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 CO, OH and CC containing functionalities, ethanol (CH3CH2OH) with a model metal-oxide interface. We have discovered that this reactant can adsorb molecularly on Au(111) (Au-0), while on OAu(111) (Au+) and on inverse CeOxAu(111) (Ce4+/Ce3+/Au+) surfaces it forms ethoxy (CH3CH2O-) species. Decomposition temperatures for the ethoxy on Au(111) surface are low (similar to 200 K) but much higher on CeOx covered surfaces (>500 K). Neither scission of the CC or CO bond of ethanol, nor surface aldehyde/acetate species was observed on these surfaces. However, O was lost from CeOx after reaction showing a clear reduction from Ce4+ to Ce3+. Most interestingly, the fractionally covered Au(111) surface with CeOx showed evidence for ethoxy being bound to both Au and CeOx at 300 K, which is not observed on either Au(111) or OAu(111) at this temperature. Based on these results we hypothesize that the interface between CeOx 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 CeOx 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.