Theoretical Insights into Dual-Metal-Site Catalysts for the Nonoxidative Coupling of Methane

Abstract

Direct conversion of methane to C 2 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, Fe 2 –N–C, and Co 2 –N–C) for nonoxidative coupling of methane to C 2 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, Co 2 –N–C exhibits the best catalytic activity and superior selectivity to ethane in the whole reaction pathway. Our microkinetic modeling reveals that the Co 2 –N–C catalyst can convert methane to CH 3, C 2 H 6, and H 2 at 1200 K. The electronic structure analysis and ab initio molecular dynamics simulations demonstrate that Co 2 –N–C possesses both intrinsic stability and high-temperature stability. Moreover, Co 2 –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 C 2 hydrocarbons under nonoxidative conditions.