Molecular adsorption of methane and methyl onto MgO(100) An embedded-cluster study

Abstract Embedded cluster models have been used to model the molecular adsorption of methane and methyl at the perfect (100) surface of MgO. Energies are computed using the modified coupled pair functional method, with corrections for basis set superposition errors applied both during geometry optimization and to adsorption energies. In the case of methane, interadsorbate interactions are taken into account through ab initio pair-interaction energies, facilitating adsorption energies at monolayer coverage. Methane is found to adsorb preferentially at magnesium sites, in a dipod configuration, i.e. with two hydrogen atoms pointed down and towards oxide anions. At monolayer coverage, neighboring methane molecules are rotated 90° relative to each other, keeping the dipod orientation. An adsorption energy of 8.5 kJ mol−1 is obtained for methane, which is somewhat low compared to experimental estimates. Methyl adsorbs preferably over Mg2+ sites, with a binding energy only slightly higher than for methane. No elements of covalency was detected in the bond between the radical and the MgO(100) surface.

[1]  B. Deprick,et al.  A theoretical study of adsorption of CH4 on the (100) faces of MgO and NaCl , 1987 .

[2]  J. Lunsford,et al.  Secondary reactions of methyl radicals with lanthanide oxides: their role in the selective oxidation of methane , 1989 .

[3]  Tomoko Watanabe,et al.  Activation of methane on the MgO surface at low temperatures , 1987 .

[4]  J. Duffy,et al.  Bonding, Energy Levels and Bands in Inorganic Solids , 1990 .

[5]  L. Seijo,et al.  The ab initio model potential representation of the crystalline environment. Theoretical study of the local distortion on NaCl:Cu+ , 1988 .

[6]  R. Dovesi,et al.  Ab initio Hartree-Fock treatment of ionic and semi-ionic compounds: state of the art , 1992, Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences.

[7]  L. Pettersson,et al.  BONDING BETWEEN CO AND THE MGO(001) SURFACE : A MODIFIED PICTURE , 1994 .

[8]  C. Girardet,et al.  Potential surfaces and adsorption energy of Xe, CH4, N2, CO, NH3 and CH3F molecules on a MgO substrate , 1991 .

[9]  G. Matthews,et al.  An intermolecular pair potential energy function for methane , 1976 .

[10]  Lauter,et al.  Evidence of a square two-dimensional solid of methane physisorbed on the (100) surface of magnesium oxide. , 1985, Physical review letters.

[11]  J. Goodwin,et al.  Surface phenomena during the oxidative coupling of methane over Li/MgO , 1991 .

[12]  M. O'loughlin,et al.  Methane–methane isotropic interaction potential from total differential cross sections , 1985 .

[13]  D. Ferguson,et al.  A computational analysis of interaction energies in methane and neopentane dimer systems , 1997, J. Comput. Chem..

[14]  Stocker,et al.  Rotational diffusion of methane molecules adsorbed on MgO(100). , 1992, Physical Review B (Condensed Matter).

[15]  Kazutoshi Tanabe,et al.  Basis set effects on the intermolecular interaction energies of methane dimers obtained by the Moeller-Plesset perturbation theory calculation , 1991 .

[16]  Delano P. Chong,et al.  A modified coupled pair functional approach , 1986 .

[17]  V. Staemmler,et al.  Ab initio calculations for the adsorption of small molecules on metal oxide surfaces. I. Cluster calculations for carbon monoxide CO on nickel oxide NiO(100) , 1992 .

[18]  K. Klabunde,et al.  Interaction of activated magnesium oxide surfaces with spin traps , 1988 .

[19]  R. M. Lambert,et al.  Chemisorption and reactivity on supported clusters and thin films : towards an understanding of microscopic processes in catalysis , 1997 .

[20]  Knut J. Bo rve.  Methane dissociation on a nonplanar MgO(001) surface. Theoretical modeling of surface defects , 1991 .

[21]  L. Pettersson,et al.  Core–valence correlation effects using approximate operators , 1991 .

[22]  J. Coulomb,et al.  Diffusivity of a two-dimensional lattice fluid: CH4 adsorbed on MgO(100) , 1987 .

[23]  S. F. Boys,et al.  The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors , 1970 .

[24]  P. Siegbahn,et al.  First row benchmark tests of the parametrized configuration interaction with parameter X (PCI‐X) scheme , 1995 .

[25]  B. Asmussen,et al.  Rotational tunneling studies of methane films adsorbed on MgO: Crossover from two-to-three dimensions? , 1996 .

[26]  L. Seijo,et al.  Ab initio model potential study of environmental effects on the Jahn–Teller parameters of Cu2+ and Ag2+ impurities in MgO, CaO, and SrO hosts , 1993 .

[27]  Kazutoshi Tanabe,et al.  Refinement of Nonbonding Interaction Potential Parameters for Methane on the Basis of the Pair Potential Obtained by MP3/6-311G(3d,3p)-Level ab Initio Molecular Orbital Calculations: The Anisotropy of H/H Interaction , 1994 .

[28]  Jung,et al.  Dynamics and kinetics of monolayer CH4 on MgO(001) studied by helium-atom scattering. , 1991, Physical review. B, Condensed matter.

[29]  S. Scheiner,et al.  Intermolecular potential of the methane dimer and trimer , 1990 .

[30]  Alavi.  Evidence for a Kosterlitz-Thouless transition in a simulation of CD4 adsorbed on MgO. , 1990, Physical review letters.

[31]  T. H. Dunning.  Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First‐Row Atoms , 1970 .

[32]  S. Tsang,et al.  Influence of homogeneous gas phase reactions in the partial oxidation of methane to methanol and formaldehyde in the presence of oxide catalysts , 1991 .

[33]  A. Thomy,et al.  Adsorption de molécules simples sur graphite - III. — Passage de la première couche par trois états successifs , 1970 .

[34]  Christian Girard,et al.  Potential energy calculations for argon and methane adsorbed on MgO(001) substrate , 1987 .

[35]  S. Huzinaga,et al.  A systematic preparation of new contracted Gaussian‐type orbital sets. III. Second‐row atoms from Li through ne , 1980 .

[36]  S. Huzinaga,et al.  Gaussian‐Type Functions for Polyatomic Systems. II , 1970 .

[37]  Ali Alavi,et al.  Molecular-dynamics simulation of methane adsorbed on MgO: Evidence for a Kosterlitz-Thouless transition , 1990 .

[38]  S. Fraga,et al.  Computational chemistry : structure, interactions, and reactivity , 1992 .

[39]  J. Coulomb,et al.  Adsorption physique de molécules simples sur une surface homogène de symétrie carrée. I. Préparation et caractérisation du substrat d'oxyde de magnésium , 1984 .

[40]  J. Lunsford,et al.  Formation of gas-phase methyl radicals over MgO , 1985 .

[41]  W. M. Haynes.  CRC Handbook of Chemistry and Physics , 1990 .

[42]  D. Richter,et al.  Rotational tunneling of methane on MgO surfaces: A neutron scattering study , 1991 .

[43]  M. Blomberg,et al.  PCI-X, a parametrized correlation method containing a single adjustable parameter X , 1994 .

[44]  J. Novoa,et al.  Interactions energies associated with short intermolecular contacts of C–H bonds. II. Ab initio computational study of the C–H⋅⋅⋅H–C interactions in methane dimer , 1991 .

[45]  Jack H. Lunsford.  The Catalytic Oxidative Coupling of Methane , 1995 .