Defective Graphene-Supported Diatomic Catalysts for Dry Reforming of Methane: A DFT Study on High Performance and Anti-Coking

Dry reforming of methane (DRM) converts greenhouse gases CH₄ and CO₂ into industrially valuable syngas. Using density functional theory (DFT), we evaluated the DRM catalytic performance of ten diatomic TM1-TM2 combinations (TM1, TM2 = Fe, Co, Ni, Cu) supported on double-vacancy defective graphene (DG). CoCo@DG, FeCo@DG, and CoNi@DG show markedly lower activation barriers for key steps than Pt₄ cluster-doped single-vacancy graphene (Pt₄/SV): CH* → CO* conversion (<1.61 eV), CO₂ dissociation (<1.82 eV), and coke elimination (<1.51 eV), the latter being only half that of its formation. This demonstrates their superior intrinsic activity. Pathway analysis reveals that CoCo@DG and CoNi@DG, which follow the same dominant pathway (where CH* reacts with surface O* via CHO* to form CO*), exhibit the lowest overall barriers, identifying them as the most promising non-precious candidates. Most importantly, the activation barrier for the rate-determining step (RDS) on CoCo@DG — CH₂* + * → CH* + H*—is 1.26 eV, which is substantially lower than the RDS barrier on Pt₄/SV (1.61 eV), thereby corroborating its superior catalytic activity. The activity origin is rationalized via projected density of states (PDOS), differential charge density, and Hirshfeld charge distribution analyses. This work theoretically supports the rational design of high-performance diatomic DRM catalysts.