Efficient depolymerization of alkali lignin to monophenols using one-step synthesized Cu–Ni bimetallic catalysts inlaid in homologous biochar

Abstract

The efficient depolymerization of lignin for the production of high-value chemicals is essential for the development of a sustainable and competitive biorefinery. In this study, we report the preparation of homologous biochar-supported inlaid Cu–Ni catalysts (CuxNiy/BC) using a one-step method, and their application for lignin depolymerization in mild water without the need for external hydrogen, additives, or co-catalysts. The Cu1Ni3/BC (0.05 g catalyst, 8 h, 280 °C, and 18 mL water) showed exceptional catalytic activity, with a monophenol yield of 94.35 ± 2.92 mg/g, bio-oil yield of 68.98 ± 1.42%, and a lignin conversion rate of 92.36 ± 1.99%, which outperformed both the biochar support and monometallic catalysts. The outstanding catalytic performance of Cu1Ni3/BC was attributed to its strong metal-support interaction, alloy sites, and well-dispersed nanoparticles. Reusability experiments demonstrated that the Cu1Ni3/BC exhibited relatively good stability for up to four reuses, with only a 2.32% reduction in catalytic activity per cycle. Mechanism investigation revealed that the Cu1Ni3/BC, with its abundant mesoporous structure and enhanced acid sites, displayed excellent deoxygenation ability, enabling effective cleavage of C–O/C–C bonds and the production of G-type phenols. This approach provides new insights into the large-scale utilization of lignin for the production of high-value chemicals.