DISSOCIATIVE CHEMISORPTION OF CH4 ON NI(111)

The dissociative chemisorption of methane at an atop-atom site on a (1 11) surface of nickel is treated using a many-electron embedding theor y 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 exp licitly included on seven nickel atoms on the surface. The calculated activation energy of CH4 adsorbed at an atop Ni site to produce CH3 an d H coadsorbed at separated threefold sites is 17 kcal/mol. The dissoc iation of CH4 to CH3 (ads) + H (ads) is predicted to be 2.8 kcal/mol e xothermic. The Ni 3d orbitals contribute to the bonding by directly mi xing with methane C-H orbitals during the dissociation process and thr ough a direct interaction of 3d9 and 3d10 configurations at the transi tion state. The dissociation pathway and the bonding properties of ads orbed CH4 and coadsorbed CH3 and H are discussed.