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

Development of axial nitrogen-coordination engineering strategy Regulation of single-atom catalyst coordination environment Fenton-like reaction performance enhancement Structure-performance relationship establishment • Axial coordination regulation strategy of single-atom catalyst is developed. • Intrinsic catalytic activities of Fe-N x single-atom sites are identified. • Axial N-coordination enhances Fenton-like reaction performance over Fe-N 5 species. • Role of axial N-coordination for weakening H 2 O adsorption is revealed. Activating hydrogen peroxide (H 2 O 2 ) 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-N 4 single atom catalysts (SACs) suffer from unsatisfactory catalytic performance. Herein, a novel Fe 1 /C 3 N 4 SAC with Fe-N 5 active site was constructed. Using this SAC, the electron/structure-symmetry of Fe-N 4 site can be broken by axial nitrogen-coordination, which transforms less active Fe-N 4 species into highly active Fe-N 5 species in Fenton-like reaction. Specifically, Fe-N 5 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-N 4 /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 H 2 O over Fe-N 5 site without influencing H 2 O 2 activation. This discovery provides a new approach for rationally designing efficient catalysts in Fenton-like reactions.