Density functional theory on the structures and adsorption properties of CuxAgyAuz (x + y + z = 7, x, y, z > 0) and monometallic Cu7, Ag7, and Au7 clusters.

CONTEXT: Au-based ternary clusters have attracted the interest of researchers because of their stronger catalytic activity, higher selectivity and better chemical and physical stability. This study aims to investigate the structures and adsorption properties of CuxAgyAuz (x + y + z = 7, x, y, z > 0) and monometallic Cu7, Ag7, and Au7 clusters. Genetic algorithm combined density functional theory (DFT) method has been used. The computational method is TPSSh-D3(BJ). According to the computational results, Cu atoms of CuxAgyAuz clusters like to locate at the center of the clusters, while Au and Ag atoms tend to be at the edge. When Cu atoms are not sufficient to be located at the center, Ag atoms also appear at the central part of the cluster. CuxAgyAuz clusters prefer three-dimensional structures rather than planar ones. Only Cu1Ag1Au5 is a planar structure. The three-dimensional structures include two types: capped-tetrahedron structure and pentagonal bipyramid. Cu₇ and Ag₇ adopt a three-dimensional pentagonal bipyramidal geometry, whereas Au₇ favors a planar structure. The adsorption sites of CuxAgyAuz clusters are mainly Cu atoms, occasionally Au atoms. After adsorption of CO and NO, the frameworks of CuxAgyAuz and Cu7, Ag7 and Au7 change little. The adsorption of CO on CuxAgyAuz, Cu7, and Au7 belongs to chemical adsorption, while that of NO includes chemical and physical adsorption. The formed Cu(Au)-C bonds in CuxAgyAuzCO are stronger than Cu(Au)-N bonds in CuxAgyAuzNO. It is harder for NO adsorption on CuxAgyAuz clusters than CO from the point of view of thermodynamic. The HOMO-LUMO gap decreases upon adsorption, with charge transfer from clusters to CO/NO, and thermodynamic analysis confirms all adsorption processes are spontaneous.

METHODS

The combined method of genetic algorithm and density functional theory has been studied to obtain the structures of CuxAgyAuz (x + y + z = 7, x, y, z > 0) and monometallic Cu7, Ag7, and Au7 clusters. CuxAgyAuzCO and CuxAgyAuzNO are optimized according to the global minimum structures by adding CO or NO on different positions of CuxAgyAuz clusters. The initial optimization method used is TPSSh-D3(BJ)/Def2-SVP. After optimization with small basis set, lower energy isomers are reoptimized by TPSSh-D3(BJ)/Def2-TZVP method with Def2-TZVP effective core potential and the frequencies are also obtained at this level. Gaussian 16 software is used for the calculations. Gauss view 6.0.16 software is a visualization software used to obtain the structures. Multiwfn 3.8 software is used the bond orders.