmente orgánicos, muchos de origen natural), no es, en general, difícil obtener una alta conversión, pero dado que estos compuestos presentan multiples funcionalidades y/o puntos susceptibles de ser oxidados , el reto se centra en la obtención de una alta selectividad, generalmente incluso a nivel enantiomérico.

En el marco del proyecto, se han seleccionado procesos de interés en la industria cosmética y alimentaria, con objeto de conseguir el desarrollo a escala industrial de procesos basados en sistemas de catálisis heterogénea para la obtención de compuestos intermedios de gran valor añadido en el mercado de los perfumes y aromas, como son, entre otros, el proceso de obtención de la l-carvona a partir de la oxidación catalítica del d-limoneno.


Nuevos fotocatalizadores basados en compuestos de Bi3+ altamente fotoactivos en el visible



Investigador Principal: Gerardo Colon Ibáñez
Periodo: 11-03-2011 / 31-03- 2015
Organismo Financiador: Junta de Andalucía
Código: P09-FQM-4570
Componentes: M. Carmen Hidalgo López, José Antonio Navío Santos, Manuel Macías Azaña, Sebastián Murcia López

Resumen [+]

El objetivo principal de este proyecto es el desarrollo de una nueva generación de materiales nanoestructurados alternativos al TiO2 que presenten una alta fotoactividad en la región del visible y que puedan ser utilizados de forma competitiva y eficiente en procesos de tratamiento de efluentes líquidos y gaseosos mediante el aprovechamiento de la luz solar. El presente proyecto pretende desarrollar nuevos sistemas de nanocatalizadores heterogéneos basados en Bi3+ (Bi2WO4, Bi2MoO6, BiVO4, Bi3O4Cl, CaBi2O4, PbBi2Nb2O9,…) que presenten unas propiedades optoelectrónicas adecuadas para el aprovechamiento de la energía solar en el rango del visible (Fotocatálisis Solar) y que al mismo tiempo exhiban unas propiedades fisicoquímicas mejoradas que optimicen el proceso fotocatalítico desde el punto de vista de difusión y transferencia de portadores de carga fotogenerados.


Catalizadores nanoestructurados basados en Au para reacciones de oxidación selectiva



Investigador Principal: Juan Pedro Holgado Vázquez
Periodo: 1-01-2011 / 31-12-2011
Organismo Financiador: Ministerio de Ciencia y Tecnología
Código: CTQ2010-21348-C02-01
Componentes: Alfonso Caballero Martínez, Víctor Manuel González de la Cruz, Fátima Ternero Fernán-dez, Richard M. Lambert

Resumen [+]

El objetivo del proyecto es el desarrollo de catalizadores con base oro, con alta reactividad en los procesos de oxidación selectiva. En este contexto, se abordan reacciones tales como la oxidación selectiva del alcohol bencílico (y derivados) o la oxidación selectiva de CO.  esta última conectada con su aplicación en Catálisis Ambiental como es el control de la calidad del aire y en aplicaciones energéticas como la purificación de corriente de H2 procedente de procesos de reformado (PROX).

Las propiedades del oro, metal biocompatible y no tóxico, puede ser explotadas en catálisis cuando se usa en forma soportada y muy dispersa. Se pretende optimizar el rendimiento de los catalizadores mediante el control del tamaño, forma de las nanopartículas y su interacción con el soporte, en base a la “dependencia de la estructura” de estas reacciones.  Así, se preparan catalizadores basados en Au, doblemente nanoestructurados (tanto a nivel de la fase activa como del soporte) soportados sobre CeO2 y TiO2 (Al2O3 y SiO2 como referencia) mediante distintas estrategias de síntesis; evaluando sus propiedades mediante técnicas de caracterización avanzadas y evaluando su comportamiento en reactividad (en régimen estacionario y transitorio) en procesos de oxidación. En el mismo contexto, y considerando la reciente aparición de catalizadores bimetálicos (AuCu, AuPd) para estas reacciones con elevados rendimientos, se prepararan sistemas AuPt, AuCu y Au Ni con control del tamaño y la composición de la fase activa.


Reformado Catalítico de Glicerina



Investigador Principal: José Antonio Odriozola Gordón
Periodo: 01-01-2010 / 31-12-2012
Organismo Financiador: Junta de Andalucía
Código: P09-TEP-5454 (Proyecto de Excelencia)
Componentes: Luis F. Bobadilla Baladrón, Sylvia A. Cruz Torres, M. Isabel Domínguez Leal, Anna Dimitrova Penkova, Francisca Romero Sarria, Andrea Alvarez Moreno

Resumen [+]

Este proyecto pretende la producción de hidrógeno a partir del reformado de glicerina. La glicerina es el producto secundario principal en la producción de bio-diesel a través de la transesterificatión de ácidos grasos. Si tenemos en cuenta el desarrollo actual, la producción de bio-combustibles se estima en 9.9 Mtoe para 2010, lo que representa el 50% de los objetivos de la Unión Europea. Los sistemas de energía actuales necesita el desarrollo de modelos energéticos alter-nativos. El empleo de hidrógeno como vector energético representa una de esas alternativas, aunque para asegurar la sostenibilidad se requiere que el hidrógeno se produzca a partir de fuentes renovables. La principal ventaja del planteamiento que proponemos, aprovechamiento de la glicerina, reside en que además de sostenible el balance de carbono es prácticamente neutro. Además, su valorización debe conducir a aumentar la rentabilidad de las bio-refinerías que de otro modo se verían afectadas por el incremento de costes asociados a la eliminación de este producto.


Integración de reactores catalíticos de microcanales para la producción de hidrógeno a partir de alcoholes



Investigador Principal: José Antonio Odriozola Gordón
Periodo: 1-08-2009 / 31-07-2012
Organismo Financiador: Ministerio de Ciencia y Tecnología
Código: ENE2009-14522-C05-01
Componentes: Miguel Angel Centeno, Svetlana Ivanova, Francisca Romero Sarria, M.Isabel Domínguez, Sandra Palma, Oscar Laguna, Ana Penkova, Sylvia Cruz, W.Yesid Hernández, Luis Bobadilla

Resumen [+]

El uso masivo y generalizado de dispositivos eléctricos y electrónicos portátiles aumenta la necesidad de fuentes de potencia autónomas y eficientes, de hasta unos 50 We, capaces de reemplazar la tecnología actual basada en el uso de baterias. El uso de combustibles o productos químicos convencionales, hidrocarburos o alcoholes por ejemplo, es una alternativa prometedora cuando se combina con los recientes desarrollos en intensificación de procesos basados en la tecnología de reactores de microcanales. El desarrollo de la tecnología de microcanales para la producción de hidrógeno, in situ y a de-manda, a partir de alcoholes, se comenzó a estudiar en el proyecto anterior (MAT2006-12386-C05). Este estudio permitió la construcción de reactores de microcanales para las reacciones de reformado catalítico de metanol y oxidación preferente de CO (PROX) . En el presente proyecto se pretenden aplicar los conocimientos adquiridos para acoplar los microrreactores entre sí integrando flujos térmicos y materiales, escalarlos, y unirlos a una celda de combustible comercial de 50 We (PEMFC). En paralelo, se desarrollarán reactores de microcanales para el reformado catalítico de etanol y la reacción de desplazamiento del gas de agua (WGS) lo que permite aumentar la versatilidad el dispositivo diseñado. La viabilidad de estas fuentes de potencia autónomas requiere el estudio no sólo de la fabricación, escalado de los microreactores e integración de los flujos térmicos y materiales sino también explorar el uso de materiales de mayor disponibilidad (aceros ferríticos adaptados al uso), su durabilidad (aceros, catalizadores, soldaduras, juntas, …) y el desarrollo de un algoritmo de control para el conjunto formado por el procesador de combustible (reformado + eliminación de CO) y la pila de combustible.


Desarrollo de estrategias para la preparación y optimización de materiales altamente fotoactivos



Investigador Principal: José Antonio Navío Santos
Periodo: 01-01-2009 / 31-12-2011
Organismo Financiador: Ministerio de Ciencia y Tecnología
Código: CTQ2008-05961-C02-01
Componentes: Gerardo Colón Ibáñez, M. Carmen Hidalgo López, Manuel Macías Azaña, Marina Maicu

Resumen [+]

El objetivo general de este proyecto coordinado es “diseñar una nueva generación de materiales en forma de polvo con tamaño manométrico basados en TiO2, SnO2 y ZnO simples, mixtos y/o dopados con otros iones, con alta actividad fotocatalítica en el visible y su fijación en otros materiales (membranas, vidrios, arcillas y láminas metálicas) que permitan emplear-los, de manera eficiente y competitiva en procesos de descontaminación fotocatalítica de efluentes líquidos y gases contaminados”. La hipótesis fundamental de la que se parte es que existen pigmentos inorgánicos (tales como el TiO2, SnO2, ZnO, etc.) con actividad fotocatalítica en UV capaces de degradar de forma no selectiva a especies tóxicas presentes en nuestro medio ambiente. El reto es superar los problemas derivados de la utilización sólo de la parte UV del espectro solar y extender la respuesta hacia el visible, implementando al mismo tiempo, las propiedades fisicoquímicas de los fotocatalizadores. Para realizar este estudio se proponen dos bloques principales de actividad que serán el diseño y desarrollo de catalizadores heterogéneos de tamaño nanométricos altamente fotoactivos, basados en TiO2, SnO2 y ZnO que puedan hacer las transformaciones de degradación de contaminantes mediante el concurso de luz solar visible (Química Solar Medioambiental) y la inmovilización de nanopartículas de estos semiconductores, simples, mixtos y/o dopados, en soportes adecuados (membranas, vidrios, láminas metálicas, fibras, placas cerámicas, etc,) con el fin de desarrollar dispositivos fotocatalíticos con alta actividad para el tratamiento de contaminantes en gases y aguas, para la generación de superficies autolimpiables.


Producción de gas de síntesis e hidrógeno mediante reformado de hidrocarburo con catalizadores nanoestructurados de niquel



Investigador Principal: Alfonso Caballero Martínez
Periodo: 1-12-2007 / 30-11-2011
Organismo Financiador: Ministerio de Educación y Ciencia
Código: ENE2007-67926-C02-01
Componentes: Juan Pedro Holgado Vázquez, Agustín R. Gon-zález-Elipe, Victor Manuel González de la Cruz, Rosa Pereñiguez Rodríguez

Resumen [+]

Este proyecto coordinado de investigación, que puede considerarse como extensión de los anteriores ENE2004-01660 y ENE2004-06176, pretende la preparación de nuevos sistemas catalíticos,con tamaños de partícula discretos y con alta resistencia a la desactivación. El objetivo ultimo es la mejora de la reacción de reformado de hidrocarburos para producción de H2(+CO), principalmente metano y propano, al ser esta una reacción dependiente de la estructura, y por tanto sensible al tamaño de partícula.

Para ello, se prepararán diferentes series de nanopartículas de níquel de tamaño y morfología bien definidos, utilizando métodos ex-situ como la irradiación mediante plasma de microondas, líquidos iónicos, microemulsión inversa o la impregnación con modificación externa del soporte por sililación.

Estos métodos nos permitirán obtener partículas con un rango de tamaños muy amplio, desde menos de 10nm hasta valores entorno a los 100nm y con una estrecha distribución de tamaños de partícula.

La actividad catalítica de estas nanopartículas, una vez depositadas en soportes como ZrO2 or Al2O3, será evaluada en las reacciones de reformado de metano y propano; estableciendo una correlación estructura-reactividad. Se estudiarán con una especial atención los procesos de deposición de carbón sobre los catalizadores en condiciones de reacción, ya que son los principales responsables de la disminución en la eficiencia de estos sistemas catalíticos. El control estricto de la morfología de las nanopartículas metálicas nos permitirá, por tanto, correlacionar la cinética de estos procesos de desactivación con sus características estructurales. Por otro lado, estudiaremos el efecto en la mejora de las prestaciones catalíticas globales de la adición de promotores como Pt, Au, Sr, K, etc.

Alternativamente, se realizará un estudio de la reacción de reformado inducida por un plasma de microondas, con el fin último de desarrollar un sistema integrado térmico-plasma, que esperamos mejore las condiciones de reacción, reduciendo la temperatura necesaria y/o disminuyendo los procesos de deposición de coque sobre los catalizadores.


Diseño de sistemas fotocatalíticos con alta actividad en el visible para aplicaciones ambientales



Investigador Principal: Gerardo Colón Ibáñez
Periodo: 01-01-2007 / 31-12-2010
Organismo Financiador: Junta de Andalucía
Código: FQM-1406
Componentes: José Antonio Navío Santos, Manuel Macías Azaña, Carmen Hidalgo López, Marina Maicu

Resumen [+]

La Fotocatálisis ha demostrado ser una técnica muy eficiente en la oxidación de una gran variedad de sustratos en cortos tiempos de reacción. Es conocido que los catalizadores más utilizados, solo pueden ser activados por radiaciones menores de 390 nm, constituyéndose en una limitación para su empleo a mayor escala por el impedimento de usar luz solar. El objetivo principal de este proyecto se basa en el desarrollo en nuestro laboratorio de sistemas basados en TiO2 de alta eficiencia fotocatalítica en UV, capaz de degradar de forma no selectiva a especies tóxicas presentes en nuestro medio ambiente. El reto es superar los problemas derivados de la utilización sólo de la parte UV del espectro solar. El bloque central de la actividad de este proyecto consistirá en el desarrollo de sistemas de óxidos de Ti y Zn dopados, de forma que podamos obtener sistemas cuyo umbral de absorción esté en la región del visible. 

Así, desde el punto de vista de la mejora en las eficiencias de los procesos fotocatalíticos, es evidente que el diseño y desarrollo de fotocatalizadores alternativos al TiO2 es de un interés considerable. Se pretende la obtención de materiales altamente eficientes en procesos fotocatalíticos heterogéneos (en fase líquida y gaseosa) mediante la incorporación de distintos dopantes y la inmovilización de estos sistemas en distintos soportes. Para ello se abordarán distintas rutas de síntesis de polvo, y métodos de deposición. La evaluación la actividad fotocatalítica de los catalizadores se abordará estudiando procesos de fotooxidación de distintos compuestos orgánicos tóxicos (fenol y pigmentos orgánicos).




2018


New concept for old reaction: Novel WGS catalyst design


Garcia-Moncada, N; Gonzalez-Castano, M; Ivanova, S; Centeno, MA; Romero-Sarria, F; Odriozola, JA
Applied Catalysis A-General, 238 (2018) 1-5

ABSTRACT

The viability of water gas shift catalytic system for mobile application passes through obligatory reactor volume reduction, achieved normally by using less charge of more efficient catalyst. Completely new concept for catalyst design is proposed: a catalytic system including classically reported WGS catalysts of different nature or active phase (Cu, Pt or Au) mechanically mixed with an ionic conductor. The influence of the later on catalyst activity is studied and discussed, more precisely its effect on the rate of the reaction-limiting step and catalysts' efficiency. It is demonstrated with this study, that the presence of an ionic conductor in contact with a WGS catalyst is essential for the water supply (dissociation and transport), thereby potentiating the water activation step, whatever the mechanism and catalyst overall performance.


Diciembre, 2018 | DOI: 10.1016/j.apcatb.2018.06.068

CO/H-2 adsorption on a Ru/Al2O3 model catalyst for Fischer Trospch: Effect of water concentration on the surface species


Jimenez-Barrera, E; Bazin, P; Lopez-Cartes, C; Romero-Sarria, F; Daturi, M; Odriozola, JA
Applied Catalysis B-Environmental, 237 (2018) 986-995

ABSTRACT

Water presence and concentration strongly influence CO conversion and CS+ selectivity in the Fischer Tropsch reaction. In this work, the influence of the water concentration was investigated using a model Ru/Al2O3 (5 wt. %) catalyst. The surface species formed after CO and H-2 adsorption in dry and wet (different water concentrations) conditions were analyzed by FTIR. Firstly, water adsorption was carried out up to complete filling of the pores and then CO was put in contact with the catalyst. The absence of adsorbed CO species in these conditions evidences that CO diffusion in water controls the access of the gas to the active sites and explains the negative effect of high water concentrations reported by some authors. Moreover, the adsorption of a mixture of CO + H-2 + H2O, being the water concentration close to that needed to have a monolayer, and a dry mixture of CO + H-2 were carried out and compared. Results evidence that water in this low concentration, is able to gasify the surface carbon species formed by CO dissociation on the metallic sites. This cleaning effect is related to the positive effect of water on CO conversion detected by some authors.


Diciembre, 2018 | DOI: 10.1016/j.apcatb.2018.06.053

Selective CO methanation with structured RuO2/Al2O3 catalysts


Munoz-Murillo, A; Martinez, LM; Dominguez, MI; Odriozola, JA; Centeno, MA
Applied Catalysis B-Environmental, 236 (2018) 420-427

ABSTRACT

Active and selective structured RuO2/Al2O3 catalysts for CO methanation using a flow simulating CO2-rich reformate gases from WGS and PROX units (H-2 excess, CO2 presence and 300 ppm CO concentration) were prepared. Both, the RuO2/Al2O3 powder and the slurry prepared from it for its structuration by washcoating of the metallic micromonolithic structure, were also active and selective. Both the slurry (S-RuAl) and micro monoliths (M-RuAl) were able to completely and selectively methanate CO at much lower temperatures than the parent RuAI powder. The optimal working temperature in which the CO conversion is maximum and the CO2 conversion is minimized was determined to be from 149 degrees C to 239 degrees C for S-RuAl and from 165 degrees C to 232 degrees C for M-RuAl, whilst it was from 217 degrees C to 226 degrees C for RuAI powder. TPR, XRD and TEM measurements confirmed that the changes in the activity and selectivity for CO methanation among the considered catalysts can be related with modifications in the surface particle size of ruthenium and its reducibility. These were ascribed to the metallic substrate, the presence of PVA and colloidal alumina in the slurry preparation, the aqueous and acidic media and the thermal treatment used, resulting in a more active and selective catalysts than the parent powder.


Noviembre, 2018 | DOI: 10.1016/j.apcatb.2018.05.020

Photocatalytic H2 production from glycerol aqueous solutions over fluorinated Pt-TiO2 with high {001} facet exposure


V. Vaiano; M.A. Lara; G. Iervolino; M. Matarangolo; J.A. Navío; M.C. Hidalgo
Journal of Photochemistry and Photobiology A-Chemistry, 365 (2018) 52-59

ABSTRACT

An optimized fluorinated TiO2 catalyst with high {001} facet exposure loaded with platinum (TiO2-PtFAC) was tested in the photocatalytic hydrogen production from glycerol solution under UV light irradiation. The samples were synthesized by direct hydrothermal treatment starting from two different types of precursors that are titanium tetraisopropoxide (I) or titanium butoxide (B), while platinisation was performed by photodeposition method. The obtained catalysts were characterised by different techniques (XRD, FESEM, TEM, BET, UV–vis DRS, XRF and XPS) and the results evidenced that anatase is the only crystalline phase present in all TiO2 samples. The morphology of the samples was seen as rectangular platelets particles where Pt particles were was observed all over the surface. The presence of Pt and F in the platinised samples was also confirmed by XRF and XPS analysis. The photocatalytic results have shown that the presence of Pt on TiO2{001}facet surface remarkably enhanced the hydrogen production from aqueous solution at 5 wt % of glycerol. Comparing the results obtained from the photocatalysts prepared by the two different precursors, it was found that the best performances in terms of H2 production was achieved with TiO2-PtFAC(I) (about 13 mmol L−1 after 4 h of irradiation time), while the H2 production was lower for TiO2-PtFAC(B) (about 9 mmol L−1 after 4 h of irradiation time). The effect of the operating conditions using TiO2-PtFAC(I) evidenced that the highest H2 production was obtained with a photocatalyst dosage equal to 1.5 g L−1, initial glycerol concentration at 5 wt% and a pH value equal to 7. Finally, a photocatalytic test was also performed on glycerol solution prepared with a real water matrix. Despite the presence of ions scavengers (chlorides and carbonates) in solution, TiO2-PtFAC(I) was able to reach a photocatalytic H2production of about 6 mmol L−1 after 4 h of UV light irradiation.


Octubre, 2018 | DOI: 10.1016/j.jphotochem.2018.07.032

A direct in situ observation of water-enhanced proton conductivity of Eu-doped ZrO2: Effect on WGS reaction


Garcia-Moncada, N; Bobadilla, LF; Poyato, R; Lopez-Cartes, C; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 231 (2018) 343-356

ABSTRACT

Eu-doped ZrO2 solid solutions have been synthesized in order to prepare proton conductors as water-enhancer additives for the WGS reaction. Elemental characterization has been carried out revealing homogeneous dopant distribution resulting in fluorite-type solid solutions for Eu2O3 contents up to similar to 9 mol.%. Representative samples of the Eu-doped ZrO2 series have been analysed by Impedance Spectroscopy (IS) in inert, oxygen and wet conditions. The solid solution with 5 mol.% of Eu2O3 has presented the highest conductivity values for all tested conditions indicating an optimal amount of dopant. Moreover, the presence of vapour pressure results in an increment of the conductivity at temperatures lower than 300 degrees C, meanwhile at higher temperatures the conductivity is the same than that in inert conditions. To elucidate these results, in situ DRIFTS studies were carried out. These experiments evidenced the existence of water dissociation at oxygen vacancies (band at 3724 cm(-1)) as well as the presence of physisorbed water at temperatures up to similar to 300 degrees C where the band at 5248 cm(-1) characteristic of these species disappeared. These results points to a layer model where the physisorbed water interacts with surface hydroxyls generated by dissociated water that improves the proton conductivity through Grotthuss' mechanism in the RT-300 degrees C temperature range. These samples were successfully tested in WGS reaction as additive to a typical Pt-based catalyst. The presence of the mixed oxide reveals an increase of the catalyst' activity assisted by the proton conductor, since improves the water activation step.


Septiembre, 2018 | DOI: 10.1016/j.apcatb.2018.03.001

ZnO and Pt-ZnO photocatalysts: Characterization and photocatalytic activity assessing by means of three substrates


Jaramillo, C; Navio, J.A.; Hidalgo, M.C.; Macías, M.
Catalysis Today, 313 (2018) 12-19

ABSTRACT

ZnO nanoparticles have been previously synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without the addition of a template. The as-prepared ZnO material was anealed at 400 °C in air for 2 h. The Pt-ZnO catalysts (0.5 or 1.0 Pt wt.%) were obtained by photochemical deposition method on the surface of the prepared ZnO sample, using hexachloroplatinic acid (H2PtCl6). It has been shown that Zn2+ is lost from the photocatalyst to the medium and a replacement of the cationic vacancies of Zn2+ by Pt4+ cations occurs during the platinization process of the ZnO samples, regardless of whether the platinum metal photodeposition process. The as-prepared catalysts were characterized by XRD, BET, FE-SEM, TEM, XPS and diffuse reflectance spectroscopy (DRS). Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination: Methyl Orange and Rhodamine B were chosen as dye substrates and Phenol as a transparent substrate. High conversion values (ca. 100%) and a total organic carbon (TOC) removal of 90–96%, were obtained over these photocatalysts after 160 min of UV illumination. In general, it was observed that the presence of Pt on ZnO affects the lattice parameters and the crystallite size. Although ZnO can completely degrade RhB, MO and Phenol totally in ca. 60 min, the process is more efficient for Pt–ZnO photocatalysts.


Septiembre, 2018 | DOI: 10.1016/j.cattod.2017.12.009

Unravelling the Role of Oxygen Vacancies in the Mechanism of the Reverse Water-Gas Shift Reaction by Operando DRIFTS and Ultraviolet-Visible Spectroscopy


Bobadilla, LF; Santos, JL; Ivanova, S; Odriozola, JA; Urakawa, A
ACS Catalysis, 8 (2018) 7455-7467

ABSTRACT

The reaction mechanism of the reverse water gas shift (RWGS) reaction was investigated using two commercial gold-based catalysts supported on Al2O3 and TiO2. The surface species formed during the reaction and reaction mechanisms were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that RWGS reaction over Au/Al2O3 proceeds through the formation of formate intermediates that are reduced to CO. In the case of the Au/TiO2 catalyst, the reaction goes through a redox mechanism with the suggested formation of hydroxycarbonyl intermediates, which further decompose to CO and water. The Ti-3+ species, the surface hydroxyls, and oxygen vacancies jointly participate. The absence of carbonyl species adsorbed on gold particles during the reaction for both catalysts indicates that the reaction pathway involving dissociative adsorption of CO2 on Au particles can be discarded. To complete the study, operando ultraviolet visible spectroscopy was successfully applied to confirm the presence of Ti3+ and to understand the role of the oxygen vacancies of TiO2 support in activating CO2 and thus the subsequent RWGS reaction.


Agosto, 2018 | DOI: 10.1021/acscatal.8b02121

Solar pilot plant scale hydrogen generation by irradiation of Cu/TiO2 composites in presence of sacrificial electron donors


Maldonado, MI; Lopez-Martin, A; Colon, G; Peral, J; Martinez-Costa, JI; Malato, S
Applied Catalysis B-Environmental, 229 (2018) 15-23

ABSTRACT

A Cu/TiO2 photocatalyst has been synthesised by reducing a Cu precursor with NaBH4 onto the surface of a sulphate pretreated TiO2 obtained by a sol-gel procedure. The catalyst, that shows a clearly defined anatase phase with high crystallinity and relatively high surface area, and contains Cu2O and CuO deposits on its surface, has been used to produce hydrogen in a solar driven pilot plant scale photocatalytic reactor. Different electron donor aqueous solutions (methanol, glycerol, and a real municipal wastewater treatment plant influent) have been tested showing similar or even higher energy efficiency than those obtained using more expensive noble metal based photocatalytic systems. The glycerol solutions have provided the best reactive environments for hydrogen generation.


Agosto, 2018 | DOI: 10.1016/j.apcatb.2018.02.005

Effect of milling mechanism on the CO2 capture performance of limestone in the Calcium Looping process


Benitez-Guerrero, M; Valverde, JM; Perejon, A; Sanchez-Jimenez, PE; Perez-Maqueda, LA
Chemical Engineering Journal, 346 (2018) 549-556

ABSTRACT

This work analyzes the relevant influence of milling on the CO2 capture performance of CaO derived from natural limestone. Diverse types of milling mechanisms produce contrasting effects on the microstructure of the CaO formed after calcination of the milled limestone samples, which affects crucially the kinetics of carbonation at conditions for CO2 capture. The capture capacity of CaO derived from limestone samples milled using either shear or impact based mills is impaired compared to as-received limestone. After calcination of the milled samples, the resulting CaO porosity is increased while crystallinity is enhanced, which hinders carbonation. Conversely, if the material is simultaneously subjected to intense impact and shear stresses, CaO porosity is promoted whereas CaO cristanillity is reduced, which enhances carbonation in both the reaction and solid-state diffusion controlled regimes.


Agosto, 2018 | DOI: 10.1016/j.cej.2018.03.146

Structural Reversibility of LaCo1-xCuxO3 Followed by In Situ X-ray Diffraction and Absorption Spectroscopy


Pereniguez, Rosa; Ferri, Davide
Chemphyschem, 19 (2018) 1876-1885

ABSTRACT

Combinations of perovskite-type oxides with transition and precious metals exhibit a remarkable self-regenerable property that could be exploited for numerous practical applications. The objective of the present work was to study the reversibility of structural changes of perovskite-type oxides under cyclic reducing/oxidizing atmosphere by taking advantage of the reducibility of LaCoO3. LaCoO3 +/- and LaCo0.8Cu0.2O3 +/- were prepared by ultrasonic spray combustion and were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and temperature-programmed reduction (TPR). XRD and XAS data confirmed that copper adopted the coordination environment of cobalt at the B-site of the rhombohedral LaCoO3 under the selected synthesis conditions. The structural evolution under reducing atmosphere was studied by insitu XRD and XANES supporting the assignment of the observed structural changes to the reduction of the perovskite-type oxide from ABB'O-3 (B'=Cu) to B'(0)/ABO(3) and to B'B-0(0)/A(2)O(3). Successive redox cycles allowed the observation of a nearly complete reversibility of the perovskite phase, i.e. copper was able to revert into LaCoO3 upon oxidation. The reversible reduction/segregation of copper and incorporation at the B-site of the perovskite-type oxides could be used in chemical processes where the material can be functionalized by segregation of Cu and protected against irreversible structural changes upon re-oxidation.


Agosto, 2018 | DOI: 10.1002/cphc.201800069

Hydrodeoxygenation of vanillin over carbon supported metal catalysts


Santos, JL; Alda-Onggar, M; Fedorov, V; Peurla, M; Eranen, K; Maki-Arvela, P; Centeno, MA; Murzin, DY
Applied Catalysis A-General, 561 (2018) 137-149

ABSTRACT

Different carbon supported metal catalysts were synthesized, and characterized with various physico-chemical methods and tested in vanillin hydrodeoxygenation under 30 bar total pressure in water as a solvent at 100 degrees C. The catalysts exhibited high specific surface area and the metal dispersion decreased in following order: Pt/ C > Pd/C > Au/C > Rh/C > Ru/C. The most active catalyst was Pd/C followed by Ru/C. Vanillin hydrodeoxygenation proceeded via hydrogenation forming vanillyl alcohol further to its hydrogenolysis forming p-creosol. Both hydrogenation and hydrogenolysis were promoted by Pd/C, which exhibited rather high dispersion. The highest selectivity to p-creosol, 95% at complete vanillin conversion, was obtained with Pd/C. Kinetic modelling of vanillyl alcohol selectivity as a function of vanillin conversion was performed.


Julio, 2018 | DOI: 10.1016/j.apcata.2018.05.010

Design of Ag/ and Pt/TiO2-SiO2 nanomaterials for the photocatalyti degradation of phenol under solar irradiation


Matos, J; Llano, B; Montana, R; Poon, PS; Hidalgo, MC
Environmental Science and Pollution Research, 25 (2018) 18894-18913

ABSTRACT

The design of hybrid mesoporous TiO2-SiO2(TS1) materials decorated with Ag and Pt nanoparticles was performed. The photocatalytic degradation of phenol under artificial solar irradiation was studied and the activity and selectivity of the intermediate products were verified. TiO2-SiO(2)was prepared by sol-gel method while Ag- and Pt-based photocatalysts (TS1-Ag and TS1-Pt) were prepared by photodeposition of the noble metals on TS1. Two series of photocatalysts were prepared varying Ag and Pt contents (0.5 and 1.0 wt%). An increase in the photocatalytic activity up to two and five times higher than TS1 was found on TS1-Ag-1.0 and TS1-Pt-1.0, respectively. Changes in the intermediate products were detected on Ag- and Pt-based photocatalysts with an increase in the catechol formation up to 3.3 and 6.6 times higher than that observed on TS1, respectively. A two-parallel reaction mechanism for the hydroquinone and catechol formation is proposed. A linear correlation between the photocatalytic activity and the surface concentration of noble metals was found indicating that the electron affinity of noble metals is the driven force for both the increase in the photoactivity and for the remarkable changes in the selectivity of products.


Julio, 2018 | DOI: 10.1007/s11356-018-2102-3

Photo/Electrocatalytic Properties of Nanocrystalline ZnO and La–Doped ZnO: Combined DFT Fundamental Semiconducting Properties and Experimental Study


Ahsaine, A.H.; Slassi, A.; Naciri, Y.; Chennah, A.; Jaramillo‐Páez, C.; Anfar, Z.; Zbair, M.; Benlhachemi, A.; Navío, J.A.
Chemistry Select, 3 (2018) 77778-7791

ABSTRACT

This work reports the synthesis of nanocrystalline ZnO and 5% La‐doped ZnO (La/ZnO) materials for photo/electrocatalytic degradation of Rhodamine B. The samples were characterized by X‐Ray diffraction, scanning and transmission electron microscopy, X‐Ray photoelectron spectroscopy and diffuse reflectance spectra. The effect of La doping on electronic structure was investigated using density functional theory calculations (DFT), La‐doped ZnO showed an n‐type metallic nature compared to pristine ZnO and La doping creates occupied states within the band gap edge. Under UV light, La/ZnO showed higher kinetic constant and efficiency than ZnO. A possible mechanism was elaborated on the basis of DFT and active trapping measurements. Different initial Rhodamine B concentration were studied to assess the electro‐oxidation of RhB. The electrochemical degradation of RhB over La/ZnO spindles electrode was pronounced with three time's high kinetic constant. The superior electro/photoactivity of La/ZnO was due to its unique morphology, high charge separation of the charge carriers and higher conductivity induced by La‐doping (intermediary levels). Superoxide ions and holes were the main active species for the photodegradation. Whereas, synergetic effect of hydroxyl radicals and hypochlorite ions were responsible of the high RhB electrocatalytic degradation.


Julio, 2018 | DOI: 10.1002/slct.201801729

Chemical CO2 recycling via dry and bi reforming of methane using Ni-Sn/Al2O3 and Ni-Sn/CeO2-Al2O3 catalysts


Stroud, T; Smith, TJ; Le Sache, E; Santos, JL; Centeno, MA; Arellano-Garcia, H; Odriozola, JA; Reina, TR
Applied Catalysis B-Environmental, 224 (2018) 125-135

ABSTRACT

Carbon formation and sintering remain the main culprits regarding catalyst deactivation in the dry and bi-reforming of methane reactions (DRM and BRM, respectively). Nickel based catalysts (10 wt.%) supported on alumina (Al2O3) have shown no exception in this study, but can be improved by the addition of tin and ceria. The effect of two different Sn loadings on this base have been examined for the DRM reaction over 20 h, before selecting the most appropriate Sn/Ni ratio and promoting the alumina base with 20 wt.% of CeO2. This catalyst then underwent activity measurements over a range of temperatures and space velocities, before undergoing experimentation in BRM. It not only showed good levels of conversions for DRM, but exhibited stable conversions towards BRM, reaching an equilibrium H-2/CO product ratio in the process. In fact, this work reveals how multicomponent Ni catalysts can be effectively utilised to produce flexible syngas streams from CO2/CH4 mixtures as an efficient route for CO2 utilisation.


Mayo, 2018 | DOI: 10.1016/j.apcatb.2017.10.047

Multicomponent Ni-CeO2 nanocatalysts for syngas production from CO2/CH4 mixtures


le Sache, E.; Santos, J. L.; Smith, T. J.; Centeno, M. A.; Arellano-Garcia, H.; Odriozola, J. A.; Reina, T. R.
Journal of CO2 utilization, 25 (2018) 68-78

ABSTRACT

The dry reforming of methane with CO2 is a common route to transform CO2/CH4 mixtures into added value syngas. Ni based catalysts are highly active for this goal but suffer from deactivation, as such promoters need to be introduced to counteract this, and improve performance. In this study, mono- and bi-metallic formulations based on 10 wt.% Ni/CeO2-Al2O3 are explored and compared to a reference 10 wt.% Ni/gamma-Al2O3. The effect of Sn and Pt as promoters of Ni/CeO2-Al2O3 was also investigated. The formulation promoted with Sn looked especially promising, showing CO2 conversions stabilising at 65% after highs of 95%. Its increased performance is attributed to the additional dispersion Sn promotion causes. Changes in the reaction conditions (space velocity and temperature) cement this idea, with the Ni-Sn/CeAl material performing superiorly to the mono-metallic material, showing less deactivation. However, in the long run it is noted that the mono- metallic Ni/CeAl performs better. As such the application is key when deciding which catalyst to employ in the dry reforming process.


Mayo, 2018 | DOI: 10.1016/j.jcou.2018.03.012

Influence of gold particle size in Au/C catalysts for base-free oxidation of glucose


Megias-Sayago, C; Santos, JL; Ammari, F; Chenouf, M; Ivanova, S; Centeno, MA; Odriozola, JA
Catalysis Today, 306 (2018) 183-190

ABSTRACT

A series of gold colloids were prepared and immobilized on commercial activated carbon. The influence of the colloid preparation and stability were studied and related to the gold particle size in the final catalyst. The catalysts show an important activity in the glucose to gluconic acid oxidation reaction, leading to gluconic acid yield close to 90% in base free mild conditions (0.1 MPa O-2 and 40 degrees C). The size-activity correlation and probable mechanism were also discussed. Finally, the viability of the catalyst was tested by recycling it up to four times. 


Mayo, 2018 | DOI: 10.1016/j.cattod.2017.01.007

Multicomponent Au/Cu-ZnO-Al2O3 catalysts: Robust materials for clean hydrogen production


Santos, JL; Reina, TR; Ivanov, I; Penkova, A; Ivanova, S; Tabakova, T; Centeno, MA; Idakiev, V; Odriozola, JA
Applied Catalysis A-General, 558 (2018) 91-98

ABSTRACT

Clean hydrogen production via WGS is a key step in the development of hydrogen fuel processors. Herein, we have designed a new family of highly effective catalysts for low-temperature WGS reaction based on gold modified copper-zinc mixed oxides. Their performance was controlled by catalysts' composition and the Au-Cu synergy. The utilization of hydrotalcite precursors leads to an optimal microstructure that ensures excellent Au and Cu dispersion and favors their strong interaction. From the application perspective these materials succeed to overcome the major drawback of the commercial WGS catalysts: resistance towards start/stop operations, a mandatory requisite for H-2-powered mobile devices.


Mayo, 2018 | DOI: 10.1016/j.apcata.2018.04.002

Study of the effectiveness of the flocculation-photocatalysis in the treatment of wastewater coming from dairy industries


Murcia, J.J., Hernández-Laverde, M., Rojas, Muñoz, E., Navío, J.A., Hidalgo, M.C.
Journal of Photochemistry and Photobiology A: Chemistry, 358 (2018) 256-264

ABSTRACT

The aim of the present work was to evaluate the effectiveness of flocculation-photocatalysis as combined processes in the treatment of dairy industries wastewater. Different commercial and lab prepared flocculants and photocatalysts were evaluated. All the materials prepared were extensively characterized. Commercial materials presented the best physicochemical properties and performance in the treatment of the studied wastewater. On one hand, all the photocatalysts evaluated showed bactericidal activity for E. Coli, total coliforms and other enterobacteriaceae. Total elimination of E. coli was obtained by using commercial TiO2 P25 Evonik, under 120 W/m2 of UV–vis light intensity and 5 h of total illumination time. Other species of bacteria remained after treatment under these conditions. It was also found that the highest light intensity of 120 W/m2 led to increase the Chemical Oxygen Demand and Total Organic Carbon in the samples treated, it can be due to the faster formation of new organic compounds as intermediaries during the photocatalytic reactions at the highest photonic flux. Flocculation pre-treatment of the wastewater samples led to improve the effectiveness of the photocatalytic treatment; thus, the combination of flocculation-photocatalysis treatments at low light intensity of 30 W/m2 leads to achieve the total elimination of E. coli, and under this intensity the elimination of total coliforms and other enterobacteriaceae increased 5.48% compared to the photocatalytic treatment alone. These treatment conditions led to comply the Colombian regulations for dairy wastewater.


Mayo, 2018 | DOI: 10.1016/j.jphotochem.2018.03.034

Photo-induced processes on Nb2O5 synthesized by different procedures


Jaramillo-Páez, C., Sánchez-Fernández, F.J., Navío, J.A., Hidalgo, M.C.
Journal of Photochemistry and Photobiology A: Chemistry, 359 (2018) 40-52

ABSTRACT

The properties of Nb2O5 strongly depend on its synthesis procedure as well as the conditions of ulterior thermal treatment. We report the synthesis of Nb2O5 powders prepared by sol-gel precipitation method using niobium(V) ethoxide as precursor. Two chemical routes were chosen: the presence of tryethyl amine (TEA) as precipitant/template agent, or the oxidant peroxide method. In addition, microwave-assisted activation was also used. The as-prepared samples by the above procedures were amorphous. Structural changes upon heating from room temperature up to 800 °C were investigated by X-ray powder diffraction technique combined with thermogravimetric analysis. The sequential thermal treatment up to 800 °C promotes the crystallization of hexagonal phase to orthorhombic phase whereas the ulterior cooling to room temperature lead to a mixture of both phases. Samples calcined at selected temperatures of either 600 °C or 800 °C for 2 h, were characterized by XRD, SEM, N2-adsorption and diffuse reflectance spectroscopy (DRS). The synthetic approach routes as well as the combined microwave activation followed by ulterior thermal treatment lead to changes not only on particle size but also on the textural properties of the synthesized catalysts. The catalysts synthesized have been evaluated using Rhodamine B (RhB) as a substrate, under both UV and visible lighting conditions. None of the catalysts synthesized showed activity in the visible. Under UV-illumination conditions, some of the catalysts exhibited a relatively low photoactivity in the degradation of RhB, which is associated with a photo-sensitizing effect. However, the addition of Ag+ ions considerably increased the activity of all the catalysts in the degradation of RhB under UV-illumination conditions. A mechanism is proposed to explain the photo-induced processes obtained, leaving the door open to the possible implications of the observed results in relation to the interaction of RhB dye with noble metal nanoparticles such as silver.


Mayo, 2018 | DOI: 10.1016/j.jphotochem.2018.03.040

Silver-modified ZnO highly UV-photoactive


Jaramillo-Páez, C.; Navío, J.C.; Hidalgo, M.C.
Journal of Photochemistry and Photobiology A: Chemistry, 356 (2018) 112-122

ABSTRACT

ZnO nanoparticles were successfully synthesized by a controlled precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without template addition and ulterior calcination at 400 °C for 2 h. The Ag-ZnO catalysts (ranging from 0.5 to 10 Ag wt.-%) were obtained by photochemical deposition method at the surface of the prepared ZnO sample, using AgNO3 as precursor. The as-prepared catalysts (with and without silver) were characterized by XRD, BET, FE-SEM, TEM, and XPS and diffuse reflectance spectroscopy (DRS). The effect of Ag-phodeposition on the photocatalytic properties of ZnO nanoparticles was investigated. Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination and visible illumination: Methyl Orange and Rhodamine B were chosen as hazardous dyes and Phenol as a transparent substrate. For each of the chosen substrates, it was observed that the UV-photocatalytic properties of ZnO improved with the amount of Ag deposited, up to an optimum percentage around 1–5 wt.-% Ag, being even better than the commercial Evonik-TiO2(P25) in the same conditions. Above this amount, the UV-photocatalytic properties of the Ag-ZnO samples remain unchanged, indicating a maximum for Ag-deposition. While ZnO and Ag-ZnO catalysts can photodegrade Rhodamine B, Methyl Orange and Phenol totally within 60 min under UV-illumination, the process is slightly faster for the case of Ag–ZnO nanoparticles. Under Vis-illumination, the silver-metalized samples did not present photocatalytic activity in the degradation of Methyl Orange. However, a very low photoactivity was present for phenol degradation (10% conversion) and a moderate conversion of ca. 70% for Rhodamine B degradation, after 120 min of Visible-illumination. High conversion values and a total organic carbon (TOC) removal of 86–97% were obtained over the Ag-ZnO photocatalysts after 120 min of UV-illumination, suggesting that these Ag-modified ZnO nanoparticles may have good applications in wastewater treatment, due to its reuse properties.


Abril, 2018 | DOI: 10.1016/j.jphotochem.2017.12.044

Bimetallic Ni-Co/SBA-15 catalysts for reforming of ethanol: How cobalt modifies the nickel metal phase and product distribution


Rodriguez-Gomez, A; Caballero, A
Molecular Catalysis, 449 (2018) 122-130

ABSTRACT

In this study, five mono and bimetallic xNi-(10-x)Co/SBA-15 catalysts (x = 10, 8, 5, 2 and 0, with a total metallic content of 10 wt%) have been synthesized using a deposition-precipitation (DP) methodology. Catalytic performances on the steam reforming of ethanol reaction (SRE) have been determined and correlated with their physical and chemical state. A nickel content of 5% or higher yields catalytic systems with good activity, high selectivity to hydrogen and a low production of acetaldehyde (less than 5%). However, in the systems where the cobalt is the main component of the metallic phase (8-10%), the selectivity changes, mainly due to the production of an excess of acetaldehyde, which is also reflected in the larger H-2/CO2 ratio. In agreement with previous findings, this important modification in the selectivity comes from the formation of a cobalt carbide phase, where only takes place in the cobalt enriched systems, and is inhibited with nickel content larger than 5%. The formation of this carbide phase seems to be responsible for the decrease of cobalt particle size during the SRE reaction. Even though this cobalt carbide phase is thermodynamically metastable against decomposition to metallic cobalt and graphite carbon, our results have shown that it only reacts and decomposes after a hydrogen treatment at 600 degrees C.


Abril, 2018 | DOI: 10.1016/j.mcat.2018.02.011

Tailoring structured WGS catalysts: Impact of multilayered concept on the water surface interactions


Gonzalez-Castano, M; Le Sache, E; Ivanova, S; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 222 (2018) 124-132

ABSTRACT

A novel multilayer approach for designing structured WGS catalyst is employed in this study as a response to the lack of new strategies in the literature. The approach proposes the use of two successive layers with different functionalities on metallic micromonolith substrate. The WGS catalyst behavior is modulated by the nature of the inner layer which determines the active species surface population by acting on the water activation step. The catalytic promotion attained by introducing inner ceria containing solids with increasing number of oxygen defects is intensely analyzed through FT-IR and H2O-TPD. Several evidences about the participation of the oxygen vacancies, as key sites, for water absorption processes are established. Besides, remarkable relationships between the water absorption strengths and the water splitting processes within their influence on the catalyst performance are also discussed.


Marzo, 2018 | DOI: 10.1016/j.apcatb.2017.10.018

Epimerization of glucose over ionic liquid/phosphomolybdate hybrids: structure-activity relationship


Megias-Sayago, C; Alvarez, E; Ivanova, S; Odriozola, JA
Green Chemistry, 20 (2018) 1042-1049

ABSTRACT

The influence of the crystal structure and chemical nature of some ionic liquid/phosphomolybdate hybrids on their catalytic activity in the epimerization of glucose was studied. A clear evidence of structure-activity relationship was found. The inorganic part of the hybrid ensured the availability of active sites for the reaction, while the organic cation part organized the structure and controled the diffusion of the reactants. This study can be used as a first approach to predict the symmetry, long range order and availability of active sites in the presented class of imidazolium based polyoxometalate hybrids.


