Grupo de Energia Y Quimica Sostenibles

Madrid, Spain

Grupo de Energia Y Quimica Sostenibles

Madrid, Spain
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Escudero-Cid R.,Autonomous University of Madrid | Hernandez-Fernandez P.,Autonomous University of Madrid | Perez-Flores J.C.,University of San Pablo - CEU | Rojas S.,Grupo de Energia y Quimica Sostenibles | And 6 more authors.
International Journal of Hydrogen Energy | Year: 2012

The long-term stability of PtCoRu/C to methanol crossover has been evaluated in a direct methanol fuel cell (DMFC) configuration. The DMFC has been subjected to continuous operation under potential step cycles. The degradation of the DMFC with PtCoRu/C has been followed by comparison of the power density curves recorded after 0, 60 and 312 h of continuous operation, and compared to that recorded for a DMFC with Pt/C. Electrochemical Impedance Spectra (EIS) were recorded directly from the DMFCs and used to identify the main degradation phenomena responsible for the loss of performance of the used fuel cell. AC impedance spectra show that the resistance of the anode reaction increases while resistance associated to the cathode reaction decreases after the long-term stability tests; however, the analysis of the power density curves unequivocally show that the performance of the DMFCs goes down during the stability tests. This apparent contradiction can be explained by taking into account the changes between the fresh and used PtCoRu/C observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. During the potential step cycles Ru dissolves form PtCoRu/C leading to Pt-enriched catalysts which are more active for the oxygen reduction reaction (lower resistance) but less tolerant to methanol (lower power density). Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.


Guil-Lopez R.,Grupo de Energia Y Quimica Sostenibles | Guil-Lopez R.,CSIC - Institute of Catalysis | Navarro R.M.,Grupo de Energia Y Quimica Sostenibles | Navarro R.M.,CSIC - Institute of Catalysis | And 4 more authors.
International Journal of Hydrogen Energy | Year: 2015

Steam reforming of acetone, as representative molecule of bio-oil, was investigated over different Ni-Mg-Al oxides with different Ni-environments which were obtained by the preparation of different Ni-Mg-Al materials: Ni-supported, Ni-mixed oxides and Ni likespinel structures. Physico-chemical characterization of samples showed different Nisupport interactions depending on the nature of the support and the method of preparation. Ni-incorporation into the Mg-Al structure increases its stability. Reforming activity results showed that the Ni-environment interaction plays an essential role on the catalytic behaviour of Ni-Mg-Al catalysts. The sequence of gasification capacity over Ni-Mg-Al samples points out that acidity of supports participates in the acetone reforming mechanism over these catalysts. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Guil-Lopez R.,Rey Juan Carlos University | Guil-Lopez R.,CSIC - Institute of Catalysis | Botas J.A.,Rey Juan Carlos University | Fierro J.L.G.,Grupo de Energia y Quimica Sostenibles | And 2 more authors.
Applied Catalysis A: General | Year: 2011

The CO x-free hydrogen production by decomposition of methane was carried out over metal-free carbons and bulk and supported metal catalysts. Catalysts based on Ni or Fe (oxides, spinels and ex-hydrotalcite mixed oxides) and carbon-catalysts of different types (carbon black, activated carbon, carbon nanotubes and graphite) have been used and the performance of both different kinds of catalyst compared in the target reaction, focussing the comparative study on the initial activity and the resistance against deactivation. Catalytic results showed that activity of carbon catalysts is similar to that of the non-prereduced metal catalysts. Carbon blacks, and specifically vulcan-type, were found to be most resistant catalysts against deactivation, while the most active ones were nickel catalysts derived from hydrotalcite-like precursors (ex-LDH). It was also shown that pre-reduction treatment of nickel precursor to generate the metallic Ni 0 phase before the reaction decreases the threshold temperature to generate hydrogen by about 200 °C. Along the course of the reaction, nanotubes and nanofibers are formed on the surface of metal catalysts. These carbon structures encapsulate metal particles and deactivate the catalysts. However, when carbons are used as catalysts, the nature of carbon deposits depends largely on the type of carbon material employed as catalyst in the methane decomposition. Thus, the use of carbon blacks and graphite yielded amorphous turbostratic carbon, whereas activated carbons mainly produced carbon, which showed the carbon black structure. Finally, the carbon by-product of the reaction, when carbon nanotubes were used bas catalysts, accumulates in the form of extra layers over the walls of carbon nanotubes thus increasing their wall thickness. © 2011 Elsevier B.V. All rights reserved.


