Toward Computational Screening of Bimetallic Alloys for Methane Activation: A Case Study of MgPt Alloy

CH 4 is the main component of natural gas; there is a need for heterogeneous catalysts that can directly convert it into useful substances. On active metal surfaces, e.g., Pt surfaces, CH 4 is sequentially dehydrogenated to CH or C. It is very difficult to obtain useful C 2 products from them. We here present a catalytic informatics strategy with DFT calculations and databases to discover bimetallic alloy catalysts for selective methane coupling, which cannot be achieved with monometal catalysts. Considering two properties required for a methane conversion catalyst, i.e., reactivity and selectivity, alloy surfaces that allow the initial C–H bond cleavage reaction of methane to proceed and that stabilize CH 2 and CH 3 species more than CH and C species will be suitable catalysts for direct methane conversion. An exhaustive screening of alloys satisfying such conditions is carried out using density functional theory calculations. As a result, MgPt is predicted to be one of the most useful catalysts; on its surface, the activity of Pt is moderately suppressed due to Mg, and CH 3 and CH 2 species get more stable than CH and C species. The calculations predict that the C–C coupling reaction with the lowest activation barrier on the MgPt surface occurs for the pair of CH 3 and CH 2, producing the C 2 H 5 adsorbed species; it becomes ethane if hydrogenated and ethylene if dehydrogenated. In addition, the optimal Mg/Pt ratio for the reaction is computationally explored, and it is found that the Mg/Pt ratio of 1:1 is the best. Eventually, experimental verification is carried out by actually synthesizing an alloy satisfying this ratio; the nonoxidative coupling reaction of methane molecules is tested in the presence of the MgPt catalyst, and the formation of C 2 hydrocarbons as primary products is confirmed.