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Ethanol photoreaction on RuO<inf>x</inf>/Ru-modified TiO<inf>2</inf>(110)

Abstract:

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 RuOx/TiO2(110) surfaces. Ethanol dissociatively adsorbs on both TiO2 and RuOx/TiO 2 surfaces forming ethoxide. Our DFT calculations indicate that the ethoxide formation is more exothermic on RuOx/TiO2(110) surfaces (ΔE= -1.61 eV) than on the clean rutile TiO2(110) surface (ΔE= -0.95 eV). Defect sites present on RuOx/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 RuOx 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/TiO2 system is more active for the photo-oxidation of ethanol to acetaldehyde than TiO2. A linear trend of the rate of acetaldehyde and carbon dioxide production from exposure to ethanol of Ru/TiO2 surfaces in the presence of O2 indicates that more surface sites are available for the adsorption of O2 than on bare TiO2 surfaces, possibly at the interface of the Ru metal nanoparticles and TiO2 surfaces, which facilitates the photo-oxidation. © 2013 American Chemical Society.