Lignin is a renewable source of phenolic precursors for fuels and chemicals. Hydrogenolysis of lignin cleaves the abundant β-O-4 bonds and releases phenolics. However, selective hydrogenolysis of lignin’s β-O-4 bonds is challenging because it requires molecular hydrogen, contributing to the production costs of phenolics. Here we show hydrogenolysis of lignin by Ru/C catalyst without molecular hydrogen. The aliphatic hydroxyl groups (C<sub>a</sub>-OH) in lignin enabled Ru-catalyzed dehydrogenation of internal hydrogen and the formation of reactive keto intermediate, which facilitated the β-O-4 cleavage into phenolic monomers. Furthermore, solvents that had a high donor number (Lewis basicity) enhanced the yield of phenolic monomers, equal to 27.9 wt.% from lignin. These results offer a novel approach for biorefineries to design lignin isolation processes and/or solvent systems to maximize phenolic monomers and to control product selectivity/stability.

Hydrogen-free catalytic hydrogenolysis of lignin into phenolics

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