Improved ethanol steam reforming on Rh/Al2O3 catalysts doped with CeO2 or/and La2O3: Influence in reaction pathways including coke formation

Abstract

In this paper, Rh catalysts supported over bare γ-Al2O3 and γ-Al2O3 modified with different promoters (15wt%La2O3 and/or 2.5wt%CeO2) were reported. The catalysts were prepared by successive impregnation: first the rare earth oxide promoter and then Rh. Hydrogen production by ethanol steam reforming (ESR) over these catalysts was investigated. Among the catalysts, Rh/La2O3–CeO2–γ-Al2O3 catalyst shows the highest hydrogen yield as well as the best stability during the reaction. Reaction pathways of the ESR over these Rh catalysts are investigated from the analysis of the adsorbed species and gas phase products formed during temperature programmed desorption of ethanol and ethanol steam reforming reaction. The differences in the reaction pathways and products distribution are as a result of the modification of the stability of some reaction intermediates caused by the presence of a small quantity of CeO2 and La2O3 on the support surfaces: in effect, acetaldehyde was formed as an intermediate over the modified-γ-Al2O3 supported catalysts while in the case of the bare Al2O3 support the main route of the steam reforming reaction is the direct ethanol decomposition. Analysis of the used catalysts by XPS, TGA and RAMAN showed that changes in reaction pathways associated to the presence of promoters in the Al2O3 support also modifies the extension and type of carbon deposited on catalyst surfaces.