Density Functional Theory Study Of The Adsorption Of Cyanide On The Metal Surfaces And Clusters

The studies of the interaction of cyanide with the transition metal clusters andsurfaces not only are important topics in the domain of many sciences, such as incatalyze, electrochemistry, environmental conservation and chemical defense areas, etc.,but also are of high commercial value. Theoretically and experimentally, thus it is ofgreat attention to investigate the surface phenomena and the bonding mechanism for thecyanide adsorbed on transition metal clusters and surfaces.In this paper, a series of cyanides adsorbed on metal clusters and surfaces arestudied systematically by using the density functional theory. The main investigativecontents are as following:1. The favorable adsorption modes for HCN and HNC on Pd (100) surface areparallel bonding on hollow site with both C and N atoms and perpendicularly bonding onbridge site through C atom, respectively. The calculated results show that HCN is facileto decompose on Pd (100) and under certain temperature the dissociation products can bere-generated to HCN, while the dissociation of HNC is relatively more difficult. On Pd(100) surface, surface HCN not only can isomerize to surface HNC, also can hydrogenateto intermediate HCNH molecule and then isomerize into surface HNC. The calculationsshow that the later reaction is easier than the former.2. The most favorable geometries and the electronic structures for CN radicalsadsorption on M (100)(M=Cu, Ag, Au) are investigated. It is shown that C-down is morefavorable than N-down modes with CN axis perpendicular to the same surface. Inaddition, the adsorption energy decreases with the increasing of the metal atomic numberfor the same adsorption site. CN radical is parallel adsorbed on Cu and Ag surfaces andperpendicularly absorbed on Au surface, respectively. The Mulliken population analysisresults show that the charge transfer from metal surfaces to CN is in the range from0.4to0.6e. 3. For HCN adsorption on Aun(n=2~7) clusters, no dependence was found withrespect to the even–odd alternation in relation to the number of gold atoms in the clusters.The HCN molecule is adsorbed at simple adsorption sites (1-fold coordination),perpendicular to the adsorption site. The most calculated value of adsorption energy isonly about0.77eV, indicating that the HCN molecule does not decompose and the C–Nbond retains triple bond, and suggests that C–H and C–N stretching frequencies are onlyweakly perturbed. The adsorbed C-N and C–H stretching frequencies are blue-shiftedand red-shifted comparable with the values of free HCN, respectively.4. The calculations show that the most stable structure for CH3CN and CH3NC on Pd(100) is through CN parallel to hollow site and C atom perpendicular to bridge site,respectively. In both structures, the CH3CN and CH3NC transforms from linear structureof gas molecule to bending structure, and adsorbate cause surface atoms to which it bindsto relax outward. The dissociation mechanism for CH3CN and CH3NC on Pd surface isalso discussed.