Direct electro-synthesis of valuable C=N compound from NO

Abstract

Cyclohexanone oxime (CHO), a key C=N organic compound in the manufacture of nylon 6, is conventionally synthesized via a multistep process that consumes expensive NH3 and H2 under harsh conditions. Herein, we report the direct electro-synthesis of CHO from low-cost NO, H2O, and cyclohexanone over a carbon catalyst under ambient conditions. A high Faradaic efficiency of 44.8% and a formation rate of 10.7 mg cm−2 h−1 for CHO were achieved at −0.4 V versus the reversible hydrogen electrode through optimizing the surface hydrophobicity of the catalyst to facilitate diffusion of reactants. Controlled experiments and 15N-labeling tests verified that the nitrogen in the CHO product originates from NO. Density functional theory calculations showed that the armchair edge of carbon could be the active site with a reaction mechanism following NO → NO∗ → HNO∗ → HNOH∗ → NH2OH → CHO. This work suggests a direct, green, and low-cost synthesis strategy for high-value CHO from pollutant NO.