Synergistic magnetic Cu-Fe catalysts on N-doped biochar for efficient alkali lignin catalytic depolymerization into monophenols

Abstract

Alkali lignin, a major by-product of papermaking, poses disposal challenges, hindering the full valorization of lignocellulose in sustainable biorefineries. One-pot lignin catalytic depolymerization (LDP) in water offers a promising route for producing valuable phenolic compounds. This study reports the successful synthesis of in-situ N-doped biochar supported Cu_xFe_y catalysts (Cu_xFe_y/N-BC) via a one-step carbothermal reduction method, enabling LDP in water without the need for external hydrogen, additives, alcohol solvent, or co-catalysts. Notably, the Cu₅Fe₁/N-BC could achieve remarkable catalytic performance under mild reaction conditions (280 °C, 6 h, 18 mL water), yielding 80.84±2.23 mg/g of monophenol, 56.17±1.32 % of bio-oil, and a lignin conversion rate of 80.66±0.73 %. This significantly surpassed the performance of monometallic catalysts and bare biochar. The synergistic effects of intermetallic interactions and nitrogen doping were proposed to create abundant active sites and rich pore structures, promoting efficient LDP reactions. Furthermore, the Cu₅Fe₁/N-BC exhibited excellent recyclability, with minimal activity loss (2.79 %) per cycle, due to its strong magnetism and favorable interactions. Mechanism investigation revealed that the Cu₅Fe₁/N-BC efficiently cleaved the C-O and C-C bonds in lignin, and led to the targeted production of guaiacyl phenols. This study provides valuable insights and practical strategy for valorizing lignin into valuable chemicals, advancing its utilization in various applications.