Theory Study Of Structure, Optical Properties And Surface Adsorption Performance Of Gold Palladium Alloy Clusters

The photocatalytic activities of some coin-metal nanoparticles (Au, Ag, Cu) contributed by their surface plasmon resonance (SPR) under visible light irradiation have attracted tremendous attentions and have been extensively studied. In recent years,it is found that the Pd, Pt, Rh and Au-Pd nanoparticles, with no SPR effect under visible light irradiation, show light enhanced catalytic performance and can accelerate some organic reactions more efficiently. However, there are little knowledge about the mechanism of the optical absorption, the adsorption of the reactant of the metal surface, and so on.The rapid development of theoretical chemistry and computer technology provide us a chance to use computer to investigate the problems mentioned above.In this work, the optical absorption of Au-Pd alloy clusters were simulated by using the density functional method. We also have explored the adsorption of some small molecules on the Au-Pd surface.The following works were included:1. The geometry and optical adsorption property of Au32-nPdn (n=1,2,4,6) alloy clusterIn this work, we use Au32(C2) cluster as a model to investigate the structures and optical absorption properties of Au-Pd alloy cluster. The geometries of Au32-nPdn(n=1,2,4,6) cluster were systematacially explored by means of density functional theory (DFT) calculations. We want to know how Pd atoms impact the structure of the Au-Pd alloy cluster. Various initial structures were considered to find the most stable gold palladium alloy clusters configuration. The calculations showed that Pd atoms favor the inner site rather than the surface site of the alloy clusters, and cluster together to form Pdcore, while gold atoms distribute around the palladium core to form AushellPdcore structure. The doped Pd atoms significantly change the optical absorption properties of the gold clusters. The optical absorptions of the Au-Pd alloy clusters under visible light are previously enhanced, compared to Au32, especially in the lower energy sections. As a result, the Au-Pd alloy nanoparticles should be a more efficient photocatalyst in the visible light range. The analysis of the DOS of Au-Pd alloy cluster was preformed. We found that the doped Pd atoms do increase the DOS around the Fermi level, which fully illustrates why the optical absorptions of Au-Pd alloy clusters enhanced in the visible region.2. The study of benzyl alcohol and O2adsorption on AuPd (111) surfaceA9x9size supercell structure with the Au/Pd molar ratio of1:2were built to simulate the Au-Pd nanoparticle catalyst. By using density functional theory method, the adsorptions of PhCH2OH, O2, H2O and OH’on AuPd (111) catalyst model w ere investigated. Research results are as follows:(1) O2adsorbed on the AuPd (111) surface by bridge style. PhCH2OH adsorbed on the surface through the benzene plane. When O2was adsorbed on the surface, the O-O bond length elongated obviously by about0.075-0.107A compared to the freedom O2molecule.(2) When H2O or OH" are coadsorption on AuPd (111)-PhCH2OH-O2, the presence of H2O or OH’ promoted the O2activation on the AuPd (111) surface, mainly due to the formation of hydrogen bonds between H2O or OH’ with02. The strong hydrogen bonds between OH’ and O2will elongate the O-O bond length further and weaken the strength of the O-O bond. At the same time,OH’can bind with the PhCH2OH through hydrogen bond, in which the O in the OH’interact with the H in the OH group of PhCH2OH. This hydrogen bond can weaken the O-H bond in the PhCH2OH.In conclusion, the optical absorption of the Au-Pd alloy cluster and the adsorption of small molecules on the Au-Pd alloy cluster were investigated in our works. The research results are useful for further investigation on the photocatalytic mechanism involved in Au-Pd alloy cluster catalyst.