Comprehensive mechanism and microkinetic model-driven rational screening of 4N-modulated single-atom catalysts for selective oxidation of benzene to phenol

Abstract

Exploring effective transition metal single-atom catalysts for selective oxidation of benzene to phenol is still a great challenge due to the lack of a comprehensive mechanism and mechanism-driven approach. Here, robust 4N-coordinated transition metal single atom catalysts embedded within graphene (TM₁-N₄/C) are systematically screened by density functional theory and microkinetic modeling approach to assess their selectivity and activity in benzene oxidation reaction. Our findings indicate that the single metal atom triggers the dissociation of H₂O₂ to form an active oxygen species (O*). The lone-electronic pair character of O* activates the benzene C-H bond by constructing C-O bond with C atom of benzene, promoting the formation of phenol products. In addition, after benzene captures O* to form phenol, the positively charged bare single metal atom activates the phenol O-H bond by electron interaction with the O atom in the phenol, inducing the generation of benzoquinone by-products. The activation process of O-H bond is accompanied by H atom falling onto the carrier. On this basis, it can be inferred that adsorption energy of the C atom on the O* atom (E_C) and the H atom on the TM₁-N₄/C (E_H), which respectively represent activation ability of benzene C-H bond and phenol O-H bond, could be labeled as descriptors describing catalytic activity and selectivity. Moreover, based on the as-obtained volcano map, appropriate E_C (−8 to −7 eV) and weakened E_H (−1.5 to 0 eV) contribute to the optimization of catalytic performance for benzene oxidation to phenol. This study offers profound opinions on the rational design of metal single-atom catalysts that exhibit favorable catalytic behaviors in hydrocarbon oxidation.