Adsorption of AuxCuy (x + y = 1, 2, 3) nanoclusters on the anatase TiO2(101) surface and their catalytic activity: a density functional theory study

Abstract

Noble metal–TiO₂ composites are systems of interest for their potential catalytic applications. Density functional theory calculations were carried out to study the adsorption structures of Au_xCu_y (x + y = 1, 2, 3) nanoclusters and the growth mechanisms of AuCu bimetallic clusters on the perfect anatase TiO₂(101) surface to understand the metal–support interactions, and the resulting catalytic behavior toward water splitting. The results showed that the bimetallic AuCu/TiO₂ systems always have a large cluster adsorption energy and binding energy, and there is a strong interaction between the cluster and the support. Meanwhile, the shift of active sites for the growth of the AuCu bimetallic clusters on the anatase TiO₂(101) surface is observed. Mulliken charge and overlap population analysis revealed that the bond length of a metal atom at the hollow site and the surface two-coordinated bridge O atom (O_2c) and the amount of charge transfer of each adsorbed clusters are proportional to the adsorption energy, and the interaction between Au_xCu_y clusters and the anatase TiO₂(101) surface depends primarily on the metal–O_2c bond. In addition, the investigation on the catalytic behavior of Au_xCu_y/TiO₂ toward single water molecule adsorption and decomposition showed that: for Au_xCu_y (x + y = 1)/TiO₂, the loading of a Au or Cu atom can completely change the catalytic process of the clean TiO₂(101) surface; for Au_xCu_y (x + y = 2)/TiO₂, the decomposed OH + H group is very unstable and can spontaneously recombine into H₂O without any energy barrier; and for Au_xCu_y (x + y = 3)/TiO₂, modification by replacing the Au₃ cluster with the bimetallic AuCu cluster can promote the initial decomposition of H₂O. This research will be helpful for designing and developing novel Au_xCu_y/TiO₂ composite catalysts.