Investigation of Sm2O3-CeO2-supported palladium catalysts for the reforming of methanol: The role of the support

With a view to their use as catalytic anode materials for direct methanol solid oxide fuel cells (DM-SOFCs), the performance of Pd/CeO2-Sm2O3 (Pd/CS), Pd/CeO2 and Pd/Sm2O3 catalysts in the steam reforming of methanol as well as their physicochemical properties - analyzed by N2 adsorption, XRD, temperature programmed reduction (TPR), CO chemisorption and X-ray photoelectron spectroscopy (XPS) - have been investigated. The catalytic activity in methanol steam reforming was evaluated in a tubular microreactor at atmospheric pressure in the 300-500 °C reaction temperature interval (space velocity = 0.32 mol/(h gcat), H2O/CH3OH molar ratio = 1.2, methanol concentration 15 mole%). H2, CO and CO2 were the main reaction products. Methanol conversions up to 72% and H2 productivities as high as 0.46 mol/(h gcat) were obtained on the Pd/CS catalyst. Moreover, low H2 productivity (0.09 mol/(h gcat)) was found on the Pd/CeO2 catalyst, while Pd/Sm2O3 appeared to be inactive. This behaviour can be partly assigned to the higher dispersion and the more favourable distribution of Pd particles observed in the Pd/CS catalyst. A strong association of Pd and samarium oxide and an enrichment in both components at the external surface of the Pd/CS catalyst grains was found by means of TPR and XPS. This could be explained by the partial dissolution of Sm2O3 in the acid medium used during catalyst preparation leading to the re-precipitation of a Pd/Sm-containing phase. Higher activity per exposed Pd atom was also observed for the Pd/CS catalyst. This was attributed to enhancement of diffusion and adsorption of reactants on the basic sites of the Sm-containing support.