A computational investigation of the adsorption of small copper clusters on the CeO₂(110) surface

We report a detailed density functional theory (DFT) study of the geometrical and electronic properties, and the growth mechanism of a Cu (n = 1-4) cluster on a stoichiometric, and especially on a defective CeO₂(110) surface with one surface oxygen vacancy, without using pre-assumed gas-phase Cu cluster shapes. This gives new and valuable theoretical insight into experimental work regarding debatable active sites of promising CuO/CeO₂-nanorod catalysts in many reactions. We demonstrate that CeO₂(110) is highly reducible upon Cu adsorption, with electron transfer from Cu clusters, and that a Cu cluster grows along the long bridge sites until Cu₃, so that each Cu atom can interact strongly with surface oxygen ions at these sites, forming stable structures on both stoichiometric and defective CeO₂(110) surface. Cu-Cu interactions are, however, limited, since Cu atoms are distant from each other, inhibiting the formation of Cu-Cu bonds. This monolayer then begins to grow into a bilayer as seen in the Cu₃ to Cu₄ transition, with long-bridge site Cu as anchoring sites. Our calculations on Cu₄ adsorption reveal a Cu bilayer rich in Cu⁺ species at the Cu-O interface.