Scientific Papers in SCI

2012


Title: Deactivation, reactivation and memory effect on Co–B catalyst for sodium borohydride hydrolysis operating in high conversion conditions
Author(s): Arzac, GM; Hufschmidt, D; De Haro, MCJ; Fernandez, A; Sarmiento, B; Jimenez, MA; Jimenez, MM
Source: International Journal of Hydrogen Energy, 37 (2012) 14373-14381

abstract | fulltext

A system with a continuous reactor to produce hydrogen by sodium borohydride hydrolysis was designed and built. The purpose was to test a supported Co–B catalyst durability upon cycling and long life experiments in high conversion conditions. A Stainless Steel monolith was built and calcined to improve adherence. For comparison a Ru–B catalyst was tested upon cycling. Both Co–B and Ru–B catalysts are durable during 6 cycles and then deactivate. A known reactivation procedure has proven to be more effective for the Co–B than for the Ru–B catalyst. This is related to stronger adsorption of B–O based compounds on the Co–B catalyst which is reversible upon acid washing. For the Ru–B catalyst deactivation may be more related to particle agglomeration than to the adsorption of B–O based species. The continuous system enlarges the catalysts durability because of the continuous borate elimination at elevated temperatures.

October, 2012 | DOI: 10.1016/j.ijhydene.2012.06.117

Title: Sonication induced reduction of the Ojen (Andalucia, Spain) vermiculite under air and under nitrogen
Author(s): Poyato, J; Perez-Rodriguez, JL; Lerf, A; Wagner, FE
Source: Ultrasonics Sonochemistry, 19 (2012) 373-375

abstract | fulltext

March, 2012 | DOI: 10.1016/j.ultsonch.2011.07.004

Title: XRF, μ-XRD and μ-spectroscopic techniques for revealing the composition and structure of paint layers on polychrome sculptures after multiple restorations
Author(s): Franquelo, ML; Duran, A; Castaing, J; Arquillo, D; Perez-Rodriguez, JL
Source: Talanta, 89 (2012) 462-469

abstract | fulltext

This paper presents the novel application of recently developed analytical techniques to the study of paint layers on sculptures that have been restored/repainted several times across centuries. Analyses were performed using portable XRF, μ-XRD and μ-Raman instruments. Other techniques, such as optical microscopy, SEM-EDX and μ-FTIR, were also used. Pigments and other materials including vermilion, minium, red lac, ivory black, lead white, barium white, zinc white (zincite), titanium white (rutile and anatase), lithopone, gold and brass were detected. Pigments from both ancient and modern times were found due to the different restorations/repaintings carried out. μ-Raman was very useful to characterise some pigments that were difficult to determine by μ-XRD. In some cases, pigments identification was only possible by combining results from the different analytical techniques used in this work. This work is the first article devoted to the study of sculpture cross-section samples using laboratory-made μ-XRD systems.

January, 2012 | DOI: 10.1016/j.talanta.2011.12.063

Title: Development of multicomponent-multiphase materials based on (Ti,Ta,Nb)CxN1-x carbonitride solid solutions
Author(s): Cordoba, JM; Chicardi, E; Gotor, FJ
Source: Chemical Engineering Journal, 192 (2012) 58-66

abstract | fulltext

A set of powdered cermets based on (Ti,Ta,Nb)C xN 1-x carbonitride solid solutions were synthesized from mixtures of elemental powders by a mechanically induced self-sustaining reaction (MSR) method and subsequently sintered using a pressureless method. Differing nominal compositions of the hard phase were used, and the nature of the metallic-binder phase (Co, Ni, or Co-Ni) was varied. For comparative purposes, the design of the material was performed using two different synthesis pathways. The composition and microstructure of the ceramic and binder phases before and after sintering were analyzed and related to the microhardness of the material, which was found to increase with increasing contiguity of the hard phase and with decreasing particle size.The samples synthesized in one step (SERIES 2) showed higher microhardness and a more homogeneous microstructure with smaller particle size of the hard phase due to the presence of Ti, Ta, and Nb in the molten binder that hindered ceramic growth during liquid phase sintering.

June, 2012 | DOI: 10.1016/j.cej.2012.03.046

Title: Sub-ambient CO oxidation over mesoporous Co3O4: Effect of morphology on its reduction behavior and catalytic performance
Author(s): Alvarez, A; Ivanova, S; Centeno, MA; Odriozola, JA
Source: Applied Catalysis A-General, 431 (2012) 9-17

abstract | fulltext

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.

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

Title: Photocatalytic activity of single and mixed nanosheet-like Bi2WO6 and TiO2 for Rhodamine B degradation under sunlike and visible illumination
Author(s): Murcia-Lopez, S; Hidalgo, MC; Navio, JA
Source: Applied Catalysis A-General, 423-424 (2012) 34-41

abstract | fulltext

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.

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

Title: Gold supported cryptomelane-type manganese dioxide OMS-2 nanomaterials deposited on AISI 304 stainless steels monoliths for CO oxidation
Author(s): Martinez, LM; Romero-Sarria, F; Hernandez, WY; Centeno, MA; Odriozola, JA
Source: Applied Catalysis A-General, 423 (2012) 137-145

abstract | fulltext

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.

May, 2012 | DOI: 10.1016/j.apcata.2012.02.026

Title: Sub-ambient CO oxidation over Au/MOx/CeO2-Al2O3 (M = Zn or Fe)
Author(s): Reina, TR; Ivanova, S; Dominguez, MI; Centeno, MA; Odriozola, JA
Source: Applied Catalysis A-General, 419-420 (2012) 58-66

abstract | fulltext

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.

March, 2012 | DOI: 10.1016/j.apcata.2012.01.012

Title: Mechanism of complete n-hexane oxidation on silica supported cobalt and manganese catalysts
Author(s): Todorova, S; Naydenov, A; Kolev, H; Holgado, JP; Ivanov, G; Kadinov, G; Caballero, A
Source: Applied Catalysis A-General, 413-414 (2012) 43-51

abstract | fulltext

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.

January, 2012 | DOI: 10.1016/j.apcata.2011.10.041

Title: Effect of hydrothermal treatment on structural and photocatalytic properties of TiO2 synthesized by sol-gel method
Author(s): Melian, EP; Diaz, OG; Rodriguez, JMD; Colon, G; Navio, JA; Pena, JP
Source: Applied Catalysis A-General, 411 (2012) 153-159

abstract | fulltext

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.

January, 2012 | DOI: 10.1016/j.apcata.2011.10.033

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