High Activity of Au/K/TiO₂(110) for CO Oxidation: Alkali-Metal-Enhanced Dispersion of Au and Bonding of CO

Images from scanning tunneling microscopy show high mobility for potassium (K) on an oxidized TiO 2 (110) surface. At low coverages, the alkali metal occupies mainly terrace sites of the o-TiO 2 (110) system. The results of X-ray photoelectron spectroscopy indicate that K is fully ionized. The electron transferred from K to the titania affects the reactivity of this oxide, favoring the dispersion of Au particles on the terraces of the o-TiO 2 (110) surface. When small coverages of K and Au are present on the o-TiO 2 (110) system, only a few K–Au pairs are formed and the alkali metal affects Au chemisorption mainly through the oxide interactions. Addition of K to Au/o-TiO 2 (110) enhances the reactivity of the system, opening new reaction paths for the adsorption and oxidation of carbon monoxide. CO can undergo disproportionation (2CO → C ads + CO 2,ads ) on K/o-TiO 2 (110) and Au/K/o-TiO 2 (110) surfaces. The Au–KO x interface binds CO much better than plain Au–TiO 2, increasing the surface coverage of CO and facilitating its oxidation. Kinetic tests show that K promotes CO oxidation on Au/TiO 2 . Turnover frequencies of 2.1 and 10.8 molecules (Au site) −1 s –1 were calculated for oxidation of CO on Au/o-TiO 2 (110) and Au/K/o-TiO 2 (110) catalysts, respectively.