Synergistic C─N Coupling for Efficient Cyclohexanone Oxime Synthesis from Ambient Air by Supported Molecular Catalysts

Electrocatalytic synthesis of cyclohexanone oxime from rich nitrogen resources is a promising alternative to traditional industrial processes. However, the difficulties in unraveling atomic-scale catalytic mechanisms and managing selective C─N coupling still pose great challenges to realizing considerable yield and selectivity, and therefore rational catalyst design to boost collaborative C─N coupling for oxime synthesis is particularly attractive. In the present work, molecular catalysts are demonstrated to be unique for oxime synthesis under mild conditions, i.e., iron bis(pyridyl)amine-bipyridine (FeBPAbipyH) modified MWCNTs@CP (multi-walled carbon nanotubes coated carbon fiber paper) cathodes produced cyclohexanone oxime from NO₂ ^- and cyclohexanone, attaining mass-specific efficiency of 87.00 mg h^-1 cm^-2 mg_cat ^-1, Faradaic efficiency (FE) of 77.3%, and exclusive carbon selectivity, which is the best efficiency known to date in H-cell. Mechanistic studies showed that the FeBPAbipyH molecular skeleton exhibited intimate interaction with both cyclohexanone and NO₂ ^-, and catalyzed selective NO₂ ^--to-NH₂OH reduction for C─N bond in situ. The in-depth understanding of substrate-catalyst interactions and synergic C─N coupling from molecular points of view offers valuable insights to boost collaborative synthesis of organic nitrogen compounds. Further integrating plasma-driven N₂ oxidation and electrocatalysis enabled cyclohexanone oxime formation at 61.73 mg h^-1 cm^-2mg_cat ^-1 on the FeBPAbipyH/MWCNTs@CP electrode, and the whole synthetic and separation process is projected to be profitable with a promising cost of $2709 ton^-1, which is much lower than the breakeven point (∼$10 000 ton^-1), representing a sustainable pathway to nitrogenous chemical synthesis from abundant resources under ambient conditions.