Redox-neutral depolymerization of lignin over heterogeneous Co-NC catalyst

Green and atom-economic depolymerization of lignin remains a great challenge due to its complex non-repetitive structure and the inert property for chemo-digestion. A redox-neutral lignin depolymerization system without the use of extra oxidant and/or reductant over a Co-NC catalyst has been developed in this work, providing the first non-noble metal heterogeneous catalytic system for redox-neutral valorization of lignin. Mechanistic studies based on control reactions and deuterium labeling experiments suggest that the reaction proceeds via a metal-catalyzed dehydrogenation of Cα-OH to afford a carbonyl intermediate, followed by Cβ-O bond cleavage (via hydrogenolysis) to afford monophenols and aromatic ketone products. The hydrogen used for the cleavage of the Cβ-O bond originates from the alcohol moiety in the substrate, and the cascade dehydrogenation and hydrogenolysis steps are highly coupled, rendering it an efficient and atom-economic process.