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Zimicz M.G.,CONICET | Larrondo S.A.,CONICET | Larrondo S.A.,Laboratorio Of Procesos Cataliticos | Prado R.J.,Federal University of Mato Grosso | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2012

The aim of this paper is to gain further insight in the reduction and reoxidation processes taking place when Ce 0.9Zr 0.1O 2 mixed oxides are in reducing or oxidizing atmospheres, respectively. The reduction process of these mixed oxides synthesized by two stoichiometric nitrate-aminoacid gel-combustion routes using glycine and lysine as fuels is studied by conventional H 2-Temperature Programmed Reduction experiments. The results are compared with those obtained by time-resolved in situ X-ray absorption near-edge spectroscopy (XANES) in the energy level corresponding to the Ce L III absorption edge. The reoxidation process by this last technique is also studied. Even though the identical composition and crystal structure of both samples, the redox processes resulted very different for each solid, suggesting the influence of specific surface area, pore volume and particle size on them. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

Diaz-Rey M.R.,University of Malaga | Cortes-Reyes M.,University of Malaga | Herrera C.,University of Malaga | Larrubia M.A.,University of Malaga | And 3 more authors.
Catalysis Today | Year: 2015

H2 rich gas produced from Scenedesmus almeriensis biomass residue after lipidic extraction by low temperature catalytic gasification is addressed. The pyrolysis-gasification behavior under different atmospheres (CO2/He, H2O/He and CO2 + H2O/He) were investigated using thermal gravimetric analysis. The conversion of the biomass takes place into three stages, according to its composition and corresponding to: loose of water bonded (30-200°C), major pyrolysis involving devolatilization (200-500°C) and decomposition of bio-char produced (500-800°C). The calculated apparent activation energy for the main pyrolysis stage was 97 kJ mol-1. Ni-based supported alumina catalysts (Ni, Ni-Pt and Ni-Rh) were prepared by impregnation. The catalyst influence on the final gas composition as well as in its HHV determined in mixed CO2 + H2O/He gasification carried out in a double fixed bed reactor configuration with the catalyst located in the second bed upstream. Parallel and secondary reactions as reforming of tar and char together with WGS and Boudouard also take place favoring gas fraction yield with a value close to 0.3 Nm3 of gas per kg of biomass. The catalytic role of Ni-Pt/Al2O3 catalyst in further reforming of the gas resulting from the gasification improves H2 content even at low temperature interval (600-700°C). © 2014 Elsevier B.V. All rights reserved. Source

Milberg H.,Laboratorio Of Procesos Cataliticos | Juan A.,National University of the South | Amadeo N.,Laboratorio Of Procesos Cataliticos | Irigoyen B.,Laboratorio Of Procesos Cataliticos
Journal of Molecular Catalysis A: Chemical | Year: 2010

In this work, we performed density functional theory (DFT) calculations to study carbon adsorption on the Ni(1 0 0) surface and absorption in the bulk of nickel-based catalysts. The ideal catalyst surface was modeled as a five-layer Ni(1 0 0) slab. We also studied the influence of magnesium, considered as an atomic substitutional impurity, on carbon adsorption and migration into the bulk. To study the effect of Mg on the structure of Ni-based catalysts, we replaced a Ni atom by a Mg atom, on the surface and also in the bulk. Then, we relaxed the Mg and Ni positions. Our results showed that Ni atoms were pushed away from Mg. We also performed energy calculations to evaluate carbon interactions on different preferential sites of the Ni-slab, and also the effect of Mg atom on these deposition processes. The calculations showed that carbon adsorption on the bare Ni(1 0 0) surface was more favorable than deposition on this surface doped with magnesium. Our results also indicated that Mg could improve the interaction of surface-adsorbed carbon with gas phase oxygen, leading to the formation of a CO precursor species. In this way, magnesium promotes Ni-based catalysts hindering the surface from attaining a high carbon coverage, and thus making difficult the formation of carbon agglomerates and carbon whiskers. We also considered the effect of Ca in the C-O interaction on the metal surface. © 2009 Elsevier B.V. All rights reserved. Source

Poggio Fraccari E.,Laboratorio Of Procesos Cataliticos | D'Alessandro O.,CONICET | Sambeth J.,CONICET | Baronetti G.,Laboratorio Of Procesos Cataliticos | Marino F.,Laboratorio Of Procesos Cataliticos
Fuel Processing Technology | Year: 2014

Cerium-manganese mixed oxides with different composition were prepared by co-precipitation, characterized and evaluated for the water-gas shift (WGS) reaction. Base metal (5 wt.% Cu and 5 wt.% Ni) catalysts supported on Ce-Mn mixed oxides were also tested for the WGS reaction. The activity of the bare supports is higher in the mixed samples than in pure ceria or manganese oxide. This result can be explained by a combination of greater reducibility and surface area in the mixed samples. Addition of base metals produces superior WGS catalysts. Particularly, nickel catalysts tested are able to reduce typical CO concentrations entering the WGS process to the CO levels tolerated by phosphoric acid fuel cells in a single unit operated at 400 C. © 2013 Elsevier B.V. Source

Graschinsky C.,Laboratorio Of Procesos Cataliticos | Laborde M.,Laboratorio Of Procesos Cataliticos | Amadeo N.,Laboratorio Of Procesos Cataliticos | Le Valant A.,University of Poitiers | And 3 more authors.
Industrial and Engineering Chemistry Research | Year: 2010

A kinetic study of ethanol steam-reforming reaction on Rh catalyst supported over a spinel structure (MgAl2O4/Al 2O3) was carried out. From the analysis of products distribution, the following four reactions were proposed as the reaction scheme: C2H5OH → CO + CH4 + H2 (ED), C2H5OH + H2O → CO2 + CH 4 + 2H2 (ER), water-gas shift reaction, and methane steam-reforming reaction. When the initial rate method was applied, it was demonstrated that in the rate-determining step (RDS) two active sites of the same type are involved. With use of our experimental results and data obtained from the literature, a sequence of 14 elementary steps were proposed, in agreement with the reaction scheme. Taking into account both the reaction mechanism and the occurrence of two active sites in the RDS, four different kinetic expressions can be formulated in which the RDS is (1) dissociative adsorption of ethanol, (2) dehydrogenation of ethoxide, (3) C-C bond scission, or (4) reaction between two adsorbed species. Finally, when discrimination models were applied, it was verified that the mechanism that fits experimental data is that in which the RDS is the surface reaction. © 2010 American Chemical Society. Source

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