Insights into reductive catalytic deconstruction of lignin over ultralow-loading palladium-zinc catalysts derived from zinc imidazolate frameworks

Abstract

The development of high-performance noble metal catalysts at the atomic scale for the selective chemical catalysis of lignin conversion into monophenolic compounds is highly desirable but remains a challenge. Herein, we report a single-atom strategy to fabricate highly active and stable hydrogenolysis catalyst containing ultra-low Pd content (0.1 wt%) through using cobalt and zinc imidazolate frameworks as precursors. The resultant Pd-Zn@NC catalyst exhibits outstanding activity in the reductive catalytic deconstruction of lignin into aromatic compounds. The catalyst affords a phenolic monomer yield up to 49.6 wt%, which is superior to commercial Pd/C, and a selectivity of more than 90% for unsaturated propylene-based monomers. The mechanism studies using β-O-4' mimics reveal that the highly dispersion of Zn contributes to the dissociation of hydroxyl groups, while the atomically dispersed Pd further significantly enhances the hydrogenation performance. The synergistic interactions between Pd and Zn active sites activate the C−O bonds, thereby enhancing reductive aryl-ether scission in lignin.