A metal-free, carbon-based catalytic system for the oxidation of lignin model compounds and lignin

<p>Nitrogen-containing graphene material (LCN) has been identifiedas an effective catalyst for the oxidation of b-O-4 and a-O-4 types of lignin model compounds in the presence of tertbutylhydroperoxide, to provide aromatic aldehydes, acids andother organic chemicals in high yield. The transformations offive lignin model compounds over LCN were investigated systematically.Instrumentation analysis, kinetic study and radicaltrapping experiments highlight the mechanistic features of thereaction, including: 1) the reaction pathway starts by benzylicCH or COH bond activation, followed by CaCb or CaObond cleavage, and finally further oxidation of intermediate aromatics;and 2) the reaction follows a free-radical mechanismwith all the key steps involving radical species. In addition, theLCN proved to be a highly stable catalyst; no significant activitydecrease was observed for four consecutive runs, and X-rayphotoelectron spectroscopy analysis indicates negligible decreasein the content of the active nitrogen species in the catalyst.Notably, this new catalytic system can be extended to theoxidative depolymerisation of real lignin, to produce a significantportion of liquefied, low-molecular-mass products.</p>