Scientific Papers in SCI

2011


Title: An improved model for the kinetic description of the thermal degradation of cellulose
Author(s): Sanchez-Jimenez, PE; Perez-Maqueda, LA; Perejon, A; Pascual-Cosp, J; Benitez-Guerrero, M; Criado, JM
Source: Cellulose, 18 (2011) 1487-1498

abstract | fulltext

In spite of the large amount of work performed by many investigators during last decade, the actual understanding of the kinetics of thermal degradation of cellulose is still largely unexplained. In this paper, recent findings suggesting a nucleation and growth of nuclei mechanism as the main step of cellulose degradation have been reassessed and a more appropriate model involving chain scission and volatilization of fragments has been proposed instead. The kinetics of cellulose pyrolysis have been revisited by making use of a novel kinetic method that, without any previous assumptions regarding the kinetic model, allows performing the kinetic analysis of a set of experimental curves recorded under different heating schedules. The kinetic parameters and kinetic model obtained allows for the reconstruction of the whole set of experimental TG curves.

December, 2011 | DOI: 10.1007/s10570-011-9602-3

Title: Rhodamine 6G and 800 J-heteroaggregates with enhanced acceptor luminescence (HEAL) adsorbed in transparent SiO2 GLAD thin films
Author(s): Sanchez-Valencia, JR; Aparicio, FJ; Espinos, JP; Gonzalez-Elipe, AR; Barranco, A
Source: Physical Chemistry Chemical Physics, 13 (2011) 7071-7082

abstract | fulltext

An enhanced fluorescent emission in the near infrared is observed when the Rhodamine 800 (Rh800) and 6G (Rh6G) dyes are coadsorbed in porous SiO 2 optical thin films prepared by glancing angle deposition (GLAD). This unusual behavior is not observed in solution and it has been ascribed to the formation of a new type of J-heteroaggregates with enhanced acceptor luminescence (HEAL). This article describes in detail and explains the main features of this new phenomenology previously referred in a short communication [J. R. Sánchez-Valencia, J. Toudert, L. González-García, A. R. González-Elipe and A. Barranco, Chem. Commun., 2010, 46, 4372-4374]. It is found that the efficiency and characteristics of the energy transfer process are dependent on the Rh6G/Rh800 concentration ratio which can be easily controlled by varying the pH of the solutions used for the infiltration of the molecules or by thermal treatments. A simple model has been proposed to account for the observed enhanced acceptor luminescence in which the heteroaggregates order themselves according to a "head to tail" configuration due to the geometrical constrains imposed by the SiO2 porous matrix thin film. The thermal stability of the dye molecules within the films and basic optical (absorption and fluorescence) principles of the HEAL process are also described.

April, 2011 | DOI: 10.1039/c0cp02421j

Title: Selective CO removal over Au/CeFe and CeCu catalysts in microreactors studied through kinetic analysis and CFD simulations
Author(s): Arzamendi, G; Uriz, I; Dieguez, PM; Laguna, OH; Hernandez, WV; Alvarez, A; Centeno, MA; Odriozola, JA; Montes, M; Gandia, LM
Source: Chemical Engineering Journal, 167 (2011) 588-596

abstract | fulltext

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.

March, 2011 | DOI: 10.1016/j.cej.2010.08.083

Title: Design and testing of a microchannel reactor for the PROX reaction
Author(s): 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
Source: Chemical Engineering Journal, 167 (2011) 634-642

abstract | fulltext

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.

March, 2011 | DOI: 10.1016/j.cej.2010.08.088

Title: Fischer-Tropsch synthesis in microchannels
Author(s): Almeida, LC; Echave, FJ; Sanz, O; Centeno, MA; Arzamendi, G; Gandia, LM; Sousa-Aguiar, EF; Odriozola, JA; Montes, M
Source: Chemical Engineering Journal, 167 (2011) 536-544

abstract | fulltext

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.

