Axial nitrogen-coordination engineering over Fe-N_x active species for enhancing Fenton-like reaction performance

Activating hydrogen peroxide (H₂O₂) to produce hydroxyl radical (^•OH) (Fenton-like process) is of great importance in heterogeneous catalytic oxidations. However, most of transition metal nano-catalysts as well as recently reported carbon supported Fe-N₄ single atom catalysts (SACs) suffer from unsatisfactory catalytic performance. Herein, a novel Fe₁/C₃N₄ SAC with Fe-N₅ active site was constructed. Using this SAC, the electron/structure-symmetry of Fe-N₄ site can be broken by axial nitrogen-coordination, which transforms less active Fe-N₄ species into highly active Fe-N₅ species in Fenton-like reaction. Specifically, Fe-N₅ site exhibits an unprecedented activity for 3,3′,5,5′-tetramethylbenzidine oxidation, which is at least one order of magnitude more active than reported Fe-N₄/C SACs. Mechanism studies reveal that the unique role of axial nitrogen-coordination over Fe-N_x sites is to change the adsorption behavior of H₂O over Fe-N₅ site without influencing H₂O₂ activation. This discovery provides a new approach for rationally designing efficient catalysts in Fenton-like reactions.