Coadsorption of carbon monoxide and hydrogen on the nickel(100) surface: a theoretical investigation of site preferences and surface bonding

Abstract

The CO/H coadsorption on the Ni(100) surface is discussed in this study. Relative stabilities of various possible surface structures are compared for the initial state (lower temperature form), as well as the final state (higher temperature form) of the coadsorption system. The surface-adsorbate bonding in the Ni(100)/H(4)/CO(t) structure (H(4) stands for hydrogen atoms adsorbed in a 4-fold hollow site and CO(t) stands for carbon monoxide in the on-top position), 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. Destabilization of the CO 2{pi} orbitals due to the 2{pi}-1s(H) interaction results in a depopulation of the 2{pi} states and a strengthening of the C-O bond. For the observed higher temperature c(2{radical}2{times}{radical}2)R45{degree} geometry of CO, possible H and H{sub 2} (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 H{sub 2} gives good agreement with the experimental observations.