High-Efficiency Dual-Site Biomimetic Catalyst for Lignin Depolymerization

Abstract

Developing biomimetic catalysts with enhanced catalytic efficiency is a promising strategy to address the challenges of lignin depolymerization under mild conditions. In this study, we designed a dual-site biomimetic catalyst, Pd@Ce-PZDC, engineered to emulate the lignin-degrading functions of natural laccase and peroxidase enzymes, thereby facilitated lignin depolymerization. The laccase-like activity of Pd@Ce-PZDC exhibited a catalytic efficiency (V_max/K_m) of 1.3 × 10^–2 min^–1, which is 3.14 times higher than that of natural laccase and 1.62 times greater than that of the single-site bioinspired laccase MOF catalyst Ce-PZDC. Its peroxidase-like activity, assessed with TMB and H₂O₂, is 5.6 and 11.2 times higher, respectively, than that of Ce-PZDC. Density Functional Theory (DFT) calculations indicated a synergistic dual-site effect where Pd NPs activate Ce(IV) within the MOF, imparting it with laccase-like activity akin to Ce(III), thereby increasing the number of active sites and enhancing overall catalytic efficiency. Under mild conditions (60 °C in aqueous solution), Pd@Ce-PZDC demonstrated high efficiency in the oxidative depolymerization of birch lignin, selectively cleaving β-O-4 and β–β linkages. This resulted in a reduction in molecular weight of lignin and produced aromatic monomers (approximately 13.0%), including vanillin, syringaldehyde, and vanillic acid. This dual-site synergistic strategy offers a promising avenue for valorization of lignin and the development of effective catalytic systems for biomass conversion.