Co catalysts supported on La2O3-SiO2 binary systems were used in the steam ethanol reforming reaction for the production of hydrogen. Calcined and used catalysts were characterized by different techniques, in situ Raman spectroscopy, XPS and HRTEM to determine the Co species present in the solids before and after the reaction. The Co catalysts were active and stable for H-2 production. In order to improve catalyst stability and H-2 production, the contact time (W/F) effect was studied (4.9 10(-3) g h L-1 to 3.3 10(-2) g h L-1). In the case of the catalytic measurements with lower W/F, the catalyst with 15 wt% of Co presented higher selectivity to H-2. It was observed that a higher content of Co-0 species increased the hydrogen yield, suggesting that metallic cobalt could be the active species in most of the parallel reactions that occur in the reforming of ethanol. In the solid with lower Co content, the low formation of carbon nanotubes produced a slight decrease of ethanol conversion with a decrease in the hydrogen yield. On the other hand, in the catalyst with higher cobalt content the carbonaceous deposits are of the amorphous type and the hydrogen yield equal to 3.5 remained constant with time on stream. The most active and stable catalyst with 15 wt% of Co was tested in a membrane reactor, obtaining a high H-2 recovery of 54% under moderate reaction conditions (H2O/ethanol = 5, 500 degrees C and 1 bar).

The aim of the present work was to investigate Rh nanoparticle catalysts supported on La2O3-SiO2, with different contents of La2O3, in the ethanol steam reforming reaction. The size of Rh particles was determined by both XPS, applying the Davis model, and CO chemisorption measurements. Particle sizes between 1.2 and 3 nm were estimated with these techniques. The catalyst with 15 wt.% of La2O3 was the most stable one under the different reaction conditions under study, i.e. 773 K and water to ethanol molar ratios of 3 and 5. In order to explain the deactivation observed in the other catalysts, the samples used in the reaction were characterized by XPS, TEM and in situ Raman spectroscopy. The TEM results allowed a direct visualization of the carbon deposits that presented different degrees of catalyst coverage. The surface of the most stable catalyst was not fully covered by carbon while the Rh/La2O3(40)-SiO2 sample, which deactivated partially, exhibited a carbon layer uniformly distributed over the surface. The oxidation of the carbon deposits was analyzed using in situ Raman spectroscopy. Results were in agreement with those obtained by TEM microscopy. DRIFTS experiments under reaction conditions suggested that the direct decomposition of ethoxy species would produce hydrogen, CO, and CHx species, which could result in carbon formation. (C) 2014 Elsevier B.V. All rights reserved.

A dense Pd–Ag membrane reactor (MR) with 100% hydrogen selectivity packed with either Rh/La2O3 or Rh/La2O3–SiO2 as catalysts was used to carry out the dry reforming of methane. The membrane reactor simulation was performed using a well-known reactor model. For this purpose, we employed the equations derived from complete kinetic studies of the dry reforming of methane reaction in connection with both catalysts. In addition, we developed the kinetic equation for the reverse water gas shift reaction (RWGS). The combination of detailed kinetic studies with the measured permeation flux for the Pd–Ag membrane allowed a complete comparison between experimental and simulated operation variables. The variables studied for both catalysts were methane conversion and hydrogen permeation as a function of the sweep gas flow rate. The correlation between methane conversion enhancement and hydrogen recovery confirmed that a good prediction was obtained with this model. The performance of two reactor configurations (membrane reactor and conventional fixed-bed reactor) and both co-current and counter-current flow modes were compared. The effect of various operating variables such as permeation area, sweep gas flow rate and feed composition upon conversion, product compositions and hydrogen recovery were analyzed.

A review is presented here of our previous contributions concerning the production of ultrapure hydrogen through the dry reforming of methane conducted in a membrane reactor. The reaction equilibration ratio is the criterion to compare the catalytic performance of the La-based catalysts used in these studies. The solids were characterized by Laser Raman, X- ray photoelectron spectroscopy, X-ray diffraction and temperature-programmed reduction. The different behaviors are discussed taking into account the characterization results. To predict the influence of key process variables on conversion and product Composition, a mathematical model is proposed to simulate the membrane reactor built around a palladium-silver membrane with 100% hydrogen selectivity. This study uses the kinetic equations developed for the dry reforming reaction on a Rh/La2O3 catalyst. (C) 2009 Curtin University of Technology and John Wiley & Sons, Ltd.