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Quantum mechanical calculation of ethylene hydrogenation on nickel 111 single crystal surface and nickel nanoclusters

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2005
Sayar, Aslı
Ethylene hydrogenation on Ni(111); equilibrium geometry calculations for Ni2 dimer, Ni13 and Ni55 nanoclusters; and ethylene adsorption on Ni(100), Ni(111), Ni2, and Ni13 were studied quantum mechanically by means of energetic and kinetic differences. Ethylene hydrogenation on Ni(111) was simulated by use of DFT/B3LYP/6-31G** formalism. The reaction mechanism was mainly composed of three elementary steps. Firstly, ethylene adsorption on bare Ni(111) surface was performed. Second step and third step were the formation of ethane from adsorbed ethylene by use of two types of hydrogen atom, bulk and surface. During the hydrogenation reaction of ethylene on Ni(111), bulk hydrogen atom, representing for hydrogen atoms emerging from the bulk of Ni metal, was determined to be rather reactive than surface hydrogen atom, as suggested by experimental findings. Small Ni clusters, Ni2 and Ni13, were investigated by means of DFT/B3LYP/modified-6-31G**. Equilibrium geometry calculations resulted in Ni2 binding energy of 1.078eV/atom, showing good agreement with experimental value. Ni13 was found to have a structure of icosahedral, suggested experimentally, and binding energy of 2.70eV/atom. Ni55 was, also, studied by semi-empirical PM3 formalism, resulting in expected icosahedral structure. Finally, DFT/B3LYP/6-31G** investigation of ethylene adsorption was performed on Ni(111), Ni(100) and Ni13 surfaces which were selected according to their nickel atom coordination numbers of 9, 8 and 6, respectively. Comparison of adsorption energies of -18.00kcal/mol, -31.4kcal/mol and -43.42kcal/mol, respectively, indicated that the change in energies for ethylene adsorption on different nickel surfaces was directly proportional to coordination number of the nickel atoms constructing the surfaces.