Methane Activation by Metals and Semiconductors. Molecular Orbital Theory. Annual Report September 1986-August 1987

摘要

A predictive molecular orbital theoretical study of CH4 activation on coordinatively unsaturated transition metal centers shows high activity for the metal surfaces studied, (100) and (110) and rough (100) Fe, (100) and (111) Ni, and (111) Pt; the more open surfaces are more reactive because the surface atoms have fewer coordination neighbors. This allows a surface atom greater flexibility for stabilizing C...H...M and C...M bonding orbitals as the metal atom inserts into the CH bond. A 4-coordinate MoIV cation on the edge of a MoS2 crystal is predicted to easily activate CH4 by inserting into a CH bond. Initial products are oxidative homolytic but H will shift to S(2-), resulting in heterolytic products. CH3 bound to Mo can dehydrogenate to yield doubly bound CH2 but further dehydrogenations are not energetically favorable. These findings indicate it may be possible to incorporate CH4 in Fischer-Tropsch catalysis over MoS2. A review of theoretical work on structure and electronic factors in heterogeneous catalysis dealing in C=C, C=O, and CH activation by metals and oxides has been prepared. The importance of 0- to CH4 activation is explained.