Density functional theory study the mechanism of two CO* forming *OC-CO on different size of Cu_n (n = 3 to 20) clusters supported on TiO₂

Cu_n@TiO₂ nanocatalytic materials are widely used in experiments to catalyze the reduction of CO₂ to hydrocarbon fuels and oxygenated alcohols. However, due to the complexity of the coupling reaction of the Cu_n@TiO₂ catalyst to form key C–C bonds to C2 products, it is unclear. In this paper, the density functional theory (DFT) is employed to systematically study the influence of the size of Cu_n clusters on the C–C bond formation with the Cu_n cluster supporting on the TiO₂ surface. It was discovered that the adsorption of Cu metal clusters of different sizes on TiO₂ was primarily determined by the bonding of TiO₂ oxygen atoms. Subsequently, in the CO*+CO* → COOC* coupling reaction on each different Cu_n cluster size, we found that the active site was the interface position, when the Cu_n cluster showed a three-dimensional configuration, with the increase of the Cu cluster, that is, the coordination number increased, the activation energy barrier gradually decreased, and when the coordination of Cu cluster reached saturation, the coupling energy barrier size also stabilized. This work provides new sight of the size of co-catalyst in the CO₂ reduction reaction and may guide to synthesis higher efficiency co-catalyst.