Rhombohedral ZnIn2S4-catalysed anodic direct electrochemical oxidative cleavage of C–O bond in α-O-4 linkages in ambient conditions

Qi Zhu; Bo Gong; Shuquan Huang; Yangxin Jin; Shengqin Liu; Shan Shao; Yuwei Yang; Taren Cataldo; Nicholas M. Bedford; Jason Chun-Ho Lam

doi:10.1039/D4GC00338A

Rhombohedral ZnIn₂S₄-catalysed anodic direct electrochemical oxidative cleavage of C–O bond in α-O-4 linkages in ambient conditions†

Qi Zhu,^a Bo Gong,^a Shuquan Huang,^ac Yangxin Jin,^a Shengqin Liu,^a Shan Shao,^a Yuwei Yang,^d Taren Cataldo,

^d Nicholas M. Bedford

^d and Jason Chun-Ho Lam

*^ab

Author affiliations

* Corresponding authors

^a School of Energy and Environment, City University of Hong Kong, Kowloon Tong, Hong Kong SAR
E-mail: jason.lam@cityu.edu.hk

^b State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon Tong, Hong Kong SAR

^c Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming, PR China

^d School of Chemical Engineering, University of New South Wales, Sydney, NSW 2052, Australia

Abstract

The electrochemical selective oxidative transformation of lignin feedstocks into valuable oxygenated aromatics is essential to establish a sustainable biorefinery. In this study, we used a rhombohedral ZnIn₂S₄ (R-ZIS) electrocatalyst to realise the efficient anodic cleavage of C–O bonds in benzyl phenyl ether (BPE), an α-O-4 lignin model compound, to a series of industrially relevant oxygenated mono-aromatics. The reaction occurred at +2 V_Ag/AgCl, 65 °C, and atmospheric pressure. In optimised conditions, the reaction achieved over 99% conversion rate with a Faraday efficiency of 51.6% at 91.3% conversion of BPE, that is greater than most known electrocatalytic oxidative cleavage examples. The ZnIn₂S₄ electrocatalyst was deposited on a carbon cloth support, and its structural properties and surface morphology were extensively investigated. Systematic potential controlled electrolysis coupled with ¹⁸O isotopic labelling confirmed that C–O scission occurred exclusively between the benzylic carbon and phenolic oxygen. Furthermore, substrate competition studies were conducted to compare the electrocatalytic performance of the R-ZIS catalyst with that of its structural analogue, hexagonal ZnIn₂S₄, in terms of BPE and mono-aromatics conversion. The experimental results were supported by density functional theory calculations. The substrate scoping study revealed the suitability of the R-ZIS induced electrocatalytic system for a variety of substituted α-O-4/β-O-4 model dimers. Overall, this work demonstrates an efficient anodic process that can enable the atom-efficient valorisation of lignin to produce oxygenated aromatics. The proposed approach can complement the numerous existing reductive lignin cleavage methods.

This article is part of the themed collection: Advances in Electrosynthesis for a Greener Chemical Industry

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Rhombohedral ZnIn₂S₄-catalysed anodic direct electrochemical oxidative cleavage of C–O bond in α-O-4 linkages in ambient conditions†

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Rhombohedral ZnIn₂S₄-catalysed anodic direct electrochemical oxidative cleavage of C–O bond in α-O-4 linkages in ambient conditions

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