Theoretical Study of the Direct Conversion of Methane by First-Row Transition-Metal Oxide Cations in the Gas Phase

The direct conversion of methane to methanol is a thermodynamically favorable process compared with the available commercial process that uses synthesis gas. This chapter reviews quantum chemical approaches, especially by means of density functional theory (DFT) calculations, to elucidate the reaction pathway and energetics for methane-to-methanol conversion by first-row transition-metal oxide ions (MO+s, where M is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). We introduce the electronic structures of MO+ and the potential-energy diagrams for the methane hydroxylation by MO+. In the FeO+/CH4 system, surface crossing seams were computed along the reaction pathway. Spin–orbit coupling (SOC) was calculated to estimate the probability of spin-inversion.SOCdecreases along the reaction pathway, approaching zero in the product complex.