March, 2011 | DOI: 10.1016/j.cej.2010.09.091

Title: Artificial weathering pools of calcium-rich industrial waste for CO2 sequestration
Author(s): Morales-Florez, V; Santos, A; Lemus, A; Esquivias, L
Source: Chemical Engineering Journal, 166 (2011) 132-137

abstract | fulltext

Processes of carbonation of calcium-rich aqueous industrial wastes from acetylene production were performed mimicking rock weathering, using the atmospheric carbon dioxide as reactant. This residue was carbonated exposing it to the air in artificial pools with controlled solid-to-liquid and surface-to-volume ratios, and the efficiency of this simple mineral carbonation process was maximized. Considering realistic values of just one acetylene production plant, the intelligent handling of the calcium-rich waste would make it possible to counteract the emission of around 800t of carbon dioxide per year, so the CO2 emissions of the acetylene production could be completely compensated and its carbon footprint significantly reduced.X-ray diffraction patterns and thermogravimetric analyses reported the conversion, up to 88%, of the calcium hydroxide into calcium carbonate under atmospheric conditions. So, considering a realistic industrial scale-up, 476kg of CO2 could be captured with 1t of dry waste. The morphology of the grains is resolved by electron microscopy, and can be described as needles 15nm wide and 200nm long arranged in grains smaller than 1 micron. We exploit these nanometric textural parameters (nanometric pores and particles having a specific surface area ∼50m2/g) to design an efficient carbon fixation procedure. The aim of this work is to propose this simple carbonation technology, based on aqueous alkaline industrial waste, as a contribution to reducing global CO2 emissions.

January, 2011 | DOI: 10.1016/j.cej.2010.10.039

Title: Enhanced photoactivity in bilayer films with buried rutile-anatase heterojunctions
Author(s): Romero-Gomez, P; Borras, A; Barranco, A; Espinos, JP; Gonzalez-Elipe, AR
Source: ChemPhysChem, 12 (2011) 191-196

abstract | fulltext

Herein, we study the photoactivity of anatase–rutile bilayer thin films consisting of an anatase overlayer of variable thickness from some tenths to some hundred nanometers deposited onto a rutile thin film. As references single anatase layers of equivalent thickness were deposited onto silicon. All the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The photoactivity of the samples was assessed by following the evolution with the UV illumination time of both the wetting angle on the thin film surface and the decoloration of a dye in a water solution. While a similar efficiency is found for the first type of experiments irrespective of the anatase thickness, in the second type a maximum in the photoactivity is found for a thickness of the anatase layer of about 130 nm. This enhanced photoactivity in bilayer systems with a buried anatase–rutile heterojunction is related to the formation of different Schottky potential barriers in the anatase layer, depending on its thickness and the substrate (i.e. rutile or SiO2) where it is deposited.

January, 2011 | DOI: 10.1002/cphc.201000734

Title: Ionic liquid protected heteropoly acids for methanol dehydration
Author(s): Ivanova, S., Nitsch, X., Romero-Sarria, F., Louis, B., Centeno, M.A., Roger, A.C., Odriozola, J.A.
Source: Catalysis Today, 171 (2011) 236-241

abstract | fulltext

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.

August, 2011 | DOI: 10.1016/j.cattod.2011.03.077

Title: Oxidation of CO over gold supported on Zn-modified ceria catalysts
Author(s): Laguna, O.H., Centeno, M.A., Romero-Sarria, F., Odriozola, J.A.
Source: Catalysis Today, 172 (2011) 118-123

abstract | fulltext

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.

August, 2011 | DOI: 10.1016/j.cattod.2011.02.015

Title: Remediation of metal-contaminated soils with the addition of materials – Part I: Characterization and viability studies for the selection of non-hazardous waste materials and silicates
Author(s): R. González-Núñez, M.D. Alba, M.M. Orta, M. Vidal, A. Rigol
Source: Chemosphere, 85 (2011) 1511-1517

abstract | fulltext

Contamination episodes in soils require interventions to attenuate their impact. These actions are often based on the addition of materials to increase contaminant retention in the soil and to dilute the contaminant concentration. Here, non-hazardous wastes (such as sugar foam, fly ash and a material produced by the zeolitization of fly ash) and silicates (including bentonites) were tested and fully characterized in the laboratory to select suitable materials for remediating metal-contaminated soils. Data from X-ray fluorescence (XRF), N2 adsorption/desorption isotherms, X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM–EDX) analyses revealed the chemical composition, specific surface area and the phases appearing in the materials. A pH titration test allowed the calculation of their acid neutralization capacity (ANC). The metal sorption and desorption capacities of the waste materials and silicates were also estimated. Sugar foam, fly ash and the zeolitic material were the best candidate materials. Sugar foam was selected because of its high ANC (17 000 meq kg−1), and the others were selected because of their larger distribution coefficients and lower sorption reversibilities than those predicted in the contaminated soils.

November, 2011 | DOI: 10.1016/j.chemosphere.2011.09.042

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