Elucidation of Active Sites for the Reaction of Ethanol on TiO2/Au(111)

Obtaining a molecular-level understanding of the reaction of alcohols with heterogeneous model catalysts is critical for improving industrial catalytic processes, such as the production of H2 from alcohols. Gold has been shown to be an excellent oxidation catalyst once oxygen is added to it. The use of reducible oxides provides a source of oxygen on Au(111) for the reaction of ethanol, which is easily regenerated in the presence of an oxygen background. In this work, ethanol operates as a probe molecule to investigate the role of Au(111), TiO2 nanoparticles, and TiO2/Au interfacial surface sites on the catalytic properties of TiO2/Au­(111). Ultrahigh vacuum temperature-programmed desorption (TPD) studies with ethanol/Au(111) elucidate previously unreported adsorption sites for ethanol. Ethanol molecularly adsorbs to Au terrace sites, step edges, and undercoordinated kink sites with adsorption energies of −51.7, −55.8, and −65.1 kJ/mol, respectively. A TPD coverage study of ethanol on TiO2/Au­(111) indicates ethanol undergoes dissociative adsorption to form H*­(a) and CH3CH2O*­(a) on the inverse model catalyst surface. The desorption temperature of low coverages of ethanol from TiO2/Au­(111) (T des ≈ 235 K) is at an intermediate temperature between the desorption temperatures from bulk Au(111) and TiO2(110), indicating both Au and TiO2 play a role in the adsorption of ethanol. Both low-temperature adsorption and high-temperature reactions are studied and indicate that ethanol-derived products such as acetaldehyde and ethylene desorb from TiO2/Au­(111) at ∼500 K. Herein, we report the identification of catalytically active sites on TiO2/Au­(111) as interfacial sites between the oxide and Au(111) surface through the use of temperature-programmed desorption and infrared reflection absorption spectroscopy.