Theoretical insights into dual-metal-site catalysts for the nonoxidative coupling of methane

Direct conversion of methane to C₂ hydrocarbons under nonoxidative conditions is an attractive technology but is challenging due to high reaction temperature, severe coke deposition, and low selectivity. Here, we report three dual-metal-site catalysts (DMSCs) based on nitrogen-doped graphene (FeCo−N−C, Fe₂−N−C, and Co₂−N−C) for nonoxidative coupling of methane to C₂ hydrocarbons from a theoretical perspective. Our calculated results reveal that DMSCs present universally better performance in methane activation than single-metal-site catalysts (Fe−N− C and Co−N−C). Among the three DMSCs, Co₂−N−C exhibits the best catalytic activity and superior selectivity to ethane in the whole reaction pathway. Our microkinetic modeling reveals that the Co₂−N−C catalyst can convert methane to CH₃, C₂H₆, and H₂ at 1200 K. The electronic structure analysis and ab initio molecular dynamics simulations demonstrate that Co₂−N−C possesses both intrinsic stability and high-temperature stability. Moreover, Co₂−N−C also manifests better coke resistance compared with larger Co clusters, indicated by the difficult kinetics of methane deep dehydrogenation to naked carbon. This work provides a potential catalyst prototype for the selective conversion of methane to C₂ hydrocarbons under nonoxidative conditions.