Mechanism and active sites of CO oxidation over single-crystal Au surfaces and a Au/TiO2(110) model surface

Abstract

We describe the reaction mechanism and active sites for CO oxidation over a Au/TiO2(110) model surface and Au single-crystal surfaces, along with the role of H2O, on a molecular scale. At low temperature (< 320 K), H2O played an essential role in promoting CO oxidation, and the active site for CO oxidation was the perimeter of the interface between the gold nanoparticles and the TiO2 support (Auδ+−Oδ−−Ti). We believe that the O−O bond was activated by the formation of OOH, which was produced directly from O2 and H2O at the perimeter of the interface between the gold nanoparticles and the TiO2 support, and consequently OOH reacted with CO to form CO2. This reaction mechanism explains the dependence of the CO2 formation rate on O2 pressure at 300 K. In contrast, at high temperature (> 320 K), low-coordinated gold atoms built up on the surface as a result of surface reconstruction due to exposure to CO. The low-coordinated gold atoms adsorbed O2, which then dissociated and oxidized CO on the metallic gold surface.