ELECTRONIC AND STRUCTURAL EFFECTS IN CO CHEMISORPTION ON CU3PT(111)

It is generally observed for CO adsorption on alloys composed of an sp-metal and a transition metal that the adsorption energy is decreased compared to adsorption on the pure transition metal, although the adsorption site is above a transition metal atom. We explain this behaviour for CO/Cu3Pt(111) by means of a model Hamiltonian investigation and compare to an earlier study of CO/NiAl(110). For the latter systems the decrease of the adsorption energy can be traced to the filling of the d-band and the change in sp-d hybridization, whereas for CO/Cu3Pt(111) the reduced density of Pt atoms in the surface decreases the heat of adsorption. The adsorption site is determined by different physical effects as well. On NiAl(110) the adsorption geometry is controlled by minimising 5sigma-3d repulsion and on Cu3Pt(111) sp-band corrugation is important for obtaining the right adsorption place.