Adsorption Of Gas Molecules On Small Pt-alloy Clusters

Bimetallic clusters, which o ften show electronic and chemical propert ies dist inct fro m those o f the bulk metals, are widely used in nanophase materials, fuel cell, opt ics and other interdisciplinary research, and offer a new perspect ive to obtain new catalysts with enhanced select ivit y, activit y, and stabilit y, and Pt, one representative noble metal element, doping in the clusters play a significant role in broad applicat ions, such as industrial catalysis and bio logical science, have drawn considerable attent ion.In recent years, the major o f studies st ill focus on the certain kinds of metal allo y clusters both in experimental and theoret ical studies, while adsorpt ion o f gas molecules on small allo y clusters are less investigated, and there are ev en few research on the correlat ion between properties structure o f allo y clusters. The mechanism of gas mo lecules absorb on the transit ion metal surface can provide theoret ical foundat ion for interact ion of metal surfaces with gas mo lecules. This thesis st udied the geo metric and electronic structure o f the adsorption of small gas mo lecules H2, N2, and CO on Pt allo y clusters with two ato ms and three transit ion metal ato ms in the fourth, fift h, and sixt h periods using densit y funct ional theory based method. All the calculat ions were carried out with the Gaussian03 program packages. The structural data and properties include adsorpt ion energy, geometry, charge, energy gap and so on were analyzed.For the Pt-based clusters absorbing H2, N2 and CO, the majorit y o f bonding energies are negative, indicat ing that the gas mo lecules adsorbed on the surface of the allo y are stable. According to the result of adsorption energy, for the allo y clusters of Hf and Pt atom with ato mic rat io 1:1, Hg and Pt atom with ato mic ratio of 1: 2, and Zr, Os and Pt with ato mic ratio o f 2:1, the adsorption energy o f H2 adsorpt ion on these clusters are quite large; for the allo y clusters of Hf, Os, Ni and Pt with ato mic number rat io of 1:1, Hg and Pt with atomic number rat io of 1:2, Os and Pt with ato mic number ratio of 2:1, have strong N2 adsorpt ion; or the allo y clusters of Ir and Pt with ato mic ratio 1:1, Ir and Pt with ato mic rat io of 1:2, Hf and Pt with ato mic rat io 2:1, the CO adsorption on those Pt-based clusters are rather stable.T hose outstanding adsorptions of gas mo lecules on Pt-based clusters belong to chemisorption, and they can be used to catalyze the dissociat ion of the corresponding gas molecules. The bond order o f N2 adsorption on Pt M2 is larger than that on other clusters, therefore with strong bonding of N2. As CO is isoelectronic with N2, so that HOMO-LUMO energ y gap o f the Pt2 M clusters adsorbing CO has similar pattern with that of Pt M2 adsorbing N2, though with large variation magnitude. Based on the Mulliken charge analysis, charge transfer most occurs from transit ion metal M to Pt o f Ptallo y clusters.