Catalytic depolymerization of lignin for hydrocarbon rich bio-oil production: Influence of Ni doped on LaCoO3 catalysts and hydrogen sources

Abstract

The catalytic properties of metals and metal oxides are vital for lignin depolymerization into phenolic and cyclohexane compounds production. This study investigated the lignin depolymerization of with different Ni content LaCoO₃ perovskite catalysts at different reaction conditions such as reaction temperature, time, catalysts amount. Furthermore, various hydrogen sources, including formic acid, ethanol, and pure hydrogen were tested. The highest bio-oil yield (75.3 wt%) was achieved with hydrogen under ethanol solvent, but selectivity for cyclohexane and phenolic monomers compound was low. Using formic acid (FA) with 7 % Ni-LaCoO₃ catalysts at 280 °C, a bio-oil yield of 72.4 wt% was obtained, with higher selectivity for 2,6-dimethoxyphenol (19.5 %), cyclohexane (18.5 %), and methylcyclohexane (14.2 %). This suggests that Ni with presence of FA facilitates the cleavage of lignin's β-O (C-O) and β-β (C-C) bonds efficiently. The reaction using FA, resulted in the lowest O/C ratio (0.06), highest H/C ratio (0.14), and the highest HHV (36.6 MJ/kg). The catalyst exhibited the highest reaction rate and hydrogenation activity, attributed to the presence of highly dispersed surface Co and Ni species. Notably, after three recycling test, the Ni-LaCoO₃ catalyst maintained very good catalytic activity. These results suggest that catalysts with this composite support have the potential to convert lignin-derived phenolic compounds into higher-grade hydrocarbon liquid fuels.