First-Principles Studies For The Interaction Between Gold Cluster And CO, O₂, H₂O

Au clusters have outstanding low-temperature catalytic activity and have many unique properties.Many experimental and theoretical researches have been done on them.Properties of small molecules adsorption on the Au clusters have been studied because it is the first step to study the catalytic properties of Au clusters.In this paper,the interactions between gold cluster and CO,O₂,H₂O have been researched using density functional theory(DFT) calculations and aims to interpret the experimental fact that the presence of H₂O promotes the oxidation of CO on Au cluster.The adsorption theory of CO on cage-like Au₃₂ has been researched using DFT methods. The density functional calculations were conducted using the Accelrys Dmol³ code.All calculations involved used the generalized gradient approximation(GGA) functional by perdew-wang functional(PW91).A relativistic semi-core pseudopotential(DSPP) and the 'double numerical plus polarization'(DNP) basis set(a polarized split valence basis set of numeric atomic functions) were employed.All calculations were based on Pulay's direct inversion of iterative subspace(DIIS) technique to accelerate SCF convergence.Through analyzing adsorption energy,energy gap,etc.CO is adsorbed favorably on the 5-coordinate (5top) and 6-coordinate sites(6top) of free Au₃₂.The adsorption stability of 5top is larger than 6top sites.The structures of CO adsorption on edge and inside sites of cage Au₃₂ are unstable. Partial Densities of States(PDOS) and Mulliken analysis show that the electronic state of Au₃₂ cage(doped K atom) are changed.The stability of CO on the top sites of Au₃₂ is added, and CO adsorption on edge sites is allowed to exist.K atom can be used to enhance the adsorption activity of Au₃₂ clusters.Au₃₈-O₂,Au₃₈-H₂O,and Au₃₈-H₂O-O₂ systems have been investigated by DFT.The results show that,O₂ tends to be adsorbed stablily on the edge sites and can not exist on the top,face sites of Au₃₈.There are many different adsorption properties between H₂O and O₂. H₂O tends to exist stably on the top sites.It is found that O₂,H₂O are more favorable on Au (100) than Au(111) surface,which is in agreement with experimental result.The results of H₂O and O₂ coadsorption on Au₃₈ cluster indicate that Au3s cluster surface is actived in the presence of H₂O and promotes the stable absorption of O₂.Mulliken population and PDOS show electrons transfer from H₂O to O₂ in coadsorption structures,which promotes the activation and dissociation of O₂,and generates a hydrogen peroxide-like intermediate state that provides O active species.