Integration of plasma and electrocatalysis to synthesize cyclohexanone oxime under ambient conditions using air as a nitrogen source

Abstract

Direct fixation of N₂ to N-containing value-added chemicals is a promising pathway for sustainable chemical manufacturing. There is extensive demand for cyclohexanone oxime because it is the essential feedstock of Nylon 6. Currently, cyclohexanone oxime is synthesized under harsh conditions that consume a considerable amount of energy. Herein, we report a novel approach to synthesize cyclohexanone oxime by in situ NO₃⁻ generation from air under ambient conditions. This process was carried out through an integrated strategy including plasma-assisted air-to-NO_x and co-electrolysis of NO_x and cyclohexanone. A high rate of cyclohexanone oxime formation at 20.1 mg h⁻¹ cm⁻² and a corresponding faradaic efficiency (FE) of 51.4% was achieved over a Cu/TiO₂ catalyst, and the selectivity of cyclohexanone oxime was >99.9% on the basis of cyclohexanone. The C–N bond formation mechanism was examined by in situ experiments and theoretical calculations, which showed that cyclohexanone oxime forms through the reaction between an NH₂OH intermediate and cyclohexanone.