Understanding the Direct Methane Conversion to Oxygenates on Graphene-Supported Single 3d Metal Atom Catalysts

Direct methane conversion to value-added oxygenate products is an important approach for the effective utilization of CH4. However, selective C─H bond activation of CH4 remains challenging. Herein, we investigated the methane-to-methanol conversion mechanism on MN4-embedded graphene (M = V, Mn, Cr, Fe, Co, Ni, and Cu) via density functional theory computations. We found that the Cu@N4graphene and Ni@N4graphene catalysts showed an outstanding C─H bond activation with low barrier energy of 0.45 and 0.28 eV, respectively. In addition, a detailed investigation of the electronic proprieties of the metal site, the CH3 intermediate adsorption energy and C─H bond cleavage barrier energy demonstrates that the d-band center of metal can be a descriptor for C─H bond cleavage activity and reveal a thermodynamic-kinetic relationship: thus, the high affinity to CH3 intermediate led to facile activation of C─H bond. Overall, this work provides a better understanding of graphene-supported single metal atom activity and selectivity toward methane oxidation, facilitating the design and fabrication of new 2D materials supported by single-atom catalysts for selective methane conversion.