Effect of the surface state on the catalytic performance of a Co/CeO2 ethanol steam-reforming catalyst

This work examines the impact of the Co/CeO2 catalysts' surface oxidation state and composition on the ethanol steam reforming (ESR) reaction performance. To this purpose, in situ and ex situ X-ray photoelectron spectroscopy (XPS) combined with on-line mass spectrometry were applied in a wide pressure range (0.2-20 mbar). When the reaction was performed at 0.2 mbar, metallic cobalt and partly reduced cerium oxide were found regardless of the catalysts' pretreatment conditions. This surface state favors CO and H-2 production, indicating that C-C bond cleavage is the most important pathway in this pressure regime. A higher reduction degree of ceria gave rise to a larger population of adsorbed hydroxyl groups, which, contrary to the expected behavior, suppressed the activity and the C-C bond cleavage yield. Under higher pressure (4-20 mbar), gradual oxidation of cobalt and ceria was noted. The presence of ionic cobalt species appears to enhance CO2 and acetaldehyde yields. On the basis of the present results and the available literature a plausible pressure-dependent reaction mechanism is proposed. (C) 2016 Elsevier Inc. All rights reserved.