The mechanism of emerging catalytic activity of gold nano-clusters on rutile TiO ₂(110) in CO oxidation reaction

This paper reveals the fact that the O adatoms (O _ad) adsorbed on the 5-fold Ti rows of rutile TiO ₂(110) react with CO to form CO ₂ at room temperature and the oxidation reaction is pronouncedly enhanced by Au nano-clusters deposited on the above O-rich TiO ₂(110) surfaces. The optimum activity is obtained for 2D clusters with a lateral size of ∼1.5 nm and two-atomic layer height corresponding to ∼50 Au atomscluster. This strong activity emerging is attributed to an electronic charge transfer from Au clusters to O-rich TiO ₂(110) supports observed clearly by work function measurement, which results in an interface dipole. The interface dipoles lower the potential barrier for dissociative O ₂ adsorption on the surface and also enhance the reaction of CO with the O _ad atoms to form CO ₂ owing to the electric field of the interface dipoles, which generate an attractive force upon polar CO molecules and thus prolong the duration time on the Au nano-clusters. This electric field is screened by the valence electrons of Au clusters except near the perimeter interfaces, thereby the activity is diminished for three-dimensional clusters with a larger size.