Enhanced Electrosynthesis of Valuable C═N Compounds through Nitrite Reduction via Mesoporous Carbon Supporting Highly Accessible FeN x Sites

Electrocatalytic C–N reductive coupling provides a promising alternative for wastewater remediation and the sustainable synthesis of cyclohexanone oxime (CHO), a key C═N compound for manufacturing nylon-6. However, it still suffers from low selectivity and Faraday efficiency (FE) due to the reactive intermediates (*NOH, *NHOH, *NH 2 OH) involved in nitrogen source (e.g., NO x –, NO x ) reduction, which preferably convert to NH 3 rather than react with cyclohexanone. Based on the favorable properties of single-atom sites for *NH 2 OH generation and the moderate adsorption of NH 2 OH on the Fe surface, herein, we prepared an Fe-SAC-MIL-101 catalyst enriched with accessible FeN x monatomic sites by the pyrolysis of NH 2 -MIL-101(Al), adsorption of the Fe(II)-phenanthroline complex, and secondary annealing. Since a high utilization of FeN x sites was achieved for NO 2 – reduction to selectively generate *NH 2 OH, in CHO electrosynthesis from NO 2 – and cyclohexanone, almost 100% yield and 51.5% FE for CHO were realized at −0.9 V vs Ag/AgCl in H-type cell, with a yield rate of 8.53 g h –1 g cat –1 and a TOF of 0.15 s –1 . Both yield (78.8%) and FE (40.6%) were also attained even when the NO 2 – concentration was decreased to 93 mM. The promotion of exposed FeN x active sites in electrocatalysis performance was demonstrated by a series of electrochemical tests. In situ spectroscopic characterizations also evidenced the selective generation of *NH 2 OH for cyclohexanone oximation. This work provides a feasible catalyst modification method for promoting *NH 2 OH generation to facilitate CHO electrosynthesis from nitrogen-containing wastes.