Laccase-Inspired Cu–POM Catalysts with Support-Regulated Interfaces for Oxidative Depolymerization of Lignin

Abstract

Lignin is the only abundant renewable aromatic polymer in nature and is therefore an important feedstock for the sustainable production of aromatic chemicals and functional materials. Its selective depolymerization, however, remains difficult because of the structural heterogeneity of lignin and the coexistence of multiple C–O and C–C interunit linkages. In this work, a series of Cu-substituted polyoxometalate catalysts were developed based on a laccase-inspired design concept, in which redox–active Cu sites, oxygen-rich inorganic clusters, and support-regulated interfacial electron transfer were integrated into a heterogeneous oxidation system. Single–walled carbon nanotubes (SWCNT), UiO–66, and MCM–41 were used as supports, and their effects on catalyst structure, oxygen activation, reactive oxygen species generation, and lignin depolymerization performance were systematically compared. The results showed that the Keggin structure of CuPOM was retained after immobilization on all three supports, while CuPOM@SWCNT displayed the most uniform dispersion and the strongest interfacial coupling. NH3–TPD, N2 adsorption–desorption, and EPR analyses further showed that SWCNT provided a more favorable catalytic interface for O2 activation and the generation of 1O2, ·O2–, and ·OH. Using veratryl glycerol β–guaiacyl ether as a lignin model compound, CuPOM@SWCNT gave the best performance, affording a total target monomer yield of 40.65% under the optimized conditions. When applied to real lignin, 2D HSQC NMR showed a marked decrease in β–O–4 related side–chain linkages, while the aromatic framework was largely retained. The catalyst also maintained good structural stability and appreciable activity over five consecutive cycles. These results show that combining a laccase-inspired catalyst design with support engineering is an effective way to regulate interfacial electron transfer, O2 activation, and selective lignin depolymerization, and provides a useful basis for the development of biomimetic oxidation catalysts for lignin valorization.