Pyrolysis-assisted catalytic hydrogenolysis of lignin in Japanese cedar: Roles of polysaccharides and cell wall structure

Pyrolysis-assisted catalytic hydrogenolysis of milled wood lignin (MWL), MWL-holocellulose blends, and Japanese cedar wood (250-350 °C) was conducted to investigate the roles of polysaccharides and cell wall ultrastructure in aromatic monomer production. β-Ether bonds in lignin were thermally cleaved during pyrolysis, forming coniferyl alcohol (CA), which was then hydrogenated to dihydroconiferyl alcohol (DHCA). Holocellulose addition suppressed catalytic deformylation, demethoxylation, and oligomer-to-monomer conversion. In Japanese cedar wood, recondensation of lignin-derived products occurred within the intact cell wall. Model studies using levoglucosan (LG) showed that polysaccharide-derived compounds inhibited catalytic cleavage of 4-O-5 and α-aryl linkages by competing for Pd/C active sites. Under inert N₂, polysaccharides acted as a hydrogen source, promoting side-chain saturation as well as CC and 4-O-5 bond cleavage. These findings reveal the dual roles of polysaccharides in the catalytic lignin transformation in the cell wall and offer insights for efficient lignocellulosic biorefineries.