Near ambient pressure XPS investigation of the interaction of ethanol with Co/CeO2(111)

Near ambient pressure X-ray photoelectron spectroscopy was applied to study the interaction of ethanol (CH3CH2OH) with a well-ordered CeO2(1 1 1) film on Cu(1 1 1) and with a Co/CeO2(1 1 1)/Cu(1 1 1) model catalyst. The oxidation state of the surface and the chemical nature of reaction intermediates were analyzed. At 300 K, the oxidation state of ceria decreased gradually with increasing ethanol pressure. At a constant pressure of 0.1 mbar, the reduction of Ce4+ to Ce3+ increased significantly between 320 and 600 K due to a higher mobility of oxygen or Ce3+ centers at elevated temperatures. The main intermediate, ethoxide, was formed by dissociative adsorption of ethanol at room temperature. No coke formation was observed up to 600 K on CeO2. Upon deposition of metallic cobalt, partial reduction of ceria was observed, leading to the formation of Co2+ sites but still leaving metallic Co in the metal particles. During the reaction of ethanol with the Co/CeO2(1 1 1) model catalyst, the amount of Co2+ decreased drastically with increasing temperature, and at 600 K, the majority of Co was metallic. This process was accompanied by the severe reduction of ceria and the formation of significant carbon deposits. (C) 2013 Elsevier Inc. All rights reserved.