Ethanol Photoreaction on RuO_x/Ru-Modified TiO₂(110)

During the photochemical reaction of organic molecules on oxide surfaces, radicals are formed and participate in heterogeneous photocatalytic processes; however, understanding the mechanistic origins and the fate of such species under reaction conditions is difficult. In this work we carry out a combined experimental and theoretical study on the thermal and photochemical interaction of ethanol with RuO x /TiO 2 (110) surfaces. Ethanol dissociatively adsorbs on both TiO 2 and RuO x /TiO 2 surfaces forming ethoxide. Our DFT calculations indicate that the ethoxide formation is more exothermic on RuO x /TiO 2 (110) surfaces (Δ E = −1.61 eV) than on the clean rutile TiO 2 (110) surface (Δ E = −0.95 eV). Defect sites present on RuO x /TiO 2 surfaces can dissociate part of the ethoxide to acetaldehyde even below 300 K, which can be further oxidized to acetate resulting in the reduction of the RuO x nanoparticles. Exposure to UV irradiation of the ethoxide covered surfaces in the presence of oxygen at 300 K resulted in considerable decrease in ethoxide species by conversion to acetate. It is found that the Ru/TiO 2 system is more active for the photo-oxidation of ethanol to acetaldehyde than TiO 2 . A linear trend of the rate of acetaldehyde and carbon dioxide production from exposure to ethanol of Ru/TiO 2 surfaces in the presence of O 2 indicates that more surface sites are available for the adsorption of O 2 than on bare TiO 2 surfaces, possibly at the interface of the Ru metal nanoparticles and TiO 2 surfaces, which facilitates the photo-oxidation.