The Unique Properties of the Oxide-Metal Interface: Reaction of Ethanol on an Inverse Model CeOx–Au(111) Catalyst

The metal and oxide interface has been implicated through rigorous investigation as being pivotal to catalytic processes such as the production of H 2 by reforming of alcohols. In this work, using high resolution X-ray photoelectron spectroscopy (XPS), we extend the study further by looking at the interaction of an oxygenate composed of the simplest C–O, O–H and C–C containing functionalities, ethanol (CH 3 CH 2 OH) with a model metal-oxide interface. We have discovered that this reactant can adsorb molecularly on Au(111) (Au 0 ), while on O–Au(111) (Au + ) and on inverse CeO x –Au(111) (Ce 4+ /Ce 3+ /Au + ) surfaces it forms ethoxy (CH 3 CH 2 O−) species. Decomposition temperatures for the ethoxy on Au(111) surface are low (∼200 K) but much higher on CeO x covered surfaces (>500 K). Neither scission of the C–C or C–O bond of ethanol, nor surface aldehyde/acetate species was observed on these surfaces. However, O was lost from CeO x after reaction showing a clear reduction from Ce 4+ to Ce 3+ . Most interestingly, the fractionally covered Au(111) surface with CeO x showed evidence for ethoxy being bound to both Au and CeO x at 300 K, which is not observed on either Au(111) or O–Au(111) at this temperature. Based on these results we hypothesize that the interface between CeO x and Au is providing a site for either (1) direct deprotonation of ethanol and adsorption of ethoxy, (2) adsorption for the spillover of ethoxy from the oxide to the interface, or (3) spillover of O from CeO x to Au(111) followed by direct deprotonation of ethanol/adsorption of ethoxy. We discuss the implication of these results involving inverse catalysts at dynamic steady state conditions.