Abstract
Pd/NbOPO4 multifunctional catalyst was prepared and used for catalytic hydrotreatment upgrading of bio-oil, which was obtained from low-temperature torrefaction (LTT) of pubescens and contained mainly lignin oligomers. The upgrading temperatures were investigated at 220-280 °C. Pd/NbOPO4 exhibited good performance for the effective depolymerization of oligomers with increasing temperature. It was revealed that both Brönsted acid sites and Lewis acid sites existed on NbO x , which contributed to the cleavage of the C-O-C bond. Furthermore, esterification, hydrogenation, and O-alkylation of monomeric derivatives also occurred simultaneously during the depolymerization process. After hydrotreatment upgrading, the average molecular weight of bio-oil decreased from M w = 320 Da (M n = 298 Da) to M w = 273 Da (M n = 254 Da) and the bio-oil quality was improved dramatically. The oxygen content decreased from 29.53 to 9.78 wt %. The upgraded bio-oil obtained at 280 °C had a heating value of 40.48 MJ kg-1, which was much higher than that of the original bio-oil (26.96 MJ kg-1).