Marzo, 2018 | DOI: 10.1039/c7gc03738d

CO2 reforming of methane over Ni-Ru supported catalysts: On the nature of active sites by operando DRIFTS study


Alvarez, A; Bobadilla, LF; Garcilaso, V; Centeno, MA; Odriozola, JA
Journal of CO2 utilization, 24 (2018) 509-515

ABSTRACT

The present paper addresses the nature of the active sites of a bimetallic Ni-Ru supported catalyst on the dry reforming of methane (DRM). The structural characterization by XRD and Raman spectroscopy, along with the reducibility study (TPR-H-2) of the samples, evidenced the existence of a strong Ni-Ru interaction in the bimetallic system. We have assumed that Ru atoms block the most reactive Ni sites (step-edge sites) leaving less reactive centers for methane activation (terraces). In this way, operando DRIFTS measurements revealed that Ru decreases the catalytic activity but favors the carbon gasification and prevents the CO dissociation.


Marzo, 2018 | DOI: 10.1016/j.jcou.2018.01.027

Synthesis of Pd-Al/biomorphic carbon catalysts using cellulose as carbon precursor


Cazana, F; Galetti, A; Meyer, C; Sebastian, V; Centeno, MA; Romeo, E; Monzon, A
Catalysis Today, 301 (2018) 226-238

ABSTRACT

This work presents the results obtained with novel Pd and Pd-Al catalysts supported on carbon, which have been prepared using a biomorphic mineralization technique. The catalyst synthesis procedure includes a stage of thermal decomposition under reductive atmosphere of cellulose previously impregnated with the metallic precursors. We have studied the influence of the temperature and time of decomposition, and of the Al precursor addition, on the textural and catalytic properties. The characterisation results indicate that the preparation method used leads to the formation of carbonaceous supports with a high microporosity (up to 97% micropore volume) and values of the BET surface up to 470 m2/g while maintaining the original external structure. The use of low temperatures (ca. 600 °C) during the decomposition step allows the preparation of highly dispersed catalysts with narrow Pd particle size distributions. However, the thermal decomposition at elevated temperatures (ca. 800 °C) increases the Pd particle size due to the sintering of the metallic phase. This phenomenon is augmented with the decomposition time and is not affected by the presence of Al. Consequently, the catalytic activity of these materials in cyclohexene hydrogenation is strongly affected by the operational conditions used during the thermal decomposition step. Unexpectedly, the more sintered catalysts, i.e. those prepared at 800 °C, show the highest activity. According to the characterization results, this fact can be explained considering that the smaller Pd particles obtained after preparation at e.g. 600 °C are quite inactive because they are confined in the internal structure of the micropores of the support and/or embedded inside the carbon matrix. In contrast, after decomposition at 800 °C, the larger Pd particles formed are placed at the external surface of the catalyst, being accessible to the reactants. In addition, for the specific conditions under which the Pd is accessible, the presence of Al favours the cyclohexene conversion due to the enhancement of the adsorption on the Pd surface as a consequence of a charge transfer phenomenon. These results can serve as a guideline for the preparation of these catalysts based on raw lignocellulosic materials in order to maximize their catalytic performance.


Marzo, 2018 | DOI: 10.1016/j.cattod.2017.05.026

Gold catalyst recycling study in base-free glucose oxidation reaction


Megias-Sayago, C.; Bobadilla, L. F.; Ivanova, S.; Penkova, A.; Centeno, M. A.; Odriozola, J. A.
Catalysis Today, 301 (2018) 72-77

ABSTRACT

This work is devoted to the study of viability of immobilized gold colloids on carbon as catalysts for the base-free glucose oxidation reaction with a special emphasis made on catalysts' recycling, operational life and possible routes for deactivation/reactivation under batch conditions. The observed catalytic behavior is related to all possible manners of deactivation, like gold metal state changes (particle size agglomeration or leaching), support modifications or active sites blocking by intermediates. In an attempt to recover the initial catalytic activity, the samples are subjected to different treatments such as H2O and NaOH washings and calcination. The failure of the regeneration procedures to recover the initial activity and after detailed catalyst' characterization allows us to find out the main cause of deactivation


Marzo, 2018 | DOI: 10.1016/j.cattod.2017.03.022

LaFeO3 ceramics as selective oxygen sensors at mild temperature


Jaouali, I; Hamrouni, H; Moussa, N; Nsib, MF; Centeno, MA; Bonavita, A; Neri, G; Leonardi, SG
Ceramics International, 44 (2018) 4183-4189

ABSTRACT

In this study, an investigation about the oxygen sensing properties of lanthanum orthoferrite (LaFeO3) ceramics is reported. LaFeO3 nanoparticles were synthesized by using tartaric sol-gel route and annealed in air at different temperatures (500, 700 and 900 degrees C). The samples have been characterized by using thermal analysis (TA), BET surface area and porosity, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results of sensing tests indicate that LaFeO3 nanoparticles exhibit good response to oxygen at mild temperatures (300-450 degrees C). The effect of annealing temperature on gas sensing performance was investigated, demonstrating that LaFeO3 ceramics obtained after annealing at 500 degrees C display better characteristics with respect to others. The oxygen sensor developed shows also high stability in humid environment and excellent selectivity to oxygen over other interfering gases such as CO, NO2, CO2, H-2 and ethanol.


Marzo, 2018 | DOI: 10.1016/j.ceramint.2017.11.221

Numerical study of the accuracy of temperature measurement by thermocouples in small-scale reactors


Blay, V; Bobadilla, LF
Chemical Engineering Research & Design, 131 (2018) 545-556

ABSTRACT

Proper temperature measurement is imperative in any laboratory study if reliable data are to be obtained, particularly in the field of chemical kinetics. In this paper we analyze in silico some typical thermowell configurations used in small-scale reactors by coupling computational fluid dynamics (CFD) with conjugated heat transfer phenomena. This allows us to identify deviations in measurements arising from thermal radiation and self-conductivity in mid and high temperature ranges, in addition to radial temperature gradients. A novel design is proposed and optimized by additional simulation, showing potential for faster and more accurate temperature measurements.


Marzo, 2018 | DOI: 10.1016/j.cherd.2017.06.003

Urban wastewater treatment by using Ag/ZnO and Pt/TiO2 photocatalysts


J.J. Murcia, L.G. Arias Bolivar, H.A. Rojas Sarmiento, E.G. Ávila Martínez, C. Jaramillo Páez, M.A. Lara, J.A. Navío Santos, M.C. Hidalgo López
Environmental Science and Pollution Research (2018) 1-9

ABSTRACT

In this study, the treatment of wastewater coming from a river highly polluted with domestic and industrial effluents was evaluated. For this purpose, series of photocatalysts obtained by ZnO and TiO2 modification were evaluated. The effect of metal addition and Ti precursor (in the case of the titania series) over the physicochemical and photocatalytic properties of the materials obtained was also analyzed. The evaluation of the photocatalytic activity showed that semiconductor modification and precursor used in the materials synthesis are important factors influencing the physicochemical and therefore the photocatalytic properties of the materials obtained. The water samples analyzed in the present work were taken from a highly polluted river, and it was found that the effectiveness of the photocatalytic treatment increases when the reaction time increases and for both, wastewater samples and isolated Escherichia coli strain follow the next order Pt/TiO2 << ZnO. It was also observed that biochemical and chemical demand oxygen and turbidity significantly decrease after treatment, thus indicating that photocatalysis is a non-selective technology, which can lead to recover wastewater containing different pollutants.


Marzo, 2018 | DOI: 10.1007/s11356-018-1592-3

High {0 0 1} faceted TiO2 nanoparticles for the valorization of oxygenated compounds present in aqueous biomass-derived feedstocks


Fernández-Arroyo, A.; Lara, M.A.; Domine, M.E.; Sayagués,M.J.; Navío, J.A.; Hidalgo, M.C.
Journal of Catalysis, 358 (2018) 266-276

ABSTRACT

{0 0 1} faceted TiO2 catalysts are hydrothermally synthesized by using titanium(IV) isopropoxide and butoxide precursors (ISO and BUT TiO2 samples) together with HF addition. Their activity and stability are evaluated in the catalytic condensation of light oxygenated organic compounds present in an aqueous model mixture simulating a real bio-refinery effluent, under moderate operation conditions. High {0 0 1} faceted TiO2 catalysts show organic products yields superior to those attained with other TiO2 samples (anatase, rutile, and P25). This enhanced catalytic activity relates to their physico-chemical and textural properties, such as high surface area (≈100 m2/g), regular morphology (platelets conformed by partially agglomerated TiO2 nanoparticles), and adequate Lewis acidity. XRD and Raman measurements evidence the unique presence of anatase crystalline phase in both ISO and BUT materials, in which the use of HF during synthesis produces the preferential growth of TiO2 crystals mainly exposing the {0 0 1} plane. This effective {0 0 1} facet exposition directly determines catalytic results. Moreover, TiO2 ISO catalyst shows outstanding stability under reaction conditions, maintaining practically unaltered their activity after several re-uses. In particular, Lewis acid sites present in TiO2 faceted materials are more stable in the presence of organic acids under aqueous environments. This opens new possibilities for the application of these materials in the valorization of light oxygenated compounds present in biomass-derived aqueous effluents.


Febrero, 2018 | DOI: 10.1016/j.jcat.2017.12.018

Improving the direct synthesis of hydrogen peroxide from hydrogen and oxygen over Au-Pd/SBA-15 catalysts by selective functionalization


Rodriguez-Gomez, A; Platero, F; Caballero, A; Colon, G
Molecular Catalysis, 445 (2018) 142-151

ABSTRACT

A series of gold-palladium catalysts supported in a mesoporous surface functionalized silica SBA-15 was studied for H2O2 direct synthesis. Support functionalization was performed using different organic groups (namely-SO3H, -NH2 and-SH) while metal was then supported by an ion exchanged method. Different Au-Pd/SBA-15 catalysts were tested in the Direct Synthesis of Hydrogen Peroxide (DSHP). Organic functional groups (-SH, -SO3H and-NH2) with acid-base properties acted as anchoring sites controlling both the dispersion of the metallic active phase and the chemical state of gold and palladium species as Au+ and Pd2+, respectively. Compared to a Au-Pd/SBA-15 system prepared by incipient wetness impregnation over non-functionalized SBA-15, catalytic performance is improved upon functionalization, increasing hydrogen peroxide rate in sulfonic-SBA-15 systems and reducing the hydrogenation/decomposition activity by adding amine groups. The occurrence of amine groups clearly suppresses the support microporosity and probably condition the metal cluster size. The analysis of particle size by TEM showed that sulfonated samples lead to a Pd size compromise which improves the H2O2 production hindering the competitive side reactions, particularly suppressed by the presence of amine groups.


Febrero, 2018 | DOI: 10.1016/j.mcat.2017.10.034

Phase-Contact Engineering in Mono- and Bimetallic Cu-Ni Co-catalysts for Hydrogen Photocatalytic Materials


Munoz-Batista, MJ; Meira, DM; Colon, G; Kubacka, A; Fernandez-Garcia, M
Angewandte Chemie-International Edition, 57 (2018) 1199-1203

ABSTRACT

Understanding how a photocatalyst modulates its oxidation state, size, and structure during a photocatalytic reaction under operando conditions is strongly limited by the mismatch between (catalyst) volume sampled by light and, to date, the physicochemical techniques and probes employed to study them. A synchrotron micro-beam X-ray absorption spectroscopy study together with the computational simulation and analysis (at the X-ray cell) of the light-matter interaction occurring in powdered TiO2-based monometallic Cu, Ni and bimetallic CuNi catalysts for hydrogen production from renewables was carried out. The combined information unveils an unexpected key catalytic role involving the phase contact between the reduced and oxidized non-noble metal phases in all catalysts and, additionally, reveals the source of the synergistic Cu-Ni interaction in the bimetallic material. The experimental method is applicable to operando studies of a wide variety of photocatalytic materials.


Enero, 2018 | DOI: 10.1002/anie.201709552

Enhanced photocatalytic removal of phenol from aqueous solutions using ZnO modified with Ag


Vaiano, V.; Matarangolo, M.; Murcia, J.J.; Rojas, H.; Navío, J.A.; Hidalgo, M.C.
Applied Catalysis B-Environmental, 225 (2018) 197-206

ABSTRACT

Different photocatalysts based on commercial ZnO modified by silver photodeposition were prepared in this work. The samples were characterized by X-ray fluorescence spectrometry (XRF), specific surface area (SSA), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and UV–vis diffuse reflectance (UV–vis DRS). XRD and XPS showed that Ag/ZnO samples are composed of metallic Ag (Ag0) and ZnO structure was identified. Furthermore, TEM analysis evidenced that the number of silver particles increased with the Ag content. At last, UV–vis DRS results revealed a reflectance band for Ag/ZnO samples, ascribed to the surface plasmon resonance (SPR) absorption of metal silver particles. Commercial ZnO and Ag/ZnO samples were evaluated in the phenol removal under UV light irradiation. It was observed an enhancement of photocatalytic phenol removal from aqueous solutions by silver addition in comparison to commercial ZnO. In particular, the phenol removal increased with the silver content from 0.14 to 0.88 wt%, after this content (i.e 1.28 wt%) the phenol degradation significantly decreased indicating that the optimal Ag content was equal to 0.88 wt%. The influence of the best photocatalyst dosage and the change of the initial phenol concentration in solution were also investigated in this work and the best photocatalytic performance was obtained by using 50 mg L−1 of phenol initial concentration and 0.15 g L−1 of photocatalyst dosage. Finally, the optimized Ag/ZnO photocatalyst was employed for the treatment of a real drinking wastewater containing phenol in which the almost total phenol removal was achieved after 180 min of UV irradiation time.


Enero, 2018 | DOI: 10.1016/j.apcatb.2017.11.075

Outstanding performance of rehydrated Mg-Al hydrotalcites as heterogeneous methanolysis catalysts for the synthesis of biodiesel


Navajas, A; Campo, I; Moral, A; Echave, J; Sanz, O; Montes, M; Odriozola, JA; Arzamendi, G; Gandia, LM
Fuel, 211 (2018) 173-181

ABSTRACT

There is still a need for active, selective and stable heterogeneous catalysts for the synthesis of biodiesel. In this work, magnesium-aluminium hydrotalcites with Mg/Al molar ratios within the 1.5-5 range were synthesized by coprecipitation and used as transesterification catalysts for the synthesis of biodiesel. The mixed oxides obtained after calcination recovered the hydrotalcite structure in the form of meixnerite after rehydration in boiling water. The solids were characterized by XRD, TGA, N-2 adsorption-desorption, and SEM. Basic properties were assessed by means of Hammett indicators and CO2-TPD. Rehydrated materials with the highest Mg/Al ratios showed some distinctive features: low surface area, well defined flake-like crystals, high basicity and strong basic sites with H_ values above 11. They were also the most active catalysts allowing to achieve 51-75% sunflower oil methanolysis conversion after 8 h of reaction under mild conditions (60 degrees C, 1 atm), methanol/oil molar ratio of 12 using between 2 and 6 wt% of catalyst. The conversion increased up to 96% (92% fatty acid methyl esters yield) using 2 wt% catalyst and methanol/oil molar ratio of 48. Catalyst leaching was not a serious problem with these solids that could be reutilized maintaining very good activities. A general accordance between solids basic properties and their catalytic performance has been observed. These results are among the best reported in the literature for heterogeneous methanolysis catalysts and have been attributed to the high basicity of the rehydrated solids and the presence of strong and accessible basic sites probably consisting in interlayer hydroxide anions at the edges of the crystals.


Enero, 2018 | DOI: 10.1016/j.fuel.2017.09.061

Nickel Particles Selectively Confined in the Mesoporous Channels of SBA-15 Yielding a Very Stable Catalyst for DRM Reaction


Rodriguez-Gomez, A; Pereniguez, R; Caballero, A
Journal of Physical Chemistry B, 122 (2018) 500-510

ABSTRACT

A series of four Ni catalysts supported on SBA-15 and on a high SiO2 surface area have been prepared by modified impregnation (ImU) and deposition-precipitation (DP) methods. The catalysts have been extensively characterized, including in situ XAS (bulk sensitive) and XPS (surface sensitive) techniques, and their catalytic activities evaluated in the dry reforming reaction of methane (DRM). The combined use of XPS and XAS has allowed us to determine the location of nickel particles on each catalyst after reduction at high temperature (750 degrees C). Both Ni/SiO2-DP and Ni/SBA-15-DP catalysts yield well-dispersed and homogeneous metallic phases mainly located in the mesoporosity of both supports. On the contrary, the Ni/SiO2-ImU and Ni/SBA-15-ImU catalysts present a bimodal distribution of the reduced nickel phase, with nickel metallic particles located out and into the mesoporous structure of SiO2 or the SBA-15 channels. The Ni/SBA-15-DP catalyst was found the most stable and performing system, with a very low level of carbon deposition, about an order of magnitude lower than the equivalent ImU catalyst. This outstanding performance comes from the confinement of small and homogeneous nickel particles in the mesoporous channels of SBA-15, which, in strong interaction with the support, are resistant to sintering and coke deposition during the demanding reaction conditions of DRM.


Enero, 2018 | DOI: 10.1021/acs.jpcb.7b03835

A facile shape-controlled synthesis of highly photoactive fluorine containing TiO2 nanosheets with high {001} facet exposure


Lara, M. A.; Sayagues, M. J.; Navio, J. A.; Hidalgo, M. C.
Journal of Materials Science, 53 (2018) 435-446

ABSTRACT

Surface-fluorinated TiO2 materials with high {001} facet exposure were prepared by a simple and high-yield preparation procedure. Faceted/fluorinated samples showed a high photocatalytic performance not only in oxidation processes, tested in phenol and methyl orange degradation, but also in a reduction process as Cr(VI) photoreduction. Reaction rates for these materials greatly exceeded the ones obtained for materials prepared without fluorine addition and for commercial TiO2 Degussa (Evonik) P25 used as reference photocatalyst. A broad characterisation of the samples allowed us to estimate the percentages of different facets and the amount and form in which the fluorine is found on the surfaces. Good photocatalytic behaviour can be ascribed to both high {001} facet exposure and adsorbed fluorine on the photocatalysts surfaces.


Enero, 2018 | DOI: 10.1007/s10853-017-1515-6



2017


Photochemical methane partial oxidation to methanol assisted by H2O2


López Martin, A.; Caballero, A.; Colón, G.
Journal of Photochemistry and Photobiology A: Chemistry, 349 (2017) 216-223

ABSTRACT

The photochemical conversion of methane into methanol from H2O2 aqueous solution as well as the effect of the addition mode were studied. Direct addition of different amounts H2O2 leads to increasing methanol production at the first stage of the reaction. The excess of H2O2 would lead to the reactive oxygen species scavenging and the subsequent O2 production. It was also corroborated that extra hydroxyl radicals in the aqueous medium do not improve the formation of methanol but a noticeable increase in the formation of HCOOH with respect to methanol was evidenced. In contrast, dosing addition at relatively low rates leads to constant methane consumption towards methanol. Methanol formation would be in this case in equilibrium with further oxidation to HCOOH or CO2. This suggests that only a controlled constant availability of HO’s at low concentration can enhance the performance of methanol generation in the photochemical process.


Diciembre, 2017 | DOI: 10.1016/j.jphotochem.2017.09.039

Redox and Catalytic Properties of Promoted NiO Catalysts for the Oxidative Dehydrogenation of Ethane


Delgado, D; Solsona, B; Ykrelef, A; Rodriguez-Gomez, A; Caballero, A; Rodriguez-Aguado, E; Rodriguez-Castellon, E; Nieto, JML
Journal of Physical Chemistry C, 121 (2017) 25132-25142

ABSTRACT

NiO and metal-promoted NiO catalysts (M-NiO, with a M/(M+Ni) atomic ratio of 0.08, with M = Nb, Sn, or La) have been prepared, tested in the oxidative dehydrogenation (ODH) of ethane, and characterized by means of XRD, TPR, HRTEM, Raman, XPS, and in situ XAS (using H-2/He, air or C2H6/He mixtures). The selectivity to ethylene during the ODH of ethane decreases according to the following trend: Nb NiO Sn NiO > La NiO > NiO, whereas the catalyst reducibility (determined by both TPR and XAS using H-2/He mixtures) shows the opposite trend. However, different reducibility and catalytic behavior in the absence of oxygen (ethane/He mixtures) have been observed, especially when comparing Nb- and Sn-promoted NiO samples. These differences can be ascribed mainly to a different phase distribution of the promoter. The results presented here are discussed in terms of the nature of active and selective sites for ODH of ethane in selective and unselective catalysts, but also the role of promoters and the importance of their phase distribution.


Noviembre, 2017 | DOI: 10.1021/acs.jpcc.7b07066

Fischer-Tropsch Synthesis Over Zr-Promoted Co/gamma-Al2O3 Catalysts


Barrientos, J; Garcilaso, V; Venezia, B; Aho, A; Odriozola, JA; Boutonnet, M; Jaras, S
Topics in Catalysis, 60 (2017) 1285-1298

ABSTRACT

Two Zr-modified alumina supports were synthetized containing the same amount of Zr but a different distribution of this modifier over the alumina surface. These supports, together with the unmodified alumina carrier, were used to prepare three cobalt-based catalysts which were characterized and tested under relevant Fischer-Tropsch conditions. The three catalysts presented very similar porosity and cobalt dispersion. The addition of Zr nor its distribution enhanced the catalyst reducibility. The catalyst activity was superior when using a carrier consisting of large ZrO2 islands over the alumina surface. The use of a carrier with a homogeneous Zr distribution had however, a detrimental effect. Moreover, a faster initial deactivation rate was observed for the Zr-promoted catalysts, fact that may explain this contradictory effect of Zr on activity. Finally, the addition of Zr showed a clear enhancement of the selectivity to long chain hydrocarbons and ethylene, especially when Zr was well dispersed.


Noviembre, 2017 | DOI: 10.1007/s11244-017-0813-1

Towards Extending Solar Cell Lifetimes: Addition of a Fluorous Cation to Triple Cation-Based Perovskite Films


Salado, M; Fernandez, MA; Holgado, JP; Kazim, S; Nazeeruddin, MK; Dyson, PJ; Ahmad, S
Chemsuschem, 10 (2017) 3846-3853

ABSTRACT

Organohalide perovskites have emerged as highly promising replacements for thin-film solar cells. However, their poor stability under ambient conditions remains problematic, hindering commercial exploitation. The addition of a fluorous-functionalized imidazolium cation during the preparation of a highly stable cesium-based mixed perovskite material Cs-0.05(MA(0.15)FA(0.85))(0.95)Pb(I0.85Br0.15)(3) (MA= methylammonium; FA= formamidinium) has been shown to influence its stability. The resulting materials, which vary according to the amount of the fluorous-functionalized imidazolium cation present during fabrication, display a prolonged tolerance to atmospheric humidity (> 100 days) along with power conversion efficiencies exceeding 16%. This work provides a general route that can be implemented in a variety of perovskites and highlights a promising way to increase perovskite solar cell stability.


Octubre, 2017 | DOI: 10.1002/cssc.201700797

Synthesis and characterization of Rh/MnO2-CeO2/Al2O3 catalysts for CO-PrOx reaction


Martinez, TLM; Laguna, OH; Lopez-Cartes, C; Centeno, MA
Molecular Catalysis, 440 (2017) 9-18

ABSTRACT

Rh/MnO2-CeO2/Al2O3 catalysts with different manganese-to-ceria ratios have been synthesized, characterized and tested in CO-PrOx reaction. The physicochemical properties of the solids were studied by XRD, Raman spectroscopy, BET surface area, H-2-TPR, TGA-DTG and TEM. The differences observed in the textural, structural and redox properties were related to the Mn-to-ceria ratio of the samples. The segregation of Mn species was observed at high Mn-to-Ce ratios. In opposite way, MnO2-CeO2 solid solutions were obtained at low Mn to Ce ones. In this last case, the physicochemical properties of the solids were favored by the intimate Rh-Ce-Mn contact. The effect of the Mn-Ce presence on Rh catalysts which promotes the catalytic behavior towards selective CO oxidation was observed to be better at low temperatures. At higher temperatures, Mn species promote the Reverse Water Gas Shift reaction, whilst ceria promotes the H-2 oxidation in the whole range of working temperatures.


Octubre, 2017 | DOI: 10.1016/j.mcat.2017.06.018

Cobalt Carbide Identified as Catalytic Site for the Dehydrogenation of Ethanol to Acetaldehyde


A. Rodríguez-Gómez; J.P. Holgado; A. Caballero
ACS Catalysis, 7 (2017) 5243-5247

ABSTRACT

Two cobalt catalysts, Co/SBA-15 and Co/SiO2, have been studied in steam reforming of ethanol (SRE). Besides the steam reforming products, ethoxide dehydrogenation to acetaldehyde is observed as one of the main reactions. Although by hydrogen treatment cobalt is reduced to the metallic state, under SRE conditions, a phase appears that has been identified as cobalt carbide and correlates with acetaldehyde production. These findings provide insights about the catalytic sites, for SRE, in cobalt catalysts. Comparison with previous results shows that these conclusions are not translatable to other cobalt catalysts, stressing the importance of the support on the catalytic behavior of cobalt.


Julio, 2017 | DOI: 10.1021/acscatal.7b01348

Analysis of Ni species formed on zeolites, mesoporous silica and alumina supports and their catalytic behavior in the dry reforming of methane


Drobna, Helena; Kout, Martin; Soltysek, Agnieszka; Gonzalez-Delacruz, Victor M.; Caballero, Alfonso; Capek, Libor
Reaction Kinetics Mechanisms and Catalysis, 121 (2017) 255-274

ABSTRACT

The presented investigation is focused on the analysis of Ni species formed on microporous (zeolites MFI and FAU) and mesoporous materials (Al-MCM- 41 and SBA-15) and alumina supports and their catalytic behavior in the dry reforming of methane. The paper lays emphasis on the relationship between the catalytic behavior of Ni-based catalysts and their textural/structural properties. Ni-based catalysts were prepared by wet impregnation (11 wt% of Ni) followed by calcination in air and reduction in hydrogen. The properties of Ni-based catalysts were also compared prior and after the catalytic tests. The critical role was played by the high value of the specific surface area and the high strength of the interaction between the Ni species and the support, which both determined the high dispersion and stability of metal Ni-0 particles. Ni-Al-MCM-41 and Ni-SBA-15 showed the values of the conversion of CO2 and CH4 above 90% (stable during 12 h). Slightly lower values of the conversion of CO2 and CH4 were observed over Ni-Al2O3 (also stable during 12 h). In contrast to these materials, Ni-MFI and Ni-FAU exhibited the worse metallic Ni-0 particles dispersion and very bad catalytic behavior.


Junio, 2017 | DOI: 10.1007/s11144-017-1149-3

NO photooxidation with TiO2 photocatalysts modified with gold and platinum


Rodriguez, MJH; Melian, EP; Santiago, DG; Diaz, OG; Navio, JA; Rodriguez, JMD
Applied Catalysis B-Environmental, 205 (2017) 148-157

ABSTRACT

In this study, a comparative analysis is made of TiO2 modified with Pt or Au in NO photoxidation under different radiation and humidity conditions. The metals were deposited on the TiO2 surface using two methods, photodeposition and chemical reduction. All catalysts were supported on borosilicate 3.3 plates using a dip-coating technique. These modified photocatalysts were characterized by X-ray diffraction analysis (XRD), UV-vis diffuse reflectance spectra (DRS), Brunauer-Emmett-Teller measurements (BET), transmission electron microscopy (TEM) and X-ray photoelectron spectrum analysis (XPS). It was found from the XPS results that Pt and oxidized Pt species coexist on the samples obtained by photodeposition and chemical reduction. In the case of Au, though other oxidation states were also detected the dominant oxidation state for both catalysts is Au. TEM results showed most Au-C particles are below 5 nm, whereas for Au-P the nanoparticles are slightly bigger. With UV irradiation, the Pt modified catalysts do not show any significant improvement in NO photocatalytic oxidation in comparison with the unmodified P25. For Au, both modified photocatalysts (Au-P and Au-C) exceed the photocatalytic efficiency of the unmodified P25, with Au-C giving slightly better results. The incorporation of metals on the TiO2 increases its activity in the visible region. 


Mayo, 2017 | DOI: 10.10161/j.apcatb.2016.12.006

Critical Role of Oxygen in Silver-Catalyzed Glaser-Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles


Orozco, N; Kyriakou, G; Beaumont, SK; Sanz, JF; Holgado, JP; Taylor, MJ; Espinos, JP; Marquez, AM; Watson, DJ; Gonzalez-Elipe, AR; Lambert, RM
ACS Catalysis, 7 (2017) 3113-3120

ABSTRACT

The essential role of oxygen in enabling heterogeneously catalyzed Glaser–Hay coupling of phenylacetylene on Ag(100) was elucidated by STM, laboratory and synchrotron photoemission, and DFT calculations. In the absence of coadsorbed oxygen, phenylacetylene formed well-ordered dense overlayers which, with increasing temperature, desorbed without reaction. In striking contrast, even at 120 K, the presence of oxygen led to immediate and complete disruption of the organic layer due to abstraction of acetylenic hydrogen with formation of a disordered mixed layer containing immobile adsorbed phenylacetylide. At higher temperatures phenylacetylide underwent Glaser–Hay coupling to form highly ordered domains of diphenyldiacetylene that eventually desorbed without decomposition, leaving the bare metal surface. DFT calculations showed that, while acetylenic H abstraction was otherwise an endothermic process, oxygen adatoms triggered a reaction-initiating exothermic pathway leading to OH(a) + phenylacetylide, consistent with the experimental observations. Moreover, it was found that, with a solution of phenylacetylene in nonane and in the presence of O2, Ag particles catalyzed Glaser–Hay coupling with high selectivity. Rigorous exclusion of oxygen from the reactor strongly suppressed the catalytic reaction. Interestingly, too much oxygen lowers the selectivity toward diphenyldiacetylene. Thus, vacuum studies and theoretical calculations revealed the key role of oxygen in the reaction mechanism, subsequently borne out by catalytic studies with Ag particles that confirmed the presence of oxygen as a necessary and sufficient condition for the coupling reaction to occur. The direct relevance of model studies to a mechanistic understanding of coupling reactions under conditions of practical catalysis was reaffirmed.


Mayo, 2017 | DOI: 10.1021/acscatal.7b00431

Deep insight into Zr/Fe combination for successful Pt/CeO2/Al2O3 WGS catalyst doping


Gonzalez-Castano, M; Ivanova, S; Ioannides, T; Centeno, MA; Odriozola, JA
Catalysis Science & Technology, 7 (2017) 1556-1564

ABSTRACT

Efficient promotion of the Pt/CeO2/Al2O3 catalytic system was achieved by the addition of two different ceria promoters, Zr and Fe. From the exhaustive data analysis, the key features for enhanced catalytic performance and the roles of each doping metal are established. The combination of both doping agents manifests a synergistic effect reflected in noteworthy improvements in H2 reducibility. In addition, the catalyst's doping influences its chemisorptive properties, which is reflected in an increase of the easiness of carbonaceous species desorption, thus leading to superior catalyst resistance toward deactivation.


Abril, 2017 | DOI: 10.1039/c6cy02551j

High UV-photocatalytic activity of ZnO and Ag/ZnO synthesized by a facile method


C. Jaramillo-Páez; J.A. Navío; M.C. Hidalgo; M. Macías
Catalysis Today, 284 (2017) 121-128

ABSTRACT

ZnO nanoparticles have been successfully synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without template addition. We have investigated the effect of annealing temperature in the final surface and structural properties. Photocatalytic studies were performed using two selected substrates, Methyl Orange and Phenol, both as single model substrates and in mixtures of them.

It has been stated that calcination treatments lead to a significant improvement in the photocatalytic properties of the studied samples, even better than TiO2(P25). As expected, the addition of Ag+ during the photocatalytic degradation of MO increases the reaction rate of the degradation of MO, giving a resultant Ag/ZnO photocatalyst which, after recovery, can be reused at least 18 times for the MO degradation tests, being even more photoactive than ZnO.


Abril, 2017 | DOI: 10.1016/j.cattod.2016.11.021

Structural and catalytic properties of Au/MgO-type catalysts prepared in aqueous or methanol phase: application in the CO oxidation reaction


Hernandez, Willinton Y.; Alic, Funda; Navarro-Jaen, Sara; Centeno, Miguel A.; Vermeir, Pieter; Van der Voort, Pascal; Verberckmoes, An
Journal of Materials Science, 52 (2017) 4727-4741

ABSTRACT

Au/MgO and Au/Mg(OH)(2)-type catalysts for CO oxidation reaction were prepared by using two different synthesis methods in presence of either an aqueous or methanol phase. The influence of the porous and morphological properties of the starting magnesium oxide supports was analyzed and correlated with the catalytic performances of the final gold-supported catalysts. It was found that the deposition of gold in the presence of methanol as a solvent avoids the total rehydration of the MgO support and maintains the textural and morphological properties of the starting oxides. The support synthesized by a surfactant-assisted hydrothermal route, having a combined meso-macroporous structure (i.e., MgO-P) showed a positive influence on the CO oxidation reaction as it favored the dispersion of gold and the surface-to-gas phase interaction during the catalytic process.


Abril, 2017 | DOI: 10.1007/s10853-016-0715-9

Monitoring the Reaction Mechanism in Model Biogas Reforming by InSitu Transient and Steady-State DRIFTS Measurements


Bobadilla, LF; Garcilaso, V; Centeno, MA; Odriozola, JA
Chemsuschem, 10 (2017) 1193-1201

ABSTRACT

In this work, the reforming of model biogas was investigated on a Rh/MgAl2O4 catalyst. In situ transient and steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were used to gain insight into the reaction mechanism involved in the activation of CH4 and CO2. It was found that the reaction proceeds through of an initial pathway in which methane and CO2 are both dissociated on Rh metallic sites and additionally a bifunctional mechanism in which methane is activated on Rh sites and CO2 is activated on the basic sites of the support surface via a formate intermediate by H-assisted CO2 decomposition. Moreover, this plausible mechanism is able to explain why the observed apparent activation energy of CO2 is much lower than that of CH4. Our results suggest that CO2 dissociation facilitates CH4activation, because the oxygen-adsorbed species formed in the decomposition of CO2 are capable of reacting with the CHx species derived from methane decomposition.


Marzo, 2017 | DOI: 10.1002/cssc.201601379

Preferential oxidation of CO on a La-Co-Ru perovskite-type oxide catalyst


Pereniguez, R; Caballero, A; Ferri, D
Catalysis Communication, 92 (2017) 75-79

ABSTRACT

A Ru-containing perovskite-type oxide La(Co,Ru)O3 of nominal composition LaCo0.8Ru0.2O3 was prepared by ultrasonic spray combustion and tested for the preferential oxidation of CO (PROX). EXAFS indicated that Ru adopted the coordination environment of Co in LaCoO3 while Co was present as LaCoO3 and Co3O4. PROX activity was replaced by CO hydrogenation activity above 250 °C. Short oxidation at 500 °C between temperature programmed reaction ramps did not restore the initial La(Co,Ru)O3 structure but generated a catalyst with improved PROX activity compared to the initial La(Co,Ru)O3. Under reductive PROX conditions the material experienced structural changes that improved its overall catalytic activity only if the catalyst was oxidized after each temperature programmed ramp.


Marzo, 2017 | DOI: 10.1016/j.catcom.2016.12.020

Identification of Outer and Inner Nickel Particles in a Mesoporous Support: How the Channels Modify the Reducibility of Ni/SBA-15 Catalysts


Rodriguez-Gomez, A; Caballero, A
Chemnanomat, 3 (2017) 94-97

ABSTRACT

Two different nickel supported on SBA-15 catalytic systems have been prepared by means of impregnation (Ni/SBA-15-ImU) and deposition-precipitation (Ni/SBA-15-DP) methodologies. Upon calcination, Ni/SBA-15DP presents a well-developed nickel phyllosilicate phase, which after reduction gives rise to a dispersed and homogeneous metallic phase, mainly located inside the 5 nm in diameter mesoporous structure of the support. On the contrary, as evidenced by XRD and a double temperature programmed reduction (TPR) peak, the Ni/SBA-15-ImU catalyst presents two different NiO phases, which after reduction in hydrogen generate nickel particles in a wide range of sizes. In situ XAS and XPS have unambiguously showed that the distinct TPR profiles obtained for each system are related with particles located in and out the mesoporous structure of the SBA-15 channels. The particles inside the porous are more difficult to reduce, clearly showing a kind of confinement effect of the SBA-15 mesostructure, modifying the reducibility of the NiO phase.


Febrero, 2017 | DOI: 10.1002/cnma.201600297

Gold promoted Cu/ZnO/Al2O3 catalysts prepared from hydrotalcite precursors: Advanced materials for the WGS reaction


Santos, JL; Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA
Applied Catalysis B-Envionmental, 201 (2017) 310-317

ABSTRACT

Outstanding catalysts for the water was shift reaction are reported in this work. The combination of gold nanoparticles with Cu/ZnO/Al2O3 prepared from hydrotalcite-like precursors leads to very promising systems for pure hydrogen production. Full CO conversion is reached at temperatures as low as 180 degrees C. The key point seems to be the cooperation of Au and Cu and the optimal metal-oxide contact derived from the synthesis method. The high activity of gold for low temperature CO oxidation and the suitability of copper for the WGS results in a perfect synergy. Moreover the materials developed in this work present good stability and tolerance towards start/stop cycles an indispensable requisite for a realistic application in an integrated hydrogen fuel processor.


Enero, 2017 | DOI: 10.1016/j.apcatb.2016.08.017

Structuring Pt/CeO2/Al2O3 WGS catalyst: Introduction of buffer layer


Gonzalez-Castano, M; Ivanova, S; Laguna, OH; Martinez, LM; Centeno, MA; Odriozola, JA
Applied Catalysis B-Envionmental, 200 (2017) 420-427

ABSTRACT

This work is devoted to the development of novel structured catalytic system for WGS reaction. The new concept is related to the presence of a pre-catalytic "buffer" layer formed by WGS-inert oxide, i.e. not involved in CO conversion, but able to increase the number of participating sites in water dissociation step during the reaction. The performance of the proposed systems appears to depend strongly on the stream composition, being its effect beneficial in highly reducing atmospheres making it ideal for cleanup application. An increment of the partial kinetic order for water species is observed and reveals the key role of the water activation for superior catalytic behavior. 


Enero, 2017 | DOI: 10.1016/j.apcatb.2016.07.039

Study of the E. coli elimination from urban wastewater over photocatalysts based on metallized TiO2


Murcia, JJ; Avila-Martinez, EG; Rojas, H; Navio, JA; Hidalgo, MC
Applied Catalysis B-Envionmental, 200 (2017) 469-476

ABSTRACT

In this study, a series of photocatalysts based on TiO2 was tested in the elimination of Escherichia coli (E. coli) from urban wastewater. Firstly, TiO2 obtained by sol-gel method was modified by sulfation, and then gold or platinum nanoparticles were photodeposited on sulfated titania surface. Platinized samples were also prepared with different Pt content of 0.5 and 2 wt.%. The samples thus obtained were extensively characterized and it was found that sulfation considerably increases the S-BET value of TiO2 and promotes the anatase phase formation; it was also found that 0.5 wt.% Pt-TiO2 sample presents the lowest noble metal particle size and the best particle dispersion. All the photocatalysts synthesized have shown bactericidal effect and the results obtained by using bare and metalized TiO2 were considerably better than the results obtained with the commercial TiO2 P25 Evonic. Different light intensities were also evaluated in the photocatalytic tests and it was found that 120 W/m(2) leads to obtain the highest E. coli elimination from wastewater samples; however no total elimination of E. coli or other species of bacteria was achieved even after 5 h of photocatalytic treatment without catalyst. Total elimination of the E. coli was achieved after 3 h of photocatalytic reaction by using 120 Wim(2) of light intensity and 2 wt.% Pt-TiO2 as photocatalyst; no bacterial regrowth was observed even after 72 h. 


Enero, 2017 | DOI: 10.1016/j.apcatb.2016.07.045

Gold catalysts screening in base-free aerobic oxidation of glucose to gluconic acid


Megias-Sayago, C.; Ivanova, S.; Lopez-Cartes, C.; Centeno, M.A.; Odriozola, J.A.
Catalysis Today, 279 (2017) 148-154

ABSTRACT

Base-free aerobic oxidation of glucose in presence of Au/Al2O3, Au/CeO2, Au/CeO2(20 wt%)/Al2O3, Au/CeO2(25 wt%)/ZrO2 and Au/CeO2(50 wt%)/ZrO2 catalysts using molecular oxygen at atmospheric pressure is studied. Within the whole series high conversion and selectivity to gluconic acid are observed after 18 h of reaction at 120 degrees C. The activity and especially the selectivity changes are related to the support nature in a way that the higher the Lewis acidity of the support the lower the selectivity to gluconic acid and the higher the production of lactic acid. The highest yield to gluconic acid is obtained over Au/Al2O3 for which the influence of the reaction time, temperature and stirring rate are further evaluated and discussed.


Enero, 2017 | DOI: 10.1016/j.cattod.2016.06.046

Outstanding visible photocatalytic activity of a new mixed bismuth titanatate material


Zambrano, P; Sayagues, MJ; Navio, JA; Hidalgo, MC
Applied Surface Science, 394 (2017) 16-24

ABSTRACT

In this work, a new photocatalyst based on bismuth titanates with outstanding visible photocatalytic activity was prepared by a facile hydrothermal method. The synthesised material showed visible activity as high as UV activity of commercial TiO2 P25 under the same experimental conditions for phenol degradation. A wide characterisation of the photocatalyst was performed. The material was composed of three phases; majority of Bi20TiO32 closely interconnected to Bi4Ti3O12 and amorphous TiO2. The high visible activity showed by this material could be ascribed to a combination of several features; i.e. low band gap energy value (2.1 eV), a structure allowing a good separation path for visible photogenerated electron-holes pairs and a relatively high surface area. This photocatalyst appeared as a promising material for solar and visible applications of photocatalysis.


Enero, 2017 | DOI: 10.1016/j.apsusc.2016.10.042

Mixed alpha-Fe2O3/Bi2WO6 oxides for photoassisted hetero-Fenton degradation of Methyl Orange and Phenol


Jaramillo-Paez, C; Navio, JA; Hidalgo, MC; Bouziani, A; El Azzouzi, M
Journal of Photochemistry and Photobiology A-Chemistry, 332 (2017) 521-533

ABSTRACT

Mixed oxides, alpha-Fe2O3/Bi2WO6, were prepared using a mechanical mixing procedure by adding to the Bi2WO6 previously obtained by hydrothermal method the corresponding amount of a prepared alpha-Fe2O3, the latter obtained by thermal decomposition of Fe(NO3)center dot 9H(2)O. The physicochemical surface, structural, morphological characteristics and optical properties of the samples, single and mixed, were determined by BET, XRD, FE-SEM, XPS and UV-vis diffuse reflectance spectroscopy. UV-vis diffuse reflectance spectra showed that incorporating a 5%wt. of alpha-Fe2O3 to the corresponding amount of Bi2WO6 sample broadened the visible light absorption of Bi2WO6 as expected. The photocatalytic activity, of single and mixed catalysts, to degrade a selected dye such as Methyl Orange (MO) as well as the transparent substrate Phenol (Ph) was studied, in aqueous medium (pH 5.5) under UV and sun-like illumination conditions in the absence and presence of H2O2. In the present study the use of a alpha-Fe2O3/Bi2WO6/H2O2 system demonstrate much higher photocatalytic efficiency to degrade both MO and Ph than pristine Bi2WO6 or alpha-Fe2O3, single or mixed. Using the system alpha-Fe2O3/Bi2WO6/H2O2, around 85% of MO was degraded in 60 min under sun-like illumination whereas 100% was degraded in 60 min under UV-illumination. However, just around 30% of Ph was degraded in 120 min in the alpha-Fe2O3/Bi2WO6/H2O2 system under sun-like illumination whereas around a 95% was degraded in 90 min under UV-illumination. Under UV illumination, the generation of hydroxyl radicals is favorable; whereas under sun-like illumination, only the small fraction of the UV can produces the center dot OH. Under illumination, the H2O2 could react with photoinduced electrons from the photocatalysts leading to the production of hydroxyl radicals (center dot OH).


Enero, 2017 | DOI: 10.1016/j.jphotochem.2016.09.031



2016


Intensifying glycerol steam reforming on a monolith catalyst: A reaction kinetic model


Bobadilla, LF; Blay, V; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Chemical Engineering Journal, 306 (2016) 933–941

ABSTRACT

In this work, a structured monolithic catalyst has been tested under a wide range of conditions (partial pressure, residence time, temperature and time-on-stream), with the aim of modeling its kinetic behavior and assessing its economic and upscaling potential. We have developed a sequential model to help us interpret both main trends and salient features. Unexpected behavior was found for certain parameter values, which led us to consider kinetic parasitic effects such as mass or heat transfer limitations. By independently invoking these effects, a conciliatory view of the results observed could not be reached. A combined explanation may prove successful, although overfitting could not be ruled out at this point. More importantly, however, the observed salient features of this stable and selective monolith catalyst may hold potential for process intensification of glycerol steam reforming, thus contributing to a more sustainable industry.


Diciembre, 2016 | DOI: 10.1016/j.cej.2016.08.021

Influence of the ionic liquid presence on the selective oxidation of glucose over molybdenum based catalysts


Megias-Sayago, C; Carrasco, CJ; Ivanova, S; Montilla, FJ; Galindo, A; Odriozola, JA
Catalysis Today, 278 (2016) 82-90

ABSTRACT

Two different approaches are proposed in this work in order to study the influence of the ionic liquid presence in the reaction of glucose oxidation by H2O2 in mild conditions. The ionic liquids are applied either as a solvent by using homogeneous Mo based catalyst, [Mo(O)(O2)2(H2O)n] complex, or by using it as an integral part of a heterogeneous catalyst, organic inorganic hybrids based on Mo Keggin structure. Both catalytic strategies resulted in acceptable glucose transformation degrees but lead to different oxidation products depending on the role of the ionic liquid. The hybrid approach restrains the number of the received products being the most selective one. A detailed study of the effect of the hybrid nature and reaction conditions is proposed in the second part of this study.


