Support Effects Examined by a Comparative Theoretical Study of Au, Cu, and CuAu Nanoclusters on Rutile and Anatase Surfaces

Abstract

The role of the support anatase TiO 2 (100) and rutile TiO 2 (110) on the energetics, the shape, and the charge transfer of deposited CuAu nanoclusters (∼1 nm) has been examined by using density functional theory (DFT) calculations including Hubbard correction (DFT + U). Regular truncated octahedron clusters, Cu (1-x) Au (x) (x being in the range 0.15-0.36), representing different alloy types (core@shell, regular alloy, skin-heart), have been considered. From a thermodynamic standpoint, the core-shell-deposited nanoclusters present the strongest adsorption strength on both rutile and anatase supports, although they are the least stable homotops in vacuum. Interestingly, for skin-heart and regular alloy CuAu clusters, the stability on these supports decreases with the Au content. CuAu nanoclusters present larger adsorption energies on rutile than on the anatase support. This result has been explained by a Bader analysis of charge transfers and an energy decomposition analysis model, which shows a larger binding energy between the metal and the rutile support than that on anatase, in part compensated by the stronger deformation of the structure of rutile. At the size of 38 atoms, the bimetallic cluster exhibits a significant propensity to distort its structure and adapt it to the geometry of the oxide surface to maximize the stability of the formed metal-oxide chemical bonds. Such an interesting property is expected to decay with the increasing size of the metallic nanocluster. This work provides an original discussion related to the support effect, which is rarely evoked in the literature of DFT studies of such supported alloy clusters at the nanoscale.