Nitrogen-Doped Carbon-Modified Cobalt-Nanoparticle-Catalyzed Oxidative Cleavage of Lignin β-O-4 Model Compounds under Mild Conditions

A noble-metal-free Co-based catalyst, derived from pyrolysis of natural vitamin B12 on activated carbon, is developed for the first time for one-pot oxidative cleavage of lignin linkages to phenols and aromatic esters with molecular oxygen as the oxidant under mild reaction conditions. High yields of phenol were obtained, and no oxidative coupling of phenol was produced based on the present cobalt catalyst. Compared to the previous report, the present catalyst can achieve the oxidative cleavage of β-O-4 ketones even at room temperature using a dioxygen balloon. The heterogeneous catalyst shows robust recyclability and can be conveniently recovered and reused up to eight times without an appreciable loss of catalytic activity. Moreover, this catalyst system can realize the bond cleavage of organosolv lignin. The evidence of depolymerization was given by two-dimensional heteronuclear single quantum coherence NMR and gel permeation chromatography. Characterization of the catalyst by inductively coupled plasm...