Diciembre, 2016 | DOI: 10.1016/j.cattod.2016.06.040

Selectivity control in oxidation of 1-tetradecanol on supported nano Au catalysts


Martinez-Gonzalez, S; Ivanova, S; Dominguez, MI; Corberan, VC
Catalysis Today, 278 (2016) 113-119

ABSTRACT

Selective oxidation of tetradecanol, a model higher fatty alcohol, on Au/CeO2-Al2O3 catalyst has been investigated to assess the factors that control selectivity. The analysis of the effect of operation conditions (temperature, run time and alcohol/metal (AIM) ratio) on catalytic performance revealed a quite complex reaction network, in which acid formation starts only after a certain level of conversion is reached. This level depends linearly on the total support surface available, indicating that it must be saturated by species generated by the reaction itself to allow acid formation to start. Addition of water to reaction medium did not modify this level, indicating that such species is not adsorbed water, as previously hypothesized, but probably spilled over hydrogen species. The resulting drastic change in the selectivity trends makes the ratio A/M a critical factor to control selectivity to aldehyde and to acid. Selectivity to ester is less sensible to operation parameters. It is noteworthy that aldehyde yields up to 27% with 90% selectivity, and acid yields up to 40% with 81% selectivity can be reached by proper selection of operation parameters.


Diciembre, 2016 | DOI: 10.1016/j.cattod.2016.06.019

WGS and CO-PrOx reactions using gold promoted copper-ceria catalysts: "Bulk CuO-CeO2 vs. CuO-CeO2/Al2O3 with low mixed oxide content"


Reina, TR; Ivanova, S; Laguna, OH; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 197 (2016) 62-72

ABSTRACT

A copper-ceria bulk catalyst has been compared to a series of catalysts designed according to the as called "supported approach", corresponding to the dispersion of low content mixed copper-ceria oxide on alumina matrix. The principal characteristics of both types of catalysts are contemplated and the differences in their electronic and redox properties discussed in details. As a plus, the gold metal promotion of the catalysts is also envisaged. The advantages of the systems in the CO clean up reactions, WGS and CO-PrOx are commented. While the WGS activity appears to be ruled especially by the Cu/Ce surface to volume ratio, the CO-PrOx reaction is governed by the CuO loading. Gold addition provides benefits only at the low temperature WGS regime. Very importantly, the supported systems are always superior to the bulk configuration in terms of specific activity, a key factor from the catalyst's design perspective. 


Noviembre, 2016 | DOI: 10.1016/j.apcatb.2016.03.022

Recycling of construction and demolition waste generated by building infrastructure for the production of glassy materials


Dominguez, A; Dominguez, MI; Ivanova, S; Centeno, MA; Odriozola, JA
Ceramics International, 42 (2016) 17217-175223

ABSTRACT

The use of waste materials generated by construction and demolition industry to yield valuable glassy materials, i.e. enamel for glazed ceramic tiles and cellular glasses is presented in this study. Both types of materials are produced by one-step treatment at moderate temperatures after simple waste chemical composition adjust. The enamels are manufactured directly from the initial waste powder by melting, while the expanded materials result from mixing of the vitreous material obtained after waste vitrification with an adequate foaming agent and posterior thermal treatment. Through the manuscript the feasibility of one step production of second generation profit materials is discussed in order to help achieving sustainable development and environmental protection.


Noviembre, 2016 | DOI: 10.1016/j.ceramint.2016.06.157

Forced deactivation and postmortem characterization of a metallic microchannel reactor employed for the preferential oxidation of CO (PROX)


Laguna, OH; Dominguez, MI; Centeno, MA; Odriozola, JA
Chemical Engineering Journal, 302 (2016) 650-662

ABSTRACT

This manuscript is one of the few works presenting evidences of the effect of prolonged use of a microreactor. Our reactor has been designed for the PROX reaction. Near to 550 h of operation under different feed-streams, including CO2 and H2O, in the 100-300 degrees C temperature range, and several regeneration cycles, and a final forced deactivation during similar to 360 h resulted in the permanent loss of activity of the microreactor. This could be attributed to some phenomena whose have compromised the chemical nature of the catalyst and that of the reactor including: displacement of the coating to the mouth of the channels, detachments and cracks of the catalytic layer, migration of some elements of the metallic substrate to the surface (Fe, Cr, Y), and deposition of carbonaceous species from the reaction over the catalytic layer and/or the metallic substrate. Furthermore, sulfur compounds were detected in both inlet and outlet zones of the microreactor, coming probably from a lubricant applied over the screws that sealed the assembling of the microreactor. 

This is a first approach for understanding possible effects of deactivation during long-term applications of a microreactor in the PROX reaction that could be considered as a case study useful for future designs of this kind of devices. The presented information could be extrapolated to similar reactions where thermal treatments along with highly corrosive atmospheres would be applied, in order to carry out a more appropriate design of future generations" of microreactors, with a longer useful life. For that purpose not only the adequate selection of the catalysts must be done, but also the adequate choice of the fabrication material of the reactors is needed. 


Octubre, 2016 | DOI: 10.1016/j.cej.2016.05.104

Au-supported on Fe-doped ceria solids prepared in water-in-oil microemulsions: Catalysts for CO oxidation


Laguna, OH; Centeno, MA; Boutonnet, M; Odriozola, JA
Catalysis Today, 278 (2016) 140-149

ABSTRACT

Gold catalysts were synthesized by deposition-precipitation employing Fe-doped ceria systems, previously obtained by means of the water-in-oil microemulsions methodology with different iron contents (10, 25 and 50 Fe at.%). The final catalysts were tested in the CO oxidation reaction in presence of H2. After gold deposition the crystalline structure of the supports was not altered. Moreover no XRD lines associated to gold were detected, indicating its high dispersion. Solid solution was generated in all samples, although the segregation of iron oxide was detected for the material with the highest iron loading. This phenomenon was then enhanced for the corresponding gold catalyst that also presented sintering of the gold nanoparticles.

Strong interaction between gold and the oxygen vacancies of the supports was demonstrated, as well as the promotion of the reducibility of surface Ce4+ and Fe3+species at low temperatures. A remarkable promotion of the CO conversion at lower temperatures respect to that of the supports was observed for the gold catalysts. Below 120 °C, lower the amount of iron incorporated, higher the catalytic performance of the catalyst. This behaviour is closely related not only to a high gold dispersion but also to the ability for creating additional oxygen vacancies in the support, required for the CO oxidation reaction.


Octubre, 2016 | DOI: 10.1016/j.cattod.2016.05.059

Au/CeO2 Catalysts: Structure and CO Oxidation Activity


Centeno, MA; Reina, TR; Ivanova, S; Laguna, OH; Odriozola, JA
Catalysts, 6 (2016) 158

ABSTRACT

In this comprehensive review, the main aspects of using Au/CeO2 catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reactions.


Octubre, 2016 | DOI: 10.3390/catal6100158

Liquid-phase oxidation with hydrogen peroxide of benzyl alcohol and xylenes on Ca-10(PO4)(6)(OH)(2) - CaWO4


Dominguez, MI; Cojocaru, B; Tudorache, M; Odriozola, JA; Centeno, MA; Parvulescu, VI
Comptes Rendus Chimie, 19 (2016) 1156-1165

ABSTRACT

A W-containing apatite (W/HAp) catalyst was prepared following a hydrothermal synthesis route and served as a model catalyst. Crystallographic analysis indicated that the resulting material contained hydroxyapatite, Ca10-3xWx(PO4)(6)(OH)(2), W-hydroxyapatite, calcium tungstate, CaWO4, and tricalcium phosphate, Ca-3(PO4)(2). The catalyst was investigated in liquid phase oxidation of benzyl alcohol and xylenes using hydrogen peroxide as an oxidant. For comparison, commercial calcium phosphate, hydroxyapatite and CaWO4 were tested in the same reaction. Calcium phosphate and hydroxyapatite appeared as inactive and decomposed hydrogen peroxide non-selectively. A moderate activity but low hydrogen peroxide efficiency was observed for the CaWO4 phase. In contrast, the W/HAp catalyst showed a reasonable activity and a better hydrogen peroxide efficiency in the oxidation of benzyl alcohol and xylenes. This new W/HAp catalyst showed, after six cycles, losses of the activity below 15% compared to the fresh catalyst with no effect on the selectivity. It is noteworthy that ICP-OES analyses showed no tungsten leaching that is the main advantage of this catalyst. 


Octubre, 2016 | DOI: 10.1016/j.crci.2015.10.013

Growth of carbonaceous nanomaterials over stainless steel foams. Effect of activation temperature


Latorre, N; Cazana, F; Sebastian, V; Royo, C; Romeo, E; Centeno, MA; Monzon, A
Catalysis Today, 273 (2016) 41-49

ABSTRACT

Some of the problems that occur during the operation of chemical reactors based of structured catalytic substrates, as monoliths, foams, membranes, cloths, fibres and other systems, are related to the preparation of long term stable coatings. Frequently, the deposition of the catalytic layer is carried out by washcoating, requiring this step a cautious attention, especially in the case of complex geometries, like of that of foams or cloths. In the case of the deposition of layers of carbonaceous materials (CNMs), an alternative route, avoiding the washcoating, it is their direct growth by catalytic decomposition light hydrocarbons (also called CCVD), over the surface of the metallic substrate. In this case, if the metallic substrate is of stainless steel, it already contains the catalytic active phases like Fe and Ni. 

In order to optimize the process of CNMs growth over structured metallic substrates, we are studying the effect of the main operational variables of the ethane decomposition reaction on stainless steel foams. In this contribution we present a study of the influence of the temperature of the activation (oxidation and reduction) stage on the type and morphology of the carbonaceous materials formed. The results obtained allow us to determine the optimal operating conditions to maximize the amount and the selectivity of the process to obtain a given type of CNM.


Septiembre, 2016 | DOI: 10.1016/j.cattod.2016.02.063

Photocatalytic Escherichia coli inactivation by means of trivalent Er3+, Y3+ doping of BiVO4 system


Adan, C; Marugan, J; Obregon, S; Colon, G
Applied Catalysis A-General, 526 (2015) 126-131

ABSTRACT

BiVO4 samples doped with different contents of Er3+ and Y3+ were prepared by a simple surfactant free hydrothermal method. X-ray diffraction reveals that the doped materials consist of a heterogeneous structure formed by a mixture of tetragonal and monoclinic phases, being found Er3+ and Y3+ co-doping clearly stabilize the tetragonal structure of BiVO4. The monoclinic BiVO4 samples shows a strong absorption in the visible light region leading to band-gap values of around 2.4eV while the tetragonal BiVO4 displays higher band-gap values of 2.9 eV. The photocatalytic activity of the catalysts was investigated for the oxidation of methanol and inactivation of Escherichia coli showing that all the BiVO4 catalysts are photocatalytically active in the oxidation of methanol and are able to inactivate more than 99.99% of bacteria not only under UV light but also under visible light irradiation. The results revealed that the co-doping of Er3+ and Y3+ into BiVO4 exhibited enhanced photocatalytic activity for methanol oxidation under simulated solar light irradiation. The inactivation of E.coli show similar results for the doped systems although in relative terms of activity the Er3+,Y3+-BiVO4 sample show a better use of the visible light, leading to a higher activity than P25-TiO2.


Septiembre, 2016 | DOI: 10.1016/j.apcata.2016.08.002

Impact of structured catalysts in amine oxidation under mild conditions


J.L. Santos; P. Navarro; J.A. Odriozola; M.A. Centeno; O.D. Pavel; B. Jurca; V.I. Pàrvulescu
Catalysis Today, 273 (2016) 266-272

ABSTRACT

A structured graphene/graphite catalyst grown on a commercial austenitic stainless steel sheet providing a micromonolith was obtained by submitting the nude stainless steel structure to a carbon-rich atmosphere (first 300 mL/min of a reductive H-2/N-2 (1:1) flow, then to 180 mL/min of a CH4/H-2 (1:5)) at high temperature (900 degrees C) for 2 h. The preparation procedure resulted in a homogenous surface coated with a carbon-rich film as observed by EDX and SEM images. Further characterizations by Raman spectroscopy revealed characteristic Raman lines of graphene and crystalline graphite disposed in a hierarchical organization. The disposal of the obtained surface layers was also confirmed by grazing incidence X-ray diffraction. Besides this, XRD indicated the overlapping diffraction lines of graphite, cementite and M7C3 carbides. The graphene nature of the outermost layer was also confirmed by XPS. The catalytic behavior of the structured graphene/graphite catalyst was evaluated in the selective oxidation of heptylamine. At 200 degrees C it afforded a total conversion with a combined selectivity in heptanonitrile and N-heptylidene-heptylamine of 67% (10% heptanonitrile) that corresponds indeed to a very efficient system in the absence of any metal. Kinetic experiments with the scope to calculate the activation energies were also performed. 


Septiembre, 2016 | DOI: 10.1016/j.cattod.2016.05.001

Photocatalytic removal of patent blue V dye on Au-TiO2 and Pt-TiO2 catalysts


Vaiano, V; Iervolino, G; Sannino, D; Murcia, JJ; Hidalgo, MC; Ciambelli, P; Navio, JA
Applied Catalysis B: Environmental, 188 (2016) 134-146

ABSTRACT

In this work it was studied the efficiency of a photocatalytic process for the removal of patent blue V. This dye is very difficult to remove by conventional treatments such as adsorption or coagulation therefore the photocatalytic process is a very interesting alternative for the removal this dye mainly because it does not require expensive oxidants and it can be carried out at mild temperatures and pressures. In this work it was tested the efficiency of Au-TiO2 and Pt-TiO2 photocatalysts in the Patent blue V removal. The Au-TiO2 catalysts were prepared by two different methods: chemical reduction and photochemical deposition; Pt-TiO2 catalysts were obtained only by photochemical deposition. In the synthesis of the catalysts prepared by photochemical deposition, it was evaluated the influence of some parameters, such as deposition time and the intensity of the light source over the physicochemical properties and photocatalytic activity of the materials obtained. An analysis of the effect of the catalyst dosage and initial patent blue V concentration over the dye degradation efficiency was also attempted. 
In general, it was observed that the presence of Au or Pt on TiO2 enhances the patent blue V photodegradation; it was found that noble metal particle size and distribution on TiO2 surface are important factors influencing the dye removal. The highest dye degradation was obtained over the Au-TiO2 catalyst prepared by photochemical deposition, using high light intensity and 15 min of deposition time during the synthesis. A discoloration and a total organic carbon (TOC) removal of 93 and 67% respectively, were obtained over this material after 180 min of UV irradiation. These values are higher than that the obtained on S-TiO2 (discoloration and TOC removal of about 25% and 3%, respectively).


Julio, 2016 | DOI: 10.1016/j.apcatb.2016.02.001

Photocatalytic hydrogen production from degradation of glucose over fluorinated and platinized TiO2 catalysts


Iervolino, G; Vaiano, V; Murcia, JJ; Rizzo, L; Ventre, G; Pepe, G; Campiglia, P; Hidalgo, MC; Navio, JA; Sannino, D
Journal of Catalysis, 339 (2016) 47-56

ABSTRACT

The present work reports the renewable hydrogen production by photocatalytic degradation of glucose over commercial and home prepared TiO2 modified by the simultaneous presence of fluorine and Pt (Pt-F-TiO2). The obtained materials were widely characterized by different techniques (XRD, SBF, UV-Vis DRS, XRF, SEM and TEM) and it was found that surface area, anatase/rutile ratio and the distribution and size of the platinum particles are important factors influencing the effectiveness of these materials in the H-2 production. The photocatalytic H-2 production from the glucose solution was 97 mu mol of H-2 after 3 h of irradiation on home prepared TiO2 modified by F and Pt addition, while a lower value corresponding to 31 mu mol of H-2 was obtained on commercial TiO2 modified by F and Pt, after 3 h of irradiation. The hydrogen production rate increased by decreasing the initial pH of solution reaching the highest value of about 590 mu mol h(-1) g(-1) after 3 h of irradiation time at pH = 2. Accordingly, sugar containing wastewaters from food industry has the potential for producing hydrogen by photocatalytic process while removing organics before disposal or reuse. 


Julio, 2016 | DOI: 10.1016/j.jcat.2016.03.032

The role of Au, Cu & CeO2 and their interactions for an enhanced WGS performance


Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA
Applied Catalysis B: Environmental, 187 (2016) 98-107

ABSTRACT

The WGS reaction over multicomponent Au/Ce1-xCuxO2/Al2O3 catalysts is studied in this work. The systems are carefully designed aiming to take advantage of every active phase included in the formulation: gold, ceria and copper. Special emphasis is given to the CeO2-CuO synergy and its influence on the displayed catalytic performance with and without gold. To this aim a meaningful correlation between the physicochemical properties of the mixed materials and their activity/stability is proposed. In general terms the developed catalysts present high activity under realistic WGS reaction conditions, with fairly good long term stability. In addition, the systems successfully withstand start-up/shut-downs situations, indispensable requisite for real applications in the field of pure hydrogen production for fuel cell goals. 


Junio, 2016 | DOI: 10.1016/j.apcatb.2016.01.031

In-situ hydrogasification/regeneration of NiAl-hydrotalcite derived catalyst in the reaction of CO2 reforming of methane: A versatile approach to catalyst recycling


Abdelsadek, Z; Sehailia, M; Halliche, D; Gonzalez-Delacruz, VM; Holgado, JP; Bachari, K; Caballero, A; Cherifi, O
Journal of CO2 Utilization, 14 (2016) 98-105

ABSTRACT

A novel approach describing the in-situ regeneration of NiAl hydroalcite derived catalyst between two cycle reaction systems of CO2 reforming of methane, also known as dry reforming of methane (DRM) is described herein. The catalyst was initially prepared by co-precipitation method at pH = 11 and calcined at 450 degrees C for 6 h. The obtained material was characterized using X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry (TG/ATD) and temperature programmed reduction (TPR-H-2) techniques. Following treatment of our catalyst under DRM conditions, the catalyst was subjected to in-situ hydrogasification conditions to promote regeneration followed by a second DRM cycle. An increase of 15.7% in the conversion of CH4 and 17.3% in the conversion of CO2 was attained, while the ratio of resulting H-2/CO augmented by 14%. The ratio of H-2 consumed over the course of two hours hydrogasification, to that generated over ten hours of DRM, was 9.6%. The small particle sizes of resulting Ni degrees species as well as their high stability were both key factors contributing to the increase in the amount of H-2/CO produced prior to and after regeneration. 


Junio, 2016 | DOI: 10.1016/j.jcou.2016.03.004

Nickel catalyst with outstanding activity in the DRM reaction prepared by high temperature calcination treatment


Smolakova, L; Kout, M; Capek, L; Rodriguez-Gomez, A; Gonzalez-Delacruz, VM; Hromadko, L; Caballero, A
International Journal of Hydrogen Energy, 41 (2016) 8459-8469

ABSTRACT

The catalytic performance of some Ni-Ce/Al2O3 catalytic systems (11 wt.% Ni and 3 wt.% Ce) were checked after being submitted to different calcination and reduction treatments. It was found that, the reduced Ni-Ce/Al2O3 catalysts were more active and stable in the dry reforming reaction of methane than thecorresponding not-reduced catalysts. This high activity was initially connected with the smaller size of pre-reduced Ni species, which at the same time leads on to the formation of filamentous carbon. The best overall performance was obtained for the reduced catalyst after being calcined at 1000 degrees C. This catalyst presents a very high stability, a low level of carbon formation, maintaining the nickel particle size constant during reaction. Surprisingly, although its reduction degree is only 12% at 750 degrees C, its catalytic activity is similar to the full reduced catalysts. So, the small number of reduced metallic particles of this catalyst shows a very high activity, much higher than the other catalysts.


Junio, 2016 | DOI: 10.1016/j.ijhydene.2016.03.161

Promoting effect of Sn on supported Ni catalyst during steam reforming of glycerol


Bobadilla, LF; Romero-Sarria, F; Centeno, MA; Odriozola, JA
International Journal of Hydrogen Energy, 41 (2016) 9234-9244

ABSTRACT

The promoting effect of Sn on the catalytic performance of supported Ni catalyst in the reaction of glycerol steam reforming was studied. The physico-chemical properties of the prepared samples were investigated by X-ray fluorescence (XRF), BET surface area, in situ X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and temperature-programmed oxidation (TPO) techniques. The characterization results of the samples after reduction treatment (in the same conditions than the activation before catalytic activity measurements) revealed the formation of NiSn alloy. The Sn-doped catalyst exhibited a high activity and it was demonstrated that the Sn addition increase the catalyst stability and durability by decreasing the coke deposition.


Junio, 2016 | DOI: 10.1016/j.ijhydene.2016.04.119

The role of carbon overlayers on Pt-based catalysts for H-2-cleanup by CO-PROX


Romero-Sarria, F; Garcia-Dali, S; Palma, S; Jimenez-Barrera, EM; Oliviero, L; Bazin, P; Odriozola, JA
Surface Science, 648 (2016) 84-91

ABSTRACT

In this work, we analyze the effect of the activation method on the catalytic activity of Pt-based catalysts supported on alumina in the PROX reaction. For this, model Pt/Al2O3 catalysts with variable amounts of acetic acid were prepared and their thermal evolution studied by FTIR spectroscopy. From the analysis of the nature of the platinum surface upon acetic acid decomposition and the gas phase evolved products, we have demonstrated the formation of partially hydrogenated carbon overlayers that tailor the activity of Pt-based catalysts in the PROX reaction. 


Junio, 2016 | DOI: 10.1016/j.susc.2015.12.017

O-2-assisted Water Gas Shift reaction over structured Au and Pt catalysts


Gonzalez-Castano, M; Reina, TR; Ivanova, S; Tejada, LMM; Centeno, MA; Odriozola, JA
Applied Catalysis B: Enviromental, 185 (2016) 337-343

ABSTRACT

Platinum and gold structured catalysts were compared as active phases in classical and O2-assisted Water Gas Shift (WGS) reaction. Both metals were supported on iron-doped ceria mixed oxide and then, structured on metallic micromonolithic devices. As expected the WGS activity of both micromonoliths is conditioned by the nature of the noble metals being Pt the most active metal in traditional conditions. However, the addition of oxygen to the classical water gas feed turns the balance in favor of the gold based catalysts, being the presence of gold responsible for an excessive improvement of the catalytic activity.


Mayo, 2016 | DOI: 10.1016/j.apcatb.2015.12.032

Cascade charge separation mechanism by ternary heterostructured BiPO4/TiO2/g-C3N4 photocatalyst


Obregon, S; Zhang, YF; Colon, G
Applied Catalysis B: Enviromental, 184 (2016) 96-103

ABSTRACT

A complex ternary BiPO4/TiO2/gC(3)N(4) heterostructure has been obtained from a simple impregnation method having good photoactivities for the degradation of phenol under solar-like irradiation. From the wide structural, surface and electronic characterization, we have stated that the formation of the ternary heterojunction notably affect photoactivity of pristine TiO2. Thus, the best result for the binary system was obtained for 70 wt%TiO2-30 wt% BiPO4 system. The incorporation of gC(3)N(4) leads to a further improvement on the photocatalytic activity when it is specifically done over TiO2. By means of photoluminescence spectroscopy and reactive oxygen species formation test, we propose that the effective charge carrier separation is taking place through a cascade-driven electronic mechanism. Therefore, by choosing the adequate band-engineering tailoring an important improved photoactivity can be achieved. 


Mayo, 2016 | DOI: 10.1016/j.apcatb.2015.11.027

Towards the hydrogen production by photocatalysis


Colon, G
Applied Catalysis A-General, 518 (2016) 48-59

ABSTRACT

Nowadays, problems derived from climate change urgently demand us to focus our attention on new alternatives to fossil fuels. Within this framework, the photocatalytic production of hydrogen as a clean fuel from oxygenates arises as a necessary option that must be considered. Thus, the development of highly efficient photocatalyst is crucial in order to achieve a viable technology under the industrial point of view. For this sake, it is necessary to understand the principles of photoreforming reaction. In this brief review we will revisit the different photocatalytic materials proposed in the literature highlighting on the role of different co-catalysts.


Mayo, 2016 | DOI: 10.1016/j.apcata.2015.11.042

Nanogold mesoporous iron promoted ceria catalysts for total and preferential CO oxidation reactions


Reina, TR; Ivanova, S; Idakiev, V; Tabakova, T; Centeno, MA; Deng, QF; Yuan, ZY; Odriozola, JA
Journal of Molecular Catalysis A-Chemical, 414 (2016) 62-71

ABSTRACT

Herein, a series of highly efficient gold based catalysts supported on mesoporous CeO2-Fe2O3 mixed oxides for CO elimination reactions have been developed. The materials have been fully characterized by means of XRD, Raman and UV-vis spectroscopies among other techniques. We identify the Ce-Fe synergism as a fundamental factor controlling the catalytic performance. Our data clearly reveal that the CO oxidation activity is maximized when the electronic and structural properties of the support are carefully controlled. In this situation, fairly good catalysts for environmental applications as for example H-2 streams purification for fuel cell goals or CO abatement at room temperature can be designed. 


Abril, 2016 | DOI: 10.1016/j.molcata.2016.01.003

Comparison of supported TiO2 catalysts in the photocatalytic degradation of NOx


Rodriguez, MJH; Melian, EP; Diaz, OG; Arana, J; Macias, M; Orive, AG; Rodriguez, JMD
Journal of Molecular Catalysis A-Chemical, 413 (2016) 56-66

ABSTRACT

A comparison is made in this study of the effectiveness of various commercial catalysts in the oxidation of NOx by heterogeneous photocatalysis. The following catalysts were considered: Aeroxide TiO2 P25, Aeroxide TiO2 P90, Hombikat UV-100, Kronos vlp7000, CristalACTIV PC105, CristalACTIV PC500, Kemira 650 and Anatasa Aldrich. All catalysts were deposited by a dip -coating technique onto borosilicate 3.3 glass plates. Optimization of catalyst load showed no significant enhancement of photoactivity, in general, above a deposited mass of 1.16 mg cm(-2). Differences between photocatalyst activity were more apparent at longer illumination times. Photoactivity decreased in the presence of humidity and differences in the adsorbed products were detected. Photocatalyst activity was strongly influenced by specific surface area, with the best results obtained by the catalysts with the largest surface area, namely the PC500, Hombikat and Kronos. Photocatalyst stability was demonstrated in successive reuse cycles. 


Marzo, 2016 | DOI: 10.1016/j.molcata.2015.12.007

TiO2-clay based nanoarchitectures for enhanced photocatalytic hydrogen production


Perez-Carvajal, J; Aranda, P; Obregon, S; Colon, G; Ruiz-Hitzky, E
Microporous and Mesoporous Materials, 222 (2016) 120-127

ABSTRACT

New functional TiO2-clay nanoarchitectures based on layered and fibrous silicates and incorporating Pd and Pt noble metal nanoparticles (NPs) have been synthesized by applying a sol–gel methodology that involves the use of commercial organoclays. The incorporation of the noble metal NPs can be done using two different approaches: i) direct addition to the synthesis medium of a noble metal precursor (typically acetylacetonate) during the generation of the nanoarchitecture, and ii) selective photodeposition of the noble metal NPs in a post-treatment of the TiO2-clay nanoarchitecture. The resulting materials have been characterized by means of XRD, FTIR, Raman, 29Si-NMR, FE-SEM, TEM and N2 adsorption–desorption isotherms. The efficiency of these nanoarchitectures in the photocatalytic hydrogen production has been tested in the photoreforming of methanol. The higher rate in the hydrogen production corresponds to the nanoarchitectures containing Pt and TiO2 NPs derived from sepiolite.


Marzo, 2016 | DOI: 10.1016/j.micromeso.2015.10.007

Intensification of hydrogen production by methanol steam reforming


Sanz, O; Velasco, I; Perez-Miqueo, I; Poyato, R; Odriozola, JA; Montes, M
International Journal Hydrogen Energy, 41 (2016) 5250-5259

ABSTRACT

This paper studies the methanol steam reforming intensification to enhance the hydrogen production in a multi-channel block type micro-reformer. The effects of operating parameters such as reforming temperature, space velocity and catalyst layer thickness on reforming performance are investigated. For optimized design and operating conditions, the 8 cm(3) reformer unit produced 170 LH2/h containing on dry basis 75.0% H-2, 23.5% CO2, 0.06% CH3OH and 1.44% CO at 648 K allowing the production of 218-255 Win a commercial PEMFC with 80% hydrogen utilization. This study shows that high methanol conversion can be achieved with high Pd/ZnO catalyst loading at 648 K with very low CO content (<1.5%) in the outlet stream. 


Marzo, 2016 | DOI: 10.1016/j.ijhydene.2016.01.084

In-situ Raman spectroscopy study of Ru/TiO2 catalyst in the selective methanation of CO


Martinez Tejada, LM; Munoz, A; Centeno, MA; Odriozola, JA
Journal of Raman Spectroscopy, 47 (2016) 189-197

ABSTRACT

Raman spectroscopic technique has been used to characterize a Ru/TiO2 catalyst and to follow in situ their structural changes during the CO selective methanation reaction (S-MET). For a better comprehension of the catalytic mechanism, the in-situ Raman study of the catalysts activation (reduction) process, the isolated CO and CO2 methanation reactions and the effect of the composition of the reactive stream (H2O and CO2 presence) have been carried out. Raman spectroscopy evidences that the catalyst is composed by islands of TiO2-RuO2 solid solutions, constituting Ru-TiO2 interphases in the form of RuxTi1-xO2 rutile type solid solutions. The activation procedure with H-2 at 300 degrees C promotes the reduction of the RuO2-TiO2 islands generating Ru-o-Ti3+ centers. The spectroscopic changes are in agreement with the strong increase in chemical reactivity as increasing the carbonaceous intermediates observed. The selective methanation of CO proceeds after their adsorption on these Ru-o-Ti3+ active centers and subsequent C?O dissociation throughout the formation of CHx/CnHx/CnHxO/CHx?CO species. These intermediates are transformed into CH4 by a combination of hydrogenation reactions. The formation of carbonaceous species during the methanation of CO and CO2 suggests that the CO presence is required to promote the CO2 methanation. Similar carbonaceous species are detected when the selective CO methanation is carried out with water in the stream. However, the activation of the catalysts occurs at much lower temperatures, and the carbon oxidation is favored by the oxidative effect of water.


Febrero, 2016 | DOI: 10.1002/jrs.4774

Ru-Ni Catalyst in the Combined Dry-Steam Reforming of Methane: The Importance in the Metal Order Addition


Alvarez, MA; Centeno, MA; Odriozola, JA
Topics in Catalysis, 59 (2016) 303-313

ABSTRACT

Biogas is one of the main biomass-energy resources. Its use for syngas production with a H-2/CO ratio close to two would have huge environmental, social and economic impact in the actual energetic scenario. However, the use of dry reforming, where the two main components are transformed into syngas, does not allow the desired H-2/CO ratio. For this reason, the addition of water is proposed. The process was performed with two Ru-Ni catalysts where the metal order in the impregnation process was varied. The catalysts were prepared either by simultaneous or consecutive impregnation of the active phases and its catalytic performance in the combined dry-steam reforming of methane was tested. The catalysts were characterized by XRF, XRD, S-BET, TPR-H-2 and Raman spectroscopy. The existence of a strong Ni-Ru interaction is evidenced by Raman spectroscopy and TPR-H-2 in the sample synthesized by the simultaneous impregnation. Concerning the catalytic activity, this sample presents the highest CH4 and CO2 conversion values in the entire composition rate and the lowest amount of carbon deposits after reaction. After pulse, and reactivity tests it was concluded that the higher Ni-Ru interaction displayed by the catalyst synthesized by the simultaneous impregnation, enhances the carbon gasification.


Febrero, 2016 | DOI: 10.1007/s11244-015-0426-5



2015


Cu–TiO2 systems for the photocatalytic H2 production: Influence of structural and surface support features


Obregon, S; Munoz-Batista, MJ; Fernandez-Garcia, M; Kubacka, A; Colon, G
Applied Catalysis B: Environmental, 179 (2015) 468-478

ABSTRACT

The influence of different TiO2 supports on the Cu active species has been studied. It was found that the photocatalytic H2 evolution is highly affected by the structural and electronic features of surface Cu species. Thus, metal dispersion and oxidation state appears strongly conditioned by the structural and surface properties of the TiO2 support. We have examined three TiO2 supports prepared by different synthetic methods; sol–gel, hydrothermal and microemulsion. In addition, we have induced structural and surface modifications by sulfate pretreatment over freshly prepared TiO2 precursors and subsequent calcination. Notably different copper dispersion and oxidation state is obtained by using these different TiO2 supports. From the wide structural and surface analysis of the catalysts we are able to propose that the occurrence of highly disperse Cu2+ species, the sample surface area as well as the crystallinity of the TiO2 support are directly related to the photocatalytic activity for H2 production reaction.


Diciembre, 2015 | DOI: 10.1016/j.apcatb.2015.05.043

Study of the phenol photocatalytic degradation over TiO2 modified by sulfation, fluorination, and platinum nanoparticles photodeposition


Murcia, JJ; Hidalgo, MC; Navio, JA; Arana, J; Dona-Rodriguez, JM
Applied Catalysis B: Environmental, 179 (2015) 305-312

ABSTRACT

In this work, titanium dioxide has been modified by sulfation, fluorination and simultaneous Pt nanoparticles deposition; the influence of these treatments on the photocatalytic activity of this oxide has been studied. A complete characterization study was carried out and it was observed that sulfation, fluorination and metallization were important factors influencing the TiO2 properties. The photocatalytic activity of the materials prepared was evaluated in the phenol degradation and it was found that TiO2fluorination significantly increased the phenol photodegradation rate, compared with bare TiO2, sulfated TiO2 or the commercial TiO2 Degussa P25. It was also found that Pt photodeposition on sulphated TiO2 notably increased the photocatalytic activity of this oxide, while Pt on fluorinated TiO2 did not modify significantly the phenol photodegradation rate.


Diciembre, 2015 | DOI: 10.1016/j.apcatb.2015.05.040

Enhancement of stability and photoactivity of TiO2 coatings on annular glass reactors to remove emerging pollutants from waters


Espino-Estevez, MR; Fernandez-Rodriguez, C; Gonzalez-Diaz, OM; Navio, JA; Fernandez-Hevia, D; Dona-Rodriguez, JM
Chemical Engineering Journal, 279 (2015) 488-497

ABSTRACT

TiO2 coatings of highly photoactive lab-made titania were prepared on the outer wall of the inner tube of a glass tubular reactor by dip-coating method. The effect of decreasing the size of the aggregates to improve adhesion and photoactivity of the coatings to degrade phenol, diclofenac and isoproturon was also investigated. Chemical disaggregation of the TiO2 particles resulted in a lower aggregate size, between 0.1 and 1 μm, than mechanical disaggregation, between 1 and 10 μm. The results of the adhesion tape test showed that either milling of aggregate material with a planetary mill or chemical stabilization of the particles were necessary to obtain TiO2 coatings on glass tube with acceptable quality to be used in water treatment applications. SEM images showed that coatings prepared after milling the TiO2 suspension were more homogeneous without surface aggregates. The degree of adhesion of the coatings after increasing the roughness of the support by abrasive blasting was also evaluated. Adhesion to the substrate was slightly lower when using the modified support. The photoactivity results showed that the coatings prepared after wet milling of catalyst during 30 min and after chemical disaggregation were more efficient in terms of degradation and mineralization when using phenol as model molecule. Subsequent studies with two emerging pollutants, diclofenac and isoproturon, also showed enhanced efficiency of these coatings. The reusability of the TiO2 coatings was also evaluated and a promising photocatalytic performance was observed with a very low variation of the decay rate after five consecutive usages.


Noviembre, 2015 | DOI: 10.1016/j.cej.2015.05.038

Simultaneous Production of CH4 and H-2 from Photocatalytic Reforming of Glucose Aqueous Solution on Sulfated Pd-TiO2 Catalysts


Vaiano, V; Iervolino, G; Sarno, G; Sannino, D; Rizzo, L; Mesa, JJM; Hidalgo, MC; Navio, JA
Oil & Gas Science and Technology-Revue D IFP Energies Nouvelles, 70 (2015) 891-902

ABSTRACT

In this work, the simultaneous production of CH4 and H-2 from photocatalytic reforming of glucose aqueous solution on Pd-TiO2 catalysts under UV light irradiation by Light-Emitting Diodes (LED) was investigated. The Pd-TiO2 catalysts were prepared by the photodeposition method. The Pd content was in the range 0.5-2 wt% and a photodeposition time in the range 15-120 min was used. Pd-TiO2 powders were extensively characterized by X-Ray Diffraction (XRD), SBET, X-Ray Fluorescence spectrometry (XRF), UV-Vis Diffuse Reflectance Spectra (UV-Vis DRS), TEM and X-Ray Photoelectron Spectroscopy (XPS). It was found that the lower Pd loading (0.5 wt%) and 120 min of photodeposition time allowed us to obtain homogeneously distributed metal nanoparticles of small size; it was also observed that the increase in the metal loading and deposition time led to increasing the Pd-0 species effectively deposited on the sulfated TiO2 surface. Particle size and the oxidation state of the palladium were the main factors influencing the photocatalytic activity and selectivity. The presence of palladium on the sulfated titania surface enhanced the H-2 and CH4 production. In fact, on the catalyst with 0.5 wt% Pd loading and 120 min of photodeposition time, H-2 production of about 26 lmol was obtained after 3 h of irradiation time, higher than that obtained with titania without Pd (about 8.5 lmol). The same result was obtained for the methane production. The initial pH of the solution strongly affected the selectivity of the system. In more acidic conditions, the production of H-2 was enhanced, while the CH4 formation was higher under alkaline conditions.


Noviembre, 2015 | DOI: 10.2516/ogst/2014062

Synergy between gold and oxygen vacancies in gold supported on Zr-doped ceria catalysts for the CO oxidation


Laguna, OH; Perez, A; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 176 (2015) 385-395

ABSTRACT

The CO oxidation activity of 1 wt.% gold catalysts prepared by deposition-precipitation on a series of ceria doped with Zr supports was studied. The supports (10, 25 and 50 Zr at.%) were synthesized by a pseudo sol-gel method through the thermal decomposition of the corresponding metallic propionates. All the prepared solids were characterized by means of XRF, BET, XRD, Raman spectroscopy, SEM, and H-2-TPR. Solid solution was obtained in all mixed systems, while the segregation of different Ce-Zr oxides was observed for the solid with the 50 Zr at.%. The oxygen vacancies population and the amount of easier reducible Ce4+ species in the solids increase with the Zr content. No major textural or structural modifications were detected after gold deposition, although a strong Au-support interaction was generated. Such interaction is strongly influenced by the nucleation of gold deposits on the oxygen vacancies and consequently the amount of Zr inserted in the ceria network also determines the dispersion of gold. The presence of gold eases the surface reduction at lower temperatures, and as higher the amount of Zr in the gold catalysts, higher the CO conversion at low temperatures, probably due to the enhancement of the electronic transfer at the surface of the catalysts. 


Octubre, 2015 | DOI: 10.1016/j.apcatb.2015.04.019

Oxodiperoxomolybdenum complex immobilized onto ionic liquid modified SBA-15 as an effective catalysis for sulfide oxidation to sulfoxides using hydrogen peroxide


Carrasco, Carlos J.; Montilla, Francisco; Bobadilla, Luis; Ivanova, Svetlana; Antonio Odriozola, Jose; Galindo, Agustin
Catalysis Today, 255 (2015) 102-108

ABSTRACT

A supported ionic-liquid-phase (SILP) was prepared by the reaction of 1-methyl-3-(3-(triethoxysilyl) propyl)-1H-imidazol-3-ium chloride with a mesoporous SBA-15 silica and then an oxodiperoxomolybdenum complex was immobilized onto the obtained SILP. The resulting material, identified as SBA-15 + ImCl+ MoO5, was characterized by solid state NMR (H-1, C-13 and Si-29), and their textural and thermogravimetric properties were determined. The SBA-15 + ImCl+ MoO5 material was investigated as catalyst for the oxidation of methylphenylsulfide, as model reaction, with aqueous hydrogen peroxide as oxidant at room temperature. The presence of the molybdenum species was crucial for achieving good conversions and methanol was selected as the best solvent (conversion of 95% and selectivity toward sulfoxide 98%). The optimized reaction conditions were applied for the oxidation of several selected sulfides. In general, good catalytic activity and selectivity to sulfoxide were obtained and, remarkably, the selectivity toward sulfoxide is higher than those observed in the study of the same process carried out in [C(4)min][PF6] (C(4)mim = 1-buty1-3-methylimidazolium) and catalyzed by a molecular molybdenum complex, under the same reaction conditions. The importance of the IL-functionalization in the SBA-15 material was evidenced by recycling experiments. The SBA-15 + ImCl+ MoO5 catalyst was used for the sulfoxidation of the methylphenylsulfide substrate for ten reaction cycles without a significant change in conversion, selectivity to sulfoxide and molybdenum content.


Octubre, 2015 | DOI: 10.1016/j.cattod.2014.10.053

Microreactors technology for hydrogen purification: Effect of the catalytic layer thickness on CuOx/CeO2-coated microchannel reactors for the PROX reaction


Laguna, O. H.; Castano, M. Gonzalez; Centeno, M. A.; Odriozola, J. A.
Chemical Engineering Journal, 271 (2015) 45-52

ABSTRACT

Two blocks of microreactors composed by 100 microchannels and coated, respectively, with 150 and 300 mg of a CuOx/CeO2 catalyst, were prepared and tested in the preferential oxidation of CO in presence of H2 (PROX). The deposition of different amount of catalyst resulted in different catalytic layer thicknesses thus modifying the catalytic performances of the microreactor. The evaluation of the main reaction variables (the space velocity, the O2-to-CO ratio and the presence of H2O and/or CO2 in the stream) was performed over both microreactors and compared to that of the parent powder catalyst. The least loaded microreactor, with a coating thickness around 10 μm, presented the highest CO conversion and selectivity levels at temperatures below 160 °C. This result evidences (i) the improvement of the catalytic performances got by the structuration of the powder catalyst and (ii) the importance of the selection of the adequate thickness of the catalytic layer on the microreactor, which have not to exceed and optimal value. An adequate coating thickness allows minimizing the mass and heat transport limitations, thus resulting in the enhancement of the catalytic performance during the PROX reaction.


Septiembre, 2015 | DOI: 10.1016/j.cej.2015.04.023

Boosting the activity of a Au/CeO2/Al2O3 catalyst for the WGS reaction


Reina, T. R.; Ivanova, S.; Centeno, M. A.; Odriozola, J. A.
Catalysis Today, 253 (2015) 149-154

ABSTRACT

Herein a strategy to design highly efficient Au/CeO2/Al2O3 based WGS catalysts is proposed. The inclusion of transition metals, namely Fe, Cu and Zn as CeO2 dopant is considered. All the promoters successfully increased the WGS performance of the undoped sample. The activity improvement can be correlated to structural and/or redox features induced by the dopants. The comparative characterization of the doped samples by means of XRD, Raman spectroscopy and OSC evaluation permits an accurate understanding of the boosted WGS activity arising from the Ce-promoter interaction. This study establishes distinction among both, structural and redox sources of promotion and provides a useful strategy to develop highly active Au/CeO2 based catalysts for the WGS reaction.


Septiembre, 2015 | DOI: 10.1016/j.cattod.2015.01.041

Boosting the visible-light photoactivity of Bi2WO6 using acidic carbon additives


Carmona, RJ; Velasco, LF; Hidalgo, MC; Navio, JA; Ania, CO
Applied Catalysis A-General, 505 (2015) 467-477

ABSTRACT

We have explored the role of the physicohemical properties of carbon materials as additives to bismuth tungstate on its structure, optical properties, and photocatalytic activity for the degradation of rhodamine B under visible light. For this purpose, C/Bi2WO6 hybrid composites were prepared following two different routes: (i) physical mixture of the catalyst components, and (ii) one-pot hydrothermal synthesis of the semiconductor in the presence of the carbon additive. Three carbons with different properties were selected as additives: biomass-derived activated carbon, carbon nanotubes and carbon spheres obtained from polysaccharides. Data has shown the outstanding role of the acidic/basic nature of the carbon additive, and of the synthetic method on the photocatalytic performance of the resulting composites. For a given additive, the degradation rate of RhB is greatly improved for the catalysts prepared through a one-step hydrothermal synthesis, where there is low shielding effect of the carbon matrix. Carbon additives of acidic nature boost the surface acidity of the hybrid photocatalyst, thereby enhancing the photodegradation of RhB under visible light via a coupled mechanism (photosensitization, semiconductor photocatalysis and carbon-photon mediated reactions).


Septiembre, 2015 | DOI: 10.1016/j.apcata.2015.05.011

A comparative study of Bi2WO6, CeO2, and TiO2 as catalysts for selective photo-oxidation of alcohols to carbonyl compounds


Lopez-Tenllado, FJ; Murcia-Lopez, S; Gomez, DM; Marinas, A; Marinas, JM; Urbano, FJ; Navio, JA; Hidalgo, MC; Gatica, JM
Applied Catalysis A-General, 505 (2015) 375-381

ABSTRACT

Several semiconductors based on ceria or bismuth tungstate were tested for selective oxidation of alcohols to carbonyl compounds in a search for photocatalysts more selective than TiO2. Gas-phase selective photo-oxidation of propan-2-ol to acetone and liquid-phase transformation of 2-buten-1-ol (crotyl alcohol) to 2-butenal (crotonaldehyde) were studied as test reactions. In both processes the highest selectivities were achieved with Bi2WO6-based solids. Further studies on crotyl alcohol transformation evidenced the lower adsorption of the aldehyde on these systems which could minimize the decrease in crotyl alcohol yield observed for TiO2 or CeO2 at high conversions. Incorporation of titania (5% molar) to the Bi2WO6 system increased the reaction rate significantly whereas the aldehyde yield remained high. 


Septiembre, 2015 | DOI: 10.1016/j.apcata.2015.08.013

Facile Synthesis of Decahedral Particles of Anatase TiO2 with Exposed {001} Facets


Perales-Martinez, IA; Rodriguez-Gonzalez, V; Obregon-Alfaro, S; Lee, SW
Journal of Nanoscience and Nanotechnology, 15 (2015) 7351-7356

ABSTRACT

This paper reports a facile synthesis of decahedral particles of anatase TiO2 dominated by {101} and {001} faces. The decahedral particles has been enhanced by means a microwave-assisted hydrothermal method using TiF4 as a titanium precursor and HF as capping agent to promote oriented growth and formation of {001} faces in only 4 h. The prepared samples were characterized by scanning electron microscopy, high resolution of transmission electron microscopy and X-ray diffraction. The morphology of anatase TiO2 particles is consisted of near-perfect-truncated-bipyramid-shape. Reaction time is a key factor to obtain truncated-bipyramid-shaped particles with sharp and well-defined edges. Reaction times longer than 4 h induce irregular particles. Decahedral anatase TiO2 particles are truncated bypiramid crystals which have eight {101} and two {001} facets at top/bottom surfaces. The average size of decahedral anatase TiO2 particles are similar to 250 nm for the samples obtained without applying the microwave irradiation and similar to 350 nm for reaction 4 h.


