Decarbonizing Chemical Synthesis: Nitrate Electroreduction to Cyclohexanone Oxime on Zn-Cu Alloys
Max García-Melchor a c d, Jonathan Sharp b, Anna Ciotti a, Hayley Andrews b, Shaktiswaran R. Udayasurian b, Tengfei Li b
a School of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin D02 PN40, Ireland
b School of Chemistry and Environment, Manchester Metropolitan University, Chester Street, Manchester, M1 5GD, United Kingdom.
c Center for Cooperative Research on Alternative Energy (CIC EnergiGUNE), Basque Research and Technology Alliance (BRTA), Alava Technology Park, Albert Einstein 48, 01510 Vitoria-Gasteiz, Spain.
d IKERBASQUE, Basque Foundation for Science, Plaza de Euskadi 5, 48009 Bilbao, Spain.
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)
#C&T - electrocat - Computational and theoretical electrocatalysis
Lausanne, Switzerland, 2024 November 12th - 15th
Organizers: Federico Calle-Vallejo and Max Garcia-Melchor
Oral, Max García-Melchor, presentation 409
DOI: https://doi.org/10.29363/nanoge.matsusfall.2024.409
Publication date: 28th August 2024

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.

We are very grateful for the financial support by the RSC Research Fund (R21-3641011632), Science Foundation Ireland Research Centre Award (12/RC/2278_P2), and Manchester Metropolitan University Research Accelerator Grant. We also thank Dr. Gary Miller, Dr. David McKendry, and Dr. Claudio Dos Santos for technical support.

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