Sustainable electrosynthesis of cyclohexanone oxime through nitrate reduction on a Zn-Cu alloy catalyst

Sharp, Jonathan, Ciotti, Anna, Andrews, Hayley, Udayasurian, Shaktiswaran R, García-Melchor, Max ORCID: https://orcid.org/0000-0003-1348-4692 and Li, Tengfei ORCID: https://orcid.org/0000-0002-8378-7130 (2024) Sustainable electrosynthesis of cyclohexanone oxime through nitrate reduction on a Zn-Cu alloy catalyst. ACS Catalysis, 14 (5). pp. 3287-3297. ISSN 2155-5435

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Abstract

Cyclohexanone oxime is an important precursor for Nylon-6 and is typically synthesized via the nucleophilic addition-elimination of hydroxylamine with cyclohexanone. Current technologies for hydroxylamine production are, however, not environment-friendly due to the requirement of harsh reaction conditions. Here, we report an electrochemical method for the one-pot synthesis of cyclohexanone oxime under ambient conditions with aqueous nitrate as the nitrogen source. A series of Zn-Cu alloy catalysts are developed to drive the electrochemical reduction of nitrate, where the hydroxylamine intermediate formed in the electroreduction process can undergo a chemical reaction with the cyclohexanone present in the electrolyte to produce the corresponding oxime. The best performance is achieved on a Zn93Cu7 electrocatalyst with a 97% yield and a 27% Faradaic efficiency for cyclohexanone oxime at 100 mA/cm2. By analyzing the catalytic activities/selectivities of the different Zn-Cu alloys and conducting in-depth mechanistic studies via in situ Raman spectroscopy and theoretical calculations, we demonstrate that the adsorption of nitrogen species plays a central role in catalytic performance. Overall, this work provides an attractive strategy to build the C-N bond in oxime and drive organic synthesis through electrochemical nitrate reduction, while highlighting the importance of controlling surface adsorption for product selectivity in electrosynthesis.