Coadsorption of Carbon Monoxide and Hydrogen on the Ni(100) Surface: ATheoretical Investigation of Site Preferences and Surface Bonding

摘要

The Carbon monoxide/hydrogen coadsorption on the Nickel(100) surface is discussedin this study. Relative stabilities of various possible surface structures of the coadsorption system are compared. The surface-adsorbate bonding in the Ni(100)/H(4)/CO(t) structure, the most favorable choice of the lower temperature state, resembles that of the singly adsorbed systems. The adsorbate-adsorbate interaction does not lead to any chemical bonds but does affect the surface-CO pi bonding. For the observed higher temperature geometry of CO, possible H and H2 (adsorbed hydrogen molecule) arrangements in the final surface state are compared. Energy and crystal overlap population analyses show that the 4-fold adsorption site for both H and H2 gives good agreement with the experimental observations. A new adsorbate-adsorbate coupling between CO(t) and H2(4) is seen, but this coupling does not significantly affect the surface-adsorbate bonding. Again, no C-H or O-H bonds are formed. Besides the favorable CO(t)CO(4) (half of the CO's adsorbed terminally and the other half in the 4-fold hollow site) configuration our calculations also reveal the possibility of a CO(t)/CO(b) combination in the final state.