Role of gold nanoclusters supported on TiO₂(110) model catalyst in CO oxidation reaction

It was reported previously that O adatoms adsorbed dissociatively on the five-fold Ti rows of rutile TiO₂(110) made the surface O-rich and reacted with CO molecules to form CO₂. An electronic charge transfer taking place from gold nanoclusters to the O-rich TiO₂(110) support played a crucial role to enhance the catalytic activity [Mitsuhara, J. Chem. Phys. 136, 124303 (2012)]. In this study, the authors have further accumulated experimental data for the CO oxidation reaction enhanced by gold nanoclusters on the TiO₂(110) surface. Based on the results obtained here and previously, the authors propose an "interface dipole model," which explains the strong activity of Au nanoclusters supported on O-rich TiO ₂(110) in CO oxidation reaction. Simultaneously, the authors also discuss the cationic cluster model proposed by Wang and Hammer [Phys. Rev. Lett. 97, 136107 (2006)] and the d-band model predicted by Hammer and Nørskov [Adv. Catal. 45, 71 (2000)]. The latter is, in particular, widely accepted to explain the activities of heterogeneous catalysts. Contrary to the d-band model, our ab initio calculations demonstrate that the d-band center for Au nanoclusters moves apart from the Fermi level with decreasing the cluster size and this is due to contraction of the Au-Au bond length.