Decarbonizing Chemical Synthesis: Nitrate Electroreduction to Cyclohexanone Oxime on Zn-Cu Alloys

García-Melchor, Max, Sharp, Jonathan, Ciotti, Anna, Andrews, Hayley, Udayasurian, Shaktiswaran R and Li, Tengfei ORCID: https://orcid.org/0000-0002-8378-7130 (2024) Decarbonizing Chemical Synthesis: Nitrate Electroreduction to Cyclohexanone Oxime on Zn-Cu Alloys. In: Materials for Sustainable Development Conference (MATSUS) Fall 2024 Conference (MATSUSFall24), 12th November 2024 - 15th November 2024, Lausanne, Switzerland.

File not available for download.

Abstract

A key strategy for decarbonising our economy is electrifying industrial syntheses using 'power-to-X' technologies.[1,2] These methods, marrying electrocatalysis with renewable energy sources such as solar or wind power, show great promise for generating platform chemicals and high-value products. For instance, the increasing demand for Nylon-6 has intensified the need for greener routes to synthesize cyclohexanone oxime, a precursor to this polymer. Current methods rely on hydroxylamine derived from environmentally demanding processes, often involving harsh conditions, acidic or alkaline environments, and hazardous reagents. To address these issues, we developed a novel one-pot electrochemical synthesis of cyclohexanone oxime using aqueous nitrate as the nitrogen source under ambient conditions.[3] Our approach utilizes Zn-Cu alloy catalysts to drive nitrate electroreduction, forming a hydroxylamine (*NH₂OH) intermediate that subsequently reacts with cyclohexanone in the electrolyte to yield the oxime. Optimal performance was achieved with a Zn93Cu7alloy, which reached a 97% yield and a 27% Faradaic efficiency at 100 mA/cm². Mechanistic insights from in situ Raman spectroscopy and density functional theory (DFT) calculations highlighted the importance of binding strength of key reaction intermediates in controlling product selectivity within the electrochemical-chemical (EChem-Chem) tandem process. Specifically, weak surface adsorption (e.g., pure Zn) requires higher potentials for the EChem step, whereas stronger binding (e.g., pure Cu) facilitates this process at lower potentials but leads to the complete reduction of *NH2OH to NH3 rather than oxime formation. This presentation will focus on our computational DFT studies, which provided detailed insights into the resting states of the electrocatalysts, the reaction mechanisms, and how surface interactions dictate catalytic activity and selectivity. Overall, this work introduces a sustainable pathway for organonitrogen synthesis via electrochemical nitrate reduction, demonstrating how tuning surface properties enables selective production. These findings are expected to inspire novel approaches for nitrate utilization and the development of other EChem-Chem processes for environmentally friendly organic synthesis.