Density Functional Theory Study On Alau Alloy Clusters Catalyst

In catalytic chemistry and chemical engineering, real catalystsmainly consist of a heterometallic or bimetallic system, which canprofoundly enhance reactivity and selectivity. Gold nanoparticleshave attracted public attention since the pioneering discovery thatAu can exhibit surprisingly high catalytic activity. Pure andsupported Au clusters and nanoparticles have now become one ofthe most promising catalysts for many important chemicalreactions at low temperature. Further, aluminum is a common andcheap metal with lighter mass. Especially, aluminum alloy clustersprovide a matter of increasing interest in pure and applied materialssciences and traditional fields of physics and chemistry. What arethe properties of Al-Au alloy? In recent years, some theoreticalworks are devoted to the geometric structures and electronicproperties, but investigates of catalytic properties is a little. So, inthis paper, the main purpose studies the catalytic properties ofAl-Au bimetallic clusters, expect to provide a theoretical basis and guidance for the development of the new catalyst materials. Fulloptimized structures and normal-mode frequencies are found usingthe DFT/PBE method. An all-electron basis set6–31G*is used for Al,H, C and O atoms. The LANL2DZ pseudopotential is adopted for thevalence electrons of Au atom. The main contents are listed asfollows:1. Calculated the H2adsorption and dissociation on small-sizedAlnAu clusters for n=1-13. The growth pattern for AlnAu (n=1-7,12)clusters is Au atom occupying a peripheral position of Alnclusters.And the growth pattern for AlnAu (n=8,10and13) clusters isAu-substituted Aln+1clusters. It is found that the Au atomsubstituted the surface atom of Aln+1cluster and occupies aperipheral position. H2is easily physically absorbed on the top Auatom of AlnAu clusters with an end-on orientation rather thanside-on orientation because of the more effective orbital overlap inthe end-on orientation. The reaction of AlnAu with H2would produceAlnAuH2because of large exothermic energy changes and relativelysmall activation energies especially for Al3Au and Al7Au, whichmight serve as highly efficient and low-cost catalysts for hydrogendissociation.2. Investigated the adsorption properties of O2and CO on AlAun(n=1-12) clusters, and the catalytic mechanism of CO oxidation on the surface of AlAunclusters. The adsorption of O2prefers to Alatom, except for AlAu12. Contrary to the O2case, the adsorption ofCO is located Au atom when n=4-12. Further, adsorption propertiesof O2, as well as CO, which shows odd-even effects depend stronglyon the AlAuncluster size, such as bond distance increase, vibrationfrequency decreases, and transfer of electronic charge. It is foundthat the active sites in AlAuncluster would be first occupied by thecoming O2rather than CO, in view of its more negative BE than thoseof CO. The catalytic reactions of CO oxidation have largeexothermic energy changes and relatively small activation energiesespecially for AlAu6and AlAu12, which might serve as highlyefficient. By analyzing the local density of states, it shows theinteraction between cluster and O2/CO, in order to clarify thecatalytic mechanism of CO oxidation.