Septiembre, 2015 | DOI: 10.1166/jnn.2015.10578

On the origin of the photocatalytic activity improvement of BIVO4 through rare earth tridoping


Obregon, S; Colon, G
Applied Catalysis A-General, 501 (2015) 56-62

ABSTRACT

Rare earth (Tm3+/Er3+,Yb3+,Y3+) tri-doped BiVO4 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of methylene blue and O-2 evolution reactions. The improved photocatalytic performance has been attained by multiple approach of the overall photocatalytic mechanism. From the structural and morphological characterization it has been stated that the presence of Y3+ induces the stabilization of the tetragonal phase probably due to its substitutional incorporation in the BiVO4 lattice. Moreover, the extensive doping with rare earth ions such as Yb3+ and Er3+/Tm3+ t-BiVO4 evidenced that important structural, electronic changes as well as the luminescence properties were also exalted. Ternary doping clearly prompts the higher photocatalytic activities. A more packed tetragonal structure in conjunction leading to improved charge carriers mobility, with the observed visible and NIR photoactivities of t-BiVO4 could be the responsible of the improved photocatalytic activity under solar-like irradiation.


Julio, 2015 | DOI: 10.1016/j.apcata.2015.04.032

Photocatalytic propylene epoxidation on Bi2WO6-based photocatalysts


Murcia-Lopez, S.; Vaiano, V.; Sannino, D.; Hidalgo, M. C.; Navio, J. A.
Research on Chemical Intermediates, 41 (2015) 4199-4212

ABSTRACT

The photocatalytic epoxidation of propylene (PR) with molecular oxygen was carried out in a fluidized-bed reactor with several Bi2WO6-based materials under UV-A illumination. Three different photocatalysts were tested: one of single Bi2WO6 and two of coupled Bi2WO6-TiO2 heterostructures, thus showing that a mixed system of Bi2WO6 with commercial TiO2 Degussa-P25 leads to the best combination of conversion and PO selectivity. Then, direct support on glass spheres and silica gel was made, being a good alternative for improving the Bi2WO6 performance. Additionally, several reaction conditions of temperature and PR to O-2 feed ratio were studied.


Julio, 2015 | DOI: 10.1007/s11164-013-1523-3

H-2 oxidation as criterion for PrOx catalyst selection: Examples based on Au-Co-O-x-supported systems


Reina, TR; Megias-Sayago, C; Florez, AP; Ivanova, S; Centeno, MA; Odriozola, JA
Journal of Catalysis, 326 (2015) 161-171

ABSTRACT

A new approach for understanding PrOx reaction over gold catalysts is proposed in this work. The competition between H-2 and CO oxidation has been studied over a series of Au/MOx/Al2O3 (M = Ce and Co) catalysts in simulated post-reforming gas stream, containing H2O and CO2 for H-2 cleanup goals. The catalysts' behavior is correlated to their oxygen storage capacity, redox behavior, and oxidation ability. The estimation of the reaction rates reveals that in these solids the H-2 combustion, the selectivity limiting factor in the PrOx process, is mainly controlled by the support and not by the gold presence. The possible use of the hydrogen oxidation reaction as a catalyst selection criterion is discussed. 


Junio, 2015 | DOI: 10.1016/j.jcat.2015.03.015

A novel two-steps solvothermal synthesis of nanosized BiPO4 with enhanced photocatalytic activity


Zhang, YF; Sillanpaa, M; Obregon, S; Colon, G
Journal of Molecular Catalysis A-Chemical, 402 (2015) 92-99

ABSTRACT

Nano-sized BiPO4 has been successfully synthesized via a novel designed two-steps solvothermal route using ethylene glycol as solvent. Comparing with traditional hydrothermal method, the novel approach could readily prepare BiPO4 with shorter time. The photocatalytic activity of prepared BiPO4 has been tested via degradation of methylene blue (MB) under light irradiation. The experimental results show that the BiPO4 prepared by novel route had enhanced photocatalytic activity and the synthetic parameters also impact the reaction rate meaningfully. Finally, the obtained samples have been widely characterized by means of powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (DRS) and Fourier transformed infrared (FTIR) spectra. BiPO4 prepared by this novel approach have a particles size below 100 nm, which is a big improvement by comparing with previous works (few micrometer). The effect of EG during the formation of BiPO4 has been discussed and a possible formation mechanism is proposed.
 


Junio, 2015 | DOI: 10.1016/j.molcata.2015.03.011

Theory and Practice: Bulk Synthesis of C3B and its H2- and Li-Storage Capacity


King, TC; Matthews, PD; Glass, H; Cormack, JA; Holgado, JP; Leskes, M; Griffin, JM; Scherman, OA; Barker, PD; Grey, CP; Dutton, SE; Lambert, RM; Tustin, G; Alavi, A; Wright, DS
Angewandte Chemie International Edition, 54 (2015) 5919-5923

ABSTRACT

Previous theoretical studies of C3B have suggested that boron-doped graphite is a promising H2- and Li-storage material, with large maximum capacities. These characteristics could lead to exciting applications as a lightweight H2-storage material for automotive engines and as an anode in a new generation of batteries. However, for these applications to be realized a synthetic route to bulk C3B must be developed. Here we show the thermolysis of a single-source precursor (1,3-(BBr2)2C6H4) to produce graphitic C3B, thus allowing the characteristics of this elusive material to be tested for the first time. C3B was found to be compositionally uniform but turbostratically disordered. Contrary to theoretical expectations, the H2- and Li-storage capacities are lower than anticipated, results that can partially be explained by the disordered nature of the material. This work suggests that to model the properties of graphitic materials more realistically, the possibility of disorder must be considered.


Mayo, 2015 | DOI: 10.1002/anie.201412200

Mono and bimetallic Cu-Ni structured catalysts for the water gas shift reaction


O. Arbeláez, T.R. Reina, S. Ivanova, F. Bustamante, A.L. Villa, M.A. Centeno, J.A. Odriozola
Applied Catalysis A-General, 497 (2015) 1-9

ABSTRACT

The water-gas shift (WGS) reaction over structured Cu, Ni, and bimetallic Cu-Ni supported on active carbon (AC) catalysts was investigated. The structured catalysts were prepared in pellets form and applied in the medium range WGS reaction. A good activity in the 180–350 °C temperature range was registered being the bimetallic Cu-Ni:2-1/AC catalyst the best catalyst. The presence of Cu mitigates the methanation activity of Ni favoring the shift process. In addition the active carbon gasification reaction was not observed for the Cu-containing catalyst converting the active carbon in a very convenient support for the WGS reaction. The stability of the bimetallic Cu-Ni:2-1/AC catalyst under continuous operation conditions, as well as its tolerance towards start/stop cycles was also evaluated.


Mayo, 2015 | DOI: 10.1016/j.apcata.2015.02.041

The role of silver nanoparticles functionalized on TiO2 for photocatalytic disinfection of harmful algae


Lee, Soo-Wohn; Obregon, S.; Rodriguez-Gonzalez, V.
RSC Advances, 5 (2015) 44470-44475

ABSTRACT

Silver loaded TiO2 samples were prepared by photodeposition of different amounts of Ag+ ions over commercial titanium dioxide (Evonik TiO2 P25) in aqueous media without the presence of sacrificial agents. The obtained photocatalysts were characterized by several techniques such as X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) in order to correlate the effect of the silver amount on the photocatalytic properties of the final nanocomposite. The effect of the silver nanoparticles on the photocatalytic behaviour of TiO2 was evaluated by means of the photodegradation of methyl orange dye and the inactivation of noxious algae Tetraselmis suecicaand Amphidium carterae under continuous exposure of low power irradiation UV-light. The sample with 1.5% wt of silver nanoparticles showed the highest photocatalytic elimination of the azo dye and both algae types. According to the results, the cells were deformed during the photocatalytic process by the attack of highly reactive species such as hydroxyl radicals, H2O2 and superoxide ions generated on the TiO2 surface. The algae cells were not regenerated by themselves after the photocatalytic process due the high degree of fragmentation that they suffered during the light irradiation.


Mayo, 2015 | DOI: 10.1039/C5RA08313C

Photocatalytic reduction of CO2 over platinised Bi2WO6-based materials


Murcia-Lopez, S; Vaiano, V; Hidalgo, MC; Navio, JA; Sannino, D
Photochemical & Photobiological Sciences, 14 (2015) 678-685

ABSTRACT

The photocatalytic reduction of CO2 with H2O to produce CH4 in the gas phase was carried out in the presence of two Bi2WO6-based materials. For this purpose, single Bi2WO6 and a coupled Bi2WO6-TiO2 system were synthesised and metallised with Pt, through a Pt photodeposition method. Then, the samples were characterised and the photocatalytic activity was evaluated in a continuous fluidised-bed reactor irradiated with UV light. Single Bi2WO6 presents an interesting behaviour under H2O rich conditions. In particular, the metallisation improves the material's performance for CH4 formation, while the TiO2 addition to Bi2WO6 increases the CH4 yield only at low H2O/CO2 ratio. The Bi2WO6-TiO2 system metallised with a Pt photocatalyst displayed the highest CH4 yield among all the prepared photocatalysts. The stability of the system can be enhanced through the addition of a blue phosphor to the reactant mixture, especially under H2O rich conditions.


Abril, 2015 | DOI: 10.1039/c4pp00407h

Role of ruthenium on the catalytic properties of CeZr and CeZrCo mixed oxides for glycerol steam reforming reaction toward H2 production


Martinez, LM; Araque, M; Centeno, MA; Roger, AC
Catalysis Today, 242 (2015) 80-90

ABSTRACT

The effect of ruthenium on the physico-chemical properties of CeZr and CeZrCo mixed oxides for H2production by glycerol steam reforming reaction has been studied. The combination of in situ Raman spectroscopy under both reductive and oxidative conditions, H2/O2 pulses and XRD, Raman, BET analysis, H2-TPR and TPD-TPO analyses contributed to the determination of the structural and textural properties, redox behavior, re-oxidation capacity and resistance to carbon deposition of the synthesized catalysts. The results show that the catalytic activity is improved by the (positive) cooperative and complementary effect between cobalt and ruthenium that favors the selectivity toward the steam reforming, selective to H2, with respect to the unselective thermal decomposition of glycerol. Ruthenium stabilizes the cobalt cations inserted in the fluorite structure preventing its rejection as Co3O4; and provides the necessary hydrogen to reduce Ce4+. The combination cobalt–ruthenium modifies positively the redoxproperties of the catalysts, increases the re-oxidation capacity (OSC) and promotes the gasification of the carbon deposits. Under the reaction conditions, the decrease in glycerol conversion came along with a change of selectivity. The formation of H2 and CO2 were strongly decreased, while the formation of CO, C2H4 and condensable products (mainly hydroxyacetone) increase. The differences in the catalytic stability and activity of the catalysts are related to the capability of the catalysts to activate H2O under the reaction conditions, favoring the steam reforming reaction over the thermal decomposition.


Marzo, 2015 | DOI: 10.1016/j.cattod.2014.07.034

Ni-CeO2/C Catalysts with Enhanced OSC for the WGS Reaction


Pastor-Perez, L; Ramirez Reina, T; Ivanova, S; Centeno, MA; Odriozola, JA; Sepulveda-Escribano, A
Catalysts, 5 (2015) 298-309

ABSTRACT

In this work, the WGS performance of a conventional Ni/CeO2 bulk catalyst is compared to that of a carbon-supported Ni-CeO2 catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO2/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation.


Marzo, 2015 | DOI: 10.3390/catal5010298

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination


Losch, Pit; Martinez Pascual, Antonio; Boltz, Marilyne; Ivanova, Svetlana; Louis, Benoit; Montilla, Francisco; Antonio Odriozola, Jose
Comptes Rendus Chimie, 18 (2015) 324-329

ABSTRACT

The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C3N3O3Cl3) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta-chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para-chlorotoluene or meta-chlorotoluene with a proper support choice. 


Marzo, 2015 | DOI: 10.1016/j.crci.2014.06.006

Synthesis and application of layered titanates in the photocatalytic degradation of phenol


Ivanova, S; Penkova, A; Hidalgo, MD; Navio, JA; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B: Environmental, 163 (2015) 23-29

ABSTRACT

This study proposes a direct synthetic route to single titanate sheets through the mild and versatile conditions of the “chimie douce”. The stages of the production include the complexation of the titanium alkoxide precursor by benzoic acid, the formation of titanium oxo-clusters and their controlled transformation into single sheet titanates during the hydrolysis stage. The resulted material appears to be an excellent precursor for self-organized TiO2 nanotubes formation which presents an excellent activity as photocatalyst in the photo-degradation of phenol.


Febrero, 2015 | DOI: 10.1016/j.apcatb.2014.07.048

Evolution of H-2 photoproduction with Cu content on CuOx-TiO2 composite catalysts prepared by a microemulsion method


Kubacka, A; Munoz-Batista, MJ; Fernandez-Garcia, M; Obregon, S; Colon, G
Applied Catalysis B: Environmental, 163 (2015) 214-222

ABSTRACT

Copper oxides in contact with anatase correspond to promising materials with high activity in the photo-production of hydrogen by aqueous reforming of alcohols. By a single pot microemulsion method we obtained a series of Cu-Ti composite systems with controlled copper content in the 0-25 wt.% range. The scanning of such a wide range of composition led to the discovery of two well differentiated maxima in the photo-reaction performance. These maxima present rather high and relatively similar reaction rates and photonic efficiencies but are ascribed to the presence of different copper species. A multi-technique analysis of the materials indicates that the maxima obtained comes from optimizing different steps of the reaction; while the first would be connected with a positive effect on anatase charge handling performance the second seems exclusively related to electron capture by surface copper species.


Febrero, 2015 | DOI: 10.1016/j.apcatb.2014.08.005

Water splitting performance of Er3+-doped YVO4 prepared from a layered K3V5O14 precursor


Obregon, S; Colon, G
Chemical Engineering Journal, 262 (2015) 29-33

ABSTRACT

Erbium-doped YVO4 have been synthesized by means of a simple solution method having good photo activities under UV-like excitation for the water splitting half reactions. From the structural and morphological characterization it has been stated that the presence of Er3+ induces the promotion of luminescence. Moreover the incorporation of erbium clearly affects to the morphology YVO4 leading to 200 nm size well-defined spindle-like particles. The improved photocatalytic performance might be associated to a better electron–hole separation mechanism, probably due to the slight increase of band-gap value. The obtained photoactivities for H2 and O2 evolution reactions make this material a promising candidate for water splitting reactions.


Febrero, 2015 | DOI: 10.1016/j.cej.2014.09.073

Photocatalytic activity of bismuth vanadates under UV-A and visible light irradiation: Inactivation of Escherichia coli vs oxidation of methanol


Adan, C; Marugan, J; Obregon, S; Colon, G
Catalysis Today, 240 (2015) 93-99

ABSTRACT

Four bismuth vanadates have been synthesized by using two different precipitating agents (NH3 and triethylamine) following a hydrothermal treatment at 100 °C for 2 h and at 140 °C for 20 h. Then, solids were characterized by X-ray diffraction, BET surface area, UV–vis spectroscopy and scanning microscopy techniques. The characterization of the synthesized materials showed a well crystallized scheelite monoclinic structure with different morphologies. All materials display optimum light absorption properties for visible light photocatalytic applications. The photocatalytic activity of the catalysts was investigated for the inactivation of Escherichia coli bacteria and the oxidation of methanol under UV–vis and visible light irradiation sources. Main results demonstrate that BiVO4 are photocatalytically active in the oxidation of methanol and are able to inactivate bacteria below the detection level. The activity of the catalyst decreases when using visible light, especially for methanol oxidation, pointing out differences in the reaction mechanism. In contrast with bacteria, whose interaction with the catalyst is limited to the external surface, methanol molecules can access the whole material surface.


Febrero, 2015 | DOI: 10.1016/j.cattod.2014.03.059

Glycerol steam reforming on bimetallic NiSn/CeO2-MgO-Al2O3 catalysts: Influence of the support, reaction parameters and deactivation/regeneration processes


Bobadilla, LP; Penkova, A; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis A: General, 492 (2015) 38-47

ABSTRACT

NiSn bimetallic catalysts supported over Al2O3 modified with different promoter (Mg and/or Ce) were prepared and characterized by powder X-ray diffraction (XRD), N2 sorptometry, and temperature programmed reduction (TPR). Hydrogen production by glycerol steam reforming over these catalysts was investigated. Among the catalysts, NiSn/AlMgCe catalyst shows the highest hydrogen yield as well as the best stability during the reaction. The effect of reaction temperature, water/glycerol molar ratio and space velocity on the glycerol steam reforming over NiSn/AlMgCe were also investigated. Finally, it was verified that the catalyst can be regenerated by oxidation of carbonaceous deposits.


Febrero, 2015 | DOI: 10.1016/j.apcata.2014.12.029

Effective photoreduction of a nitroaromatic environmental endocrine disruptor by AgNPs functionalized on nanocrystalline TiO2


Hernandez-Gordillo, A; Obregon, S; Paraguay-Delgado, F; Rodriguez-Gonzalez, V
RSC Advances, 5 (2015) 15194-15197

ABSTRACT

Unprecedented photoactivity of silver nanoparticles photodeposited on nanocrystalline TiO2 for the efficient reduction of 4-nitrophenol at room temperature is reported. The use of Na2SO3 as a harmless scavenger agent for the reduction of a nitroaromatic endocrine disruptor yields a valuable 4-aminophenol reagent.


Febrero, 2015 | DOI: 10.1039/c5ra00094g

Structural and chemical reactivity modifications of a cobalt perovskite induced by Sr-substitution. An in situ XAS study


Hueso, JL; Holgado, JP; Pereniguez, R; Gonzalez-DelaCruz, VM; Caballero, A
Materials Chemistry and Physics, 151 (2015) 29-33

ABSTRACT

LaCoO3 and La0.5Sr0.5O3O3-delta perovskites have been studied by in situ Co K-edge XAS. Although the partial substitution of La(III) by Sr(II) species induces an important increase in the catalytic oxidation activity and modifies the electronic state of the perovskite, no changes could be detected in the oxidation state of cobalt atoms. So, maintaining the electroneutrality of the perovskite requires the generation of oxygen vacancies in the network. The presence of these vacancies explains that the substituted perovskite is now much more reducible than the original LaCoO3 perovskite. As detected by in situ XAS, after a consecutive reduction and oxidation treatment, the original crystalline structure of the LaCoO3 perovskite is maintained, although in a more disordered state, which is not the case for the Sr doped perovskite. So, the La0.5Sr0.5CoO3-delta perovskite submitted to the same hydrogen reduction treatment produces metallic cobalt, while as determined by in situ XAS spectroscopy the subsequent oxidation treatment yields a Co(III) oxide phase with spinel structure. Surprisingly, no Co(II) species are detected in this new spinel phase. 


Febrero, 2015 | DOI: 10.1016/j.matchemphys.2014.11.015

Sonogashira Cross-Coupling and Homocoupling on a Silver Surface: Chlorobenzene and Phenylacetylene on Ag(100)


Sanchez-Sanchez, C; Orozco, N; Holgado, JP; Beaumont, SK; Kyriakou, G; Watson, DJ; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM
Journal of the American Chemical Society, 137 (2015) 940-947

ABSTRACT

Scanning tunneling microscopy, temperature-programmed reaction, near-edge X-ray absorption fine structure spectroscopy, and density functional theory calculations were used to study the adsorption and reactions of phenylacetylene and chlorobenzene on Ag(100). In the absence of solvent molecules and additives, these molecules underwent homocoupling and Sonogashira cross-coupling in an unambiguously heterogeneous mode. Of particular interest is the use of silver, previously unexplored, and chlorobenzene—normally regarded as relatively inert in such reactions. Both molecules adopt an essentially flat-lying conformation for which the observed and calculated adsorption energies are in reasonable agreement. Their magnitudes indicate that in both cases adsorption is predominantly due to dispersion forces for which interaction nevertheless leads to chemical activation and reaction. Both adsorbates exhibited pronounced island formation, thought to limit chemical activity under the conditions used and posited to occur at island boundaries, as was indeed observed in the case of phenylacetylene. The implications of these findings for the development of practical catalytic systems are considered.


Enero, 2015 | DOI: 10.1021/ja5115584

Catalytic screening of Au/CeO2-MOx/Al2O3 catalysts (M = La, Ni, Cu, Fe, Cr, Y) in the CO-PrOx reaction


Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA
International Journal of Hydrogen Energy, 40 (2015) 1782-1788

ABSTRACT

In this work, a series of Au/CeO2-MOx/Al2O3 catalysts has been prepared and evaluated in the PrOx reaction. Within the series of dopants Fe and Cu containing samples enhanced the catalytic performance of the parent Au/CeO2/Al2O3 catalyst being copper the most efficient promoter. For both samples an enhanced oxygen storage capacity (OSC) is registered and accounts for the high CO oxidation activity. More particularly, the Au/CeO2-CuOx/Al2O3 catalyst successfully withstands the inclusion of water in the PrOx stream and presents good results in terms of CO elimination. However to achieve a good selectivity toward, CO2 formation properly adjusting of the reaction parameters, such as oxygen concentration and space velocity is needed. Within the whole screened series the Cu-containing catalyst can be considered as the most interesting alternative for H-2 clean-up applications.


Enero, 2015 | DOI: 10.1016/j.ijhydene.2014.11.141



2014


Heterogeneous selective oxidation of fatty alcohols: Oxidation of 1-tetradecanol as a model substrate


Corberan, VC; Gomez-Aviles, A; Martinez-Gonzalez, S; Ivanova, S; Dominguez, MI; Gonzalez-Perez, ME
Catalysis Today, 238 (2014) 49-53

ABSTRACT

Selective oxidation of fatty alcohols, i.e., linear long-chain alkanols, has been scarcely investigated to date, despite its potential application in high value chemical's production. We report for the first time the liquid phase heterogeneous oxidation of 1-tetradecanol, used as a model molecule for fatty alcohols, according to green chemistry principles by using a Au/CeO2-Al2O3 catalyst and O-2 as oxidant at normal pressure. High selectivity to tetradecanal (ca. 80%) or to tetradecanoic acid (60-70%) are reached at medium conversion (up to 38%), depending on the reaction conditions used. Comparison with similar tests of 1-octanol oxidation shows that the increase of the carbon chain length decreases the alcohol conversion and the formation of ester, probably due to a greater steric effect.


Diciembre, 2014 | DOI: 10.1016/j.cattod.2014.03.033

Active Site Considerations on the Photocatalytic H-2 Evolution Performance of Cu-Doped TiO2 Obtained by Different Doping Methods


Valero, JM; Obregon, S; Colon, G
ACS Catalysis, 4 (2014) 3320-3329

ABSTRACT

A photocatalytic H2 evolution reaction was performed over copper doped TiO2. The influence of sulfate pretreatment over fresh TiO2 support and the Cu doping method has been evaluated. Wide structural and surface characterization of catalysts was carried out in order to establish a correlation between the effect of sulfuric acid treatment and the further Cu-TiO2photocatalytic properties. Notably a different copper dispersion and oxidation state is obtained by different metal decoration methods. From the structural and surface analysis of the catalysts we have stated that the occurrence of highly disperse and reducible Cu2+ species is directly related to the photocatalytic activity for the H2 production reaction. Highly active materials have been obtained from a chemical reduction method leading to 18 mmol·h–1·g–1for 3 mol % copper loading.


Octubre, 2014 | DOI: 10.1021/cs500865y

Heterostructured Er3+ doped BiVO4 with exceptional photocatalytic performance by cooperative electronic and luminescence sensitization mechanism


Obregon, S; Colon, G
Applied Catalysis B: Environmental, 158-159 (2014) 242-249

ABSTRACT

Er-BiVO4 has been synthesized by means of mw-assisted hydrothermal method having good photoactivity under sun-like excitation. It is stated that the precursor addition sequence plays a critical role which determine the further structural feature of BiVO4. From the structural and morphological characterization, it can be demonstrated that the presence of Er3+ would induce the stabilization of the tetragonal phase probably due to the formation of tetragonal-ErVO4 seeds previous to BiVO4 formation. The best photocatalytic performance is attained for the sample with 0.75 at% Er3+ content. At this dopant loading a mixture of tetragonal and monoclinic phase (70% tetragonal) is obtained. The dramatic increase in the photocatalytic activity for 0.75 at% Er-BiVO4 is related to the occurrence of such heterostructure. For this system, the MB degradation rate constant appears drastically higher as bare m-BiVO4. Furthermore, activities of photocatalysts for visible-light-driven O2 evolution have been evaluated, demonstrating that the photocatalytic activity of this Er-doped system (O2 evolution rate, 1014 μmol g−1 h−1) is 20 times as that of undoped m-BiVO4 (O2 evolution rate, 54 μmol g−1 h−1). From the obtained results, the cooperative conjunction of electronic and luminescence mechanism involved in the reaction is proposed to be the origin of the enhanced photocatalytic efficiencies of such systems.


Octubre, 2014 | DOI: 10.1016/j.apcatb.2014.04.029

Pyridine adsorption on NiSn/MgO-Al2O3: An FTIR spectroscopic study of surface acidity


Penkova, A; Bobadilla, LF; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Surface Science, 317 (2014) 241-251

ABSTRACT

The acid-base properties of MgO-Al2O3 supports and NiSn/MgO-Al2O3 catalysts were evaluated by IR spectroscopy using pyridine as a probe molecule. The results indicate that only Lewis acid sites were detected on the surface of the supports as well as on the catalysts. Nevertheless, Bronsted acid sites were not detected. In the support without MgO three kinds of coordinatively unsaturated acid sites were detected: Al3+ cations occupying octahedral, tetrahedral and tetrahedral with cationic vacancy in the neighbourhood. The last sites appear as the strongest. Moreover, they are able to activate the pyridine molecules leading to the formation of an intermediate ce-pyridone complex. When MgO or NiO were added to the alumina, the number and strength of the Lewis acid sites decreased and significant changes were observed in the tetrahedral sites with adjoining cation vacancies. The incorporation of the Mg2+ cations into the alumina's structure takes place on the vacant tetrahedral positions, forming spinel MgAl2O4. As a result, the fraction of tetrahedral sites with adjoining cationic vacancy diminished and the intermediate ce-pyridone complex in the support with the highest MgO loading was hardly detected. The addition of Ni2+ cations leads to the filling of the free octahedral positions, resulting in the formation of a NiAl2O4 spinel structure and the thermal stability of the ce-pyridone species decreases. In the catalysts, the progressive reduction of the number and strength of the Lewis acid sites is due to a competitive formation of the two types of MgAl2O4 and NiAl2O4 spinels. In the catalyst NiSn/30MgO-Al2O3 no cationic vacancies were detected and the surface reaction with ce-pyridone formation did not occur. 


Octubre, 2014 | DOI: 10.1016/j.apsusc.2014.08.093

Chromium removal on chitosan-based sorbents - An EXAFS/XANES investigation of mechanism


Vieira, RS; Meneghetti, E; Baroni, P; Guibal, E; de la Cruz, VMG; Caballero, A; Rodriguez-Castellon, E; Beppu, MM
Materials Chemistry and Physics, 146 (2014) 412-417

ABSTRACT

Chitosan is known to be a good sorbent for metal-containing ions as the presence of amino groups and hydroxyl functions act as effective binding sites. Its crosslinking, employing glutaraldehyde or epichlorohydrin, may change the sorption properties (sorption capacity or diffusion properties) of this biopolymer, since the available functional groups are different in each case. X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), Fourier-transformed infrared spectroscopy with attenuated total reflectance device (FTIR-ATR) was used along with speciation diagrams, in order to identify the binding groups involved in chromate sorption and its mechanisms. In pristine chitosan and epichlorohydrin-crosslinked chitosan membranes, amino groups are most likely responsible for adsorption, although the contribution of hydroxyl groups cannot be excluded (especially for metal-sorbent stabilization). In this case, when adsorbed about 70% of chromate ions remain in the Cr(VI) oxidation state. In the case of glutaraldehyde-crosslinked membranes, the functional groups involved are different. Carbonyl groups and imino bonds – resulting from the reaction of the crosslinking agent and amino groups – may be involved in the adsorption mechanism. Additionally, a higher fraction of chromate anions, around 44% are reduced to Cr(III) oxidation state in loaded sorbent. The presence of free aldehyde groups may explain this partial reduction.


Agosto, 2014 | DOI: 10.1016/j.matchemphys.2014.03.046

Improved O-2 evolution from a water splitting reaction over Er3+ and Y3+ co-doped tetragonal BiVO4


Obregon, S; Colon, G
Catalysis Science & Technology, 4 (2014) 2042-2050

ABSTRACT

Erbium–yttrium co-doped BiVO4 with a tetragonal structure is synthesized by means of a surfactant free hydrothermal method. The studied photocatalyst shows good photoactivity under sun-like excitation for the degradation of methylene blue (MB) and for O2 evolution. From structural and morphological characterization, it has been stated that the presence of lanthanides induces the stabilization of the tetragonal phase. This is probably due to the substitutional occupation that occurs in the BiVO4 lattice. The photocatalytic performance under visible-NIR radiation clearly evidences the occurrence of an up-conversion process involved in the overall photo-electronic mechanism. The tetragonal phase Er0.0075,Y0.03–Bi0.9625VO4 system gives the highest O2 evolution rate (425 μmol g−1 h−1) under sun-like excitation, being 8 times higher than that attained for m-BiVO4 (53 μmol g−1 h−1).


Julio, 2014 | DOI: 10.1039/C4CY00050A

Bifunctional, Monodisperse BiPO4-Based Nanostars: Photocatalytic Activity and Luminescent Applications


Becerro, AI; Criado, J; Gontard, LC; Obregon, S; Fernandez, A; Colon, G; Ocana, M
Crystal Growth & Design, 14 (2014) 3319-3326

ABSTRACT

Monodisperse, monoclinic BiPO4 nanostars have been synthesized by a homogeneous precipitation reaction at 120 °C through controlled release of Bi3+ cations from a Bi–citrate chelate, in a mixture of glycerol and ethylene glycol, using H3PO4 as the phosphate source. The set of experimental conditions necessary to obtain uniform nanoparticles is very restrictive, as the change in either the polyol ratio or the reactant concentrations led to ill-defined and/or aggregated particles. The morphology of the particles consists of a starlike, hierarchical structure formed by the ordered arrangement of nanorod bundles. Transmission electron tomography has revealed that the nanostars are not spherical but flattened particles. Likewise, Fourier transform infrared spectroscopy and thermogravimetry have shown that the synthesized nanostars are functionalized with citrate groups. The mechanism of formation of the nanostars has been analyzed to explain their morphological features. The as-synthesized BiPO4 nanostars exhibit an efficient photocatalytic performance for the degradation of Rhodamine B. Finally, it has been demonstrated that the stars can be Eu3+-doped up to 2 mol % without any change in the particle morphology or symmetry, and the doped samples show emission in the orange-red region of the visible spectrum after ultraviolet excitation. These experimental observations make this material a suitable phosphor for biotechnological applications.


Julio, 2014 | DOI: 10.1021/cg500208h

Excellent photocatalytic activity of Yb3+, Er3+ co-doped BiVO4 photocatalyst


Obregon, S.; Colon, G.
Applied Catalysis B: Environmental, 152-153 (2014) 328-334

ABSTRACT

Ytterbium-Erbium co-doped BiVO4 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue and O2 evolution reactions. From the structural and morphological characterization it has been stated that the presence of Yb3+ and Er3+ induces the stabilization of the tetragonal phase probably due to its substitutional incorporation in the BiVO4 lattice. The occurrence of the Yb3+,Er3+ co-doped monoclinic-tetragonal BiVO4 heterostructure induces the higher photocatalytic activities. The best photocatalytic performance was attained for the sample with 1:4 Er3+:Yb3+ ratio. The observed NIR photoactivity clearly denotes the occurrence of an up-conversion mechanism involved in the overall photocatalytic process.


Junio, 2014 | DOI: 10.1016/j.apcatb.2014.01.054

A study of the optical properties of metal-doped polyoxotitanium cages and the relationship to metal-doped titania


Lv, YK; Cheng, J; Matthews, PD; Holgado, JP; Willkomm, J; Leskes, M; Steiner, A; Fenske, D; King, TC; Wood, PT; Gan, LH; Lambert, RM; Wright, DS
Dalton Transactions, 43 (2014) 8679-8689

ABSTRACT

To what extent the presence of transition metal ions can affect the optical properties of structurally well-defined, metal-doped polyoxotitanium (POT) cages is a key question in respect to how closely these species model technologically important metal-doped TiO2. This also has direct implications to the potential applications of these organically-soluble inorganic cages as photocatalytic redox systems in chemical transformations. Measurement of the band gaps of the series of closely related polyoxotitanium cages [MnTi14(OEt)28O14(OH)2] (1), [FeTi14(OEt)28O14(OH)2] (2) and [GaTi14(OEt)28O15(OH)] (3), containing interstitial Mn(II), Fe(II) and Ga(III) dopant ions, shows that transition metal doping alone does not lower the band gaps below that of TiO2 or the corresponding metal-doped TiO2. Instead, the band gaps of these cages are within the range of values found previously for transition metal-doped TiO2 nanoparticles. The low band gaps previously reported for 1 and for a recently reported related Mn-doped POT cage appear to be the result of low band gap impurities (most likely amorphous Mn-doped TiO2).


Junio, 2014 | DOI: 10.1039/C4DT00555D

Phase assembly and electrical conductivity of spark plasma sintered CeO2-ZrO2 ceramics


Poyato, R; Cruz, SA; Cumbrera, FL; Moreno, B; Chinarro, E; Odriozola, JA
Journal of Materials Science, 49 (2014) 6353-6362

ABSTRACT

Cex Zr1−x O2 (x = 0.10, 0.16 and 0.33) nanocrystalline powders were obtained by a two-step synthesis technique and sintered by spark plasma sintering (SPS). As consequence of the reduction of Ce4+ to Ce3+ species by carbon in the graphite environment in SPS, phase assemblies including tetragonal, monoclinic and pyrochlore phases were generated in the ceramics during the sintering process. The electrical conductivity was highly dependent on phase assembly and atmosphere (N2, H2 and O2). A significant decrease in the activation energy was noticed in the ceramics with high pyrochlore content when measuring the conductivity in H2 atmosphere, consequence of the strong reduction promoted in these ceramics during the measurement. Equal conduction behavior with similar activation energy was observed in all the ceramics when measuring in O2 atmosphere.


Junio, 2014 | DOI: 10.1007/s10853-014-8361-6

Correlation study between photo-degradation and surface adsorption properties of phenol and methyl orange on TiO2 Vs platinum-supported TiO2


Murcia, JJ; Hidalgo, MC; Navio, JA; Arana, J; Dona-Rodriguez, JM
Applied Catalysis B: Environmental, 150-151 (2014) 107-115

ABSTRACT

Adsorption of phenol and methyl orange on the surface of TiO2 and Pt–TiO2 photocatalysts was investigated by FT-IR spectroscopy. It was found that platinum plays an important role in the adsorption properties of the studied substrates on TiO2. Platinum deposits modified the phenol-photocatalyst interaction providing new adsorption sites on TiO2 surface. On Pt–TiO2 photocatalysts, phenol mainly interacts via formation of adsorbed phenolates species. It was also found that the adsorption of methyl orange on titania and Pt–TiO2 photocatalysts occurs via interaction of the azo group with surface Ti4+. Pt photodeposition significantly increases the TiO2 photoreactivity in phenol and methyl orange photo-degradation; however, this increase depends on the properties of the Pt deposits. Moreover, it was observed that platinum content is the main factor determining the substrate-photocatalyst interaction and therefore the Pt–TiO2 photocatalytic performance.


Mayo, 2014 | DOI: 10.1016/j.apcatb.2013.12.010

In situ XAS study of an improved natural phosphate catalyst for hydrogen production by reforming of methane


Abba, MO; Gonzalez-DelaCruz, VM; Colon, G; Sebti, S; Caballero, A
Applied Catalysis B: Environmental, 150-151 (2014) 459-465

ABSTRACT

Some nickel catalysts supported on natural phosphate (NP) have been tested for the dry methane reforming reaction. Although the original impregnated 15%Ni/NP catalyst has no activity at all, the modification of the support by mechano-chemical and/or acid treatment strongly improved the catalytic performance, yielding a series of very active and stable catalysts. The chemical and physical characterization by X-ray diffraction (XRD), temperature programmed reduction (TPR), in situ X-ray absorption spectroscopy (XAS) and other techniques have shown that these treatments mainly modify the interaction between the nickel phase and the support surface. The nickel ions occupy calcium position in the surface of the phosphate phase, which stabilizes and improves the dispersion of nickel species. The final reduced catalysts present a much better dispersed metallic phase interacting with the NP surface, which has been identified as responsible for the observed outstanding catalytic performances.


Mayo, 2014 | DOI: 10.1016/j.apcatb.2013.12.031

Could an efficient WGS catalyst be useful in the CO-PrOx reaction?


Reina, TR; Papadopoulou, E; Palma, S; Ivanova, S; Centeno, MA; Ioannides, T; Odriozola, JA
Applied Catalysis B: Environmental, 150-151 (2014) 554-563

ABSTRACT

This work presents an evaluation of a high performance series of water gas shift (WGS) catalysts in the preferential CO oxidation reaction (PrOx) in order to examine the applicability of the same catalyst for both processes as a first step for coupling both reactions in a single process. Gold based catalysts are applied in an extensive study of the CO-PrOx reaction parameters, such as λ, WHSV, CO concentration and [H2O]/[CO2] ratio in order to obtain the best activity/selectivity balance. CO and H2 oxidation reactions were treated separately in order to establish the degree of CO/H2 oxidation competition. Additionally the catalysts behavior in the CO-PrOx parallel reactions such a WGS and RWGS have been also carried out to analyze their effect on product composition.


Mayo, 2014 | DOI: 10.1016/j.apcatb.2014.01.001

Pt vs. Au in water-gas shift reaction


Castano, MG; Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA
Journal of Catalysis, 314 (2014) 1-9

ABSTRACT

This work presents a comparison of the gold- and platinum-based catalysts behavior in the water–gas shift (WGS) reaction. The influence of the support, e.g., its composition and electronic properties, studied in detail by means of UV–Vis spectroscopy, of the metal nature and dispersion and of the stream composition has been evaluated. The catalytic performance of the samples is directly correlated with the electronic properties modification as a function of metal and/or support. Both metals present high activity in the selected reaction although in a different operation temperature window.


Mayo, 2014 | DOI: 10.1016/j.jcat.2014.03.014

Effect of the type of acid used in the synthesis of titania–silica mixed oxides on their photocatalytic properties


Llano, B; Hidalgo, MC; Rios, LA; Navio, JA
Applied Catalysis B: Environmental, 150-151 (2014) 389-395

ABSTRACT

TiO2–SiO2 mixed oxides were synthesized by the sol–gel technique using three different acids, i.e., acetic, sulfuric, or chlorhydric acid. Their photocatalytic behavior was evaluated on the phenol oxidation in liquid phase and correlated with the characterization results. It was found that the kind of acid used during the preparation strongly influences the phase composition and stability of the TiO2 phases incorporated in the silica structure as well as the photocatalytic activity. In all cases, silica introduced a dispersive effect that stabilized the TiO2 crystalline phases upon calcination at 700 °C. SO42− and CH3COO− ions stabilized the anatase phase at high calcination temperatures (700 °C) leading to samples with the highest photoactivities. Cl− ions induced the formation of traces of rutile and brookite resulting in a lower photoactivity. The highest photoactivity was achieved with the catalyst synthesized with acetic acid and calcined at 700 °C (TS1-700-ace). The photocatalytic performance of this material was even better than that obtained with the commercial catalyst Degussa P-25.


Mayo, 2014 | DOI: 10.1016/j.apcatb.2013.12.039

Viability of Au/CeO2-ZnO/Al2O3 Catalysts for Pure Hydrogen Production by the Water-Gas Shift Reaction


Reina, TR; Ivanova, S; Delgado, JJ; Ivanov, I; Idakiev, V; Tabakova, T; Centeno, MA; Odriozola, JA
ChemCatChem, 6 (2014) 1401-1409

ABSTRACT

The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the water–gas shift reaction. Herein, a series of gold catalysts supported on ZnO-promoted CeO2–Al2O3 are presented as interesting systems for the purification of H2 streams through the water–gas shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn-containing solids. High activity and good stability and resistance towards start-up–shut-down situations was found, which makes these catalysts a promising alternative for CO clean-up applications.


Mayo, 2014 | DOI: 10.1002/cctc.201300992

Metallic structured catalysts: Influence of the substrate on the catalytic activity


Dominguez, MI; Perez, A; Centeno, MA; Odriozola, JA
Applied Catalysis A-General, 478 (2014) 45-57

ABSTRACT

In order to study the influence of the metallic substrate on the catalytic activity of structured micromonolithic catalysts, a CuOx/CeO2 catalyst was deposited on different oxidized or enameled metallic micromonoliths and tested in the PROX reaction under ideal and realistic conditions. The obtained results show as both activity and selectivity depend on the nature of the alloy and the nature of the interphase between the metal substrate and the catalyst layer. In oxidized micromonoliths, diffusion of Cr and Fe has been observed. For enameled micromonoliths, together with that diffusion, the interaction of the glass-ceramic interphase with the reactive gas streams resulted in the partial hydrolysis of this layer leading to diffusion toward the catalyst surface of the hydrolysis products, namely Na, Ca and Si cations. In some cases, the alteration of the surface composition favors the spreading of the copper active phase. As a result, it must be concluded that the metallic substrates are not spectators, at least in the PROX reaction, playing a fundamental role in the performances of the catalytic devices.


Mayo, 2014 | DOI: 10.1016/j.apcata.2014.03.028

Production of hydrogen by water photo-splitting over commercial and synthesised Au/TiO2 catalysts


Mendez, JAO; Lopez, CR; Melian, EP; Diaz, OG; Rodriguez, JMD; Hevia, DF; Macias, M
Applied Catalysis B: Environmental, 147 (2014) 439-452

ABSTRACT

H2 production from methanol/water photo-splitting was compared using various commercial photocatalysts (Evonik P25 (P25), Hombikat UV-100 (HB) and Kronos vlp7000 (KR)) and others synthesised with a sol–gel-hydrothermal (HT) process and a sol–gel method followed by calcination (SG400 and SG750). All photocatalysts had been surface modified with Au at different concentrations, from 0.2 to 6.0 wt.%, using the photodeposition method. A complete characterisation study of the different photocatalysts was performed (BET, XRD, TEM, SEM-EDX, FTIR, UV–vis Reflectance Diffuse Spectra and aggregate size). The experiments were conducted for 3.5 h using 1 g L−1 of photocatalyst with methanol (25 vol.%) as sacrificial agent. In addition to H2 generation, production of the main intermediates, formaldehyde and formic acid, and of CO2 was also evaluated. The commercial photocatalyst KR at 0.8 wt.% Au had the highest H2 production of all the photocatalysts studied with 1542.9 μmol h−1. Of the photocatalysts synthesised by our group, SG750 at Au loading of 2.0 wt.% gave the highest H2 production of 723.1 μmol h−1. The SG750 photocatalyst at Au loading of 2.0 wt.% also had the highest H2 production yield per unit of surface area at 45.5 μmol g h−1 m−2.


Abril, 2014 | DOI: 10.1016/j.apcatb.2013.09.029

Surface Oxygen Vacancies in Gold Based Catalysts for CO Oxidation


Romero-Sarria, F; Plata, JJ; Laguna, OH; Marquez, AM; Centeno, MA; Sanz, JF; Odriozola, JA
RSC Advances, 4 (2014) 13145-13152

ABSTRACT

Experimental catalytic activity measurements, Diffuse Reflectance Infrared Fourier Spectroscopy, and Density Functional Theory calculations are used to investigate the role and dynamics of surface oxygen vacancies in the CO oxidation with O2 catalyzed by Au nanoparticles supported on a Y-doped TiO2 catalyst. Catalytic activity measurements show that the CO conversion is improved in a second cycle of reaction if the reactive flow is composed by CO and O2 (and inert) while if water is present in the flow, the catalyst shows a similar behaviour in two successive cycles. DRIFTS-MS studies indicate the occurrence of two simultaneous phenomena during the first cycle in dry conditions: the surface is dehydroxylated and a band at 2194 cm-1 increases (proportionally to the number of surface oxygen vacancies). Theoretical calculations were conducted in order to explain these observations. On one hand, the calculations show that there is a competition between gold nanoparticles and OH to occupy the surface oxygen vacancies and that the adsorption energy of gold on these sites increases as the surface is being dehydroxylated. On another hand, these results evidence that a strong electronic transfer from the surface to the O2 molecule is produced after its adsorption on the Au/TiO2 perimeter interface (activation step), leaving the gold particle in a high oxidation state. This explains the appearance of a band at a wavenumber unusually high for the CO adsorbed on oxidized gold particles (2194 cm-1) when O2 is present in the reactive flow. These simultaneous phenomena indicate that a gold redispersion on the surface occurs under reactive flow in dry conditions generating small gold particles very actives at low temperature. This fact is notably favoured by the presence of surface oxygen vacancies that improve the surface dynamics. The obtained results suggest that the reaction mechanism proceeds through the formation of a peroxo-like complex formed after the electronic transfer from the surface to the gas molecule.


