Depolymerization of Kraft lignin to liquid fuels with MoS2 derived oxygen-vacancy-enriched MoO3 in a hydrogen-donor solvent system

Depolymerization of Kraft lignin represents an attractive strategy to obtain alternatives to fossil fuels. In this work, via the controlled oxidation of MoS2 precursor, an oxygen-vacancy-enriched MoO3 was synthesized and employed to catalyze the depolymerization of Kraft lignin in a new solvent system without external H2 gas. Systematic characterizations exemplified that the calcination temperature significantly affected the morphology and concentration of oxygen vacancy of prepared MoO3, and the appropriate temperature in this work was proved to be 350 °C. In the optimized hydrogen-donor solvent system that contained 20 mL 1, 4-dioxane, 20 mL isopropanol and 5 mL methanol, MoO3-350 catalyst gave a 87 wt% yield of petroleum ether soluble products, and the higher heating value (HHV) of liquid fuels (33.4 MJ/kg) was dramatically increased compared with the original Kraft lignin (25.23 MJ/kg). Methanol and isopropanol were analyzed to be capable of promoting the solubility of Kraft lignin and supplying hydrogen in the reaction system, respectively. Underpinned by characterizations and products analysis, the schematic representation of possible reaction pathway was given.