Hydrothermal liquefaction of lignin to aromatics over the perovskite catalysts

The catalytic performance of three LaBO3 perovskites including LaCoO3, LaFeO3 and LaNiO3 in the liquefaction of lignin was investigate through a series of experimental characterization methods such as GC-MS, FT-IR and elemental analysis as well as DFT calculation. The effects of reaction time, temperature, catalyst amount and B cation on the lignin conversion, bio-oil yield and products distribution were considered. The results indicate that all three perovskite catalysts can promote the liquefaction of lignin to produce aromatic compounds; among them, LaCoO3 shows the highest catalytic performance, following by LaNiO3 and LaFeO3. In particular, by using 5% LaCoO3, the bio-oil yield achieves 67.20% after reaction at 180 °C for 60 min, whilst the relative content of mono-aromatic compounds reaches 89.59%. The adsorption of oxygen atoms on the LaBO3 crystal surface conduces to the decrease of bond dissociation energy for lignin (LaCoO3 shows the moderate redox capacity and greatest adsorption energy), whilst the loose and porous morphology can effectively promote the fracture of C−C and CAr−OCH3 of lignin. All these contribute to the macromolecular depolymerization and demethoxylation reaction, producing high value-added compounds such as phenol.