Abril, 2014 | DOI: 10.1039/c3ra46662k

Influence of the acid–base properties over NiSn/MgO–Al2O3 catalysts in the hydrogen production from glycerol steam reforming


Bobadilla, LF; Penkova, A; Romero-Sarria, F; Centeno, MA; Odriozola, JA
International Journal of Hydrogen Energy, 39 (2014) 5704-5712

ABSTRACT

In this work we have investigated the hydrogen production from glycerol steam reforming. The effect of the acid-base properties was evaluated using four catalysts based in an alloy Ni-Sn as active phase supported over (Upsilon)-Al2O3 with different content in MgO, varying between 0 and 30 wt.% The incorporation of MgO results in the formation of MgAl2O4 spinel, which modifies the acid-base properties of the catalyst. Addition of MgO favored the glycerol conversion into gas, and the catalyst loaded with 10 wt.% MgO exhibited better catalytic performance and higher stability. A blank test with quartz was performed indicating that pyrolysis of glycerol takes place in the quartz.


Abril, 2014 | DOI: 10.1016/j.ijhydene.2014.01.136

Understanding the Role of the Cosolvent in the Zeolite Template Function of Imidazolium-Based Ionic Liquid


Ayala, R; Ivanova, S; Blanes, JMM; Romero-Sarria, F; Odriozola, JA
Journal of Physical Chemistry B, 118 (2014) 3650–3660

ABSTRACT

In this work, a study for understanding the role played by [ClBmim], [BF4Bmim], [PF6Bmim], and [CH3SO3Bmim] ionic liquids (ILs) in the synthesis of zeolites is presented. The use of [ClBmim] and [CH3SO3Bmim] ILs, as reported earlier [ Chem. Eur. J. 2013, 19, 2122] led to the formation of MFI or BEA type zeolites. Contrary, [BF4Bmim] and [PF6Bmim] ILs did not succeed in organizing the Si–Al network into a zeolite structure. To try to explain these results, a series of quantum mechanical calculations considering monomers ([XBmim]) and dimers ([XBmim]2) by themselves and plus cosolvent (water or ethanol) were carried out, where X ≡ Cl–, BF4–, PF6–, or CH3SO3–. Our attention was focused on the similarities and differences among the two types of cosolvents and the relation between the structure and the multiple factors defining the interactions among the ILs and the cosolvent. Although a specific pattern based on local structures explaining the different behavior of these ILs as a zeolite structuring template was not found, the calculated interaction energies involving the Cl– and CH3SO3– anions were very close and larger than those for BF4– and PF6– species. These differences in energy can be used as an argument to describe their different behavior as structure directing agents. Moreover, the topology of the cosolvent is also an ingredient to take into account for a proper understanding of the results.


Abril, 2014 | DOI: 10.1021/jp410260g

Gold supported on CuOx/CeO2 catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX)


Laguna, OH; Hernandez, WY; Arzamendi, G; Gandia, LM; Centeno, MA; Odriozola, JA
Fuel, 134 (2014) 9-20

ABSTRACT

Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H2-TPR of a gold catalyst supported on a copper−cerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper–cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold.


Febrero, 2014 | DOI: 10.1016/j.fuel.2013.10.072

Spinodal decomposition and precipitation in Cu–Cr nanocomposite


Sheibani, S; Heshmati-Manesh, S; Ataie, A; Caballero, A; Criado, JM
Journal of Alloys and Compounds, 587 (2014) 670-676

ABSTRACT

In this study, spinodal decomposition and precipitation mechanism of mechanically alloyed supersaturated Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions was investigated under nonisothermal aging. Decomposition mechanism and kinetics were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. Also, the microstructure was characterized by transmission electron microscopy (TEM). Effect of Al2O3 reinforcement on the aging kinetics was also evaluated. It was found that Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions undergo spinodal decomposition at initial stages of ageing. However, decomposition mechanism was changed to nucleation and growth by the aging progress. The aging kinetics for the Cu–Cr/Al2O3 composition appeared to be slightly faster than that for Cu–Cr, since the ageing activation energy is decreased in presence of Al2O3 nano-particles. This behavior is probably due to the higher dislocation density and other structural defects previously produced during ball milling. A detailed comparison of the DSC results with those obtained by TEM, showing good consistency, has been presented. The average size of Cr-rich precipitates was about 10 nm in the copper matrix.


Febrero, 2014 | DOI: 10.1016/j.jallcom.2013.11.019

Wall paintings studied using Raman spectroscopy: A comparative study between various assays of cross sections and external layers


Perez-Rodriguez, JL; Robador, MD; Centeno, MA; Siguenza, B; Duran, A
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 120 (2014) 602-609

ABSTRACT

This work describes a comparative study between in situ applications of portable Raman spectroscopy and direct laboratory measurements using micro-Raman spectroscopy on the surface of small samples and of cross sections. The study was performed using wall paintings from different sites of the Alcazar of Seville.

Little information was obtained using a portable Raman spectrometer due to the presence of an acrylic polymer, calcium oxalate, calcite and gypsum that was formed or deposited on the surface. The pigments responsible for different colours, except cinnabar, were not detected by the micro-Raman spectroscopy study of the surface of small samples taken from the wall paintings due to the presence of surface contaminants.

The pigments and plaster were characterised using cross sections. The black colour consisted of carbon black. The red layers were formed by cinnabar and white lead or by iron oxides. The green and white colours were composed of green emerald or atacamite and calcite, respectively. Pb3O4 has also been characterised. The white layers (plaster) located under the colour layers consisted of calcite, quartz and feldspars. The fresco technique was used to create the wall paintings.

A wall painting located on a gypsum layer was also studied. The Naples yellow in this wall painting was not characterised due to the presence of glue and oils.

This study showed the advantage of studying cross sections to completely characterise the pigments and plaster in the studied wall paintings.


Febrero, 2014 | DOI: 10.1016/j.saa.2013.10.052

Promoting effect of Ce and Mg cations in Ni/Al catalysts prepared from hydrotalcites for the dry reforming of methane


Djebarri, B; Gonzalez-Delacruz, VM; Halliche, D; Bachari, K; Saadi, A; Caballero, A; Holgado, JP; Cherifi, O
Reaction Kinetics, Mechanisms and Catalysis, 111 (2014) 259-275

ABSTRACT

Several catalytic systems containing Ni/Mg/Al/Ce were synthesized from nitrates of Ni2+, Mg2+, Al3+ and Ce3+ cations with M2+/M3+ = 2 ratios by means of the carbonate co-precipitation method and subsequent calcination at 800 A degrees C. Atomic absorption spectroscopy, X-ray diffraction (XRD), FT-IR spectroscopy, BET, temperature programmed reduction and scanning electron microscopy were used in order to describe the structural, morphological and surface characteristics of the solids completely. The effect of substitution/incorporation of Al by Ce and/or Mg on NiAl sample was studied. XRD analyses confirm that on Al-containing samples (NiAl, NiMgAl), the formation of the precursors layered double hydroxide structure. On the other hand, on cerium containing samples (NiCe, NiMgCe), poorly resolved diffractograms were observed what can be explained by the large radius of cerium. The catalysts were evaluated in the reaction of CO2 reforming of methane at 750 A degrees C. NiCe and NiMgAl catalysts exhibit higher activity and a H-2/CO ratio of almost 1. NiAl and NiMgCe samples showed lower conversions and a CH4/CO2 ratio < 1, indicating the occurrence of reverse water gas shift reaction.


Febrero, 2014 | DOI: 10.1007/s11144-013-0646-2

Improved H2 production of Pt-TiO2/g-C3N4-MnOx composites by an efficient handling of photogenerated charge pairs


Obregon, S; Colon, G
Applied Catalysis B: Environmental, 144 (2014) 775-782

ABSTRACT

Pt-TiO2/g-C3N4-MnOx hybrid structures are synthesized by means of a simple impregnation method of Pt-TiO2 and g-C3N4-MnOx. From the wide structural and surface characterization we have stated that TiO2/g-C3N4 composites are formed by an effective covering of g-C3N4 by TiO2. The modification of composite by Pt and/or MnOx leads to improved photoactivities for phenol degradation reaction. Moreover, enhanced photoactivities have been obtained for composites systems for H2 evolution reaction. The notably photocatalytic performance obtained was related with the efficient separation of charge pairs in this hybrid heterostructure.


Enero, 2014 | DOI: 10.1016/j.apcatb.2013.07.034

Effect of gold on a NiLaO3 perovskite catalyst for methane steam reforming


Palma, S; Bobadilla, LF; Corrales, A; Ivanova, S; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B: Environmental, 144 (2014) 846-854

ABSTRACT

The effect of gold addition to a supported Ni SRM catalyst has been studied in this work in order to determine the influence of gold on both the amount and type of carbon species formed during the reaction. The structure of the support, a mixed La–Al perovskite, determines the catalyst reducibility and Ni particle size. Gold addition affects the metal particle size increasing metal dispersion on increasing the gold content. Therefore, although gold blocks step Ni sites, the more active sites for Csingle bondH activation, and increases electron density on nickel, the higher dispersion results in an apparently higher activity upon gold addition. Moreover, gold addition increases the catalyst stability by decreasing the rate of growth of carbon nanotubes.


Enero, 2014 | DOI: 10.1016/j.apcatb.2013.07.055

Exalted photocatalytic activity of tetragonal BiVO4 by Er3+ doping through a luminescence cooperative mechanism


Obregon, S; Lee, SW; Colon, G
Dalton Transactions, 43 (2014) 311-316

ABSTRACT

Er-doped BiVO4 are synthesized by means of a surfactant free microwave assisted hydrothermal method having good photoactivities under sun-like excitation for the degradation of methylene blue. From the structural and morphological characterization, it has been stated that the presence of Er3+ induces a slight stabilization of the tetragonal phase, probably due to its incorporation in the BiVO4 lattice. The best photocatalytic performances were attained for the samples with Er3+ content higher than 3 at%. The occurrence of the Er3+ doped tetragonal BiVO4 clearly induces higher photocatalytic activities. The existence of a luminescence process has been related with the enhanced photoactivity observed.


Enero, 2014 | DOI: 10.1039/C3DT51923F

A ternary Er3+-BiVO4/TiO2 complex heterostructure with excellent photocatalytic performance


Obregon, S; Colon, G
RSC Advances, 4 (2014) 20765-20771

ABSTRACT

Ternary erbium doped BiVO4/TiO2 complexes are synthesized by means of a simple impregnation method with good photoactivities under sun-like excitation for the degradation of phenol. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a slight stabilization of the tetragonal phase probably due to its incorporation in the BiVO4 lattice. Therefore a ternary heterostructured material has been obtained. The best photocatalytic performance was attained for the samples with 1 wt% of Er3+-doped BiVO4 content with respect to TiO2. The occurrence of a complex structural mixture with the adequate band position leads to effective charge pair separation which induces higher photocatalytic activities.


Enero, 2014 | DOI: 10.1039/C3RA46603E



2013


Au/CeO2 metallic monolith catalysts: influence of the metallic substrate


Tejada, LMM; Dominguez, MI; Sanz, O; Centeno, MA; Odriozola, JA
Gold Bulletin, 46 (2013) 221-231

ABSTRACT

Ceria-based gold catalysts were successfully deposited on ferritic stainless steel (Fecralloy) and aluminium monoliths. The prepared monolithic and reference powder catalysts were characterized by means of S-BET, X-ray diffraction, glow discharge optical emission spectroscopy and scanning electron microscopy-energy dispersive X-ray analysis techniques and tested in the CO oxidation reaction. Characterization results put in evidence the diffusion of cations from the catalytic layer on the surface of the monoliths to the metallic oxide scale and inversely, from the oxide scale to the catalysts, thus altering the catalytic formulation and affecting the CO oxidation properties of the catalytic device. The extension and nature of the modifications produced depend on the nature of the catalysts and the metallic substrate, as well as the reaction conditions applied. These facts must be considered when gold catalysts are supported on metallic-structured devices.


Diciembre, 2013 | DOI: 10.1007/s13404-013-0102-0

Preparation of Titanium Oxide/Silicon Oxide (TiO2/SiO2) systems through the solvothermal method for applications in photocatalysis


Galeano, L.; Navío, J.A.; Restrepo, G.M.; Marín, J.M.
Información Tecnológica, 24 (2013) 81-92

ABSTRACT

Sistemas Óxido de Titanio/Óxido de Silicio (TiO2/SiO2) fueron obtenidos por anclaje de TiO2 en SiO2. El fotocatalizador TiO2 se obtuvo por alcohólisis del TiCl4 con 2-propanol y posterior cristalización a presión autógena a 200 °C, excluyendo etapas de calcinación a altas temperaturas. Se emplearon diferentes relaciones SiO2/TiCl4 para determinar su influencia en la estabilidad, propiedades y fotoactividad de los sistemas TiO2/SiO2. La actividad fotocatalítica fue evaluada por la fotodegradación de metanol en fase gaseosa. El TiO2 cristalizó como fase anatasa o como una mezcla rutilo/anatasa, dependiendo por la relación SiO2/TiCl4 inicial. Los resultados muestran que se producen materiales compuestos con alta cristalinidad del TiO2. Se encontró también que hay una fuerte relación entre la actividad fotocatalítica con las propiedades fisicoquímicas y de estas con las composiciones iniciales de síntesis.


Diciembre, 2013 | DOI: 10.4067/S0718-07642013000500010

A single-source route to bulk samples of C3N and the co-evolution of graphitic carbon microspheres


King, TC; Matthews, PD; Holgado, JP; Jefferson, DA; Lambert, RM; Alavi, A; Wright, DS
Carbon, 64 (2013) 6-10

ABSTRACT

The thermolysis of commercially available m-phenylenediamine (1,3-(NH2)2C6H4) at 800 °C under a static vacuum in a sealed quartz tube provides the first bulk synthesis of C3N, whose properties have only been predicted theoretically previously. Hollow carbon microspheres (CMSs) which do not contain significant nitrogen doping (1–3 μm diameter) are co-produced in the reaction and readily separated from the C3N flakes. The separate C3N flakes and CMSs have been characterized by electron microscopy, X-ray spectroscopy and X-ray diffraction. These studies show that the samples of C3N and CMSs both possess multi-layered turbostratic graphitic structures. A new mechanism for the template-free assembly of CMSs is proposed on the basis of electron microscopy that involves bubble evolution from a static carbonized layer.


Noviembre, 2013 | DOI: 10.1016/j.carbon.2013.04.043

Preferential oxidation of CO over Au/CuOx–CeO2 catalyst in microstructured reactors studied through CFD simulations


Uriz, I; Arzamendi, G; Dieguez, PM; Laguna, OH; Centeno, MA; Odriozola, JA; Gandia, LM
Catalysis Today, 216 (2013) 283-291

ABSTRACT

A computational fluid dynamics (CFD) simulation study of the preferential oxidation of CO (CO-PROX) in microstructured reactors consisting in square and semicircular microchannels coated with an Au/CuOx–CeO2 catalyst is presented. The CO content of the feed stream was set at 1 vol.%. A parametric sensitivity analysis has been performed under isothermal conditions revealing that an optimal reaction temperature exists that leads to a minimum CO content at the microreactor exit. The influence of the space velocity, CO2 concentration and oxygen-to-CO molar ratio in the feed stream (λ), catalyst loading, and microchannel characteristic dimension (d) on the microreactor performance has been investigated. Under suitable conditions, the CO concentration can be reduced below 10 ppm at relatively low temperatures within the 155–175 °C range. A negative effect of the increase of d from 0.35 mm to 2.8 mm on the CO removal efficiency has been found and attributed to a more detrimental effect of the mass transport limitations on the oxidation of CO than that of H2. Non-isothermal CFD simulations have been performed to investigate the cooling of the CO-PROX reactor with air or a fuel cell anode off gas surrogate in parallel microchannels. Due to the very rapid heat transfer allowed by the microreactor and the strong influence of the reaction temperature on the exit CO concentration, a careful control of the coolant flow rate and inlet temperature is required for proper reactor operation. The microreactor behavior is virtually isothermal.


Noviembre, 2013 | DOI: 10.1016/j.cattod.2013.04.023

In situ FT-IR study of the adsorption and photocatalytic oxidation of ethanol over sulfated and metallized TiO2


Murcia, JJ; Hidalgo, MC; Navio, JA; Arana, J; Dona-Rodriguez, JM
Applied Catalysis B: Environmental, 142-143 (2013) 205-213

ABSTRACT

TiO2 Degussa P25, TiO2 prepared by sol–gel submitted to sulfation pre-treatment and some metallized catalysts obtained by photodeposition of Au or Pt over the sulfated TiO2, were evaluated in the reaction of ethanol photo-oxidation. FT-IR spectroscopy was used to investigate the surface features of the photocatalysts, identifying adsorbed species and following the evolution of intermediate products in the ethanol photo-oxidation reaction. Nature of surface acidity in terms of Brönsted and Lewis centers was also studied.

Results showed that sulfation pre-treatment and metallization were important factors influencing the selectivity. Acetaldehyde was the main oxidation product on sulfated TiO2; in the case of P25 also acetates production was observed. The photodeposition of metals had a detrimental effect on the selectivity to acetaldehyde; on metallized catalysts the formation of stable secondary intermediates was detected.

Based on these findings, a reaction pathway for the ethanol photo-oxidation over the different photocatalysts, via acetaldehyde or via acetate formation is proposed.


Octubre, 2013 | DOI: 10.1016/j.apcatb.2013.05.022

Monoclinic–Tetragonal Heterostructured BiVO4 by Yttrium Doping with Improved Photocatalytic Activity


Usai, S; Obregon, S; Becerro, AI; Colon, G
Journal of Physical Chemistry C, 117 (2013) 24479-24484

ABSTRACT

Yttrium-doped BiVO4 has been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue (MB). From the structural and morphological characterization it has been stated that the presence of Y3+ induces the progressive stabilization of the tetragonal phase and the slight higher surface area values. By following the tetragonal cell parameters, the substitutional incorporation of Y3+ into the BiVO4 tetragonal lattice might be considered. Best photocatalytic performances were attained for the samples with Y3+ content of 3.0 at. % for which the MB degradation rate constant appears 2-fold higher. Furthermore, photoactivities for visible-light-driven O2 evolution demonstrate that the photocatalytic performance of the best Y-doped system (initial rate of O2 evolution, 285 μmol g–1 h–1) was more than 5 times that of undoped m-BiVO4 (initial rate of O2 evolution, 53 μmol g–1 h–1). The occurrence of Y3+ doping and a monoclinic–tetragonal heterostructured BiVO4 system induces the higher photocatalytic activities. PL analysis provides a clear evidence of the lower charge carriers recombination in heterostructured yttrium-doped systems.


Octubre, 2013 | DOI: 10.1021/jp409170y

Gold(III) stabilized over ionic liquids grafted on MCM-41 for highly efficient three-component coupling reactions


Bobadilla, LF; Blasco, T; Odriozola, JA
Physical Chemistry Chemical Physics, 39 (2013) 16927-16934

ABSTRACT

Two alkoxysilyl-modified ionic liquids (ILs) have been synthesized and further grafted onto mesoporous silica, MCM-41; these ionic liquids were used for dispersing AuCl3 catalysts that activate C–H bonds as required for the synthesis of propargylamines by coupling alkyne, aldehyde and amine (A3 coupling) species. 29Si NMR experiments demonstrate the formation of covalent bonds between alkoxysilyl-modified Bmim IL and the MCM-41 surface through silanol groups. The catalytic activities of Au(III)-supported MCM-41 and Au(III) homogeneous catalysts are lower than those obtained for the IL functionalized Au–MCM-41 solids when the same gold loading is considered. An interaction between Au(III) species and the IL is proposed for explaining the stabilization of gold(III) species. However, successive reaction cycles result in a decrease in the catalytic activity that has been explained on the basis of gold leaching.


Octubre, 2013 | DOI: 10.1039/C3CP52924J

Promotional effect of the base metal on bimetallic Au-Ni/CeO2 catalysts prepared from core-shell nanoparticles


Holgado, JP; Ternero, F; Gonzalez-delaCruz, VM; Caballero, A
ACS Catalysis, 3 (2013) 2169-2180

ABSTRACT

A set of three catalysts (a Au–Ni bimetallic and their corresponding Au and Ni monometallics) has been prepared by impregnation of previously prepared suspensions of monodisperse metallic particles to ensure the precise control of their physicochemical characteristics (size and composition). The Au–Ni/CeO2 bimetallic catalysts present better reactivity toward CO oxidation than monometallic Au/CeO2 and Ni/CeO2 prepared under identical conditions. “operando-like” characterization of Ni and Au atoms into the bimetallic particles using, among other techniques, ambient-pressure photoelectron spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy has allowed us to determine that under oxidative conditions the samples present a Au@NiO core–shell distribution, where Ni surface atoms are affected by an electronic effect from inner Au atoms.


Septiembre, 2013 | DOI: 10.1021/cs400293b

A low-temperature single-source route to an efficient broad-band cerium(III) photocatalyst using a bimetallic polyoxotitanium cage


Lv, YK; Yao, MM; Holgado, JP; Roth, T; Steiner, A; Gan, LH; Lambert, RM; Wright, DS
RSC Advances, 3 (2013) 13659-13662

ABSTRACT

Aqueous hydrolysis of a series of cerium-containing polyoxotitanium cages gives Ce(III)-doped TiO2 [TiO2(Ce)] or TiO2-supported Ce(III)2Ti2O7, depending on the starting Ti : Ce ratio of the precursor. TiO2-supported Ce2Ti2O7 exhibits superior photocatalytic activity to the Ce-doped TiO2 materials and unusual broad-band absorption behaviour across the visible and near-infrared regions.


Septiembre, 2013 | DOI: 10.1039/C3RA41524D

On the different photocatalytic performance of BiVO4 catalysts for Methylene Blue and Rhodamine B degradation


Obregon, S; Colon, G
Journal of Molecular Catalysis A: Chemical, 376 (2013) 40-47

ABSTRACT

BiVO4 hierarchical structures were synthesized by means of a surfactant free hydrothermal method having good photoactivities for the degradation of Methylene Blue and Rhodamine B under UV–vis irradiation. From the structural and morphological characterization it has been stated that BiVO4 present the monoclinic crystalline phase with different morphologies depending on the pH value. For Methylene Blue the photodegradation rate is strongly affected by the crystallite size and higher (0 0 4) facet exposition. On the contrary, for Rhodamine B, the ζ-potential of the surface clearly determines the photocatalytic performance of BiVO4 catalyst.


Septiembre, 2013 | DOI: 10.1016/j.molcata.2013.04.012

Role of activated carbon on the increased photocatalytic activity of AC/Bi2WO6 coupled materials


Murcia-López, S; Navío, J.A.; Hidalgo, M.C.
Applied Catalysis A: General, 466 (2013) 51-59

ABSTRACT

The photocatalytic activities of several Bi2WO6 and TiO2/Bi2WO6 materials with different activated carbon (AC) contents were studied for Rhodamine B (RhB) (and Phenol) photodegradation under UV–vis and vis illumination. A wide characterization of the materials was carried out. The addition of AC strongly affected the Bi2WO6 morphology although not the crystalline phase. Even in the material with the lowest AC content (2 wt% nominal content) a structure with hierarchical porosity was formed. AC presence increased the initial reaction rates in the degradation of RhB. An important improvement in the photoactivity under both UV–vis and vis illumination conditions was obtained with the lowest AC content (2 wt%) when compared to the pristine material Bi2WO6 or to the systems with higher AC additions. AC/TiO2/Bi2WO6 materials were also improved in comparison to the TiO2/Bi2WO6 heterostructure without carbon. The improvement cannot be only ascribed to adsorption capability and surface area effects. A mechanism explaining the role of AC on the photocatalytic activity improvement is proposed.


Septiembre, 2013 | DOI: 10.1016/j.apcata.2013.06.022

Effect of the alloy on micro-structured reactors for methanol steam reforming


Echave, FJ; Sanz, O; Velasco, I; Odriozola, JA; Montes, M
Catalysis Today, 213 (2013) 145-154

ABSTRACT

Micro-monoliths and foams made of aluminium, Fecralloy® and brass were studied as substrates for structured systems for methanol steam reforming (MSR). All the alloys exhibited very adherent oxide layer produced by pre-treatment to improve the adhesion between substrate and catalyst. 2.5% Pd/ZnO catalyst was prepared and deposited on structured substrates. Both, good catalyst adhesion and stable catalytic performance were achieved in the case of brass micro-monoliths. The Fecralloy® and aluminium substrates reacted with the catalytic active components resulting in catalyst modification. The aluminium based substrates promoted dimethyl ether (DME) formation. Aluminium foam produced better performance than aluminium micro-monoliths that could be related to improved mass and heat transfer properties in foams.


Septiembre, 2013 | DOI: 10.1016/j.cattod.2013.02.027

Hydrogen production using Pt-loaded TiO2 photocatalysts


Melian, EP; Lopez, CR; Mendez, AO; Diaz, OG; Suarez, MN; Rodriguez, JMD; Navio, JA; Hevia, DF
International Journal of Hydrogen Energy, 38 (2013) 11737-11748

ABSTRACT

A series of synthesised TiO2-based and commercial photocatalysts were modified by Pt photodeposition and a study made of their photocatalytic activity in hydrogen production. The modified commercial photocatalysts were Evonik P25, Kronos vlp7000 and Hombikat UV-100, and the other modified photocatalysts were synthesised by our group using sol–gel and sol–gel hydrothermal processes (SG400, SG750 and HT). Pt weight percentages used in the study were 0.5, 1.0 and 2.1 wt.% (Pt/TiO2). The photocatalysts were extensively characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance, Brunauer–Emmett–Teller (BET) surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM–EDX), Fourier transform infrared spectroscopy (FTIR) and laser light dispersion. Methanol (25% vol.) was used as sacrificial agent over the 8 h of the hydrogen production tests and measurements were taken of the final concentrations of formaldehyde and formic acid as well as initial and final TOC. Photoactivity of all photocatalysts increased in the presence of Pt. The most efficient of the synthesised photocatalysts was SG750 and of the commercial photocatalysts P25. Maximum production of SG750 was 1846 μmol h−1 at 1.0 wt.% Pt and its production per surface unit was notably higher than that of P25.


Septiembre, 2013 | DOI: 10.1016/j.ijhydene.2013.07.006

Erbium doped TiO2–Bi2WO6 heterostructure with improved photocatalytic activity under sun-like irradiation


Obregon, S; Colon, G
Applied Catalysis B: Environmental, 140-141 (2013) 299-305

ABSTRACT

Erbium doped TiO2–Bi2WO6 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Rhodamine B. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a progressive russelite cell contraction due to its incorporation in the Bi2WO6 lattice in substitutional sites. The best photocatalytic performance was attained for the samples with 1 at% of Er. From the study of the photocatalytic activity under different irradiation conditions it can be inferred that Er3+ presence induces a significant improvement of the photoactivity in the UV range. The evolution of band-gap values seems to be similarly related with the reaction rate progression. Thus, the higher band-gap values in lower Er doped systems would be the cause of a better electron hole separation under UV irradiation.


Agosto, 2013 | DOI: 10.1016/j.apcatb.2013.04.014

Degradation of Rhodamine B/Phenol Mixtures in Water by Sun-Like Excitation of a Bi2WO6–TiO2 Photocatalyst


Murcia-López, S; Navío, J.A.; Hidalgo, M.C.
Photochemistry and Photobiology, 89 (2013) 832-840

ABSTRACT

Bi2WO6 and Bi2WO6–TiO2 (5% molar Ti) nano-heterostructures were synthesized by a hydrothermal method. The properties of the synthesized catalysts were characterized, having high photoactivity for Rhodamine B degradation under sun-like illumination, explained by a synergetic mechanism previously proposed through UV and visible induced processes, in which the photosensitization effect of Rhodamine B is considered. We now report that using Phenol, a molecule which does not lead the photosensitization process, the photoactivity decreased considerably, thus emphasizing how important is the model molecule selected as degradation substrate for evaluating the photoactivity. The photocatalytic properties of the synthesized catalysts have been evaluated by exposing a mixture of Rhodamine B and Phenol in water, to different illumination conditions. It can be confirmed that the photoinduced mechanism via the photosensitization of Rhodamine B is a key factor responsible for the increase on the photocatalytic activity showed by the Bi2WO6–TiO2 compound and that the degradation mechanism of Rhodamine B is not changed by the simultaneous presence of other transparent substrate as Phenol.


Julio, 2013 | DOI: 10.1111/php.12054

Cyclohexane photocatalytic oxidation on Pt/TiO2 catalysts


Murcia, JJ; Hidalgo, MC; Navio, JA; Vaiano, V; Sannino, D; Ciambelli, P
Catalysis Today, 209 (2013) 164-169

ABSTRACT

Gas-solid heterogeneous photocatalytic oxidation (PCO) of cyclohexane in humidified air over TiO2 and Pt/TiO2 catalyst was studied.

Pt/TiO2 photocatalysts were synthesized by photodeposition method at different Pt loadings (0.5–2 wt.%). The addition of 0.5 wt.% Pt does not significantly modify the TiO2 properties. The increase in Pt loading induces to an aggregation of metallic particles on TiO2 surface.

The cyclohexane PCO was performed in a fluidized bed photoreactor at 60 and 100 °C. Pure TiO2 was more active than 1 and 2 wt.% Pt/TiO2 samples at 60 °C. Nevertheless, the conversion level increases with temperature on Pt/TiO2 photocatalysts. The cyclohexane was mineralized into CO2, water and low amount of CO. A beneficial effect of Pt addition was found, since total CO2 selectivity was obtained. The Pt/TiO2 photocatalysts prepared by photodeposition provide the total cyclohexane PCO without CO production. Photocatalysts deactivation was not observed in any performed test. Evidence of an opportune tuning of temperature is highlighted.


Junio, 2013 | DOI: 10.1016/j.cattod.2012.11.018

Steam reforming of methanol over supported Ni and Ni–Sn nanoparticles


Bobadilla, LF; Palma, S; Ivanova, S; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA
International Journal of Hydrogen Energy, 38 (2013) 6646-6656

ABSTRACT

The influence of the synthesis method and Sn addition on Ni/CeO2–MgO–Al2O3 catalyst is correlated to its catalytic behavior in the reaction of methanol steam reforming. The catalysts prepared by impregnation method are compared to samples obtained by deposition of previously obtained nanoparticles by the polyol method. X-ray diffraction (XRD), specific surface area measurements and H2-temperature programmed reduction (TPR) were used to characterize the catalysts. The differences of the structure, phase transformation and reduction behavior are discussed and related to the catalytic performance of the samples as well as the nature of the carbonaceous deposits formed during the reaction.


Mayo, 2013 | DOI: 10.1016/j.ijhydene.2013.03.143

In situ characterization of iron-promoted ceria–alumina gold catalysts during the water-gas shift reaction


Reina, TR; Xu, WQ; Ivanova, S; Centeno, MA; Hanson, J; Rodriguez, JA; Odriozola, JA
Catalysis Today, 205 (2013) 41-48

ABSTRACT

In this work an in situ XRD and XANES study of two gold catalysts supported on iron-promoted ceria–alumina carriers was carried out during the water-gas shift reaction (WGS). The first catalyst, Au/CeO2–FeOx/Al2O3, was prepared using a commercial alumina support in order to obtain a Ce–Fe oxide solid solution and in the second one, Au/FeOx/CeO2–Al2O3, an iron oxide monolayer was deposited onto a ceria–alumina commercial support to promote its redox properties. Catalytic activities in the WGS were remarkably different for both systems. The catalytic activity of the Au/CeO2–FeOx/Al2O3 catalyst was higher than the one shown by the Au/FeOx/CeO2–Al2O3 catalyst that resulted active at much higher temperatures. In situ XRD demonstrates the formation of magnetite (Fe3O4) during the WGS reaction and the presence of big gold particles, ca. 21 nm in diameter, in the low-activity system. This in contrast to the high-activity system that shows undetectable gold nanoparticles and the absence of diffraction peaks corresponding to magnetite during the WGS. The data obtained using in situ XANES states that Ce4+ species undergo reduction to Ce3+during the WGS for both catalysts, and also confirms that in the high-activity catalyst iron is just present as Fe3+ species while in the low-activity catalyst Fe3+ and Fe2+ coexist, resulting in iron spinel observed by XRD. These results allow us conclude that the Au/CeO2–Fe2O3/Al2O3 catalyst is a suitable catalyst for WGS when avoiding the formation of magnetite, in such a case Fe3+ species favors reduction and water splitting increasing the catalytic activity in the WGS reaction.


Abril, 2013 | DOI: 10.1016/j.cattod.2012.08.004

Au/TiO2 supported on ferritic stainless steel monoliths as CO oxidation catalysts


Milt, VG; Ivanova, S; Sanz, O; Dominguez, MI; Corrales, A; Odriozola, JA; Centeno, MA
Applied Surface Science, 270 (2013) 169-177

ABSTRACT

Metallic supported structured catalysts were obtained by washcoating AluchromYHf monoliths with an Au/TiO2 catalyst. The powder catalyst was synthesized by DAE (direct anionic exchange) method. Using this catalyst, a stable slurry was prepared and used to washcoat the monoliths. TEM and SEM studies revealed that gold nanoparticles in the Au/TiO2 powder catalyst had an average diameter of 3–4 nm, but during the preparation of the structured catalyst, aggregate Au particles of the slurry reached diameters of 9 nm. Before coating, Aluchrom YHf monoliths were thermally treated to generate a homogeneous and well-adhered oxide rough surface layer, mainly composed of α-Al2O3 whiskers, which favored the anchoring of the catalyst. The catalytic layer deposited was well attached and contained not only the Au/TiO2 catalyst but also metallic oxides formed from stainless steel components that diffused through the oxide scale. The structural characterization was performed by XRD, XRF, TEM, SEM, GD-OES and SBET.

The catalytic activity of the powder and structured catalysts was tested in the oxidation of the CO reaction. Catalysts demonstrated to be active at room temperature. After a first activation run, and in spite of their larger gold particle size, the catalytic activities of the structured catalysts overcame those of the powder catalyst. This improvement is probably due to the segregation of the transition metal oxides toward the surface oxide scale.


Abril, 2013 | DOI: 10.1016/j.apsusc.2012.12.159

High-performance Er3+–TiO2 system: Dual up-conversion and electronic role of the lanthanide


Obregon, S; Kubacka, A; Fernandez-Garcia, M; Colon, G
Journal of Catalysis, 299 (2013) 298-306

ABSTRACT

Erbium-doped TiO2 materials are synthesized by means of a surfactant-free hydrothermal method having good photoactivities for the liquid-phase degradation of phenol and MB and the gas phase of toluene. From the structural and morphological characterization, it has been stated that the presence of Er3+ induces a progressive anatase cell expansion due to its incorporation in the TiO2 lattice. The best photocatalytic performance was attained for the samples with 2 at% of Er3+ irrespective of the chemical degradation reaction essayed. From activity and optical studies under different irradiation excitation conditions, a dual-type mechanism is proposed to be at the origin of the photocatalytic activity enhancement. On one hand, the improvement observed under UV irradiation occurs by the effective charge separation promoted by Er3+ species which would act as electron scavenger. Besides, the up-conversion luminescence process of Er3+ allows profiting the NIR range of the lamp and transferring energy in the UV range to the TiO2. The dual action of Er ions located at anatase networks will open up a wide roadway for the developing of an integral solar active photocatalyst.


Marzo, 2013 | DOI: 10.1016/j.jcat.2012.12.021

Impact of Ce–Fe synergism on the catalytic behaviour of Au/CeO2–FeOx/Al2O3 for pure H2 production


Reina, TR; Ivanova, S; Idakiev, V; Delgado, JJ; Ivanov, I; Tabakova, T; Centeno, MA; Odriozola, JA
Catalysis Science & Technology, 3 (2013) 779-787

ABSTRACT

In this work the development of a series of gold catalysts, essentially based on γ-alumina promoted with a small superficial fraction of Ce–Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce–Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce–Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up.


Marzo, 2013 | DOI: 10.1039/C2CY20537H

Influence of the O2/CO ratio and the presence of H2O and CO2 in the feed-stream during the preferential oxidation of CO (PROX) over a CuOx/CeO2-coated microchannel reactor


Laguna, OH; Dominguez, MI; Oraa, S; Navajas, A; Arzamendi, G; Gandia, LM; Centeno, MA; Montes, M; Odriozola, JA
Catalysis Today, 203 (2013) 182-187

ABSTRACT

The catalytic performance of a CuOx/CeO2 powder catalyst and that of a microchannel reactor or microreactor (MR) coated with the same solid was determined and compared. The catalytic activity measurements were carried out with varying O2/CO molar ratios in the feed-stream. In addition, the influence of the presence of CO2 and H2O in the reaction mixture was studied. Some discrepancies were observed between the performances of the powder catalyst and the MR depending on the O2/CO ratio. The MR presented a very good performance with a superior selectivity for CO conversion. This behaviour was due to a more efficient heat removal in the case of the MR that inhibited the H2 oxidation reaction and the r-WGS. The isothermicity of the microreactor during the process was demonstrated through the monitoring of the MR inlet and outlet temperatures.

Concerning the presence of CO2 or H2O in the feed-stream, both compounds gave rise to a decrease of the CO conversion. The negative effect on the catalytic performance was more marked when both compounds were fed together, although the principal inhibitor effect was associated to the CO2. This seems to be related with the formation of stable carbonates at the catalyst surface.


Marzo, 2013 | DOI: 10.1016/j.cattod.2012.04.021

Preferential oxidation of CO in excess H2 over CuO/CeO2 catalysts: Characterization and performance as a function of the exposed face present in the CeO2 support


Gamarra, D; Camara, AL; Monte, M; Rasmussen, SB; Chinchilla, LE; Hungria, AB; Munuera, G; Gyorffy, N; Schay, Z; Corberan, VC; Conesa, JC; Martinez-Arias, A
Applied Catalysis B: Environmental, 130-131 (2013) 224-238

ABSTRACT

A series of oxidised copper-cerium nanostructured catalysts prepared by impregnation of copper over ceria supports synthesized by different methods (hydrothermal with varying preparation parameters, microemulsion/precipitation), in order to achieve different specific morphologies (nanocubes, nanorods and nanospheres), have been examined with respect to their catalytic properties for preferential oxidation of CO in excess H2 (CO-PROX). The catalysts have been characterized in detail by XRD, Raman, SBET measurement, HREM, XPS, TPR and EPR, which allows establishing a model of structural characteristics of the catalysts. The characterization results have been correlated with analysis of CO-PROX catalytic properties by means of catalytic activity measurements complemented by operando-DRIFTS. Structural dependence of the CO oxidation reaction on the dispersed copper oxide entities as a function of the exposed face present at the surface of the different ceria supports is revealed. An important overall enhancement of the CO-PROX performance is detected for the sample supported on ceria nanocubes which is proposed to be a consequence of the interaction between copper oxide and (1 0 0) faces of the ceria support.


Febrero, 2013 | DOI: 10.1016/j.apcatb.2012.11.008

Multiple Zeolite Structures from One Ionic Liquid Template


Blanes, JMM; Szyja, BM; Romero-Sarria, F; Centeno, MA; Hensen, EJM; Odriozola, JA; Ivanova, S
Chemistry-A European Journal, 19 (2013) 2122-2130

ABSTRACT

This study reports the use of 1-butyl-3-methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template-framework system and location of the template provides further insight into the mechanism of synthesis.


Febrero, 2013 | DOI: 10.1002/chem.201202556

Efficient and affordable hydrogen production by water photo-splitting using TiO2-based photocatalysts


Melian, EP; Diaz, OG; Mendez, AO; Lopez, CR; Suarez, MN; Rodriguez, JMD; Navio, JA; Hevia, DF; Pena, JP
International Journal of Hydrogen Energy, 38 (2013) 2144-2155

ABSTRACT

TiO2-based photocatalyst materials were synthesized through a sol–gel method, followed either by: (1) hydrothermal treatment (150 °C/24 h), or (2) heat treatment (calcination) in a temperature range between 400 and 900 °C. The resulting materials were characterized through BET, XRD, TEM, FTIR, RAMAN, laser diffraction and UV–Vis Diffuse Reflectance Spectroscopy. Photoactivity of the various materials was checked against photocatalytic water-splitting for hydrogen production and a relationship between TiO2 structure and hydrogen production capacity was identified. Optimum results were obtained for anatase-rutile mixtures in a ratio of 87:13. The activity of the home-made photocatalysts was also compared (under the same conditions) with the best commercially available materials which have been widely described in the literature: Hombikat UV100, Millenium PC100, Kronos vlp7000,Degussa P25and Kemira 625.


Febrero, 2013 | DOI: 10.1016/j.ijhydene.2012.12.005

Improved photocatalytic activity of g-C3N4/TiO2 composites prepared by a simple impregnation method


Miranda, C; Mansilla, H; Yanez, J; Obregon, S; Colon, G
Journal of Photochemistry and Photobiology A: Chemistry, 253 (2013) 16-21

ABSTRACT

g-C3N4 and TiO2 hybrid structures are synthesized by means of a simple impregnation method having good photoactivities for the degradation of phenol under UV irradiation. From the wide structural and surface characterization we have stated that the presence of g-C3N4 notably affect the surface feature of TiO2 (surface area and pore size distribution). Enhanced photoactivities have been obtained for composites systems. The best result was obtained for 2 wt% loading of g-C3N4 leading to a 70% of improvement with respect to bare TiO2 in the reaction rate. The effective charge carrier separation was proposed as the responsible of such improved photoactivity.


Febrero, 2013 | DOI: 10.1016/j.jphotochem.2012.12.014

Gas-phase Photocatalytic Partial Oxidation of Cyclohexane to Cyclohexanol and Cyclohexanone on Au/TiO2 Photocatalysts


Sannino, D; Vaiano, V; Ciambelli, P; Murcia, JJ; Hidalgo, MC; Navio, JA
Journal of Advanced Oxidation Technologies, 16 (2013) 71-82

ABSTRACT

The heterogeneous photocatalytic partial oxidation of cyclohexane in gas-phase as an alternative green process for fine chemicals synthesis was successfully achieved on Au/TiO2 photocatalysts prepared by photodeposition technique. Different gold loadings ranging between 0.5 and 2 wt.% of photodeposited Au on TiO2 synthesized by sol-gel method were obtained by changing the concentration of gold precursor at fixed illumination intensity and time. The cyclohexane partial photoxidation was conducted in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency. Main observed reaction products were cyclohexanol, cyclohexanone and CO2. The resulting selectivity was dramatically influenced by the gold content. The reaction temperature was a critical parameter to reach the photocatalysts stability, avoiding deactivation phenomena while the tuning of Au content of the photocatalysts, resulted in the promotion of the formation of cyclohexanol or cyclohexanone with high selectivity. In particular, by increasing Au content, the process selectivity is completely reversed, passing from high cyclohexanol selectivity (75%) to high selectivity to cyclohexanone (80%). These promising results evidenced that Au/TiO2 catalysts in the selected operating conditions, are effective materials for the synthesis of cyclohexanone and cyclohexanol in gas-phase by photocatalysis, at very low reaction temperatures and without the additional step of catalyst recovering needed in the liquid partial oxidation of cyclohexane.


Enero, 2013 | DOI: ---



2012


Hydrogenation of 2,2,2-trifluoroacetophenone: Molecular insight into the role of solvent in enantioselection


Rosa Pereñiguez; Gianluca Santarossa; Tamas Mallat; Alfons Baiker
Journal of Molecular Catalysis A: Chemical, 365 (2012) 39-49

ABSTRACT

The unique solvent effect in the enantioselective hydrogenation of α-fluorinated ketones has been investigated in ten different solvents using the  hydrogenation of 2,2,2-trifluoroacetophenone (1) on cinchonine (CN)-modified Pt/Al2O3 as a model reaction. Application of strongly basic solvents – but also increasing hydrogen pressure or conversion – inverted the sense of enantiodifferentiation from (S)-alcohol (expected enantiomer based on the stereochemistry of CN) to (R)-alcohol. The known formation of hemiketals was the origin of the inversion in alcohols. Considering only the non-reacting solvents and low conversions at low pressures, the best correlation was established between the enantiomeric excess and the solvent basicity represented by the H-bond acceptor ability (β). In contrast to former proposals, solvent acidity (α) did not play a significant role. The experimental results are validated by theoretical calculations. The docking of 1 to CN has been investigated in the absence of solvent and also in the presence of toluene and dimethyl formamide. Several competing docking complexes have been isolated that can coexist on the metal surface. Detailed analyses of these complexes show that their stabilities depend on the formation of enantiospecific local interactions between 1, CN, and the platinum surface. The presence of solvent interferes with these interactions, affecting the relative stability of the docking complexes. A correlation between the solvent-induced interactions at molecular level and changes in enantioselectivity is suggested.


Diciembre, 2012 | DOI: 10.1016/j.molcata.2012.08.006

Selective photooxidation of alcohols as test reaction for photocatalytic activity


Lopez-Tenllado, F. J.; Marinas, A.; Urbano, F. J.; Colmenares, J. C.; Hidalgo, M. C.; Marinas, J. M.; Moreno, J. M.
Applied Catalysis B-Environmental, 128 (2012) 150-158

ABSTRACT

Twenty-four different titania-based systems synthesized through the sol–gel process varying the precursor (titanium isopropoxide or tetrachloride) and/or the ageing conditions (magnetic stirring, ultrasounds, microwave or reflux) were tested for liquid-phase selective photooxidation of 2-butenol (crotyl alcohol) to 2-butenal (crotonaldehyde) and gas-phase selective photooxidation of 2-propanol to acetone. To the best of our knowledge, the former process is suggested for the first time as test reaction for photocatalytic activity. Interestingly, both test reactions (despite having very different reactant/catalyst ratio and contact times) showed quite similar results in terms of influence of the precursor (titanium isopropoxide leading to better results than titanium tetrachloride) and the metals (the presence of iron, palladium or zinc being detrimental to activity whereas zirconium and especially gold improved the results as compared to pure titania). To our mind, these results give validity to both processes as test reactions for a fast screening of catalysts for photocatalytic tranformations. Finally, some gold-containing solids even improved photocatalytic activity of Degussa P25.


Noviembre, 2012 | DOI: 10.1016/j.apcatb.2012.02.015

Ethanol partial photoxidation on Pt/TiO2 catalysts as green route for acetaldehyde synthesis


Murcia, JJ; Hidalgo, MC; Navio, JA; Vaiano, V; Ciambelli, P; Sannino, D
Catalysis Today, 196 (2012) 101-109

ABSTRACT

Heterogeneous photocatalytic partial oxidation of ethanol was studied over different Pt/TiO2 as an alternative green process for acetaldehyde production.

