Pyrolysis-assisted catalytic conversion of wood in hot-compressed water for the production of aromatic monomers and syngas without external hydrogen addition

Abstract

Efficient conversion of lignocellulosic biomass into value-added chemicals is essential for sustainable chemistry. Japanese cedar and Japanese beech were treated in hot-compressed water (300–450 °C) with Pd/C, yielding aromatic monomers and syngas without external hydrogen. Polysaccharides were hydrolyzed to monosaccharides, fragmented to syngas, and provided hydrogen via the water-gas-shift reaction. This in situ hydrogen stabilized lignin-derived aromatic monomers through hydrogenation of aliphatic C_αC_β bonds, preventing repolymerization and enabling bond cleavage for high yields. At lower temperatures, guaiacols and syringols dominated, with Japanese beech producing a more complex mixture. Above 400 °C, both woods yielded primarily catechols and phenols, and species-specific differences disappeared. At 450 °C, however, hydrogenation of aromatic rings occurred as a side reaction, reducing selectivity. Water-soluble intermediates from polysaccharides temporarily suppressed catalyst activity but were gasified to restore efficiency. These results highlight a promising biomass-based route to aromatic monomers and syngas as sustainable alternatives to petroleum-derived processes.