Toward a microscopic understanding of the catalytic oxidation of methane on metal surfaces using density functional theory: a review

The mechanism of the catalytic oxidation of methane on metal surfaces is increasingly used in different fields of chemical technology and process development. The practical desire to understand such a reaction mechanism stems from the long-held belief that a microscopic understanding may facilitate the design of more efficient chemical processes and catalysts. Density functional theory has been helpful in this regard and the pathways of the catalytic oxidation reaction have recently been determined, providing a clear indication as to how this reaction is likely to take place on metal surfaces. The state of research into the catalytic oxidation of methane on metal surfaces is critically reviewed, with emphasis on recent advances in the reaction mechanism from the quantum chemistry point of view. Special attention is given to the adsorption and activation of methane on a variety of metal surfaces. Mechanistic pathways and kinetics of the oxidation reaction are reviewed, and critical issues in the research on the oxidation mechanism are discussed. Isoelectronic adsorbates tend to go to similar sites to form transition states. The higher the valency of the adsorbate, the greater its tendency to access a transition state close to a high coordination site. Significant changes in reaction pathways could be induced by hydroxyl species. The importance of bimetallic catalysts for the catalytic oxidation reaction should not be underestimated. The current challenges to and opportunities for promoting the understanding of the oxidation mechanism are summarized, in hopes of facilitating progress in this emerging area. Potential topics of oncoming focus are finally highlighted.