The catalysts were synthesized through the photodeposition of Pt over sol–gel TiO2 with platinum loads of 0.5 and 1 wt.%. The effect of some experimental conditions during photodeposition, such as deposition time and Pt loading, was investigated. A short deposition time at 0.5 wt.% Pt nominal loading led to small average particle size of platinum (2–3 nm) homogeneously distributed all over the TiO2 surface.

Ethanol partial oxidation was tested in a gas–solid photocatalytic fluidized bed reactor at high illumination efficiency, using different reaction temperatures. Activity results have been correlated with characterization results of the different samples. Platinized samples prepared with short deposition times showed high conversion levels and high selectivity to acetaldehyde. Materials prepared at longer times, 120 min, showed selectivities >98%, although with lower ethanol conversion.

Sample with 1 wt.% Pt loading prepared with 15 min deposition time combined a good compromise between a relevant ethanol conversion and a very high selectivity to acetaldehyde at a selected reaction temperature of 80 °C, with an acetaldehyde yield higher than 80%, which make of this catalyst a good candidate for acetaldehyde production by photocatalysis.


Noviembre, 2012 | DOI: 10.1016/j.cattod.2012.02.033

Gold supported on pillared clays for CO oxidation reaction: Effect of the clay aggregate size


Alvarez, A; Moreno, S; Molina, R; Ivanova, S; Centeno, MA; Odriozola, JA
Applied Clay Science, 69 (2012) 22-29

ABSTRACT

A series of 1% m/m gold particles supported on Fe, Ce and Al pillared bentonite (from Valle del Cauca, Colombia) and clay “M64” (from Tolima, Colombia) using three different fractions of aggregate sizes (≤ 2 μm, ≤ 50 μm, and ≤ 150 μm) were characterized by particle size measurements, X-ray diffraction, transmission electronic microscopy (TEM), SBET and X-ray fluorescence spectrometry (XRF) techniques. The materials tested with CO oxidation. The separation yield for each fraction depended on the type of clay. Whatever the clay or the aggregate size, the pillaring process was successfully carried out, introducing Fe, Ce and Al pillars and increasing the microporosity and the specific surface area of the material. Gold particles presented a homogenous distribution of 2–3 nm on the pillared bentonite, and of about 10 nm on the pillared clay M64. The aggregate size slightly influenced the amount of deposited gold particles and their size. All gold catalysts were active in CO oxidation, the activity depending on the nature of the clay as well as the gold loading and average gold particle size but not on the aggregate size.


Noviembre, 2012 | DOI: 10.1016/j.clay.2012.07.008

Influence of PVP in magnetic properties of NiSn nanoparticles prepared by polyol method


Bobadilla, LF; Garcia, C; Delgado, JJ; Sanz, O; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Journal of Magnetism and Magnetic Materials, 324 (2012) 4011-4018

ABSTRACT

The influence of PVP on the magnetic properties of NiSn nanoparticles prepared by polyol method has been studied. NiSn nanoparticles exhibit superparamagnetic behavior although there is a ferromagnetic contribution due to particles agglomerated below the blocking temperature. The particle size is controlled by the addiction of PVP in varying amounts. The addition of PVP also favours the particles isolation, narrow the particle size distribution and decrease the interparticle interaction strength increasing the superparamagnetic contribution.


Noviembre, 2012 | DOI: 10.1016/j.jmmm.2012.07.005

Preparation of nanostructured nickel aluminate spinel powder from spent NiO/Al2O3 catalyst by mechano-chemical synthesis


Nazemi, M. K.; Sheibani, S.; Rashchi, F.; Gonzalez-DelaCruz, V. M.; Caballero, A.
Advanced Powder Technology, 23 (2012) 833-838

ABSTRACT

In this paper, the possibility of mechano-chemical synthesis, as a single step process for preparation of nanostructured nickel aluminate spinel powder from NiO/Al2O3 spent catalyst was investigated. Powder samples were characterized in terms of composition, morphology, structure, particle size and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and volumetric adsorption of nitrogen. It was found that formation of spinel was possible after 60 h of milling with no heat treatment. Additionally, influence of mechanical activation on the heat treatment temperature was discussed. It was observed that heat treatment of 15 h milled sample at 1100 °C is enough to produce nickel aluminate spinel. A product of direct mechanical milling showed higher value of surface area (42.3 m2/g) and smaller crystallite size (12 nm) as compared to the heat treated product.


Noviembre, 2012 | DOI: 10.1016/j.apt.2011.11.004

Effect of deposition of silver on structural characteristics and photoactivity of TiO2-based photocatalysts


Melian, EP; Diaz, OG; Rodriguez, JMD; Colon, G; Navio, JA; Macias, M; Pena, JP
Applied Catalysis B-Environmental, 127 (2012) 112-120

ABSTRACT

The homemade bare TiO2 photocatalyst obtained in a previous work was modified with nanosized silver particles by liquid impregnation and photodeposition methods to obtain different noble metal loadings (0.3–1 at.%). Characterization of the synthesized photocatalysts was carried out by the BET method, XPS, TEM, SEM-EDX, XRD and diffuse reflectance measurements. Photocatalytic activity of these silver-deposited TiO2 nanoparticles was tested by photocatalytic degradation of phenol as a reference model representing phenolic pollutants. The noble metal content on the TiO2 surface affected the efficiency of the photocatalytic process, and the photocatalytic activity of noble metal-modified TiO2 was considerably better than that of bare TiO2. Phenol decomposition rate was higher with TiO2 modified by the liquid impregnation method than with TiO2 modified by the photodeposition method.


Octubre, 2012 | DOI: 10.1016/j.apcatb.2012.08.007

Insights towards the influence of Pt features on the photocatalytic activity improvement of TiO2 by platinisation


Murcia, JJ; Navio, JA; Hidalgo, MC
Applied Catalysis B-Environmental, 126 (2012) 76-85

ABSTRACT

The influence of Pt features, such as particle size, dispersion, oxidation state and amount of metal, on the improvement of the photoactivity of TiO2 for phenol and methyl orange degradation was studied.

The size of Pt deposits was precisely controlled by changing deposition time under medium light intensity during the photodeposition, with sizes ranging from 3 to 6 nm. Pt oxidation state was also strongly dependent on the photodeposition time.

Photocatalytic activity results showed that the fraction of metallic platinum (Pt0) was the crucial factor for the improvement of the activity. When the fraction of Pt0 was similar, metal deposit size became the dominant parameter influencing the activity.

The influence of the substrate to be degraded (phenol or methyl orange) was also studied.


Septiembre, 2012 | DOI: 10.1016/j.apcatb.2012.07.013

Making Photo-selective TiO2 Materials by Cation–Anion Codoping: From Structure and Electronic Properties to Photoactivity


Marquez, AM; Plata, JJ; Ortega, Y; Sanz, JF; Colon, G; Kubacka, A; Fernandez-Garcia, M
Journal of Physical Chemistry C, 116 (2012) 18759-18767

ABSTRACT

Photoselective oxidation yielding high-added value chemicals appears as a green novel process with potential to be explored. In this study we combine spectroscopic XPS (N 1s and O 1s) and multiwavelength Raman data with density functional theory calculations to explore the structural and electronic properties of W,N-codoped TiO2 anatase surfaces and interpret the outstanding photocatalytic properties of such a system in partial oxidation reactions. Theoretical calculations allow us to examine several substitutional and N-interstitial configurations at different concentrations of the W,N dopants (similar to those experimentally found), as well as their interaction with structural point defects: Ti cation vacant sites and surface wolframyl species that are required to compensate the extra charge of the W6+ and N-containing anions. The joint use of theoretical and experimental XPS and Raman tools renders key structural information of W,N-codoped microcrystalline TiO2 solids. The incorporation of N at substitutional positions of anatase with the concomitant presence of W═O species introduces localized states in the band gap, a result that is critical in interpreting the chemical behavior of the solids. The combination of the electronic and geometric structural information leads to a simple mechanism that rationalizes the experimentally observed photoactivity and selectivity in partial oxidation reactions.


Septiembre, 2012 | DOI: 10.1021/jp3045143

A CFD study on the effect of the characteristic dimension of catalytic wall microreactors


Arzamendi, G; Uriz, I; Navajas, A; Dieguez, PM; Gandia, LM; Montes, M; Centeno, MA; Odriozola, JA
AlChE Journal, 58 (2012) 2785-2797

ABSTRACT

A three-dimensional computational fluid dynamics study of the steam methane reforming (SMR) in microreactors is presented. Emphasis has been made on investigating the effects of the characteristic dimension (d: 0.35, 0.70, 1.40, and 2.80 mm) on the performance of two microreactor geometries: square microchannels and microslits. Results have shown that for both geometries the SMR conversion decreases markedly as d increases. Conversely, the microchannels provide a methane conversion slightly higher than that of the microslits. The different performance of the microreactors is only partially due to the different surface-to-volume ratio. Pronounced transverse temperature and concentration gradients develop as the characteristic dimension increases especially for microslits in the first half of the reactor. Therefore, external transport limitations can affect the performance of microreactors for SMR, although the characteristic dimensions are of the order of very few millimeters.


Septiembre, 2012 | DOI: 10.1002/aic.12790

Obituary: Prof. Andrés Ortega


Luque, JMC; Martinez, FJG; Azana, MM; Perez, CR
Thermochimica Acta, 543 (2012) 318-319

ABSTRACT

Prof. Andrés Ortega passed away on last January after a painful and long illness. He was Professor of Inorganic Chemistry at the University of Seville (Spain) and was an outstanding researcher in the field of solid state reaction kinetics, an area to which he devoted his entire career since 1983, when he submitted his PhD thesis entitled ‘Critical study of non-isothermal methods for the kinetic analysis of solid-state reactions’. During his post doc stage and collaboration with Prof. Jean Rouquerol, his interest was raised by the Sample Controlled Thermal Analysis (SCTA) technique and its application to the kinetic study of solid state reactions, this latter one developed in Seville along with Prof. José Manuel Criado. A paper from this period should be highlighted: ‘Correlation between the shape of controlled-rate thermal analysis curves and the kinetics of solid-state reactions’ [Thermochimica Acta 157 (1990) 171], the most cited one in his research career. Most of his scientific production was published in Thermochimica Acta and in the Journal of Thermal Analysis and Calorimetry. A tireless professional, he remained active until a few weeks before dying. Being seriously ill he developed a method for the kinetic analysis of reactions with variable activation energies that notably simplifies the previous one proposed by Vyazovkin. The results were published in Thermochimica Acta under the title ‘A simple and precise linear integral method for isoconversional data’ [Thermochim. Acta 474 (2008) 81]. The high number of citations of this article – according to the ISI WEB of Knowledge – in spite of the short time elapsed since it was published reveals its impact within the scientific community.

He was also very much involved in teaching duties, developing new subjects and applying new teaching methodologies. He chaired two important academic positions at the University of Seville related to his works on teaching and educational sciences, as Director of the Institute of Educational Science and as Chairman of the Committee on Education of the University.

Though he sometimes appeared to be reserved, Andrés was a kind man, always ready to help in any problem that was presented to him. With a critical attitude and many cultural interests, he had a vast knowledge and a great ability to interpret the most diverse questions, frequently presenting a reasoning alternative to those commonly established. This was a continuous source of enrichment for both his friends and colleagues, who never will forget him.


Septiembre, 2012 | DOI: 10.1016/j.tca.2012.06.001

Evidence of upconversion luminescence contribution to the improved photoactivity of erbium doped TiO2 systems


Obregon, S; Colon, G
Chemical Communications, 48 (2012) 7865-7867

ABSTRACT

Er3+–TiO2 synthesized by a surfactant free hydrothermal method exhibits good photoactivities under sun-like excitation for the degradation of phenol. The presence of Er3+ does not affect the structural and morphological features of the TiO2 significantly. The best photocatalytic performance was attained for the samples with 2 wt% of Er. Different photocatalytic runs indicated that the incorporation of the Er3+ cation would be responsible for the enhanced photocatalytic activity, which participates in different mechanisms under UV and NIR excitation.


Agosto, 2012 | DOI: 10.1039/C2CC33391K

Effect of the active metals on the selective H-2 production in glycerol steam reforming


Araque, M; Martinez, LM; Vargas, JC; Centeno, MA; Roger, AC
Applied Catalysis B-Environmental, 125 (2012) 556-566

ABSTRACT

The production of hydrogen by glycerol steam reforming was studied using CeZr(Co, CoRh) catalysts. The effect of Co and Rh presence on the properties of the mixed oxides and the effect on the catalytic behavior were considered. The catalysts were characterized before and after testing by XRD, Raman, TPR, H 2-TPD, TPD-TPO and HRTEM. It was observed that the presence of Co allowed the selective H 2 production related with the presence of a metallic phase at the beginning of the reaction. The presence of Rh favored even more the H 2 production and also increased the stability of the catalyst. For CeZrCoRh, the presence of both metals enhanced the catalyst reduction capacity, a characteristic that significantly improved the catalytic behavior for glycerol steam reforming. The selective H 2 production was related to the capacity of the catalyst to activate H 2O under the reaction conditions. The progressive loss of this capacity decreases the production of H 2, and glycerol decomposition is actually favored over glycerol steam reforming. According to the initial distribution of products, and its evolution with time on stream, two main reaction pathways were proposed.


Agosto, 2012 | DOI: 10.1016/j.apcatb.2012.06.028

LaNiO3 as a precursor of Ni/La2O3 for CO2 reforming of CH4: Effect of the presence of an amorphous NiO phase


Rosa Pereñiguez , Victor M. Gonzalez-delaCruz, Alfonso Caballero, Juan P. Holgado,
Applied Catalysis B-Environmental, 123-124 (2012) 324-32

ABSTRACT

The objective of the present work has been the study of the physico-chemical and catalytic properties of Ni/La2O3 catalysts obtained by reduction of four LaNiO3 samples prepared by different methods. The LaNiO3 precursors as well as the resulting Ni/La2O3 catalysts, were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), temperature programmed reduction and oxidation (TPR, TPO). The catalytic performances of these systems for dry reforming of methane (DRM) were also tested. These samples show different physico-chemical properties resulting from the synthesis method used. The XAS and TPR measurements show that in all four LaNiO3 samples there is, in addition of the crystalline LaNiO3 rhombohedrical phase, a significant amount of an amorphous NiO phase, not detectable by XRD but evidenced by XAS. The amount of this NiO amorphous phase seems to play, together with some other microstructural parameters, an important role in the performance of the Ni/La2O3 samples for the DRM reaction.


Julio, 2012 | DOI: 10.1016/j.apcatb.2012.04.044

Cu-modified cryptomelane oxide as active catalyst for CO oxidation reactions


Hernandez, Willinton Y.; Centeno, Miguel A.; Ivanova, Svetlana; Eloy, Pierre; Gaigneaux, Eric M.; Odriozola, Jose A.
Applied Catalysis B-Environmental, 123-124 (2012) 27-35

ABSTRACT

Manganese oxide octahedral molecular sieves (cryptomelane structure) were synthesized by a solvent-free method and tested in the total oxidation of CO (TOX), and preferential oxidation of CO in presence of hydrogen (PROX). The influence of Cu in the cryptomelane structure was evaluated by several characterization techniques such as: X-ray fluorescence (XRF), thermogravimetric analysis (TGA), hydrogen temperature programmed reduction (TPR-H2) and X-ray photoelectron spectroscopy (XPS). The Cu-modified manganese oxide material (OMS-Cu) showed very high catalytic activity for CO oxidation in comparison to the bare manganese oxide octahedral molecular sieve (OMS). The improved catalytic activity observed in OMS-Cu catalyst was associated to a high lattice oxygen mobility and availability due to the formation of Cusingle bondMnsingle bondO bridges. In addition, under PROX reaction conditions the catalytic activity considerably decreases in the presence of 10% (v/v) CO2 in the feed while the same amount of water provokes an improvement in the CO conversion and O2 selectivity.


Julio, 2012 | DOI: 10.1016/j.apcatb.2012.04.024

Influence of the shape of Ni catalysts in the glycerol steam reforming


Bobadilla, L. F.; Alvarez, A.; Dominguez, M. I.; Romero-Sarria, F.; Centeno, M. A.; Montes, M.; Odriozola, J. A.
Applied Catalysis B-Environmental, 123-124 (2012) 379-390

ABSTRACT

Biomass is an alternative to replace the use of fossil fuels. Glycerol, a byproduct in the biodiesel production, can be used for obtaining hydrogen. The most efficient method for obtaining hydrogen from glycerol is the steam reforming (SR). So far all the published papers report the use of conventional catalyst. In this paper, a structured catalyst has been prepared and compared with the conventional ones (powder and spherical pellets). Results show that the structured catalyst (monolith) is more stable as formation of coke was not observed.


Julio, 2012 | DOI: 10.1016/j.apcatb.2012.05.004

Sub-ambient CO oxidation over mesoporous Co3O4: Effect of morphology on its reduction behavior and catalytic performance


Alvarez, A; Ivanova, S; Centeno, MA; Odriozola, JA
Applied Catalysis A-General, 431 (2012) 9-17

ABSTRACT

The influence of the Co 3O 4 morphology on its redox behavior and catalytic performance in the CO oxidation reaction is studied. Three different Co 3O 4 morphologies were synthesized by precipitation and hydrothermal methods. TEM and SEM observations clearly show the different obtained morphologies: rods, wires and a mixture of plates and cubes. The textural properties depend on the morphology and the redox ones on the particle size. XRD analysis reveals a spinel structure in all solids with a preferential exposition of the [1 1 0] plane in the Co 3O 4 rods sample. This preferential exposition, along with its higher specific surface area provides the rods with more efficient oxygen storage capacity resulting in an excellent catalytic performance compared to the other two morphologies.


Julio, 2012 | DOI: 10.1016/j.apcata.2012.04.006

Oxidative Dehydrogenation of Ethanol over Au/TiO2 Photocatalysts


Sannino, Diana; Vaiano, Vincenzo; Ciambelli, Paolo; Carmen Hidalgo, M.; Murcia, Julie J.; Antonio Navio, J.
Journal of Advanced Oxidation Technologies, 15 (2012) 284-293

ABSTRACT

Au/TiO2 photocatalysts were used in ethanol oxidative dehydrogenation. Catalysts at gold loading ranging between 0.5-2 wt.% were synthesized by photodeposition (using different deposition times: 15 and 120 min) over an own-prepared TiO2 by sol-gel method. For reference purposes, a commercial 1 wt.% Au/TiO2 catalyst (AUROlite (TM), Strem Chemicals) was also tested. Photocatalytic reactions were carried out in a gas-solid photocatalytic fluidized bed reactor. Catalytic activity depends strongly both on Au loading and on the material properties, such as particle size and distribution of metal on titania surface. Acetaldehyde was the main reaction product, with ethylene, crotonaldehyde and CO2 as by-products. An important improvement of TiO2 photoactivity was achieved for the catalyst with 0.5 wt.% gold prepared with 120 min deposition time. For an ethanol inlet concentration of 0.2 vol% at 60 degrees C, the maximum conversion and acetaldehyde selectivity were 82% and 95%, respectively. These values are considerably higher than those obtained over pristine TiO2 and over the commercial catalyst.


Julio, 2012 | DOI: ---

Hydrothermal synthesis of BiVO4: Structural and morphological influence on the photocatalytic activity


Obregon, S; Caballero, A; Colon, G
Applied Catalysis B-Environmental, 117 (2012) 59-66

ABSTRACT

BiVO 4 hierarchical heterostructures are synthesized by means of a surfactant free hydrothermal method having good photoactivities for the degradation of methylene blue under UV-vis irradiation. From the structural and morphological characterization it has been stated that BiVO 4 present the monoclinic crystalline phase with different morphologies depending on the pH value, type of precipitating agent and hydrothermal temperature and treatment time. The best photocatalytic performance was attained for the samples with needle-like morphology.


Mayo, 2012 | DOI: 10.1016/j.apcatb.2011.12.037

Photocatalytic activity of single and mixed nanosheet-like Bi2WO6 and TiO2 for Rhodamine B degradation under sunlike and visible illumination


Murcia-Lopez, S; Hidalgo, MC; Navio, JA
Applied Catalysis A-General, 423-424 (2012) 34-41

ABSTRACT

The photocatalytic activity, under sunlike illumination, for Rhodamine B (RhB) degradation using Bi2WO6-TiO2 samples, is reported. Two different kinds of Bi2WO6-TiO2 samples were studied, obtained by distinct methods: first, a mechanical mixing, by adding to synthesized nanosheet-like Bi2WO6 powder the corresponding amount of TiO2 nanoparticles (P25) in order to obtain physical mixtures of both catalysts with different percentages of TiO2 (5, 10 and 50 wt%); second, a single Bi2WO6-TiO2 heterostructure was prepared by adding commercial TiO2-P25 to the Bi2WO6 precursors (50 wt%) prior to the hydrothermal treatment, thus obtaining a sample with "in situ" TiO2 incorporation. Comparisons between the photocatalytic behaviour of these samples and those exhibited by the single materials Bi2WO6 and TiO2 (P25) were carried out, in order to establish the effect not only of the TiO2 addition but also of the way in which TiO2 (P25) is incorporated. The role of each single photocatalyst in the mixtures in the RhB degradation and mineralization under sunlike and just visible illumination was also studied.


Mayo, 2012 | DOI: 10.1016/j.apcata.2012.02.016

Gold supported cryptomelane-type manganese dioxide OMS-2 nanomaterials deposited on AISI 304 stainless steels monoliths for CO oxidation


Martinez, LM; Romero-Sarria, F; Hernandez, WY; Centeno, MA; Odriozola, JA
Applied Catalysis A-General, 423 (2012) 137-145

ABSTRACT

Gold supported on cryptomelane-type OMS-2 catalysts deposited on AISI 304 stainless steels monoliths have been prepared for the first time, characterised and tested in the CO oxidation reaction. An easy and non-conventional method of incorporation of gold to the cryptomelane solid is used. This method allows the preparation of the monolithic catalysts without altering the structural and textural characteristics of the parent OMS-2 material. Although these catalysts do not show an optimal performance for the oxidation of CO, the presence of small gold particles enhances the catalytic performances of the cryptomelane producing promissory CO oxidation catalysts. The non-conventional gold deposition favours a partial loss of K + into the channels, resulting in an increment of the average oxidation state of manganese which favours the catalytic behaviour of these kinds of materials. This study can be taken as a starting point to obtain very active gold catalysts supported on OMS-2 materials through the optimisation of the gold-support interaction and the decrease in the gold particle size.


Mayo, 2012 | DOI: 10.1016/j.apcata.2012.02.026

Influence of Vanadium or Cobalt Oxides on the CO Oxidation Behavior of Au/MOx/CeO2-Al2O3 Systems


Reina, TR; Moreno, AA; Ivanova, S; Odriozola, JA; Centeno, MA
Chemcatchem, 4 (2012) 512-520

ABSTRACT

A series of V2O5- and Co3O4-modified ceria/alumina supports and their corresponding gold catalysts were synthesized and their catalytic activities evaluated in the CO oxidation reaction. V2O5-doped solids demonstrated a poor capacity to abate CO, even lower than that of the original ceria/alumina support, owing to the formation of CeVO4. XRD, Raman spectroscopy, and H2-temperature programmed reduction studies confirmed the presence of this stoichiometric compound, in which cerium was present as Ce3+ and its redox properties were avoided. Co3O4-doped supports showed a high activity in CO oxidation at subambient temperatures. The vanadium oxide-doped gold catalysts were not efficient because of gold particle agglomeration and CeVO4 formation. However, the gold–cobalt oxide–ceria/alumina catalysts demonstrated a high capacity to abate CO at and below room temperature. Total conversion was achieved at −70 °C. The calculated apparent activation energy values revealed a theoretical optimum loading of a half-monolayer.


Abril, 2012 | DOI: 10.1002/cctc.201100373

Study of Oxygen Reactivity in La1-x Sr (x) CoO3-delta Perovskites for Total Oxidation of Toluene


Pereniguez, R; Hueso, JL; Gaillard, F; Holgado, JP; Caballero, A
Catalysis Letters, 142 (2012) 408-416

ABSTRACT

The total oxidation of toluene is studied over catalytic systems based on perovskite with general formula AA′CoO 3-δ (A = La, A′ = Sr). The systematic and progressive substitution of La 3+ by Sr 2+ cations in the series (La 1-xSr xCoO 3-δ system) of the perovskites have been studied to determine their influence in the final properties of these mixed oxides and their corresponding reactivity performance for the total oxidation of toluene as a model volatile organic compound with detrimental effects for health and environment. The structure and morphology of the samples before and after reaction have been characterized by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O 2 in vacuum and reduction in H 2 were also performed to identify the main surface oxygen species and the reducibility of the different perovskites. It is remarkable that the La 1-xSr xCoO 3-δ series presents better catalytic performance for the oxidation of toluene, with lower values for the T 50 (temperature of 50 % toluene conversion) than the previously studied LaNi 1-yCoyO 3 series.


Abril, 2012 | DOI: 10.1007/s10562-012-0799-z

Advanced nanoarchitectures for solar photocatalytic applications


Kubacka, A; Fernandez-Garcia, M; Colon, G
Chemical Reviews, 112 (2012) 1555-1614

ABSTRACT

Advanced nanostructured materials that demonstrate useful activity under solar excitation in fields concerned with the elimination of pollutants, partial oxidation and the valorization of chemical compounds, water splitting and CO 2 reduction processes, are discussed. Point defects present in nanoparticulated anatase present both 5-fold- and 6-fold-coordinated titanium atoms, as well as 2-fold- and 3-fold-coordinated oxygens. The requirement of using sunlight as the excitation source for the degradation reaction demands, as a principal requirement, the modification of the electronic characteristics of a UV absorber system such as anatase-TiO 2. Some reports also indicate the need for large doping concentrations for N-doping in specific cases where notable changes in the valence band onset are subsequently observed. The effect of cetyltrimethylammonium bromide (CTAB) on the crystallization is reported by Yin et al. They showed that the presence of CTAB induces the appearance of BiOBr during the synthesis at 80°C using an aqueous method.


Marzo, 2012 | DOI: 10.1021/cr100454n

CO-Induced Morphology Changes in Zn-Modified Ceria: A FTIR Spectroscopic Study


Penkova, A; Laguna, OH; Centeno, MA; Odriozola, JA
Journal of Physical Chemistry C, 116 (2012) 5747-5756

ABSTRACT

A FTIR study of the CO adsorption on a Zn-modified ceria is presented. The results indicate that at lower activation temperatures only Ce 4+ carbonyls were detected, which were reduced with the increase of the activation temperature. At higher activation temperatures, up to three Zn 2+ carbonyls were also identified according to the arrangement of the Zn 2+ cations. The consecutive CO adsorptions demonstrated an irreversible modification of the surface, resulting in an agglomeration of the zinc cations. A stepwise conversion of the isolated Zn 2+ carbonyls into carbonyls of the closely situated zinc cations followed by formation of bigger zinc oxide clusters was observed. The carbon monoxide coordinated on the isolated Zn 2+ cations at the interface with ceria reacts with the lattice oxygen leading to formation of oxygen vacancies. An insight into the origin of the activation during the CO oxidation process is proposed.


Marzo, 2012 | DOI: 10.1021/jp210996b

Sub-ambient CO oxidation over Au/MOx/CeO2-Al2O3 (M = Zn or Fe)


Reina, TR; Ivanova, S; Dominguez, MI; Centeno, MA; Odriozola, JA
Applied Catalysis A-General, 419-420 (2012) 58-66

ABSTRACT

A series of ZnO and Fe 2O 3 modified ceria/alumina supports and their corresponding gold catalyst were prepared and studied in the CO oxidation reaction. ZnO-doped solids show a superior catalytic activity compared to the bare CeO 2-Al 2O 3, which is attributed to the intimate contact of the ZnO and CeO 2 phases, since an exchange of the lattice oxygen occurs at the interface. In a similar way, Fe 2O 3-modified supports increase the ability of the CeO 2-Al 2O 3 solids to eliminate CO caused by both the existence of Ce-Fe contact surface and the Fe 2O 3 intrinsic activity. All of the gold catalysts were very efficient in oxidising CO irrespective of the doping metal oxide or loading, with the ZnO containing systems better than the others. The majority of the systems reached total CO conversion below room temperature with the ZnO and Fe 2O 3 monolayer loaded systems the most efficient within the series.


Marzo, 2012 | DOI: 10.1016/j.apcata.2012.01.012

Nanostructured Spark Plasma Sintered Ce-TZP Ceramics


Cruz, SA; Poyato, R; Cumbrera, FL; Odriozola, JA
Journal of the American Ceramic Society, 95 (2012) 901-906

ABSTRACT

In this work, spark plasma sintering (SPS) of 10 mol% CeO 2-doped ZrO 2 nanocrystalline powders, obtained by a two-step synthesis procedure, allows the preparation of fully densified nanostructured ceramics. The CeO 2-ZrO 2 powders with particle size below 100 nm are obtained after CeO 2 deposition on hydrothermally synthesized ZrO 2 particles by the impregnation method. Tetragonal CeO 2-ZrO 2 ceramics are obtained when sintering at 1200°C without holding time. A graded material containing tetragonal, monoclinic, and pyrochlore phases are obtained when sintering at 1200°C and for 5 min holding time. This is explained in terms of the gradual reduction of Ce 4+ to Ce 3+ species by carbon in the graphite environment during SPS. With the successful combination of the stabilizer coating technique and SPS, we achieve not only the stabilization of the tetragonal phase in the ceramics, but also good control of the grain size, by producing nanostructured ceramics with 40-70 nm grain sizes.


Marzo, 2012 | DOI: 10.1111/j.1551-2916.2011.04978.x

In Situ XAS Study of Synergic Effects on Ni-Co/ZrO2 Methane Reforming Catalysts


Gonzalez-delaCruz, VM; Pereniguez, R; Ternero, F; Holgado, JP; Caballero, A
Journal of Physical Chemistry C, 116 (2012) 2919-2926

ABSTRACT

Four different mono and bimetallic Ni–Co/ZrO2 catalysts have been studied by means of in situ XAS, X-ray diffraction, TPR, and measurements of the catalytic activity in the dry reforming reaction of methane (DRM). Even though the cobalt monometallic system has no activity for the methane reforming reaction, both bimetallic catalysts (with 1:1 and 1:2 Ni/Co ratio, respectively), showed a better activity and stability than the nickel monometallic system. The XRD data indicate that a mixed cobalt–nickel spinel is formed by calcination of the precursor solids, leading to the formation of an alloy of both metals after reduction in hydrogen. In situ XAS experiments showed a much better resistance of metals in the bimetallic systems to be oxidized under reaction conditions at temperatures until 750 °C. After these results, we proposed the formation in the bimetallic systems of a more reducible nickel–cobalt alloy phase, which remains completely metallic in contact with the CO2/CH4 reaction mixture at any temperature. The presence of adjacent nickel and cobalt sites seems to avoid the deactivation of cobalt in the DRM reaction. In the case of cobalt sites, the presence of adjacent nickel atoms seems to prevent the deposition of carbon over the cobalt sites, now showing its higher activity in the dry reforming reaction. Simultaneously, this higher activity of the cobalt sites in the bimetallic system produces more hydrogen as a product, maintaining the nickel atoms completely reduced under reaction conditions. This synergic effect accounts for the better performance of the bimetallic systems and points at both, the oxidation state of nickel particles under reaction conditions and the carbon deposition processes, as important factors responsible for differences in catalytic activities and stabilities in this hydrocarbon reaction.


Febrero, 2012 | DOI: 10.1021/jp2092048

Operando DRIFTS study of the redox and catalytic properties of CuO/Ce1−xTbxO2−δ (x = 0–0.5) catalysts: evidence of an induction step during CO oxidation


Martinez-Arias, A.; Hungria, A. B.; Fernandez-Garcia, M.; Iglesias-Juez, A.; Soria, J.; Conesa, J. C.; Anderson, J. A.; Munuera, G.
Physical Chemistry Chemical Physics, 14 (2012) 2144-2151

ABSTRACT

Catalysts of 1 wt% copper oxide supported on cerium oxide or cerium–terbium mixed oxides are comparatively examined with respect to their redox and catalytic properties for CO oxidation. Characterization of the catalysts had shown that they contain highly dispersed CuO-type entities on the corresponding nanostructured fluorite supports with copper dispersion increasing with increasing amounts of terbium in the support. In contrast, the CO oxidation catalytic activity decreases with increasing amounts of terbium in the support. On the basis of operando-DRIFTS experiments, one of the factors that could explain such behaviour is related to the greater difficulty in generating reduced copper sites active for the reaction in the presence of terbium, which in turn is evidenced to constitute an induction stage. Analysis of the redox properties is complemented by XPS which confirms the greater resistance to copper reduction in the presence of terbium.


Febrero, 2012 | DOI: 10.1039/C1CP23298C

Rapid microwave-assisted synthesis of one-dimensional silver–H2Ti3O7 nanotubes


Rodriguez-Gonzalez, V; Obregon-Alfaro, S; Lozano-Sanchez, LM; Lee, SW
Journal of Molecular Catalysis A-Chemical, 353 (2012) 163-170

ABSTRACT

The formation of silver hydrogen trititanate nanotubes, based on the controllable microwave-assisted hydrothermal nanocrystalline TiO2 transition, was investigated by means of XRD, UV–vis–DRS, Raman, FESEM and HRTEM. The results show that the rapid formation of H-trititanate nanotubes is achieved by self-assemblage of silver nanoparticles in which the lamellar intermediates react with NaOH in hydrothermal conditions. The presence of Ag° nanoparticles in the precursor promotes rapid and more complete formation of layered H2Ti3O7 nanotubes. After reacting for 4 h without subsequent thermal treatment, the inner diameters of the cylinder-like nanotubes are in the range of 3.6–4.0 nm, while their outer diameters are in the range of 7.6–8 nm. In addition, some straight nanotubes form bundles which are hundreds of nanometers in length. As-synthesized ultrathin nanotubes and crystalline precursors were evaluated by methyl orange dye (MOD) UV photo-oxidation. The complete degradation of MOD is achieved after 3.5 h of UV irradiation in the presence of silver–TiO2 nanocomposites, resulting in 50% of dye mineralization.


Febrero, 2012 | DOI: 10.1016/j.molcata.2011.11.020

Mechanism of complete n-hexane oxidation on silica supported cobalt and manganese catalysts


Todorova, S; Naydenov, A; Kolev, H; Holgado, JP; Ivanov, G; Kadinov, G; Caballero, A
Applied Catalysis A-General, 413-414 (2012) 43-51

ABSTRACT

Mono- and bi-component cobalt and manganese samples were prepared by impregnation of silica with aqueous solutions of Co(NO3)2·6H2O and/or Mn(NO3)2·6H2O. The bi-component samples were obtained by a common solution of Co- and Mn nitrates (CoMn-MS) or by deposition of cobalt on calcined Mn sample (Co + Mn). The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis and tested in reaction of complete n-hexane oxidation. It was observed that the well crystalline cobalt oxide partially covers poorly crystalline manganese oxide in the Co + Mn catalysts, while finely divided oxides (MnO2 and Mn2O3, Co3O4) are present on the surface of the (CoMn-MS) sample. Four Langmuir–Hinshelwood and two Mars–van Krevelen models were fitted with the experimental data from the catalytic tests. According to the model calculations and results from instrumental methods, the reaction pathway over single component manganese and bi-component Co-Mn catalysts proceeds through Mars–van Krevelen mechanism (the oxidation of the catalyst surface being the rate determining step), while Langmuir–Hinshelwood mechanism is more probable for the Co sample. A considerable increase in activity for the sample obtained from a mixed solution is explained by low crystallinity, simultaneous presence of Mn4+–Mn3+ and enrichment of the surface in oxygen species.


Enero, 2012 | DOI: 10.1016/j.apcata.2011.10.041

Effect of hydrothermal treatment on structural and photocatalytic properties of TiO2 synthesized by sol-gel method


Melian, EP; Diaz, OG; Rodriguez, JMD; Colon, G; Navio, JA; Pena, JP
Applied Catalysis A-General, 411 (2012) 153-159

ABSTRACT

TiO 2 nanoparticles have been prepared by sol-gel precipitation and further hydrothermal treatment. In this way, the effect of the hydrothermal treatment on the structural properties and photocatalytic activity of sol-gel synthesized catalysts has been investigated. These catalysts have been produced by hydrolysis of a mixture of isopropanol-titanium tetraisopropoxide (iPrOH-TiiP). The prepared photocatalysts were characterized by means of X-ray diffraction (XRD), surface area analysis (BET), transmission microscopy (TEM), thermogravimetric analysis (TG), scanning electron microscopy (SEM) analysis, diffuse reflectance, sedimentability analysis and aggregate size study. Besides, the structural evolution with the temperature of the photocatalysts treated or not hydrothermally was studied. It was observed that the calcination produces approaching between the characteristics of both sets of photocatalysts. The photocatalytic activity of the obtained photocatalysts was investigated, using phenol as a model pollutant. The calcination temperature is the most remarkable factor that can affect the ultimate photocatalytic activity of the prepared photocatalysts. However, the hydrothermal treatment previous to calcination led to obtain photocatalysts which exhibit larger photocatalytic activity than their homologous photocatalysts without hydrothermal treatment. The obtained photocatalyst TiO 2ht600 exhibits the same photocatalytic activity per surface area than the commercial TiO 2 Degussa P25 but with much faster sedimentability.


Enero, 2012 | DOI: 10.1016/j.apcata.2011.10.033

Preferential oxidation of CO (CO-PROX) over CuOx/CeO2 coated microchannel reactor


Laguna, OH; Ngassa, EM; Oraa, S; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Arzamendi, G; Gandia, LM; Centeno, MA; Odriozola, JA
Catalysis Today, 180 (2012) 105-110

ABSTRACT

The general aspects of the synthesis and characterization results of a CuO x/CeO 2 catalyst were presented. In addition the principal steps for manufacturing a microchannel reactor and for the coating of the CuO x/CeO 2 catalyst onto the microchannels walls, were also summarized. The catalytic activity of this microchannel reactor during the preferential oxidation of CO (CO-PROX) was evaluated employing a feed-stream that simulates a reformate off-gas after the WGS unit. Two activation atmospheres were studied (H 2/N 2 and O 2/N 2). The reducing pretreatment improved the resistance to deactivation by formation of carbonaceous species over the catalyst surface at high temperatures. The presence of H 2O and CO 2 in the feed-stream was also analyzed indicating that the adsorption of CO 2 inhibited the conversion of CO at lower temperatures because these compounds modified the active sites through the formation of carbonaceous species on the catalyst surface. Finally, the experimental results of the microreactor performance were compared with CFD simulations that were carried out using a kinetic for the CuO x/CeO 2 powder catalyst. The experimental results were reasonably well described by the model, thus confirming its validity.


Enero, 2012 | DOI: 10.1016/j.cattod.2011.03.024

Redox and catalytic properties of CuO/CeO2 under CO + O2 + NO: Promoting effect of NO on CO oxidation


Martinez-Arias, A.; Hungria, A. B.; Iglesias-Juez, A.; Fernandez-Garcia, M.; Anderson, J. A.; Conesa, J. C.; Munuera, G.; Soria, J.
Catalysis Today, 180 (2012) 81-87

ABSTRACT

A CuO/CeO2 catalyst has been studied with respect to its catalytic activity for CO oxidation under stoichiometric conditions employing either O2 or O2–NO mixture as oxidants. The obtained results are rationalised on the basis of analysis of redox properties upon interaction with CO and O2–NO by EPR as well as by redox/catalytic analysis by operando-DRIFTS. These provide useful insight into the processes involved during NO reduction, for which two well differentiated steps associated to a change in the type of active centres during the course of the reaction are evidenced. Nevertheless, the most interesting result is related to observation of a novel promoting effect of NO on CO oxidation. This is explained mainly on the basis of DRIFTS results and appears to be associated with phenomena of adsorption/desorption of NOx species at interfacial positions which apparently activate such interfacial region allowing formation of greater amounts of active reduced copper centres in the presence of NO.


Enero, 2012 | DOI: 10.1016/j.cattod.2011.02.014

DRIFTS study of methanol adsorption on Mg-Al hydrotalcite catalysts for the transesterification of vegetable oils


Navajas, A; Arzamendi, G; Romero-Sarria, F; Centeno, MA; Odriozola, JA; Gandia, LM
Catalysis Communications, 7 (2012) 189-193

ABSTRACT

Mg-Al hydrotalcites rehydrated after calcination are promising catalysts for the methanolysis of vegetable oils. To gain insight into the basis of their catalytic action, the adsorption of methanol over some commercial Mg-Al hydrotalcites was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Different species formed after methanol adsorption were identified, being the total quantity of methoxy species related to the basic character of the sample. A linear correlation between the amount of adsorbed monodentate methoxy species and the catalytic activity in the biodiesel production was found. Therefore, it is proposed that these species are the mainly involved in the transesterification reaction.


Enero, 2012 | DOI: 10.1016/j.catcom.2011.11.005

Photocatalytic Ethanol Oxidative Dehydrogenation over Pt/TiO2: Effect of the Addition of Blue Phosphors


Murcia, JJ; Hidalgo, MC; Navio, JA; Vaiano, V; Ciambelli, P; Sannino, D
International Journal of Photoenergy, 2012 (2012) 687262

ABSTRACT

Ethanol oxidative dehydrogenation over Pt/TiO2 photocatalyst, in the presence and absence of blue phosphors, was performed. The catalyst was prepared by photodeposition of Pt on sulphated TiO2. This material was tested in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency. The effect of the addition of blue phosphors into the fluidized bed has been evaluated. The synthesized catalysts were extensively characterized by different techniques. Pt/TiO2 with a loading of 0.5 wt% of Pt appeared to be an active photocatalyst in the selective partial oxidation of ethanol to acetaldehyde improving its activity and selectivity compared to pure TiO2. In the same way, a notable enhancement of ethanol conversion in the presence of the blue phosphors has been obtained. The blue phosphors produced an increase in the level of ethanol conversion over the Pt/TiO2 catalyst, keeping at the same time the high selectivity to acetaldehyde.


Enero, 2012 | DOI: 10.1155/2012/687262



2011


Well-defined negatively charged gold carbonyls on Au/SiO2


Chakarova, K., Mihaylov, M., Ivanova, S., Centeno, M.A., Hadjiivanov, K.
Journal of Physical Chemistry C, 115 (2011) 21273-21282

ABSTRACT

A Au/SiO2 sample was prepared by ammonia-assisted grafting using HAuCl4 as a gold precursor. Gold on the sample evacuated at 673 K is essentially in metallic form: adsorption of CO at 100 K results in formation of Au0-CO species (IR band at 2122 cm-1 shifting to 2103 cm-1 at high coverage). Coadsorption of CO and O2 even at ambient temperature leads to creation of Auδ+ sites and oxidation of CO. On the contrary, increase of the contact time between CO and the sample leads to a gradual reduction of Au0 to Au δ- species. The process is slightly favored by the presence of water and strongly enhanced in the presence of hydrogen. Back oxidation of Auδ- to Au0 and to Auδ+ occurs in the presence of oxygen. The Auδ- sites strongly adsorb CO and form different interconverting carbonyls observed in the 2080-2050 cm -1 region. On the basis of adsorption of CO-13CO and CO-13C18O isotopic mixtures, it is concluded that all Auδ--CO species are linear, and probably ordered structures are formed. Intensity transfer phenomena are nicely monitored during adsorption of CO isotopic mixtures. The eventual role of negatively charged gold in catalysis is discussed.


Noviembre, 2011 | DOI: 10.1021/jp2070562

Influence of the strong metal support interaction effect (SMSI) of Pt/TiO(2) and Pd/TiO(2) systems in the photocatalytic biohydrogen production from glucose solution


Colmenares, JC; Magdziarz, A; Aramendia, MA; Marinas, A; Marinas, JM; Urbano, FJ; Navio, JA
Catalysis Communications, 16 (2011) 1-6

ABSTRACT

Two different catalysts consisting of Pt/TiO2 and Pd/TiO 2 were submitted to diverse oxidative and reductive calcination treatments and tested for photocatalytic reforming of glucose water solution (as a model of biomass component) in H2 production. Oxidation and reduction at 850°C resulted in better photocatalysts for hydrogen production than Degussa P-25 and the ones prepared at 500°C, despite the fact that the former consisted in very low surface area (6-8 m2/g) rutile titania specimens. The platinum-containing systems prepared at 850°C give the most effective catalysts. XPS characterization of the systems showed that thermal treatment at 850°C resulted in electron transfer from titania to metal particles through the so-called strong metal-support interaction (SMSI) effect. Furthermore, the greater the SMSI effect, the better the catalytic performance. Improvement in photocatalytic behavior is explained in terms of avoidance of electron-hole recombination through the electron transfer from titania to metal particles.


Noviembre, 2011 | DOI: 10.1016/j.catcom.2011.09.003

Structural and catalytic properties of lanthanide (La, Eu, Gd) doped ceria


Hernandez, WY; Laguna, OH; Centeno, MA; Odriozola, JA
Journal of Solid State Chemistry, 184 (2011) 3014-3020

ABSTRACT

Ce0.9M0.1O2-δ mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO2 (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F2g Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce4/Ce3. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO2, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area.


Noviembre, 2011 | DOI: 10.1016/j.jssc.2011.09.018

CO oxidation at low temperature on Au/CePO4: Mechanistic aspects


Romero-Sarria, F., Domínguez, M.I., Centeno, M.A., Odriozola, J.A.
Applied Catalysis B: Environmental, 107 (2011), 268-273

ABSTRACT

This work reports the synthesis and characterization of a cerium phosphate supported gold catalyst as well as its catalytic activity for the oxidation of CO. A precipitation method in the presence of an organic modifier followed by a hydrothermal treatment was used for the support synthesis, resulting in high surface area nanometric particles. Gold/cerium phosphate catalyst with a 1% (w/w) nominal gold content was characterized using XRF, XRD, N2 adsorption-desorption measurements, TEM and DRIFTS-MS. The catalyst shows good catalytic activity at low temperature. The activity is related to the generation of oxygen vacancies in the support caused by the elimination of structural oxygen. In situ studies revealed that the reaction of the oxygen vacancies with gaseous oxygen resulted in the formation of peroxo species. These species are responsible for the activity detected at room temperature in both the catalyst and the support. Moreover, the presence of carbonate and hydrogen carbonate acting as reaction intermediates have been observed.


