Abstract
Ambient-pressure X-ray photoelectron spectroscopy (APXPS) and temperature-programmed desorption (TPD) have been employed to elucidate the adsorption and reaction of simple alcohols on SrTiO3(100). TPD experiments indicate molecular desorption of alcohols with a small amount of aldehydes below 100 °C, whereas no gas-phase products are observed above this temperature. APXPS spectra at 0.1 Torr show that alcohols adsorb dissociatively onto SrTiO3(100) to form alkoxies. Surface methoxides appear to react with each other to produce acetate as a surface intermediate. These surface species are eventually oxidized to gas-phase CO, CO2, and H2O. Ethoxide is readily oxidized to acetate species that undergo further reactions to form gas-phase products. CO2 is the only C-containing product during ethanol oxidation, whereas methanol can also produce the partial oxidation product, CO. When no O2 is present, alcohol oxidation yields gas-phase CO, CO2, or H2O and creates oxygen vacancies on the surface, resulting in the reduction of Ti4+. Without a source of oxygen replenishment, the availability of surface oxygen would be limited, and thus, the oxidation reactions could not progress indefinitely. At near-ambient pressures, the reactivity of the surface and the distribution of surface species and reaction products were changed by altering the alcohol/O2 ratio, consistent with an interpretation that surface vacancies are being created and that their concentration is altered when an oxygen source is present. The conversion from acetate to CO2 might be rate-limiting when sufficient O2 gas is present.
