Catalytic Hydrogenolysis of Lignin into Phenolics by Internal Hydrogen over Ru Catalyst

Lignin is a by‐product of biorefineries and pulp and paper manufacturers. 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 high‐pressure H2. Here we show efficient hydrogenolysis of lignin model compounds and technical lignin by Ru/C catalyst and internal hydrogen. The aliphatic hydroxyl groups (Cα−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 technical lignin. These findings 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. Phenolics from lignin by internal hydrogen! This study establishes that the aliphatic hydroxyl groups (Cα−OH) in lignin enable release of its internal hydrogen by Ru/C catalyst without external H2 or hydrogen‐donor solvents and facilitate the β‐O‐4 cleavage into phenolics. Hydrogen donor solvents enable Meerwein−Ponndorf−Verley cleavage products and subsequent hydrodeoxygenation into aromatics.