Graphene Supported Single Atom Transition Metal Catalysts for Methane Activation

Single-atom catalysis is a relatively new concept to enhance catalytic activity of transition metal atoms through proper choice of support. The interest in such systems is due to the fact that both the quantum size effect and support-catalyst interactions may lead to unique electronic structures that may enhance catalytic properties. This allows for the design of materials systems at the atomic scale, tailored for specific reactions. Utilizing this concept, we investigated theoretically free and graphene supported single transition metal (TM) Cr, Mn, Fe, Co, and Cu atoms for activation of methane and identified catalytically active centers through C-H bond cleavage. We employed here dispersion corrected density functional theory taking into account the generalized gradient approximation and exchange correlations. The results indicate that graphene supported TM systems display relatively low activation barriers for both TM-adsorbed and embedded types of graphene supports compared to that of free TM-methane systems. The reaction pathway for graphene-supported systems is characterized by a single spin state thereby eliminating a multi-state reactivity as observed for free TM-methane systems. Our findings show that the interaction of three d-orbitals (d(xz), d(yz) and d(z)2) with methane, their relative position, and occupancy play a key role in governing the catalytic activity of supported TM systems.