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

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 degrees C. In the second step, hydrogenolysis of LDO on Pd/NbOPO4 catalyst was carried out over the temperature range of 60-120 degrees C. Pd/NbOPO4 showed acceptable catalytic performance for efficient degradation of oligomers at low temperature. The NbOx species on the catalyst facilitated the breakage of C-O-C 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 degrees C 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.