Ionic liquids enhance the electrocatalysis of lignin model compounds towards generating valuable aromatic molecules

Abstract

The valuable exploitation of lignin depends mainly on the conversion strategy of lignin, of which the conversion of lignin into valuable aromatic molecules is a critical approach. In this study, three lignin model compounds, veratrylglycerol-β-guaiacyl ether (VG), 4-phenoxyphenol (PP), 4-ethoxyphenol (EP), are comparatively degraded by electrochemical oxidation in an aprotic ionic liquid (IL), [Bmim][OTf], and two protic ILs, [PrSO3Hmim][OTf] and [BSO3Hmim][HSO4]. The protic ILs are more favorable for the degradation of lignin-derived substrates compared to aprotic ILs. Oxygen reduction reaction (ORR) in the O2 atmosphere generates reactive oxygen species (ROSs) that play an indirect oxidation effect on substrates, which is stronger for the protic ILs. In addition, the different types of ILs allow modulating the distribution of degradation products. Combined with the identification of products and CV curves, the microscopic mechanisms of the degradation process for lignin model compounds are further elucidated.