Depolymerization of corn stover lignin with bulk molybdenum carbide catalysts

Depolymerization of lignin into aromatic compounds in high yield for production of fuels and chemicals is vital to realize an economically competitive biorefinery. In this study, undoped and nickel-doped bulk molybdenum carbides were synthesized and evaluated in reductive depolymerization of lignin model compound and corn stover lignin in the presence of hydrogen. The highest lignin monomer yield of 37.3% was obtained with NiMo2C and ethanol/water solvent. Nickel doping promoted the depolymerization performance of Mo2C, by increasing the number of metallic sites while decreasing that of acidic sites. This change in active site distribution mitigated C-C coupling reactions and coking. Ethanol addition to the water solvent also significantly suppressed C-C coupling. Mixing carbides with zeolites decreased monomer yields, presumably due to excessive repolymerization of reactive intermediates over the acidic zeolite. This work highlights the feasibility of developing effective lignin depolymerization catalysts by fine-tuning the properties of molybdenum carbide catalysts and solvent systems.