Theoretical Study On The Geometry And Electronic Structure Of Copper Clusters Supported On ZrO₂ And WO₃

Compared with traditional catalysts,supported metal catalysts have unique catalytic properties,so they are widely used in chemical sensors,microelectronic devices,and various catalytic reactions.Oxide-supported metal copper nanoparticles as catalysts not only reduce the use of precious metals,but also have the advantages of high selectivity and high activity.We know that the catalytic activity of the catalyst is related to the size,shape and size distribution of the cluster,and these factors largely depend on the surface properties of the support oxide.Therefore,it is necessary to understand the surface properties of the support oxide and the electronic structure and chemical properties of the metal clusters.In this paper,a detailed theoretical study of the stable adsorption configurations of Cu_n clusters supported on the surface of m-ZrO₂(111)(monoclinic)and m-WO₃(001)(monoclinic)and the properties of the most stable structures has been carried out using the density flooding theory(DFT)method.For Cu_n(n=1-14)/ZrO₂,we calculated the stable structures of the gas-phase Cu_n clusters,searched for the most stable structures of the Cu_n clusters on the m-ZrO₂(111)surface,and analyzed the system's interface function and electronic structure.In addition,we calculated the adsorption of CO₂,OH,O and H on the Cu₂/ZrO₂ and Cu₁₄/ZrO₂ systems.The calculation results show following conclusions.The average Cu-Cu bond lengths of gas-phase Cu_nclusters are all smaller than the Cu-Cu bond lengths of bulk copper,and E_bind(Cu_n)increases with the increase of Cu_n clusters.In the Cu_n/ZrO₂ system,the Cu_n clusters lay flat on the ZrO₂surface with a planar or planar-like structure for n=1-8,and when n?9,the Cu_n clusters show a three-dimensional structure,which is different from the gas-phase Cu_n clusters.Bader charge analysis of the most stable structure of Cu_n/ZrO₂ shows that the Cu_n clusters have a net positive charge,which indicates that the electrons are transferred from the Cu_n cluster to the ZrO₂ surface.The electron difference density indicates that the Cu-O atoms show ionic bonding interaction and the Cu-Zr atoms have covalent interactions.The analysis of the density of states shows that the band gap of the Cu_n/ZrO₂ system is significantly smaller than the band gap of the clean ZrO₂ surface.With the increase of Cu_n clusters,the density of states of Cu_n clusters moves toward the higher energy level.CO₂,OH and O are more easily adsorbed at the interface between Cu_n clusters and ZrO₂ surface,while H atoms are more easily adsorbed on Cu atoms.For the Cu_n(n=1-10)/WO₃ system,we explored the adsorption structure of Cu_n clusters on the WO₃ surface,and analyzed the interface effect and electronic structure of the system.We draw the following conclusions.For n=1-6,Cu_n is gradually filling up the bridging sites of the terminal O in the mode of"individual Cu atoms".When n>6,the Cu atoms gradually form planar clusters on the surface between the two columns of O.Cu atoms first tend to lay flat on the surface of WO₃ rather than forming a three-dimensional structure.Moreover,Cu atoms are more likely to form monoatomic adsorption on the surface of WO₃.The analysis of the Bader charge of the system shows that the Cu atoms have a net positive charge,which indicates that the electrons have transferred from the Cu_n clusters to the WO₃ surface.Through the analysis of the density of states,we found that the Cu_n cluster has a significant change in the valence electron distribution of WO₃.Due to the transfer of electrons from Cu_nto the surface of WO₃,the band gap of WO₃ has undergone a huge change.