Low temperature catalytic conversion of oligomers derived from lignin in pubescens on Pd/NbOPO4

Abstract

Two-step conversion of pubescens to aromatic monomers and small molecular weight oligomers (mainly dimers and trimers) was studied. Lignin-derived oligomers (LDO) were obtained by formic acid assisted solvo-thermal conversion of pubescens in the H2O-ethanol system at 160 ℃. In the second step, hydrogenolysis of LDO on Pd/NbOPO4 catalyst was carried out over the temperature range of 60–120 ℃. Pd/NbOPO4 showed acceptable catalytic performance for efficient degradation of oligomers at low temperature. The NbOx species on the catalyst facilitated the breakage of COC bonds to depolymerize the oligomers toward small molecules, while Pd species accelerated the selective hydrogenation of side chain and furans. The esterification of S (Syringol) unit phenols took place simultaneously with the depolymerization of LDO. The hydrogenated mixture at 100 ℃ and reaction time of 20 h had an average molecular weight of 908 g/mol, and the yield of aromatic monomers was 22.4 wt.% based on lignin contained.