A Metal‐Free, Carbon‐Based Catalytic System for the Oxidation of Lignin Model Compounds and Lignin

Abstract

AbstractNitrogen‐containing graphene material (LCN) has been identified as an effective catalyst for the oxidation of β‐O‐4 and α‐O‐4 types of lignin model compounds in the presence of tert‐butyl hydroperoxide, to provide aromatic aldehydes, acids and other organic chemicals in high yield. The transformations of five lignin model compounds over LCN were investigated systematically. Instrumentation analysis, kinetic study and radical trapping experiments highlight the mechanistic features of the reaction, including: 1) the reaction pathway starts by benzylic CH or COH bond activation, followed by CαCβ or CαO bond cleavage, and finally further oxidation of intermediate aromatics; and 2) the reaction follows a free‐radical mechanism with all the key steps involving radical species. In addition, the LCN proved to be a highly stable catalyst; no significant activity decrease was observed for four consecutive runs, and X‐ray photoelectron spectroscopy analysis indicates negligible decrease in the content of the active nitrogen species in the catalyst. Notably, this new catalytic system can be extended to the oxidative depolymerisation of real lignin, to produce a significant portion of liquefied, low‐molecular‐mass products.