Navarro R.M.,Grupo de Energia y Quimica Sostenibles | Guil-Lopez R.,Grupo de Energia y Quimica Sostenibles | Ismail A.A.,Najran University | Al-Sayari S.A.,Central Metallurgical Research and Development Institute | Fierro J.L.G.,Grupo de Energia y Quimica Sostenibles
Catalysis Today | Year: 2014

Hydrogen production from acetone steam reforming was studied using bimetallic PtNi catalysts supported on modified alumina. La-, Ce- and Mg-oxides were used as support modifiers in order to neutralize acidity and/or to improve water adsorption and OH- surface mobility of Al2O3 support. Characterization of the sample showed that metal-support interactions and the size of metallic Ni at surface differ depending on the oxide added to the alumina support. Reforming activity on Ni and Pt-Ni supported on X-modified-Al2O3 catalysts (X = La, Ce, or Mg) showed that both metal and support, play an essential role in the catalytic behavior on the steam reforming of acetone. The sequence of gasification capacity over monometallic samples (Ni/LaAl > Ni/MgAl > Ni/CeAl) points out that acidity of supports participates in the acetone reforming mechanism over these catalysts. Addition of Pt to monometallic Ni catalysts only has a beneficial effect on the reforming capacity of the Ni/LaAl sample. Improvement in the reforming capacity of the PtNi/LaAl catalyst is believed to be a consequence of the promoting effect of Pt that leads to an increase in the stability of metallic Ni particles on catalyst surface together with the ability of Pt to enhance the mobility of the H-atoms formed in the reaction could help the gasification of carbon precursors formed during the reforming of acetone. © 2014 Elsevier B.V. All rights reserved.


Navarro R.M.,Grupo de Energia y Quimica Sostenibles | Guil-Lopez R.,Grupo de Energia y Quimica Sostenibles | Ismail A.A.,Najran University | Ismail A.A.,Central Metallurgical Research and Development Institute | And 2 more authors.
Catalysis Today | Year: 2014

Hydrogen production from acetone steam reforming was studied using bimetallic PtNi catalysts supported on modified alumina. La-, Ce- and Mg-oxides were used as support modifiers in order to neutralize acidity and/or to improve water adsorption and OH- surface mobility of Al2O3 support. Characterization of the sample showed that metal-support interactions and the size of metallic Ni at surface differ depending on the oxide added to the alumina support. Reforming activity on Ni and Pt-Ni supported on X-modified-Al2O3 catalysts (X = La, Ce, or Mg) showed that both metal and support, play an essential role in the catalytic behavior on the steam reforming of acetone. The sequence of gasification capacity over monometallic samples (Ni/LaAl > Ni/MgAl > Ni/CeAl) points out that acidity of supports participates in the acetone reforming mechanism over these catalysts. Addition of Pt to monometallic Ni catalysts only has a beneficial effect on the reforming capacity of the Ni/LaAl sample. Improvement in the reforming capacity of the PtNi/LaAl catalyst is believed to be a consequence of the promoting effect of Pt that leads to an increase in the stability of metallic Ni particles on catalyst surface together with the ability of Pt to enhance the mobility of the H-atoms formed in the reaction could help the gasification of carbon precursors formed during the reforming of acetone. © 2014 Elsevier B.V.


Guil-Lopez R.,Grupo de Energia y Quimica Sostenibles | Navarro R.M.,Grupo de Energia y Quimica Sostenibles | Ismail A.A.,Najran University | Ismail A.A.,Central Metallurgical Research and Development Institute | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2015

Steam reforming of acetone, as representative molecule of bio-oil, was investigated over different Ni-Mg-Al oxides with different Ni-environments which were obtained by the preparation of different Ni-Mg-Al materials: Ni-supported, Ni-mixed oxides and Ni like-spinel structures. Physico-chemical characterization of samples showed different Ni-support interactions depending on the nature of the support and the method of preparation. Ni-incorporation into the Mg-Al structure increases its stability. Reforming activity results showed that the Ni-environment interaction plays an essential role on the catalytic behaviour of Ni-Mg-Al catalysts. The sequence of gasification capacity over Ni-Mg-Al samples points out that acidity of supports participates in the acetone reforming mechanism over these catalysts. © 2015 Hydrogen Energy Publications, LLC.


Navarro R.M.,Grupo de Energia y Quimica Sostenibles | Guil-Lopez R.,Grupo de Energia y Quimica Sostenibles | Gonzalez-Carballo J.M.,Grupo de Energia y Quimica Sostenibles | Cubero A.,Grupo de Energia y Quimica Sostenibles | And 4 more authors.
Applied Catalysis A: General | Year: 2014

The effect of Pt and Cu addition on the behaviour of Ni catalysts supported on Al2O3 modified with La for acetone steam reforming (as model molecule of bio-oil) was studied. Catalytic activity was found to depend strongly on the bimetallic formulation, achieving the bimetallic PtNi catalyst almost complete gasification of the acetone. The characterization results achieved with XRD, TPR and XPS showed differences in surface metal concentrations which depend on the presence of Pt or Cu in catalysts composition. The decrease in activity observed for the bimetallic CuNi catalyst is associated with changes in the acetone reaction mechanism due to the presence of metallic copper since formation of CuNi alloy was not formed in this catalyst. In the case of bimetallic PtNi catalyst, a lower carbon deposition and a higher thermal stability of the Ni crystallites under reaction conditions was observed with respect to monometallic Ni reference catalyst. It is suggested that the better dispersion of metallic nickel crystallites together with the enhanced H-atom mobility on Pt are responsible of the better catalytic behaviour of the bimetallic PtNi formulation in the steam reforming of acetone. © 2013 Elsevier B.V.

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