DFT study of CO oxidation catalyzed by Au/TiO<inf>2</inf>: Activity of small clusters

Abstract

CO oxidation over a rutile TiO<inf>2</inf>(110) surface supporting a tetrahedral Au<inf>10</inf> cluster has been examined by planewave DFT calculations. O<inf>2</inf> adsorbs sideon to the pentacoordinate Ti site of the oxide support with a large energy gain (∼ 2 eV), activated to a peroxide state. O<inf>2</inf> adsorption on the cluster is much weaker. The stability and activation state of sideon O<inf>2</inf> depends weakly on distance to the cluster. On a Ti site next to the cluster, a sideon O<inf>2</inf> reacts with CO adsorbed on the cluster to yield CO<inf>2</inf> with a very small energy barrier of 0.13 eV. On a more remote Ti site, a sideon O<inf>2</inf> reacts with a gaseous CO to yield CO<inf>2</inf> with a barrier of 0.55 eV. Thus, O<inf>2</inf> + CO reaction is much faster at the perimeter even for a small cluster such as Au<inf>10</inf>. Similar results are obtained for a truncated pyramidal Au<inf>9</inf>, except that a carbonate is formed at the perimeter. The carbonate formation is inhibited if H<inf>2</inf>O is adsorbed next to O<inf>2</inf>.