Septiembre, 2011 | DOI: 10.1016/j.apcatb.2011.07.022

Synthesis, characterization and photocatalytic activity of Bi-doped TiO2 photocatalysts under simulated solar irradiation


Murcia-López, S., Hidalgo, M.C., Navío, J.A.
Applied Catalysis A: General, 404 (2011) 59-67

ABSTRACT

A series of Bi3+-doped TiO2 catalysts with a doping concentration up to 2 wt% were prepared by a sol-gel hydrothermal method. The prepared photocatalysts were characterized by different techniques to determine their structure, morphology and light absorption properties. The activities were evaluated in the photocatalytic oxidation of phenol in aqueous solution under UV-vis illumination. The experimental results indicate that the presence of Bi3+ in TiO2 catalysts enhances the photocatalytic reaction of phenol degradation, although the efficiency of the process markedly depends on the nominal content of the Bi3+ and on the calcination temperature. It was found that the optimal dosage of 0.5 wt% Bi3+ in TiO2 and calcinations at 600 °C 4 h achieved the fastest reaction of phenol degradation under the experimental conditions. From the comparison of the initial rates of the photocatalytic degradation of phenol between home prepared undoped and Bi3+-doped TiO2 with commercial TiO2 Degussa P25, it can be inferred that home prepared TiO 2 calcined at temperatures above 500 °C clearly exceed the photocatalytic performance of P25. When bismuth is incorporated, the reaction rate values are even higher, especially at 600 °C. Even when Bi 3+-doped TiO2 (0.5 wt% Bi3+) calcined at 600 °C has almost the same BET surface than P25, its activity is better. In particular, the reaction rate for the sample with a 0.5% mass content of Bi 3+ calcined at 600 °C not only present higher value with respect to the other series but also a degree of mineralization close to 100%.


Septiembre, 2011 | DOI: 10.1016/j.apcata.2011.07.008

Fe-doped ceria solids synthesized by the microemulsion method for CO oxidation reactions


O.H. Laguna, M.A. Centeno, M. Boutonnet, J.A. Odriozola
Applied Catalysis B: Environmental, 106 (2011) 621-629

ABSTRACT

A series of Ce-Fe mixed oxides as well as the pure oxides were synthesized by the microemulsions method. The solid solution formation was established for all the Fe-doped systems and only a hardly noticeable segregation of &#945;-Fe2O3 was appreciated for the solid with the maximum iron content (50at.% Fe). The oxygen exchange is improved for all the Fe-doped systems; however the 10at.% Fe appears as the optimal iron content for achieving the maximum oxygen vacancies concentration and the higher reducibility efficiency. The CO oxidation (TOX, PROX) is especially achieved for the solids with the lower iron contents but with a superior oxygen vacancies proportion. These Ce-Fe systems prepared from microemulsions are very attractive to be considered as supports for depositing active phases capable of enhancing oxygen exchange ability of the whole system, allowing higher CO oxidation abilities.


Agosto, 2011 | DOI: 10.1016/j.apcatb.2011.06.025

Ionic liquid protected heteropoly acids for methanol dehydration


Ivanova, S., Nitsch, X., Romero-Sarria, F., Louis, B., Centeno, M.A., Roger, A.C., Odriozola, J.A.
Catalysis Today, 171 (2011) 236-241

ABSTRACT

We report herein the synthesis of an organic-inorganic hybrid composed by the ionic liquid protected Keggin structure, as a precursor for acid catalyst and its subsequent application in the methanol dehydration reaction. Special attention was paid to the thermal stability of the resulted hybrids as a function of the Keggin anion. The catalytic behaviour of these new materials are also studied and compared to the metal salt Cs2HPW 12O40. The prepared hybrids are less thermally stable than the metal salt, but their partial decomposition results in very active and selective catalysts for the dehydration of methanol to dimethyl ether.


Agosto, 2011 | DOI: 10.1016/j.cattod.2011.03.077

Oxidation of CO over gold supported on Zn-modified ceria catalysts


Laguna, O.H., Centeno, M.A., Romero-Sarria, F., Odriozola, J.A.
Catalysis Today, 172 (2011) 118-123

ABSTRACT

A series of Zn-modified ceria solids were prepared by thermal decomposition of the corresponding metal propionates. The formation of segregated ZnO particles on the ceria surface is evidenced for these solids using X-ray diffraction; in addition to this the characterization data may allow discarding the formation of a ZnO-CeO2 solid solution. On modifying with Zn, the reducibility of the ceria support is enhanced, being the highest reducibility the one obtained for the ZnO-CeO2 solid having a 1:9 Zn:Ce atomic ratio (CeZn10). The activity of this solid in the CO oxidation reaction was the highest among the tested Zn-modified ceria solids. Therefore, catalysts containing 1 wt.% gold, supported on pure ceria and CeZn solids, were prepared, characterized and their catalytic activities tested. The Zn-modified gold catalyst is more active than the un-modified Au/CeO2 catalyst in the oxidation of CO; this behavior is related to the higher metallic dispersion of gold on the CeZn support surface. However, the number of oxygen vacancies acting as nucleation sites for gold, is hardly modified in the Zn-modified ceria support and, therefore, the higher gold dispersion must be related to high electron density sites on the catalyst surface as a result of Au-Ce-Zn interaction, this improved gold dispersion results in higher activities for CO oxidation.


Agosto, 2011 | DOI: 10.1016/j.cattod.2011.02.015

High-stable mesoporous Ni-Ce/clay catalysts for syngas production


Daza, C.E., Gamba, O.A., Hernández, Y., Centeno, M.A., Mondragón, F., Moreno, S., Molina, R.
Catalysis Letters, 141 (2011) 1037-1046

ABSTRACT

A mesoporous-type catalytic support was synthesized through the modification of a smectite with polyvinyl alcohol (PVA) and microwaves. Texture and micro-morphology of the support was determined. Several techniques were employed in order to describe the chemical environment of active species on the surface. Ni0 particle sizes were dependent on the structural site of reducible species. High stable Ni-Ce catalysts (calcined at 800 °C) were evaluated in the CO2 reforming of methane reaction at 700 °C (WHSV = 96 L g-1 h-1, without dilution gas and pre-reduction). The catalysts have presented CH4 conversions between 40 and 65%, CO2 conversion between 35 and 65% and H2/CO ratios between 0.2 and 0.4.


Julio, 2011 | DOI: 10.1007/s10562-011-0579-1

Photocatalytic coatings of silver–TiO2 nanocomposites on foamed waste-glass prepared by sonochemical process


Lee, S.W., Obregón-Alfaro, S., Rodríguez-González, V.
Journal of Photochemistry and Photobiology A: Chemistry, 221 (2011) 71-76

ABSTRACT

Silver-TiO2 nanocomposite was prepared by photodeposition of silver nanoparticles on the surface of titanium dioxide. The sonochemical method was used for the deposition of silver-TiO2 powder on commercial foamed waste-glass strips (FWGS). The silver-TiO2 and the coated FWGS was characterized by XRD, DRS, SEM, TEM and nitrogen adsorption. In order to enhance silver-TiO2 deposition, different parameters were evaluated such as the solvent effect and use of stabilizing agents. The best deposition was obtained with an aqueous solution of polyvinyl alcohol (PVA) and an ultrasound irradiation source of 23.3 kHz. The photocatalytic activity of the silver-TiO2 coated FWGS was evaluated in the UV photo-assisted destruction of the noxious microalgae, Tetraselmis suecica. It was found that after the photocatalytic irradiation, for 180 min, the algae cells were deformed, fragmented and annihilated, thereby avoiding its regeneration.2


Junio, 2011 | DOI: 10.1016/j.jphotochem.2011.04.026

Photodeposition of gold on titanium dioxide for photocatalytic phenol oxidation


Hidalgo, MC; Murcia, JJ; Navio, JA; Colon, G
Applied Catalysis A-General, 397 (2011) 112-120

ABSTRACT

The influence of experimental conditions during the photodeposition in the preparation of supported Au on TiO2 has been studied. Besides preparation pH, light intensity and deposition time showed to have a high influence on the final properties of gold deposits. Photodeposition using illumination with a high light intensity UV-vis lamp (140 W/m2 UVA range) resulted to be an ineffective method for obtaining nanoparticles of gold on the titania, producing very large and poorly distributed gold deposits. Thus obtained materials did not show any important improvement of their photocatalytic activity tested for phenol oxidation. By contrast, photodeposition using a low light intensity of illumination (0.15 W/m 2 UVA range), produced materials with notably improved photocatalytic activity. The illumination with such a low light intensity allowed the control of the amount, aggregation and oxidation state of gold by changing deposition time, enabling a feasible method of tailoring Au-TiO2 with the appropriate properties for a high photocatalytic activity. Best photocatalytic behaviour for phenol photodegradation was obtained for Au-TiO2 samples prepared by photodeposition at low light intensity with 120 min photodeposition time for catalysts with a 0.5% and 1% nominal content of gold and with 60 min photodeposition time for catalyst with a 2% nominal content of gold.


Abril, 2011 | DOI: 10.1016/j.apcata.2011.02.030

Selective CO removal over Au/CeFe and CeCu catalysts in microreactors studied through kinetic analysis and CFD simulations


Arzamendi, G; Uriz, I; Dieguez, PM; Laguna, OH; Hernandez, WV; Alvarez, A; Centeno, MA; Odriozola, JA; Montes, M; Gandia, LM
Chemical Engineering Journal, 167 (2011) 588-596

ABSTRACT

A kinetic study of the preferential oxidation of CO in H2 rich streams (CO-PrOx) over a cerium-copper oxide (CeCu) and a gold catalyst supported on cerium-iron oxide (Au/CeFe) is presented. The gold catalyst is very active but the CeCu oxide is more selective. A kinetic model describing the CO-PrOx system with CO2 and H2O in the feed has been formulated considering the oxidation of CO and H2 and the reverse water-gas shift reaction. The rate equations have been implemented in computational fluid dynamics codes to study the influence of the operating variables on the CO-PrOx in microchannels and microslits. The CeCu catalyst is the only one capable of achieving final CO contents below 10-100ppmv. Due to the opposite effect of temperature on activity and selectivity there is an optimal temperature at which the CO content is minimal over CeCu. This temperature varies between 170 and 200°C as the GHSV increases from 10,000 to 50,000h-1. Simulations have evidenced the very good heat transfer performance of the microdevices showing that the CO-PrOx temperature can be controlled using air as cooling fluid although the inlet temperature and flow rate should be carefully controlled to avoid reaction extinction. Both microchannels and microslits behaved similarly. The fact that the microslits are much easier to fabricate may be an interesting advantage in favour of that geometry in this case. © 2010 Elsevier B.V.


Marzo, 2011 | DOI: 10.1016/j.cej.2010.08.083

Design and testing of a microchannel reactor for the PROX reaction


Cruz, S; Sanz, O; Poyato, R; Laguna, OH; Echave, FJ; Almeida, LC; Centeno, MA; Arzamendi, G; Gandia, LM; Souza-Aguiar, EF; Montes, M; Odriozola, JA
Chemical Engineering Journal, 167 (2011) 634-642

ABSTRACT

The different steps for manufacturing a microchannel reactor for the PROX reaction are discussed. Transient Liquid Phase bonding (TLP) using a Ni-B-Si amorphous melt spun is used for joining micromilled Al-alloyed ferritic stainless steel plates followed by recrystallization at 1200°C for 5h. A CuOx-CeO2 catalyst synthesized by the coprecipitation method was washcoated on the microchannel block resulting in a homogenous 20-30μm thick layer. The catalytic activity for CO-PROX reaction is similar in both the powder catalyst and the microchannel coated reactor but the selectivity is higher in the microchannel reactor. © 2010 Elsevier B.V.


Marzo, 2011 | DOI: 10.1016/j.cej.2010.08.088

Fischer-Tropsch synthesis in microchannels


Almeida, LC; Echave, FJ; Sanz, O; Centeno, MA; Arzamendi, G; Gandia, LM; Sousa-Aguiar, EF; Odriozola, JA; Montes, M
Chemical Engineering Journal, 167 (2011) 536-544

ABSTRACT

Different metallic supports (aluminum foams of 40ppi, honeycomb monolith and micromonolith of 350 and 1180cpsi, respectively) have been loaded with a 20%Co-0.5%Re/γ-Al2O3 catalyst by the washcoating method. Layers of different thicknesses have been deposited onto the metallic supports. The catalytic coatings were characterized measuring their textural properties, adhesion and morphology. These structured catalysts have been tested in the Fischer-Tropsch synthesis (FTS) and compared with a microchannel block presenting perpendicular channels for reaction and cooling. The selectivity depends on the type of support used and mainly on the thickness of the layer deposited. In general, the C5+ selectivity decreased at increasing CO conversion for all of the systems (powder, monoliths, foams and microchannels block). On the other hand, the selectivity to methane increased with the thickness of the catalytic layer due to the higher effective H2/CO ratio over the active sites resulting from the higher diffusivity of H2 compared with CO in the liquid products filling the pores. The C5+ selectivity of the microchannels reactor is higher than that of the structured supports and the powder catalyst. © 2010 Elsevier B.V.


Marzo, 2011 | DOI: 10.1016/j.cej.2010.09.091

Gold nanoparticles on yttrium modified titania: Support properties and catalytic activity


Plata, JJ; Marquez, AM; Sanz, JF; Avellaneda, RS; Romero-Sarria, F; Dominguez, MI; Centeno, MA; Odriozola, JA
Topics in Catalysis, 54 (2011) 219-228

ABSTRACT

A series of titanium oxide catalysts modified with yttrium has been prepared by sol-gel method and their structural properties have been studied. The incorporation of yttrium in the titania lattice favors the formation of oxygen vacancies while at low Y loadings the anatase structure is preserved. The catalytic activity of these solids for CO oxidation is found to be significantly dependent on their physical properties. In particular the amount of dopant controls the number of surface oxygen vacancies created as well as the gold particle size, which directly affects the catalytic activity. Also, a linear relationship between the catalytic activity and the band gap values, which depend on the Y loading, is observed. Density functional theory based calculations show that Y atoms are incorporated at the TiO2 surface at substitutional positions only, while the preferred oxygen vacancies arise by removing the bridge surface oxygen atoms. These O-vacancies are the preferential adsorption sites for Au atoms and nanoparticles, acting as nucleation centers that favor the dispersion of the catalyst active phase over the support surface. In agreement with experiment, Y doping is found to decrease the band gap of the support due to a destabilization of the valence band of the oxide. © 2011 Springer Science+Business Media, LLC 2011.


Marzo, 2011 | DOI: 10.1007/s11244-011-9639-4

Effect of thermal treatments on the catalytic behaviour in the CO preferential oxidation of a CuO-CeO2-ZrO2 catalyst with a flower-like morphology


Moretti, E; Storaro, L; Talon, A; Lenarda, M; Riello, P; Frattini, R; de Yuso, MDM; Jimenez-Lopez, A; Rodriguez-Castellon, E; Ternero, F; Caballero, A; Holgado, JP
Applied Catalysis B-Environmental, 102 (2011) 627-637

ABSTRACT

A Ce–Zr–Cu oxide system with a flower-like morphology was prepared by a slow co-precipitation method in the absence of any structure directing agent. Four portions of the oxide were thermally treated at four different temperatures (350 °C, 450 °C, 550 °C, 650 °C). The resulting materials samples were characterized by quantitative XRD, adsorption–desorption of N2 at-196 °C, SEM and TEM microscopy, –H2-TPR, XPS and Operando-XANES. All samples were tested in the preferential CO oxidation (CO-PROX) in the 40–190 °C temperature range. Thermal treatments were found to induce slight structural changes without altering the starting morphology of the samples. The samples treated at higher temperature 550–650 °C showed a quite interesting CO-PROX activity and selectivity in a temperature range suitable for a practical use within the FEMFC technology.


Febrero, 2011 | DOI: 10.1016/j.apcatb.2011.01.004

Modifying the Size of Nickel Metallic Particles by H2/CO Treatment in Ni/ZrO2 Methane Dry Reforming Catalysts


Gonzalez-Delacruz, VM; Pereñiguez, R; Ternero, F; Holgado, JP; Caballero, A
ACS Catalysis, 1 (2011) 82-88

ABSTRACT

The effect of a reduction process with CO or H-2 on the Size of nickel particles in Ni/ZrO2 dry methane reforming catalysts have been studied by means of in situ X-ray Spectroscopy (XAS) and Diffuse Reflectance FTIR Spectroscopy (DRIFTS). Our results clearly indicate that a high temperature treatment with CO increases the dispersion of the nickel metallic phase. XAS results have shown a lower coordination number of Ni in the sample treated with CO than that reduced with H-2. From the DRIFTS results, it can he established that, under the CO treatment, the formation of Ni(CO)(4) complexes corrodes the nickel particles, decreasing their size. The formation of these gas molecules occurs without measurable losses of nickel from the catalyst which maintains the same nickel content after the hydrogen or the CO treatment at high temperature:Therefore, this airborne nickel compound, by colliding with the zirconia surface, must deposit the nickel metal metal atoms around onto the support. This behavior is evidence of an important interaction b etween nickel and zirconia surface as unlike other supports there is no losses of nickel during the dispersion process on zirconia. Although different effects of CO on nickel catalysts have been previously described, we have found for the first time several experimental evidences demonstrating the whole redispersion phenomenon.


Febrero, 2011 | DOI: 10.1021/cs100116m

Aluminum anodization in oxalic acid: Controlling the Texture of Al 2O3/Al monoliths for catalytic aplications


Sanz, O; Echave, FJ; Odriozola, JA; Montes, M
Industrial and Engineering Chemistry Research, 50 (2011) 2117-2125

ABSTRACT

The anodization and postanodization processes of aluminum in order to prepare monoliths for catalytic applications have been studied in this work using oxalic acid as electrolyte. The effect of anodization variables (anodization time, current density, temperature, and electrolyte concentration) and postanodization processes on the surface morphology and textural properties of AAO (anodic aluminum oxide) films is analyzed. The anodization variables affect the two main processes taking part in the Al2O3 layer formation: alumina generation and its dissolution that are controlled by temperature, electrolyte concentration and time. The proper combination of both processes, as a result of the anodization variables choice, produces adherent alumina layers with tailored porosity and surface morphology that show excellent properties to be used as catalyst structured support. Larger pore sizes and the complete absence of sulfur that may poison reduced metal-supported active phases are main differences with the classical, most often used, sulfuric acid anodization process. © 2011 American Chemical Society.


Febrero, 2011 | DOI: 10.1021/ie102122x

Novel Bi2WO6-TiO2 heterostructures for Rhodamine B degradation under sunlike irradiation


Lopez, SM; Hidalgo, MC; Navio, JA; Colon, G
Journal of Hazardous Materials, 185 (2011) 1425-1434

ABSTRACT

Highly efficient Bi2WO6-TiO2 heterostructure is synthesized by means of a hydrothermal method having highly photoactivity for the degradation of Rhodamine B under sunlike irradiation. From the structural characterization it has been demonstrated that TiO2 is incorporated on the Aurivillius structure. Interesting synergetic effect between TiO2 and Bi2WO6 leads to an improved charge carrier separation mechanism, causing the excellent photocatalytic performance under sunlike irradiation. The photocatalytic performance of Bi2WO6 and Bi2WO6-TiO2 was compared under different irradiation conditions and using increasing Rhodamine B concentration up to 25ppm. After the photocatalytic analysis of both systems, the mineralization efficiency of the heterostructure appears significantly higher with respect to Bi2WO6.


Enero, 2011 | DOI: 10.1016/j.jhazmat.2010.10.065

Hydrogen production by methanol steam reforming on NiSn/MgO-Al2O3 catalysts: The role of MgO addition


Penkova, A; Bobadilla, L; Ivanova, S; Dominguez, MI; Romero-Sarria, F; Roger, AC; Centeno, MA; Odriozola, JA
Applied Catalysis A-General,392 (2011) 184-191

ABSTRACT

The effect of the magnesia loading on the surface structure and catalytic properties of NiSn/MgO-Al2O3 catalysts for hydrogen production by methanol steam reforming has been investigated. The catalysts have been obtained by impregnation of γ-Al2O3 by the incipient wetness method, with variation of the MgO content. X-ray diffraction (XRD), BET surface area and H2-temperature programmed reduction (TPR) have been used to characterise the prepared catalysts. From this, it has been concluded that the incorporation of MgO results in the formation of MgAl2O4 spinel, which modifies the acid-base properties of the catalysts. The formation of Ni-Sn alloys after the reductive pre-treatment has also been evidenced. The influence of the temperature of reaction and of the MgO loading on the hydrogen production by reforming of methanol has been established. Moreover, tests of catalytic stability have been carried out for more than 20 h. The carbonaceous deposits have been examined by temperature-programmed oxidation (TPO). The analysis of the catalysts after reaction has confirmed the low level of carbon formation on these catalysts. In no case, carbon nanotubes have been detected on the solids.


Enero, 2011 | DOI: 10.1016/j.apcata.2010.11.016

Comparative study of the photodeposition of Pt, Au and Pd on pre-sulphated TiO2 for the photocatalytic decomposition of phenol


Maicu, M; Hidalgo, MC; Colon, G; Navio, JA
Journal of Photochemistry and Photobiology A: Chemistry, 217 (2011) 275-283

ABSTRACT

A comparative study of the photodeposition of Pt, Au and Pd under the same experimental conditions onto pre-sulphated and non-sulphated TiO2 was performed. Morphological and surface characterisation of the samples as well as photocatalytic activity for phenol photooxidation was studied. The influence of sulphate pre-treatment on the deposits size and dispersion onto the TiO2 surface, and photodeposition yields with the different metals were also analysed. The photocatalytic activity of the doped materials was then investigated, observing that catalytic behaviour can be correlated to physical characteristics of the samples determined by (XRD) X-ray diffraction, (XPS) X-ray photoelectron spectroscopy, (XRF) X-ray fluorescence spectrometry and (TEM) transmission electron microscopy. Sulphate pre-treatment was found to influence both the level of dispersion and the size of metal clusters on the TiO2 surface. Sulphation and metallisation of samples was found to produce a synergistic enhancement in photoactivity for the degradation of phenol. The photoactivity of the catalysts with respect to the doped metal species was ordered Pt > Pd > Au.


Enero, 2011 | DOI: 10.1016/j.jphotochem.2010.10.020



2010


Gold supported on metal-doped ceria catalysts (M = Zr, Zn and Fe) for the preferential oxidation of CO (PROX)


Laguna, OH; Sarria, FR; Centeno, MA; Odriozola, JA
Journal of Catalysis, 276 (2010) 360-370

ABSTRACT

A series of ceria oxides doped with 10 mol % of Zr Zn and Fe have been prepared by a pseudo sol-gel method throughout the thermal decomposition of the corresponding metallic propionates With these supports 1 wt % gold catalysts were prepared by the deposition-precipitation method All the solids were characterized by means of XRF N-2 adsorption XRD Raman spectroscopy and SEM techniques and their catalytic activity toward preferential oxidation of CO (PROX) reaction tested The results showed solid solution when doping with Zr and Fe and ZnO surface segregation in the case of Zn We demonstrate that gold dispersion depends on not only the oxygen vacancy concentration but also the nature of the doping agent Finally the catalytic activity was highly promoted by gold in all cases being the doped gold catalysts more active than Au/CeO2 at low temperature.


Diciembre, 2010 | DOI: 10.1016/j.jcat.2010.09.027

Study of the stabilization of zinc phthalocyanine in sol-gel TiO2 for photodynamic therapy applications


Lopez, T; Ortiz, E; Alvarez, M; Navarrete, J; Odriozola, JA; Martinez-Ortega, F; Paez-Mozo, EA; Escobar, P; Espinoza, KA; Rivero, IA
Nanomedicine-Nanotechnology Biology and Medicine, 6 (2010) 777-785

ABSTRACT

Photodynamic therapy (PDT) has emerged as an alternative and promising noninvasive treatment for cancer. It is a two-step procedure that uses a combination of molecular oxygen, visible light, and photosensitizer (PS) agents; phthalocyanine (Pc) was supported over titanium oxide but has not yet been used for cell inactivation. Zinc phthalocyanine (ZnPc) molecules were incorporated into the porous network of titanium dioxide (TiO2) using the sol-gel method. It was prepared from stock solutions of ZnPc and TiO2. ZnPc-TiO2 was tested with four cancer cell lines. The characterization of supported ZnPc showed that phthalocyanine is linked by the N-pyrrole to the support and is stable up to 250 degrees C, leading to testing for PDT. The preferential localization in target organelles such as mitochondria or lysosomes could determine the cell death mechanism after PDT. The results suggest that nanoparticulated TiO2 sensitized with ZnPc is an excellent candidate as sensitizer in PDT against cancer and infectious diseases. From the Clinical Editor: Photodynamic therapy is a two-step procedure that uses a combination of molecular oxygen, visible light and photosensitizer agents as an alternative and promising non-invasive treatment for cancer. The results of this study suggest that nanoparticulated TiO2 sensitized with ZnPc is an excellent photosensitizer candidate against cancer and infectious diseases.


Diciembre, 2010 | DOI: 10.1016/j.nano.2010.04.007

Study of nanoporous catalysts in the selective catalytic reduction of NOx


Rico, MJO; Moreno-Tost, R; Jimenez-Lopez, A; Rodriguez-Castellon, E; Pereniguez, R; Caballero, A; Holgado, JP
Catalysis Today, 158 (2010) 78-88

ABSTRACT

Two SBA-15 type materials were synthesized using a low-cost route, a pure silica SBA-15 and an Al containing SBA-15 (with a Si/Al ratio of 10), where Al was added by a post-synthesis modification. The later solid was achieved without any significant loss in the textural properties of SBA-15, besides improving its properties as support of catalysts. Copper impregnated catalysts were prepared through the incipient wetness impregnation of the two supports. With both supports, the copper weight loading were 1, 3 and 6 wt%. The copper incorporation kept the support mesoporous structures, obtaining a better dispersion of the active phase in the containing aluminium support. All the catalysts showed a moderated catalytic activity in the SCR of NO with propane in presence of an excess of oxygen in the whole studied interval of temperatures and a much better performance was observed when using NH3 instead of propane. The changes of the active phases were studied by operando XAS spectroscopy. Factor analysis of in operando XANES results with sample SiAl_6 indicate that no Cu-0 was detected, but only Cu1+ and Cu2+. The temperature where the Cu1+/Cu2+ ratio is maximum occurs at the reaction temperature where the observed catalytic NO conversion is also maximum.


Diciembre, 2010 | DOI: 10.1016/j.cattod.2010.04.016

Physicochemical Characterization and Use of Wastes from Stainless Steel Mill


Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Environmental Progress & Sustainable Energy, 29 (2010) 471-480

ABSTRACT

Several types of wastes are produced during the manufacture of stainless steel (slags, refractory bricks, and dust). Most of these wastes are not recycled but stored in security deposits or landfills depending on their environmental danger This article reports the study of the physicochemical and mineralogical properties of stainless steel wastes. Their possible uses are also discussed.


Diciembre, 2010 | DOI: 10.1002/ep.10435

Modified cryptomelane-type manganese dioxide nanomaterials for preferential oxidation of CO in the presence of hydrogen


Hernandez, WY; Centeno, MA; Romero-Sarria, F; Ivanova, S; Montes, M; Odriozola, JA
Catalysis Today, 157 (2010) 160-165

ABSTRACT

Transition metal (Cu Co Ni and Zn)-modified cryptomelane-type manganese dioxide nanomaterials were synthesized by the milling method The obtained solids have been characterized by means of Xray diffraction (XRD) scanning electron microscopy and transmission electron microscopy (SEM and TEM) N-2 adsorption-desorption measurements at 77 K Raman spectroscopy and temperature programmed reduction (TPR-H-2) showing similar structural and textural properties All the solids were active in the preferential oxidation of CO in the presence of hydrogen (PROX) being the modified with copper the most active The catalytic activity correlates fairly well with the TPR results finding higher CO conversion for the material with higher reducibility (OMS-Cu) The O-2 selectivity measured as ([CO](in)-[CO](out)/2[O-2](in)-[O-2](out)) x 100 is very similar for all synthesized materials.


Noviembre, 2010 | DOI: 10.1016/j.cattod.2010.03.010

Iron-modified ceria and Au/ceria catalysts for Total and Preferential Oxidation of CO (TOX and PROX)


Laguna, OH; Centeno, MA; Arzamendi, G; Gandia, LM; Romero-Sarria, F; Odriozola, JA
Catalysis Today, 157 (2010) 155-159

ABSTRACT

Iron-modified ceria supports containing different molar percentages of Fe (0% 10% 25% and 50%) were synthesized by thermal decomposition of the metal propionates The formation of a Ce-Fe oxide solid solution is evidenced through XRF XRD BET and Raman spectroscopy For Iron contents above 25% the formation of alpha-Fe2O3 was detected pointing out the formation of the isolated oxides The catalytic activity of the Fe-modified catalysts in the Total Oxidation of CO reaction (TOX) is higher than for the bare CeO2 material The synergy between Ce and Fe shows a maximum for 10% Fe content (CeFe10) catalyst that shows the highest CO conversion per atom of Fe incorporated Gold catalyst was also prepared on CeFe10 and its catalytic activity compared with Au/CeO2 catalyst The addition of iron to the gold catalyst resulted in an enhancement of the catalytic activity for CO oxidation especially at low temperature This Au/CeFe10 catalyst was also active and selective with excellent stability in the Preferential Oxidation of CO (PROX) showing a higher CO conversion than the Au/CeO2 catalyst at temperatures below 150 C being hardly affected by the presence of CO2 and H2O in the gas stream.


Noviembre, 2010 | DOI: 10.1016/j.cattod.2010.04.011

Photocatalytic degradation of phenolic compounds with new TiO2 catalysts


Araña, J; Dona-Rodriguez, JM; Portillo-Carrizo, D; Fernandez-Rodriguez, C; Perez-Pena, J; Diaz, OG; Navio, JA; Macias, M
Applied Catalysis B-Environmental, 100 (2010) 346-354

ABSTRACT

New TiO2 catalysts have been synthesised by means of a sol-gel method in which aggregates have been selected before thermal treatment. Sieving and calcination temperature have been proved to be key factors in obtaining catalysts with greater photoactivity than that of Degussa P-25. These new catalysts have been characterized by means of transmission electron microscopy (TEM), BET surface area, diffuse reflectance spectroscopy (DRS). UV-vis spectroscopy, Fourier transformed infrared (FTIR) and X-ray diffraction (XRD). The different parameters studied were compared to those obtained from two commercial catalysts (Degussa P-25 and Hombikat-UV100). The photocatalytic efficiency of the new catalysts was evaluated by the degradation of various phenolic compounds using UV light (maximum around 365 nm, 9 mW). The catalyst sieved and calcinated at 1023 K, ECT-1023t, showed phenol degradation rates 2.7 times higher than those of Degussa P-25. Also in the degradation of different phenolic compounds, this catalyst showed a higher activity than that of the commercial one. The high photoactivity of this new catalyst has been attributed to the different distribution of surface defects (determined from FTIR studies) and its increased capacity to yield H2O2.


Octubre, 2010 | DOI: 10.1016/j.apcatb.2010.08.011

Synthesis of biodiesel from the methanolysis of sunflower oil using PURAL (R) Mg-Al hydrotalcites as catalyst precursors


Navajas, A; Campo, I; Arzamendi, G; Hernandez, WY; Bobadilla, LF; Centeno, MA; Odriozola, JA; Gandia, LM
Applied Catalysis B-Environmental, 100 (2010) 299-309

ABSTRACT

A series of commercial Mg-Al hydrotalcites have been used as catalyst precursors for the methanolysis of sunflower oil.The solids were characterized by low Mg/Al molar ratios in the 0.5-2.3 range. Additionally, a solid consisting mainly of Mg(OH)(2) but containing some Al (4.2 wt.%) was also employed. The as-received materials were inactive for biodiesel synthesis so calcination and rehydration in boiling water were considered as activation treatments. Among the calcined solids, only the material consisting of MgO was significantly active, achieving about 50% oil conversion after 24h at 60 degrees C, methanol/oil molar ratio of 12 and 2 wt.% of catalyst. The effects of the calcination temperature in the 350-700 degrees C range have been investigated; calcination at 500 degrees C led to the best catalytic performance. In the case of the rehydrated materials, only the solids with the highest Mg/Al molar ratios recovered a well-ordered layered double hydroxide structure. These samples showed an improved catalytic activity compared with their calcined counterparts. A good correlation between catalytic activity and the basic properties determined using Hammett indicators and benzoic acid titration has been found. Rehydrated hydrotalcites were slightly more selective to biodiesel (75%) at intermediate levels of oil conversion than the calcined counterparts (66%). It has been verified that no Mg or Al leaching in the reaction mixture took place; however, the rehydrated samples deactivated significantly. In the case of MgO, after washing and calcination. the recycled catalyst gave 68% of the original oil conversion.


Octubre, 2010 | DOI: 10.1016/j.apcatb.2010.08.006

Characterisation and photocatalytic properties of titania-silica mixed oxides doped with Ag and Pt


Llano, B; Restrepo, G; Marin, JM; Navio, JA; Hidalgo, MC
Applied Catalysis A-General, 387 (2010) 135-140

ABSTRACT

TiO2-SiO2 mixed oxides have been synthesised and modified by Ag and Pt deposition. Due to the effect of the silica on the mixed oxide, the prepared materials presented high surface areas and stabilised anatase as the only crystalline phase after calcination at 700 degrees C. Even using the same photodeposition experimental conditions, the yield for metal deposition depended highly on the metal considered, being much lower for Ag deposition. XPS studies permitted to estimate metal dispersion and oxidation state of the different samples, being both factors of high importance regarding photocatalytic improvement by metal deposition.


Octubre, 2010 | DOI: 10.1016/j.apcata.2010.08.021

Operando XAS and Raman study on the structure of a supported vanadium oxide catalyst during the oxidation of H2S to sulphur


Holgado, JP; Soriano, MD; Jimenez-Jimenez, J; Concepcion, P; Jimenez-Lopez, A; Caballero, A; Rodriguez-Castellon, E; Nieto, JML
Catalysis Today, 155 (2010) 296-301

ABSTRACT

The modification of crystalline phases of a vanadium oxide supported on mesoporous zirconium phosphate during the partial oxidation of H2S to sulphur has been studied by using an operando Raman-GC approach and XAS in reaction conditions. The catalyst, mainly presenting crystalline V2O5, is transformed during the oxidation of H2S at 200 degrees C, presenting crystals of V4O9, which is identified by the presence of a band at ca. 900 cm(-1) in the Raman spectra (using a 785 nm line of an Argon ion laser) and by the presence of a pre-edge at 5469.8 eV (and a main-edge at 5482.2 eV) in XANES spectra. At the same time, it is observed a high conversion of H2S to sulphur (the main reaction product) and SO2 (as minority). Both activity and selectivity depend on the time on stream. In this way, the selectivity to SO2 decreases from ca. 5 to 1% with the time on stream. This change could be explained on the basis of the nature of V-species: the initial presence of V5+-O-V5+ pairs and the appearance of V5+-O-V4+ pairs at high time on stream.


Octubre, 2010 | DOI: 10.1016/j.cattod.2010.02.050

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate


Hartmanova, M; Jergel, M; Holgado, JP; Espinos, JP
Vacuum, 85 (2010) 535-540

ABSTRACT

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500 degrees and 700 degrees C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 degrees C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 degrees C whereas no texture was found for 700 degrees C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.


Octubre, 2010 | DOI: 10.1016/j.vacuum.2010.09.003

AISI 304 austenitic stainless steel monoliths: Modification of the oxidation layer and catalytic coatings after deposition and its catalytic implications


Martinez, LMT; Sanz, O; Centeno, MA; Odriozola, JA
Chemical Engineering Journal, 162 (2010) 1082-1090

ABSTRACT

Monolithic CeO2 and Au/CeO2 catalysts were prepared using austenitic stainless steel (AISI 304) as metallic substrate. Both monolithic and powdered catalysts were characterized before and after CO oxidation reaction by N-2 adsorption desorption, XRD, SEM, TEM and GD-OES. Catalyst deposition on the stainless steel surface results in modifications of the catalyst, the oxide scale and the oxide scale/alloy interface through the interaction between the coating and the steel oxidation layer. Besides this, oxidation of the alloy is also detected. The extension and nature of these modifications depends on the catalyst nature, and on the reaction conditions. As a result of these modifications CO oxidation on Au/CeO2 catalysts is enhanced and gold surface dynamics is modified.


Septiembre, 2010 | DOI: 10.1016/j.cej.2010.07.005

Study of nanostructured Ni/CeO2 catalysts prepared by combustion synthesis in dry reforming of methane


Gonzalez-Delacruz, VM; Ternero, F; Pereniguez, R; Caballero, A; Holgado, JP
Applied Catalysis A-General, 384 (2010) 1-9

ABSTRACT

This work reports the study of several catalysts of Ni-CeO2 active for dry methane reforming process (CH4 + CO2 -> 2CO + 2H(2)). The use of Ni as active phase is highly preferred, due to its availability, high activity and low cost, although its main lack is the coke formation on the surface of Ni metal particles, resulting in a severe deactivation. Here we report a new synthesis method that allows a simple, effective and fast way to prepare Ni-CeO2 catalysts, in a wide range of metallic loadings, resulting in all the cases in well-formed NiO crystallites with sizes in the range of 12-18 nm. The use of CeO2 as a support has been based on its massive use in TWC catalysts formulations, where it is recognized to activate CH4 and lower hydrocarbon dissociation. Moreover, CeO2 has been reported to have an intrinsic activity in the CH4 reforming reaction. Besides the metallic loading, several factors that control the preparation method of the catalyst have been varied, in order to optimize their performance. Most of the catalysts prepared show activity and selectivity values close to thermodynamic ones, maintaining a good stability on long periods of time and severe conditions. Nevertheless, formation of some carbon nano-fibers has been observed, which could result in a drawback for their application at large scale.


Agosto, 2010 | DOI: 10.1016/j.apcata.2010.05.027

Determination of the local structure of a highly dispersed Pd-Nanosystem located on a titanium dioxide carrier


Kriventsov, VV; Novgorodov, BN; Yakimchuk, EP; Kochubey, DI; Zyuzin, DA; Simakova, IL; Chistyakov, AV; Zhmakin, VV; Bukhtenko, OV; Tsodikov, MV; Kozitsyna, NY; Vargaftik, MN; Moiseev, II; Maksimovskii, EA; Nechepurenko, SF; Navio, JA; Nikitenko, SG
Journal of Surface Investigation-X-Ray Synchrotron and Neutron Techniques, 4 (2010) 636-639

ABSTRACT

This work is devoted to a structural study of a highly dispersed Pd nanosystem, which is stabilized in the TiO2 matrix, by XAFS spectroscopy. Nanocomposite was prepared from bimetallic PdCo(mu-OOCMe)(4)(NCMe) precursor followed by processing in several ways: calcination in air and in argon and microwave irradiation. The local structure of Pd catalysts formed by different methods was studied. Possible structural models were considered in detail.


Agosto, 2010 | DOI: 10.1134/S1027451010040166

Sunlight highly photoactive Bi2WO6-TiO2 heterostructures for rhodamine B degradation


Colon, G; Lopez, SM; Hidalgo, MC; Navio, JA
Chemical Communications, 46 (2010) 4809-4811

ABSTRACT

Highly efficient Bi2WO6-TiO2 heterostructures are synthesized by means of a hydrothermal method; they have high photoactivity for the degradation of rhodamine B under sunlike irradiation. An interesting synergetic effect between TiO2 and Bi2WO6 leads to an improved charge carrier separation mechanism, causing the excellent photocatalytic performance.


Julio, 2010 | DOI: 10.1039/c0cc00058b

In Situ Characterization of the Dynamic Gold-Support Interaction over Ceria Modified Eu3+. Influence of the Oxygen Vacancies on the CO Oxidation Reaction


Hernandez, WY; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Journal of Physical Chemistry C, 114 (2010) 10857-10865

ABSTRACT

Gold-supported ceria and europium-doped ceria catalysts were prepared by the deposition-precipitation method. The influence of the pretreatment atmosphere and temperature on the concentration of oxygen vacancies and gold dispersion on the Au/CeEti(10) catalyst under actual reaction conditions was investigated by "in situ" X-ray diffraction and Raman analysis. By Raman spectroscopy, a preferential interaction of the gold with the support across the oxygen vacancies was established and correlated with the gold dispersion. The increase in the concentration of oxygen vacancies in the presence of hydrogen induces changes in the gold crystallite size by breaking-off and migration of gold nanoparticles toward the oxygen vacancies on the CeEu(10) support. The activity of the Au/CeEu(10) solid in the CO oxidation reaction was significantly improved when the catalyst was preactivated in a reducing atmosphere. This trend could be associated with the redispersion of gold together with the increase in the concentration of oxygen vacancies in the support.


Junio, 2010 | DOI: 10.1021/jp1013225

Computational fluid dynamics study of heat transfer in a microchannel reactor for low-temperature Fischer-Tropsch synthesis


Arzamendi, G; Dieguez, PM; Montes, M; Odriozola, JA; Sousa-Aguiar, EF; Gandia, LM
Chemical Engineering Journal, 160 (2010) 915-922

ABSTRACT

A three-dimensional computational fluid dynamics (CFD) study of heat transfer in a microchannel reactor for the low-temperature Fischer-Tropsch synthesis (FTS) is presented. The microreactor studied is a steel block with 80 square microchannels of 1 mm of side arranged in cross-flow configuration for the transport of syngas and cooling water. Syngas space velocities in the 5000-30,000 h(-1) (SIP) range have been considered. The microreactor exhibited good isothermicity under most simulated conditions. The FTS can be conducted with very low-temperature change between 483 and 523 K within a wide range of CO conversions using boiling water as coolant. To this end the pressure has to be set at the appropriate value between about Sand 35 atm. The pressure would have to be reduced as the CO conversion increases which might have a negative effect on the FTS selectivity to middle distillates. However, adjusting the cooling water flow rate in the range 0.25-250 g min(-1) allows maintaining the FTS temperature at suitable values while avoiding the use of low pressures. Relatively high values of the overall heat transfer coefficient in the 20-320 W m(-2) K-1 range have been obtained. A significant effect of the buoyancy forces on the thermal performance of the microreactor has been found.


Junio, 2010 | DOI: 10.1016/j.cej.2009.12.028

The Effect of Water on Particle Size, Porosity and the Rate of Drug Release From Implanted Titania Reservoirs


Lopez, T; Ortiz, E; Alexander-Katz, R; Odriozola, JA; Quintana, P; Gonzalez, RD; Lottici, PP; Marino, LG
Journal of Biomedical Materials Research Part-B Applied Biomaterials, 93B (2010) 401-406

ABSTRACT

The implantation of controlled drug release devices represents a new strategy in the treatment of neurodegenerative disorders Sol-gel titania implants filled with valproic acid, have been used for this purpose to treat induced epilepsy in rats The kinetics of the drug release depend on. (a) porosity, (b) chemical interactions between valproic acid and surface hydroxyl groups of titania, (c) particle size, and (d) particle size agglomerates The concentration of water used in the hydrolysis reaction is an important variable in the degree of porosity, hydroxylation, and structural defects of the nanostructured titanium oxide reservoir The titanium n-butoxide/water ratio was systematically varied during the sol-gel synthesis, while maintaining the amount of valproic acid constant. Characterization studies were performed using DTA-TGA, FTIR, Raman, TEM, SEM, BET, and in vitro release kinetic measurements The particle agglomerate size and porosity were found to depend on the amount of water used in the sol-gel reactio.


Mayo, 2010 | DOI: 10.1002/jbm.b.31595

N- and/or W-(co)doped TiO2-anatase catalysts: Effect of the calcination treatment on photoactivity


Kubacka, A; Colon, G; Fernandez-Garcia, M
Applied Catalysis B-Environmental, 95 (2010) 238-244

ABSTRACT

A series of nanosized W,N-codoped and single-doped N- and W-anatase-TiO2 catalysts have been prepared by a microemulsion method and calcined at different temperatures. The activity in the sunlight selective photo-oxidation of toluene and styrene has been correlated with structural, electronic, and surface examinations of the catalysts done with the help of XRD-Rietveld, N-2 physisorption, X-ray photoelectron, infrared, electron paramagnetic resonance (EPR) and UV-vis spectroscopies. Irrespective of the reaction, W,N-codoped nanocatalysts showed an enhanced photoactivity with respect to bare anatase and single-doped N-TiO2 and W-TiO2 materials. A strong W-N synergistic interaction appears to play a decisive role in driving the excellent photoactivity performance of W,N-codoped materials by affecting (i) electronic properties, particularly maximizing the anatase band gap decrease and enhancing the subsequent visible light photon absorption, and (ii) surface properties, in turn related to the formation of OH radicals upon light excitation. The maximum photoactivity is reached by calcination at 450 degrees C and is concomitantly observed with a near complete selectivity to partial oxidation products. Higher calcination temperatures yielded solids with significantly inferior photocatalytic performance. The properties of the W-N interaction are discussed as a function of the calcination temperature.


Abril, 2010 | DOI: 10.1016/j.apcatb.2009.12.028

Gas phase photocatalytic oxidation of toluene using highly active Pt doped TiO2


Colon, G; Maicu, M; Hidalgo, MC; Navio, JA; Kubacka, A; Fernandez-Garcia, M
Journal of Molecular Catalysis A-Chemical, 320 (2010) 14-18

ABSTRACT

Platinum doped TiO2 materials were studied for the gas phase photocatalytic degradation of toluene. Platinum deposition was achieved by photodeposition method over TiO2 prepared by means of a sol-gel route. The effect of sulphuric acid pretreatment on the further platinisation process has been extensively studied. From the wide structural and surface analysis of the catalysts an interesting synergetic effect has been demonstrated. The previous sulphate treatment over TiO2 leads to improved dispersion of the Pt which presents a lower aggregation and homogeneous cluster size. This fact, together with the adequate control of anatase structural and surface parameter due to the sulphate treatment, renders a good photocatalytic performance for toluene oxidation reaction. The highest reaction rates and CO2 selectivities have been obtained for Pt-S-TiO2 samples.


