Oxidative Depolymerization of Lignin to Aromatic Monomers Catalyzed by MgFe2O4 Under Alkaline Conditions

Lignin, a crucial natural aromatic polymer, presents a pivotal challenge in achieving high-value utilization of biomass through depolymerization into aromatic compounds. To address the limitations of conventional lignin depolymerization processes, including harsh reaction conditions, poor catalyst recovery, and low product selectivity, this study establishes a green oxidative system based on the synergistic interaction between the magnetically separable spinel-structured MgFe 2 O 4 and hydrogen peroxide (H 2 O 2 ), systematically investigating its catalytic performance for enzymatic hydrolysis lignin (EHL) depolymerization. The MgFe 2 O 4 was synthesized via a solvothermal method, demonstrating excellent catalytic activity. Under optimized reaction conditions (10% H 2 O 2 , 0.075 g catalyst, 80°C, 4 h), the lignin oil yield reached 51.30%, with significantly enhanced aromatic monomer selectivity of 134.2 mg/g. Moreover, the products exhibited a notable reduction in molecular weight along with increased phenolic hydroxyl and carboxyl group contents. Based on the Fenton-like mechanism involving the dynamic Fe 3+ /Fe 2+ redox cycle, a regulation pathway of reactive oxygen species was proposed. Additionally, the catalyst exhibited exceptional stability with 88.9% retention of initial activity after four magnetic separation cycles. This work proposes a green catalytic strategy integrating high activity, selectivity, and recyclability for efficient lignin depolymerization, providing critical insights for advancing biomass refining technologies. Graphical This work presents a sustainable MgFe 2 O 4 /H 2 O 2 catalytic system for lignin valorization. The magnetically recoverable MgFe 2 O 4 enables efficient oxidative depolymerization of enzymatic hydrolysis lignin (EHL) under mild conditions, achieving 134.2 mg/g aromatic monomers. A Fenton-like mechanism drives selective β-O-4 bond cleavage, while catalyst stability (> 88% activity after four cycles) highlights its potential for green biorefineries.