DISSOCIATIVE CHEMISORPTION OF CH4 ON NI(111)

The dissociative chemisorption of methane at an atop-atom site on a (111) surface of nickel is treated using a many-electron embedding theory to describe bonding, modeling the lattice as a 41-atom, three layer cluster. Ab initio valence orbital configuration interaction (multiple parent) calculations carried out on a local surface region permit an accurate description of bonding at the surface. Ni 3d orbitals are explicitly included on seven nickel atoms on the surface. The calculated activation energy of CH4 adsorbed at an atop Ni site to produce CH3 and H coadsorbed at separated threefold sites is 17 kcal/mol. The dissociation of CH4 to CH3 (ads) + H (ads) is predicted to be 2.8 kcal/mol exothermic. The Ni 3d orbitals contribute to the bonding by directly mixing with methane C-H orbitals during the dissociation process and through a direct interaction of 3d9 and 3d10 configurations at the transition state. The dissociation pathway and the bonding properties of adsorbed CH4 and coadsorbed CH3 and H are discussed.