Abril, 2010 | DOI: 10.1016/j.molcata.2009.12.009

Catalytic nanomedicine: Functionalisation of nanostructured cryptomelane


Lopez, T; Ortiz, E; Alvarez, M; Manjarrez, J; Montes, M; Navarro, P; Odriozola, JA
Materials Chemistry and Physics, 120 (2010) 518-525

ABSTRACT

Nanostructured cryptomelanes (KMn8O16) were synthesized from manganese sulphate and manganese acetate precursors by the reflux method. The respectively obtained samples, CRYSO4 and CRYAc, were functionalised with hydroxyl, ammonium, sulphate and phosphate groups in order to modify the biocompatibility and surface properties of cryptomelane. Characterization by FTIR and XRD confirmed bond formation of CRY-NH, CRY=S=O, CRY-NH, and CRY=PO4. In both functionalise samples (CRYSO4-F and CRYAc-F), IR bands occurred at 1399 cm(-1), corresponding to the sulphate species, and 1106 cm(-1), related to phosphate vibrations; along with the OH and NH characteristic vibration bands in the high energy region. Biocompatibility of functionalised samples was tested by implantation of cryptomelane reservoir in the basolateral amygdala and caudal nucleus of Wistar rats using stereotactic surgery. The brains of the rats were processed in order to evaluate any damage associated with the implant. The results showed that functionalised cryptomelanes did not cause tissue damage or inflammation while not functionalised cryptomelanes caused cell death.


Abril, 2010 | DOI: 10.1016/j.matchemphys.2009.11.049

Room-Temperature Reaction of Oxygen with Gold: An In situ Ambient-Pressure X-ray Photoelectron Spectroscopy Investigation


Jiang, P; Porsgaard, S; Borondics, F; Kober, M; Caballero, A; Bluhm, H; Besenbacher, F; Salmeron, M
Journal of the American Chemical Society, 132 (2010) 2858-2859

ABSTRACT

The interaction of O-2 with gold foil and gold nanoparticles grown by thermal deposition on TiO2(110) was studied by in situ ambient pressure X-ray photoelectron spectroscopy at room temperature. No spontaneous dissociation of O-2 was observed either on Au foil or oil Au nanoparticles up to 1 Torr of O-2. X-ray irradiation, however, is very effective in promoting gold oxidation on both surfaces in the presence of O-2. Our results help reconcile recent conflicting experimental observations regarding the activation of molecular oxygen, which is a crucial issue in Au catalyzed oxidation reactions.


Marzo, 2010 | DOI: 10.1021/ja909987j

In situ spectroscopic detection of SMSI effect in a Ni/CeO2 system: hydrogen-induced burial and dig out of metallic nickel


Caballero, A; Holgado, JP; Gonzalez-delaCruz, VM; Habas, SE; Herranz, T; Salmeron, M
Chemical Communications, 46 (2010) 1097-1099

ABSTRACT

In situ APPES technique demonstrates that the strong metal support interaction effect (SMSI) in the Ni-ceria system is associated with the decoration and burial of metallic particles by the partially reduced support, a phenomenon reversible by evacuation at high temperature of the previously absorbed hydrogen.


Febrero, 2010 | DOI: 10.1039/b920803h

Complete n-hexane oxidation over supported Mn-Co catalysts


Todorova, S; Kolev, H; Holgado, JP; Kadinov, G; Bonev, C; Pereniguez, R; Caballero, A
Applied Catalysis B-Environmental, 94 (2010) 46-54

ABSTRACT

Two series of Co-Mn samples were prepared by impregnation of silica with aqueous solutions or Co(NO3)(2)center dot 6H(2)O and/or Mn(NO3)(2)center dot 6H(2)O. Cobalt oxide was the predominant phase in one of the series and manganese was used as the promoter. The major component in the second series was manganese oxide and Co was the promoter. The prepared samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) and tested in the reaction of complete n-hexane oxidation. The catalytic activity of both single component cobalt and manganese samples was similar, however, a combination between the two elements changed significantly the activity and this depended on the method of preparation. Catalysts prepared by a common solution of Co- and Mn nitrates manifested a considerable increase in activity as a result of very low crystallinity of the supported metal oxide phases, partial enrichment of the surface with cobalt and uniform distribution of oxide agglomerates on the support.


Febrero, 2010 | DOI: 10.1016/j.apcatb.2009.10.019

Doping level effect on sunlight-driven W,N-co-doped TiO2-anatase photo-catalysts for aromatic hydrocarbon partial oxidation


Kubacka, A; Bachiller-Baeza, B; Colon, G; Fernandez-Garcia, M
Applied Catalysis B-Environmental, 93 (2010) 274-281

ABSTRACT

A series of nanosized W,N-co-doped anatase TiO2 catalysts with different dopant contents has been prepared by a microemulsion method and examined in the sunlight selective photo-oxidation of toluene and styrene. The activity results have been correlated with structural, electronic, and surface examinations of the catalysts done with the help of XRD-Rietveld, N-2 physisorption and NH3 chemisorption-calorimetry, XPS, Infrared, and UV-visible spectroscopies. Irrespective of the reaction, a consistent reaction rate enhancement with respect to titania (nano-TiO2, P25) references and W-doped TiO2 systems is observed for single-phase anatase W,N-co-doped samples. This is likely linked with the decrease of the band gap energy decrease and results from a combined W-N cooperative effect on structural properties of the anatase network. W,N simultaneous presence also makes a drastic effect on selectivity, maximizing the yield to partial oxidation products. This appears related with surface properties of the materials.


Enero, 2010 | DOI: 10.1016/j.apcatb.2009.09.039

Synthesis and characterization of a LaNiO3 perovskite as precursor for methane reforming reactions catalysts


Pereñiguez, R; Gonzalez-DelaCruz, VM; Holgado, JP; Caballero, A
Applied Catalysis B-Environmental, 93 (2010) 346-353

ABSTRACT

The objective of the present work has been the study of the physicochemical and catalytic properties of a Ni/La2O3 catalyst obtained by reduction of a lanthanum nickelite, LaNiO3, with perovskite structure. The perovskite, obtained by means of a spray pyrolysis method, provides a Ni/La2O3 system active in different methane reforming reactions. The catalyst was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-Ray photoemission spectroscopy (XPS), temperature-programmed reduction and oxidation (TPR, TPO) and catalytic activity tests. Although not evidenced by XRD data, XAS and TPR measurements show the presence of an amorphous NiO phase in the original sample, together with the crystalline LaNiO3 phase. Upon reoxidation treatment of the reduced Ni/La2O3 catalyst, the LaNiO3 structure is partly recovered which provides a convenient way to regenerate a waste catalyst (reoxidation and new reduction in hydrogen). The catalyst is active in several reactions of methane with oxygen, water and CO2, showing a remarkable stability specially under dry reforming of methane (DRM) reaction conditions. This quite great catalytic performance has been explained by the high resistance of the nickel particles to be oxidized, as detected by in situ XAS. In the presence of water, as in steam reforming of methane (SRM) reaction conditions, these metallic particles are gradually oxidized, which explains the linear decreasing of the catalytic performance observed for the SRM reaction.


Enero, 2010 | DOI: 10.1016/j.apcatb.2009.09.040

Supported nickel catalysts with a controlled molecular architecture for the catalytic reformation of methane


Hufschmidt, D; Bobadilla, LF; Romero-Sarria, F; Centeno, MA; Odriozola, JA; Montes, M; Falabella, E
Catalysis Today, 149 (2010) 394-400

ABSTRACT

In this work a lanthanum and nickel catalyst having perovskite structure, grown on a gamma-alumina carrier, is being presented. The structure of the catalyst was confirmed by XRD. The behaviour of this material under the conditions of steam reforming has been studied and the influence of the temperature, the space velocity and the steam/carbon ratio on the conversion of methane and the product distribution in the process was determined. In all cases at higher temperatures conversions of more than 90% and high selectivities were achieved. The experiments to determine the stability of the catalyst demonstrated that no deactivation in experimental runs of more than 17h occurred. Additionally a study of the catalyst after the reaction showed that only lowly structured carbonaceous species were formed on the catalyst surface, which is not expected to inhibit strongly the initial catalytic activity.


Enero, 2010 | DOI: 10.1016/j.cattod.2009.06.002

Chemical and electronic characterization of cobalt in a lanthanum perovskite. Effects of strontium substitution


Hueso, JL; Holgado, JP; Pereniguez, R; Mun, S; Salmeron, M; Caballero, A
Journal of Solid State Chemistry, 183 (2010) 27-32

ABSTRACT

Two different cobaltites, LaCoO3 and La0.5Sr0.5CoO3-delta, have been prepared and characterized by means of high energy Co K-edge and low energy O K-edge X-ray absorption spectroscopy (XAS). Even though half of the La(III) is substituted by Sr(II), little or no changes call be detected in the formal oxidation state of cobalt atoms. The presence of strontium cations induces two main effects in the chemical and electronic state of the perovskite. The charge balance with Sr(II) species is reached by the formation of oxygen vacancies throughout the network, which explains the well-known increase in the reactivity of this Substituted perovskite. O K-edge XAS experiments show that the Sr(II) species induce the transitions of d electrons of cobalt cations from low to high Spill Configuration. We propose that this change in Spill Multiplicity is induced by two cooperative effects: the oxygen vacancies. creating five coordinated cobalt atoms, and the bigger size of Sr(II) cations, aligning the Co-O-Co atoms, and favoring the overlapping of pi-symmetry cobalt and oxygen orbitals, reducing the splitting energy of e(g) and t(2g) levels.


Enero, 2010 | DOI: 10.1016/j.jssc.2009.10.008



2009


Self-Assembling of Er2O3-TiO2 Mixed Oxide Nanoplatelets by a Template-Free Solvothermal Route


Julian-Lopez, B; Martos, M; Ulldemolins, N; Odriozola, JA; Cordoncillo, E; Escribano, P
Chemistry-A European Journal, 15 (2009) 12426-12434

ABSTRACT

An easy solvothermal route has been developed to synthesize the first mesoporous Er2O3-TiO2 mixed oxide spherical particles composed of crystalline nanoplatelets, with high surface area and narrow pore size distribution. This synthetic strategy allows the preparation of materials at low temperature with interesting textural properties without the use of surfactants, as well as the control of particle size and shape. TEM and Raman analysis confirm the formation of nanocrystalline Er2O 3-TiO2 mixed oxide. Mesoscopic ordered porosity is reached through the thermal decomposition of organic moieties during the synthetic process, thus leading to a template-free methodology that can be extended to other nanostructured materials. High specific surface areas (up to 313 m 2g-1) and narrow pore size distributions are achieved in comparison to the micrometric material synthesized by the traditional sol-gel route. This study opens new perspectives in the development, by solvothermal methodologies, of multifunctional materials for advanced applications by improving the classical pyrochlore properties (magnetization, heat capacity, catalysis, conductivity, etc.). In particular, since catalytic reactions take place on the surface of catalysts, the high surface area of these materials makes them promising candidates for catalysts. Furthermore, their spherical morphology makes them appropriate for advanced technologies in, for instance, ceramic inkjet printers.


Noviembre, 2009 | DOI: 10.1002/chem.200901423

Ionic liquid templated TiO2 nanoparticles as a support in gold environmental catalysis


Avellaneda, RS; Ivanova, S; Sanz, O; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 93 (2009) 140-148

ABSTRACT

This work presents the synthesis of a nanostructured titania support and its subsequent utilization for the gold particles deposition and application in the reaction of the CO oxidation. A functionalized ionic liquid has been used as a templating agent for the titanium oxide synthesis resulting in a high specific surface nanostructured titania anatase. The as prepared support was then used for gold nanoparticles deposition without ionic liquid removal in order to study the possible role of the latter in the stabilization of the gold particles. The presence of ionic liquid in the catalysts results in an unusual catalytic behaviour—strong dependence on the presence of CO and changed kinetics and rate of oxidation.


Noviembre, 2009 | DOI: 10.1016/j.apcatb.2009.09.023

Methane steam reforming in a microchannel reactor for GTL intensification: A computational fluid dynamics simulation study


Arzamendia, G; Dieguez, PM; Montes, M; Odriozola, JA; Sousa-Aguiar, EF; Gandia, LM
Chemical Engineering Journal, 154 (2009) 168-173

ABSTRACT

The integration of the steam reforming and combustion of methane in a catalytic microchannel reactor has been simulated by computational fluid dynamics (CFD). Two models including 4 or 20 square microchannels of 20 mm of length and 0.7 mm of side have been developed. It has been assumed that a thin and homogeneous layer of an appropriate catalyst has been uniformly deposited onto the channels walls. The kinetics of the steam reforming of methane (SRM), water-gas shift (WGS) and methane combustion in air have been incorporated into the models. This has allowed simulating the effect of the gas streams space velocities, catalyst load, steam-to-carbon (S/C) ratio and flow arrangement on the microreformer performance. The results obtained illustrate the potential of microreactors for process intensification: complete combustion of methane is achieved at gas hourly space velocities (GHSV) as high as 130,000 h−1. As concerns the SRM, methane conversions above 97% can be obtained at high GHSV of 30,000 h−1 and temperatures of 900–950 °C. Under these conditions selectivity for syngas is controlled by the WGS equilibrium.


Noviembre, 2009 | DOI: 10.1016/j.cej.2009.01.035

Manganese and iron oxides as combustion catalysts of volatile organic compounds


Duran, FG; Barbero, BP; Cadus, LE; Rojas, C; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 92 (2009) 194-201

ABSTRACT

FeMn mixed oxides were prepared by the citrate method with Fe:Mn atomic ratio equal to 1:1, 1:3 and 3:1. The sample was characterized by means of specific surface area measurements, X-ray diffractometry (XRD), temperature programmed desorption of oxygen (O2-DTP), temperature programmed reduction (TPR), X-ray fluorescence (XRF), transmission electron microscopy (TEM and SAED) and high resolution TEM (HREM). The characterization results demonstrated the formation of a Mn2O3–Fe2O3 solid solution. The catalytic performance in ethanol, ethyl acetate and toluene total oxidation on these samples was better than on Fe2O3 and Mn2O3 pure oxides.


Octubre, 2009 | DOI: 10.1016/j.apcatb.2009.07.010

Influence of sulfur on the structural, surface properties and photocatalytic activity of sulfated TiO2


Colon, G; Hidalgo, MC; Navio, JA; Kubacka, A; Fernandez-Garcia, M
Applied Catalysis B-Environmental, 90 (2009) 633-641

ABSTRACT

TiO2 materials were prepared by sol–gel method and then impregnated with sulfuric acid and calcined using different temperatures and atmosphere (air and nitrogen). Systematic variation of these two experimental parameters makes possible to modulate the amount of surface sulfur from the impregnation procedure. The best photocatalyst for liquid phenol degradation was obtained after calcination at 700 °C in air, while gas toluene degradation optimum performance is obtained by calcination at 700 °C in nitrogen from 500 °C. Structural analysis of these materials by XRD, micro-Raman spectroscopy and FE-SEM shows that once calcined at 700 °C the material was a well-crystallized, high surface area anatase structure in all cases. The surface characterization by FTIR and XPS confirms the presence of a higher amount of sulfur species and acidic OH groups in samples partially calcined in nitrogen, and a low XPS O/Ti-atomic ratio with the O 1s peak shifted to higher binding energies (1.8 vs. 2 ± 0.1 and 530.4 eV vs. 529.8 eV, respectively, against the reference materials) for samples calcined at 700 °C, temperature at which most of sulfate species have been evolved. The paper presents an attempt to correlate the contribution of the observed structural defects within the anatase sub-surface layers and surface acidity to the different photoactivity behaviour exhibited for phenol liquid phase and toluene gas phase photodegradation.


Agosto, 2009 | DOI: 10.1016/j.apcatb.2009.04.026

Near-ambient X-ray photoemission spectroscopy and kinetic approach to the mechanism of carbon monoxide oxidation over lanthanum substituted cobaltites


Hueso, JL; Martinez-Martinez, D; Caballero, A; Gonzalez-Elipe, AR; Mun, BS; Salmeron, M
Catalysis Communications, 10 (2009) 1898-1902

ABSTRACT

We have studied the oxidation of carbon monoxide over a lanthanum substituted perovskite (La0.5Sr0.5CoO3−d) catalyst prepared by spray pyrolysis. Under the assumption of a first-order kinetics mechanism for CO, it has been found that the activation energy barrier of the reaction changes from ∼80 to ∼40 kJ mol−1 at a threshold temperature of ca. 320 °C. In situ XPS near-ambient pressure (∼0.2 torr) shows that the gas phase oxygen concentration over the sample decreases sharply at ca. 300 °C. These two observations suggest that the oxidation of CO undergoes a change of mechanism at temperatures higher than 300 °C.


Agosto, 2009 | DOI: 10.1016/j.catcom.2009.06.022

Aluminium anodisation for Au-CeO2/Al2O3-Al monoliths preparation


Sanz, O; Martinez, LM; Echave, FJ; Dominguez, MI; Centeno, MA; Odriozola, JA; Montes, M
Chemical Engineering Journal, 151 (2009) 324-332

ABSTRACT

The anodisation of aluminium monoliths was performed in order to generate an alumina layer that ensures a good adherence of the catalysts. In this study, it is demonstrated that the morphology of the produced alumina layer depends on time, temperature, current density and concentration of the selected electrolyte. When anodisation process with the extreme conditions was applied (30 °C, 50 min, 2 A dm−2 and 2.6 M of sulphuric acid) a significant cracks were obtained and used to fix the subsequent catalytic coatings. The washcoating method was used to cover the monoliths with colloidal solutions of CeO2 and/or Au-CeO2 catalysts. The resulting monolithic catalysts were tested in the CO oxidation reaction being 1%Au-CeO2 containing system the most active. The structured catalyst prepared this way changed neither the textural nor the catalytic properties of the deposited catalytic powders.


Agosto, 2009 | DOI: 10.1016/j.cej.2009.03.062

Reactivity of LaNi1−y Co y O3−δ Perovskite Systems in the Deep Oxidation of Toluene


Pereniguez, R; Hueso, JL; Holgado, JP; Gaillard, F; Caballero, A
Catalysis Letters, 131 (2009) 164-169

ABSTRACT

In the present work we have evaluated the oxidation of toluene over different lanthanum perovskites with a general composition of LaNi1−y Co y O3−δ. These catalysts, prepared by a spray pyrolysis method, have been characterised by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O2, reduction in H2 and X-ray absorption spectroscopy were also performed in order to identify the main surface oxygen species and the reducibility of the different perovskites. The catalytic behaviour toward the oxidation of toluene (as a model for VOCs compounds) was evaluated in the range 100–600 °C, detecting a total conversion for all the samples below 400 °C and higher activities for the cobalt-containing perovskites. The catalytic behaviour of these samples is consistent with a suprafacial mechanism, with the α-type oxygen playing an active role in the oxidation reaction.


Agosto, 2009 | DOI: 10.1007/s10562-009-9968-0

Structural characteristics and morphology of SmxCe1−xO2−x/2 thin films


Hartmanova, M; Jergel, M; Mansilla, C; Holgado, JP; Zemek, J; Jurek, K; Kundracik, F
Applied Surface Science, 255 (2009) 9085-9091

ABSTRACT

Effect of the deposition temperature (200 and 500 °C) and composition of SmxCe1−xO2−x/2 (x = 0, 10.9–15.9 mol%) thin films prepared by electron beam physical vapor deposition (EB-PVD) and Ar+ ion beam assisted deposition (IBAD) combined with EB-PVD on structural characteristics and morphology/microstructure was investigated. The X-ray photoelectron spectroscopy (XPS) of the surface and electron probe microanalysis (EPMA) of the bulk of the film revealed the dominant occurrence of Ce4+ oxidation state, suggesting the presence of CeO2 phase, which was confirmed by X-ray diffraction (XRD). The Ce3+ oxidation states corresponding to Ce2O3 phase were in minority. The XRD and scanning electron microscopy (SEM) showed the polycrystalline columnar structure and a rooftop morphology of the surface. Effects of the preparation conditions (temperature, composition, IBAD) on the lattice parameter, grain size, perfection of the columnar growth and its impact on the surface morphology are analyzed and discussed.


Agosto, 2009 | DOI: 10.1016/j.apsusc.2009.06.108

Kinetics of the thermal decomposition of anhydrous cobalt nitrate by SCRT method


Ortega, A; Macias, M; Gotor, FJ
Journal of Thermal Analysis and Calorimetry, 98 (2009) 441-448

ABSTRACT

It has been shown the ability of the Sample Controlled Reaction Temperature (SCRT) method for both discriminate the kinetic law and calculate the activation energy of the reaction. This thermal decomposition is best described by a Johnson–Mehl–Avrami kinetic model (with n = 2) with an activation energy of nuclei growth which fall in the range 52–59 kJ mol−1. The process is not a single-step because the initial rate of decomposition is likely to be limited by nucleation. The results reported here constitute the first attempt to use the new SCRT method to study the kinetic of the thermal decomposition of cobalt nitrate.


Agosto, 2009 | DOI: 10.1007/s10973-009-0322-y

FTIR study of photocatalytic degradation of 2-propanol in gas phase with different TiO2 catalysts


Arana, J; Alonso, AP; Rodriguez, JMD; Colon, G; Navio, JA; Pena, JP
Applied Catalysis B-Environmental, 89 (2009) 204-213

ABSTRACT

The photocatalytic efficiency of different TiO 2 catalysts in the degradation of 2-propanol in gas phase has been studied. The obtained efficiencies have been compared considering the distribution of rutile-anatase phases, surface area, particle size, distribution of surface hydroxyl groups and Brönsted or Lewis acid centres. The catalysts used were Degussa-P25 (TiO 2-P25), Hombikat, Millennium, Kemira and s/g-TiO 2, a catalyst prepared by a sol-gel method. The best photocatalytic behaviours have been obtained with those catalysts with higher surface area and the presence of only anatase phase (Hombikat and Millennium). A progressive deactivation of TiO 2-P25 and s/g-TiO 2 has been observed during the photocatalytic process. FTIR studies indicated that degradation mechanisms depended on the catalyst employed. Deactivation processes observed in TiO 2-P25 have been correlated with the formation of carboxylates.


Julio, 2009 | DOI: 10.1016/j.apcatb.2008.11.027

Effect of Sulfate Pretreatment on Gold-Modified TiO2 for Photocatalytic Applications


Hidalgo, MC; Maicu, M; Navio, JA; Colon, G
Journal of Physical Chemistry C, 113 (2009) 12840-12847

ABSTRACT

The influence of sulfated pretreatment of TiO2 on the structure, morphology, and dispersion of gold and photocatalytic properties of Au/TiO2 were studied. Notable enhancements in the photocatalytic activity of TiO2 were achieved by deposition of gold onto samples that had previously undergone sulfate treatment followed by high temperature calcination. The enhancement in activity can be attributed to the stronger bonding and improved electronic communication between gold particles and TiO2 on defect rich surfaces as are found on sulfated samples after calcination at 700 °C. Two different methods for gold deposition were evaluated: chemical reduction by citrate and photodeposition. The citrate method produced more homogeneous and smaller gold particles with a better dispersion than photodeposition, which lead to greater increases in activity in the photocatalytic degradation of phenol when the former method was used for deposition on both sulfated and nonsulfated TiO2. The combination of sulfate pretreatment and gold deposition by chemical reduction was shown to be a good strategy to obtain gold/titania catalysts possessing homogeneous particle size and dispersion of the metal and a strong bonding between the Au and the TiO2 surface.


Julio, 2009 | DOI: 10.1021/jp903432p

Deposition of Al-Fe pillared bentonites and gold supported Al-Fe pillared bentonites on metallic monoliths for catalytic oxidation reactions


Martinez, LM; Dominguez, MI; Sanabria, N; Hernandez, WY; Moreno, S; Molina, R; Odriozola, JA; Centeno, MA
Applied Catalysis A-General, 364 (2009) 166-173

ABSTRACT

Al-Fe pillared bentonite and gold supported on Al-Fe pillared bentonite catalysts deposed on Fecralloy monoliths have been prepared, characterized and tested in two oxidation reactions: gaseous oxidation of CO and phenol oxidation in aqueous medium. The deposition of the solid on the metallic substrate does not alter its structural characteristics. The use of monoliths improves the activity in both reactions and offers the additional advantage to facilitate the separation of the catalyst from the reaction medium.


Julio, 2009 | DOI: 10.1016/j.apcata.2009.05.046

ZnO activation by using activated carbon as a support: Characterisation and photoreactivity


Melian, EP; Diaz, OG; Rodriguez, JMD; Colon, G; Arana, J; Melian, JH; Navio, JA; Pena, JP
Applied Catalysis A-General, 364 (2009) 176-181

ABSTRACT

The effect of the mixing ZnO with different portions of activated carbon (AC) has been studied. The resulting catalysts were characterised and evaluated in the photocatalytic decomposition of aqueous pollutants. Changes in the catalyst colour and in the FTIR vibration bands of the surface hydroxyl groups were recorded. νOH vibrations were shifted to lower wavenumbers as AC loading increased, demonstrating modification of the acid-base character of the catalysts. Laser scattering studies showed that AC loading leads to smaller ZnO particles. BET surface area measurements and scanning electron micrograph (SEM) analysis showed agglomeration of ZnO particle pores in the AC structure.

Results showed that in addition to a synergistic effect of the AC-ZnO combination, AC content modifies the ZnO particle properties and consequently photocatalytic behaviour. This was evident in phenol degradation experiments where changes in the concentration profiles of the catechol and hydroquinone degradation intermediates, were observed. However, the AC-ZnO catalysts were less efficient than pure ZnO in the degradation of 2,4-dichlorophenol (DCP). This seems to be due to the strong adsorption of the DCP molecule on AC, resulting in lower diffusion to the catalytic ZnO and thus a lower rate of photocatalysis.


Julio, 2009 | DOI: 10.1016/j.apcata.2009.05.042

Degradation of n-Butyl tin Chlorides in Waters. A Comparative Assessment of the Process by Photo-assisted and Chemical- treatment Methods


Navio, JA; Cerrillos, C; Macias, M
Journal of Advanced Oxidation Technologies, 12 (2009) 158-163

ABSTRACT

Fibrous MnO2 Nanoparticles with (2 × 2) Tunnel Structures. Catalytic Activity in the Total Oxidation of Volatile Organic Compounds


Dominguez, MI; Navarro, P; Romero-Sarria, F; Frias, D; Cruz, SA; Delgado, JJ; Centeno, MA; Montes, M; Odriozola, JA
Journal of Nanoscience and Nanotechnology, 9 (2009) 3837-3842

ABSTRACT

Manganese oxides having 2 × 2 tunnel structures (cryptomelanes) have been synthesized by a milling method in order to test their efficiency as catalysts for the abatement of volatile organic compounds, using toluene as probe molecule. These materials present excellent textural properties, arising from the nanofiber morphology and were active for toluene total oxidation. DRIFTS of the adsorbed phase allow proposing the role of lattice oxygen in the catalytic reaction.


Junio, 2009 | DOI: 10.1166/jnn.2009.NS76

Determination of nitrogen partitioning coefficients in superduplex stainless steels by NRA using a nuclear microprobe


Munoz, C; Morilla, Y; Lopez, JG; Paul, A; Odriozola, JA
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 267 (2009) 2208-2211

ABSTRACT

Superduplex stainless steels (SDSSs) combine the good mechanical behavior and the high corrosion resistance of the ferrite (α-Fe) and austenite (γ-Fe) phases. The SDSSs properties depend strongly on the partitioning of the elements that form the alloy. The ferrite is generally enriched in P, Si, Cr and Mo while the content of Ni, Mn, Cu and N in the austenite phase is higher. Nitrogen is known to be a strong austenite stabilizer and its presence increases the strength and the pitting corrosion resistance of the stainless steels. While the global nitrogen content in SDSSs can be readily determined using elemental analyzers, it cannot be measured at a microscopic scale.

In this work, the nuclear microprobe of the Centro Nacional de Aceleradores (Sevilla) was used to obtain the quantitative distribution of nitrogen in SDSSs. A deuteron beam of 1.8 MeV was employed to determine the overall elemental concentration of the matrix by deuteron-induced X-ray emission, whereas the nitrogen partitioning coefficients were obtained by using the 14N(d, α0)12C nuclear reaction. Mappings of this element show that the nitrogen ratio between the ferrite and austenite phases ranges from 0.3 to 0.6 in the analyzed samples.


Junio, 2009 | DOI: 10.1016/j.nimb.2009.03.093

W,N-Codoped TiO2-Anatase: A Sunlight-Operated Catalyst for Efficient and Selective Aromatic Hydrocarbons Photo-Oxidation


Kubacka, A; Bachiller-Baeza, B; Colon, G; Fernandez-Garcia, M
Journal of Physical Chemistry C, 113 (2009) 8553-8555

ABSTRACT

New W,N-doped TiO2 anatase-based materials are synthesized having both unprecedent high activity and selectivity in the gas-phase partial oxidation of aromatic hydrocarbons using sunlight as excitation energy and molecular oxygen as oxidant.


Mayo, 2009 | DOI: 10.1021/jp902618g

Cationic (V, Mo, Nb, W) doping of TiO2–anatase: A real alternative for visible light-driven photocatalysts


Kubacka, A; Colon, G; Fernandez-Garcia, M
Catalysis Today, 143 (2009) 286-292

ABSTRACT

In this article we investigate the structure–activity link of anatase-type Ti–M (M = V, Mo, Nb, and W) mixed oxides used for toluene photo-oxidation under sunlight-type excitation. An analysis of the local and long-range structural and electronic characteristics of the mixed oxides show that only structurally highly homogeneous anatase-type oxides with electronic properties exclusively leading to a band gap decrease drive to efficient visible light-driven photocatalysts. Within our microemulsion preparation method, this only occurs for Ti–V and Ti–W series of samples. The isoelectronic (V4+) substitution of Ti4+ ions at the anatase lattice is characterized by a low solubility limit (ca. 2.5 at. %), and drives to a limited modification of the band gap and to a moderate enhancement of the photo-activity with respect to bare titania reference systems. W presence at anatase cation positions occurs with concomitant presence of cation vacancies derived by the charge imbalance between the W6+ and Ti4+ species. A unique W-vacancy local arrangement is detected by the structural characterization, leading to both an important band gap decrease and enhancement of the photo-activity upon sunlight excitation.


Mayo, 2009 | DOI: 10.1016/j.cattod.2008.09.028

Integration of methanol steam reforming and combustion in a microchannel reactor for H2 production: A CFD simulation study


Arzamendi, G; Dieguez, PM; Montes, M; Centeno, MA; Odriozola, JA; Gandia, LM
Catalysis Today, 143 (2009) 25-31

ABSTRACT

A computational fluid dynamics (CFD) study of the thermal integration of the steam reforming of methanol (SRM) and the combustion of methanol in a catalytic microchannel reactor is presented. This issue is of interest for in situ H2 production for portable power units based on low-temperature PEM fuel cells. Three-dimensional simulations have been carried out under relevant conditions for the SRM reaction that have shown that microreactors allow achieving complete methanol reforming and combustion at space velocities as high as 50,000 h−1, with selectivities for H2 above 99% at relatively low temperatures in the 270–290 °C range.


Mayo, 2009 | DOI: 10.1016/j.cattod.2008.09.034

AISI 304 Austenitic stainless steels monoliths for catalytic applications


Martinez, LM; Sanz, O; Dominguez, MI; Centeno, MA; Odriozola, JA
Chemical Engineering Journal, 148 (2009) 191-200

ABSTRACT

The thermal treatments of austenitic stainless steels monoliths were studied in order to generate a highly homogeneous and rough oxide scale strongly attached to the base alloy, which will subsequently ensure the good adherence of the catalysts. In this work it has been shown that the morphology, integrity and homogeneity of the scale are strongly influenced by the temperature and time of treatment. Washcoating method was used to deposit on the monolith surface a Au/CeO2 catalyst. The drying procedure turned out to be the most critical variable for the adherence and homogeneity of the catalytic ceria layer, while the ceria colloid concentrations in the starting aqueous dispersion seems to have only a threshold effect. The monolithic reactors containing Au/CeO2 layers are active in the oxidation of CO.


Mayo, 2009 | DOI: 10.1016/j.cej.2008.12.030

Gold/hydroxyapatite catalysts: Synthesis, characterization and catalytic activity to CO oxidation


Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 87 (2009) 245-251

ABSTRACT

This work reports the synthesis, characterization and catalytic activity for CO oxidation of gold catalysts supported on calcium hydroxyapatite. On both, the hydroxyapatite support and the gold-supported hydroxyapatite catalyst, the CO conversion shows a peak near 100% of conversion at room temperature. The generation of structural vacancies by interaction of CO with the solid provokes the formation of peroxide species in the presence of gaseous oxygen, which seems to be responsible of this high conversion of CO at room temperature. Moreover, the influence of the pre-treatment temperature on the activity has been observed and related with the elimination of carbonate species and the generation of structural defects in the apatite structure, which are able to modify the gold oxidation state.


Abril, 2009 | DOI: 10.1016/j.apcatb.2008.09.016

Synthesis and Characterization of Ce1−xEuxO2−x/2 Mixed Oxides and Their Catalytic Activities for CO Oxidation


Hernandez, WY; Centeno, MA; Romero-Sarria, F; Odriozola, JA
Journal of Physical Chemistry C, 113 (2012) 5629-5635

ABSTRACT

A series of Ce1−xEuxO2−x/2 mixed oxides was synthesized by coprecipitation. The solids were characterized by means of XRF, SBET, XRD, UV−vis, and Raman techniques, and their catalytic activities toward CO oxidation were tested. A solid solution, with CeO2 F-type structure, is formed for europium contents (measured as Eu2O3 by XRF) ≤20% wt. For higher contents, the solid solution is not formed, but a physical mixture is detected. The existence of oxygen vacancies in the solids with Eu2O3 contents between 3 and 17% wt was demonstrated by the presence of bands at 532 and 1275 cm−1 in their Raman spectra. The catalytic performances of the solids correlate with the amount of these punctual defects in the solid solution.


Abril, 2009 | DOI: 10.1021/jp8092989

Co3O4 + CeO2/SiO2 Catalysts for n-Hexane and CO Oxidation


Todorova, S; Kadinov, G; Tenchev, K; Caballero, A; Holgado, JP; Pereniguez, R
Catalysis Letters, 129 (2009) 149-155

ABSTRACT

Two-component Co–Ce samples deposited onto SiO2 have been prepared, characterized and tested in the reaction of complete n-hexane and CO oxidation. It was established that cerium enhanced the catalytic activity of cobalt in the reaction of n-hexane oxidation, although this depended on the sequence of cobalt and cerium introduction. Co-impregnation of Co and Ce resulted in a close interaction between Co3O4 and CeO2 leading to more surface oxygen species available and, therefore, a better reactivity.


Abril, 2009 | DOI: 10.1007/s10562-008-9805-x

Pillared clays with Al–Fe and Al–Ce–Fe in concentrated medium: Synthesis and catalytic activity


Sanabria, NR; Centeno, MA; Molina, R; Moreno, S
Applied Catalysis A-General, 356 (2009) 243-249

ABSTRACT

This paper proposes a new methodology for the modification of clays with the mixed Al–Fe and Al–Ce–Fe systems, which involves the synthesis of solid polymeric precursors and their use as pillaring agents in the modification of clays. The process of intercalation of clay with Al13, Al13 + Fe and Al13 + Ce + Fe nitrate was performed using ultrasound. The pillaring agents Al13, Al13 + Fe and Al13 + Ce + Fe were characterized by XRF, XRD, SEM and 27Al NMR techniques, and pillared clays were characterized by XRF, XRD and N2 adsorption to 77 K. The catalytic properties of pillared clays were evaluated using catalytic wet peroxide oxidation of phenol in dilute aqueous medium, demonstrating activity comparable to that of solids modified by the conventional method.


Marzo, 2009 | DOI: 10.1016/j.apcata.2009.01.013

Redox chemistry of gold in a Au/FeOx/CeO2 CO oxidation catalyst


Penkova, A; Chakarova, K; Laguna, OH; Hadjiivanov, K; Saria, FR; Centeno, MA; Odriozola, JA
Catalysis Communications, 10 (2009) 1196-1202

ABSTRACT

Calcination and evacuation of a Au/FeOx/CeO2 catalyst at 573 K leads to reduction of the deposited gold to metal. This metal state is stable under oxygen and only at 573 K some metal atoms are oxidized to Auδ+ sites (Au+ cations situated on metal gold particles). However, even at room temperature, gold is readily oxidized in a CO + O2 mixture producing, in addition to the Auδ+ sites, some isolated Au+ cations.


Marzo, 2009 | DOI: 10.1016/j.catcom.2009.01.014

Gold nanoparticles on silica monospheres modified by amino groups


Penkova, A; Blanes, JMM; Cruz, SA; Centeno, MA; Hadjiivanov, K; Odriozola, JA
Microporous and Mesoporous Materials, 117 (2009) 530-534

ABSTRACT

Silica monospheres with a diameter of 330 nm modified with aminosilane compounds of three different basicities have been prepared. Surface coverage of the silica with an organic compound leads to an increase of the point of zero charge (PZC) of the silica surface from 2.1 to 5.1, 6.5 and 7.2 values, depending on the amine used. From these silicas, gold-containing catalysts have been prepared by a deposition–precipitation method at the same pH as the PZC of the support. The best results have been obtained using 3-(Diethoxymethylsilyl) propylamine as a modifying agent, which has allowed obtaining a good dispersion of the gold particles with an average size of 3.8 nm.


Enero, 2009 | DOI: 10.1016/j.micromeso.2008.07.041



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Desarrollo de sistemas catalíticos mesoporosos nanoestructurados para la producción de hidrógeno y la síntesis directa de agua oxigenada

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Universidad de Sevilla
Viernes, 16 Marzo, 2018




Elena María Jiménez Barrera
Utilización de la Espectroscopía Infrarroja para el Estudio de Catalizadores Heterogéneos

Director/es: Francisca Romero Sarria y José Antonio Odriozola
Universidad de Sevilla
Viernes, 9 Febrero, 2018




Cristina Megías Sayago
Catalizadores híbridos bifuncionales para la valorización química de biomasa

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Universidad de Sevilla
Viernes, 29 Septiembre, 2017




Paola Zambrano Chacón
Desarrollo de materiales fotocatalizadores basados en Bi, Ti y O con alta actividad en el visible para la eliminación de contaminantes en agua

Director/es: José Antonio Navío Santos y Maria Del Carmen Hidalgo López
Universidad de Sevilla
Viernes, 22 Septiembre, 2017




Mayra Anabel Lara Angulo
Desarrollo de Materiales Basados en TIO2 Modificado con Funcionalidad Fotocatalítica para Aplicaciones Medioambientales

Director/es: José Antonio Navío Santos y Maria Del Carmen Hidalgo López
Universidad de Sevilla
Viernes, 7 Julio, 2017




Miriam González Castaño
Design, Characterization and Structuring of Pt based Catalysts for Water Gas Shift Reaction

Director/es: José Antonio Odriozola Gordón y Svetlana Ivanova
Universidad de Sevilla
Jueves, 10 Diciembre, 2015




José María Martínez Blanes
Obtención de Zeolitas utilizando Líquidos Iónicos como Agentes Directores de Estructura

Director/es: José Antonio Odriozola Gordón y Svetlana Ivanova
Universidad de Sevilla
Miércoles, 2 Diciembre, 2015




Sergio Alberto Obregón Alfaro
Síntesis y Optimización de Sistemas Fotocatalíticos basados en BiVO4 mediante Incorporación de Iones a Tierras Raras

Director/es: Gerardo Colón Ibáñez
Universidad de Sevilla
Viernes, 20 Febrero, 2015




Andrea Álvarez Moreno
Reformado Catalítico de Biomasa. Ajuste de la estequiometría de los productos para la reacción de Fischer-Tropsch

Director/es: Miguel Angel Centeno Gallego y José Antonio Odriozola Gordón
Universidad de Sevilla
Viernes, 13 Febrero, 2015




Sandra Palma del Valle
Producción de hidrógeno a partir de metanol: diseño, síntesis y caracterización de un catalizador de PROX

Director/es: Francisca Romero-Sarria y José Antonio Odriozola Gordón
Universidad de Sevilla
Viernes, 7 Noviembre, 2014




Victor Manuel González de la Cruz
Estudio de la actividad catalítica y de la interacción metal-soporte en sistemas de níquel soportados en ZrO2 y CeO2, activos en las reacciones de reformado de metano

Director/es: Alfonso Caballero Martínez y Juan Pedro Holgado Vázquez
Universidad de Sevilla
Jueves, 17 Julio, 2014




Tomás Ramírez Reina
Diseño y caracterización de cataliazadores basados en oro para la reacción de water gas shift

Director/es: José Antonio Odriozola Gordón y Svetlana Ivanova
Universidad de Sevilla
Lunes, 30 Junio, 2014




Ara Muñoz Murillo
Catalizadores de Ru/TiO2 para la metanación selectiva de CO

Director/es: José Antonio Odriozola Gordón y Miguel Angel Centeno Gallego
Universidad de Sevilla
Viernes, 31 Enero, 2014




Julie Joseane Murcia Mesa
Control de la nanoestructura de sistemas M-TiO2 (M=Pt y Au) preparados por fotodeposición con propiedades fotocatalíticas optimizadas

Director/es: Carmen Hidalgo López y José Antonio Navío Santos
Universidad de Sevilla
Viernes, 12 Julio, 2013




Sebastián Murcia López
Desarrollo de Materiales basados en Bismuto con Alta Eficiencia Fotocatalítica para Aplicaciones de Química Verde

Director/es: José Antonio Navío Santos y M. Carmen Hidalgo López
Universidad de Sevilla
Martes, 9 Abril, 2013




Fátima A. Ternero Fernández
Sistemas Catalíticos Basados en Nanopartículas Mono y Bimetálicas Activos en Procesos de Interés Medioambiental

Director/es: Alfonso Caballero Martínez y Juan Pedro Holgado Vázquez
Universidad de Sevilla
Miércoles, 27 Febrero, 2013




Oscar Hernando Laguna Espitia
Oxidación preferencial de CO en presencia de H2: diseño de catalizadores basados en CeO2 y aplicación a microrreactores

Director/es: José Antonio Odriozola Gordón y Miguel Angel Centeno Gallego
Universidad de Sevilla
Viernes, 30 Septiembre, 2011




Luis F. Bobadilla Baladrón
Obtención de hidrógeno a partir de la biomasa. Reformado catalítico de glicerina

Director/es: José Antonio Odriozola Gordon y Francisca Romero Sarria
Universidad de Sevilla
Viernes, 15 Abril, 2011




Willinton Yesid Hernández Enciso
Relación estructura de defectos – actividad catalítica en sistemas sólidos tipo Au/Ce1-xEuxO2-x/2 y MnOx. Aplicación en la reacción de oxidación preferencial de CO en presencia de H2.

Director/es: José Antonio Odriozola Gordón y Miguel Angel Centeno Gallego
Universidad de Sevilla
Viernes, 26 Noviembre, 2010




Sylvia Andrea Cruz Torres
Aplicaciones de la Técnica “Spark Plasma Sintering” a la Obtención de Materiales y Dispositivos de Interés en Catálisis

Director/es: José Antonio Odriozola Gordón
Universidad de Sevilla
Viernes, 17 Septiembre, 2010




Rosa Pereñíguez Rodríguez
Obtención de H2 mediante reformado de CH4 sobre sólidos con estructura perovskita: LaNi1-xCoxO3

Director/es: Alfonso Caballero Martínez y Juan Pedro Holgado Vázquez
Universidad de Sevilla
Viernes, 21 Mayo, 2010




Marina Maicu
Estudio de la actividad fotocatalítica de sistemas basados en TiO2, sulfatado y no sulfatado, y modificado con Pt, Au y Pd

Director/es: José Antonio Navío Santos, Gerardo Colón Ibáñez, Maria del Carmen Hidalgo López
Universidad de Sevilla
Martes, 16 Febrero, 2010




Rafael Sánchez Avellaneda
Estudio e influencia de itrio y otros modificadores superficiales en el comportamiento de catalizadores soportados en TiO2

Director/es: José Antonio Odriozola, Miguel Angel Centeno, Francisca Romero Sarria
Universidad de Sevilla
Viernes, 5 Febrero, 2010




Leidy Marcela Martínez Tejada
Deposición de catalizadores sobre superficies metálicas para aplicaciones catalíticas

Director/es: José Antonio Odriozola y Miguel Angel Centeno
Universidad de Sevilla
Viernes, 4 Abril, 2008




José Luis Hueso Martos
Eliminación de contaminantes mediante procesos de plasma-catalizador

Director/es: Alfonso Caballero Martínez y Agustín R. González-Elipe
Universidad de Sevilla
Miércoles, 19 Septiembre, 2007




Catalina Mansilla Sánchez
Síntesis, caracterización y determinación de propiedades ópticas y eléctricas de capas finas de materiales basados en óxido de cerio

Director/es: Juan Pedro Holgado Vázquez y Francisco Yubero Valencia
Universidad de Sevilla
Viernes, 13 Julio, 2007




Ana María Cordón Rodríguez
Estudio de sistemas catalíticos basados en ZrO2 para la reducción catalítica selectiva de NOx usando hidrocarburos como agentes reductores

Director/es: Alfonso Caballero Martínez y Juan Pedro Holgado Vázquez
Universidad de Sevilla
Viernes, 15 Septiembre, 2006




María Isabel Domínguez Leal
Diseño de materiales a partir de residuos industriales. Aplicaciones catalíticas

Director/es: José Antonio Odriozola y Miguel Angel Centeno
Universidad de Sevilla
Viernes, 21 Abril, 2006




Francisco Gracia Torres
Películas delgadas basadas en TiO2 y MxO2 con aplicaciones fotoelectroquímicas y ópticas

Director/es: Agustín R. González-Elipe y Juan Pedro Holgado Vázquez
Universidad de Sevilla
Lunes, 30 Mayo, 2005




José Jorge Morales Domingo
Estudio del sistema CuOx/ZrO2 en procesos de eliminación catalítica de óxidos de nitrógeno

Director/es: Alfonso Caballero Martínez y Juan Pedro Espinós Manzorro
Universidad de Sevilla
Viernes, 4 Marzo, 2005




Said El Mrabet
Diseño de aceros inoxidables austeníticos resistentes a la oxidación a alta temperatura. Efectos de la composición de la matriz y de las modificaciones superficiales

Director/es: José Antonio Odriozola Gordón y Antonio Paúl Escolano
Universidad de Sevilla
Lunes, 3 Febrero, 2003


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