The Geometric,Stability And Electronic Properties Of Gold-doped Pd Clusters(Pd_nAu,n=3～25)And Their Effect Of Catalytic On CO Oxidation

With the development of science and technology, many studies are focused on the nano-material. According to the different structures, the nano materials can be categorized into zero-dimensional nanocluster, one-dimensional nanowires, nanotubes,two-dimensional ultra-thin films and three-dimensional nano-solid material. Because of the quantum effects, surface effects, high ratio of surface and volume, the nanoclusters show unique properties of optical, electronic and magnetic aspects different from their bulk counterparts. So the nanoclusters are widely used in the field of biological research, industrial catalysis, environmental protection, pharmaceutical research and so on. Due to their wide application in oxidation reaction of CO and NO_x,most experimental and theoretical investigations on metal clusters have been carried out on transition metal（TM）, such as gold（Au）, Palladium（Pd）, Platinum（Pt） and so on. In addition, some nanoclusters are stable enough, non-poisonous and their size is comparable to proteins and organisms, viruses and genes, so they have broad application prospect in cancer treatment.According to previous studies, the interaction between the doped atoms and the mother atoms can improve the stability of the nanoclusters. Many researchers have proved that the doped metal clusters show better performance than the pure counterparts. Moreover, because of the synergy effect between the two metal elements,the binary metal clusters have a better catalytic effect on the chemical reaction. And the size of the nanoclusers can be controlled in the range of a few atoms for catalytic activities.Until now, there are many investigations onAu clusters doped with other atoms.As far as we know, the studies are scarce when gold atoms are doped into other clusters. Au has a higher electronegativity and lower cohesive energy compared with Pd. Some experimental studies have proved that large size gold-doped Pd clusters have higher activity, and now the study of small Pd_nAu clusters is currently feasible intheoretical way. We focus on the structure search of Pd_nAu（n = 3～25） and its catalytic effects in CO oxidation-reduction reaction. The calculation is carried out by using ab initio project augmented wave method implemented in Vienna ab initio simulation package（VASP）. The main contents and results are listed as following:1. After optimizing the structure of the Pd_nAu nanoclusters by using VASP and CALYPSO simulation package, we study the most stable geometric structure of the nanoclusters and their electronic, magnetic properties and so on.（1） It is found that these clusters preferred 3D structure even with very small atom number. As the the Pd atom has higher cohesive energy and Au atom has lower surface energy, the Au atom prefers the top position than the inner part.（2） By comparing the binding energy between Pd_nAu and Pd_n+1, we concluded that the connection between the atoms of Pd_nAu clusters is more tightness than the counterpart of Pd_n+1. The doped gold atom improves the stability of the clusters.（3） By analyzing the charge transfer of the clusters, we found that the charges transfer from Pd atoms to the Au atom, as the electronegativity of Au is higher than Pd. The excess of charge near the gold atom enhance the activity of Au atom, which will improve the activity of catalyzing the CO oxidation or H₂O dissociation reaction.2. We search the feasible catalytic routines of Pd_nAu nanoclusters for CO oxidation by using the nudged elastic band（NEB） method. The calculation is also carried out by using ab initio project augmented wave method implemented in VASP.We select Pd₅Au, Pd₉Au, Pd₁₂Au, Pd₁₃Au which have symmetrical structure among the Pd_nAu（n=3～25） clusters.（1） By constructing the initial and final structures of Pd_nAu（n=5,9,12,13）clusters which have combination with CO and O₂ at different position, we search the best routine of the catalytic reaction about the oxidation of CO.（2） By comparing the adsorption energy of CO and O₂ on Pd_nAu clusters, we found that the adsorption energy of CO is obviously higher than O₂, so we conclude that the cluster will adsorb CO molecule firstly.（3） The results show that the combination of carbon atom of CO and gold atom of the clusters will facilitate the CO₂ molecule separating from the Pd_nAu clusters.