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 C_Ar−OCH₃ of lignin. All these contribute to the macromolecular depolymerization and demethoxylation reaction, producing high value-added compounds such as phenol.