First-principles Investigation Of Adsorption Of Small Molecules On Au And Au-pd Alloy Clusters

Although Au is inert metal, Au nanopaticles have many unique catalytic properties.Especially its outstanding low temperature catalytic activity, for example,CO can beoxidized on Au nanoparticle even at very low temperature. CO is a kind of poisonousgas and it is harm to environment. So the study of the CO catalytic oxidation isimportant to air pollution control and environmental protection. To date, numeroustheoretical studies focus on the small gold Aun(n≦20), however, the studies of mediumand large sized gold clusters are scare andthe mechanism of gold clusters (especially forthe medium-and large-sized gold clusters) in CO catalytic oxidation is still unclear. Asis known, the gold clusters with big size are more suitable for the practicalapplication.To study it can also provide a theoretical basis for the practicalapplication ofcatalyst.In order to improve the catalytic activity of Au nanoparticles and explore thecatalytic mechanism of the gold clusters, we choose two cage-like geometry clustersAu32and Au55to study. They have Ihsymmetry and many low-coordinated atoms. Weresearchedthe adsorption of CO on these two clustersandcorrespondingAu-Pd alloyclusters. Furthermore we carried out a contrastive studyofthe adsorption of O2on Au32and corresponding Au-Pd alloy cluster on the conditions of drying and moisture, andwhat kind of conditions is useful to catalytic activity. All calculations are performedwith the density function theory implemented by First-principles and the conclusions ofthis paper are:(1) To the medium-sized clusters Au32, Au20Pd12, Au55and Au42Pd13clusters, COshould be adsorbed much more favorably on the five-coordinated sites, thelower-coordinated sites. But compared to bridge and hollow sites, the activity of COadsorbed on top sites is lower. Compared to the pure Au cluster, CO ought to prefer tobe adsorbed on the bimetallic cluster Au20Pd12and Au42Pd13clusters.(2) The adsorption energies of the adsorption and co-adsorption of O2and H2O onPd-doped gold clusters are bigger than pure gold clusters. The condition of O2and H2Oadsorption and co-adsorption on Pd doped gold clusters are more stable.(3) The presence of H2O can make the charges of O2which adsorbs on the Au32(Ih)or Au20Pd12(Ih) cluster and the O-O bond length increase. We can conclude that the H2Omolecule can enhance the activation of O2not only on the Au32cluster surface but also on the Au20Pd12cluster surface. It is useful to enhance the CO catalytic oxidationactivity.The results of this paper will provide the theoretical supports for the catalyticexperiment of small molecules on the surface of medium sized gold clusters andcorresponding alloy clusters. In addition, the conclusion that the activation of O2onAu32and Au20Pd12clusters are enhanced after the presence of H2O provide a new wayto improve the activity of gold catalysts.