Heterogeneous catalytic oxidation for lignin valorization into aromatic compounds over acid-redox bifunctional polyoxometalates

Abstract

Lignin, as the largest renewable aromatic resource on the planet, has significant potential for the production of value-added platform chemicals. In this work, we synthesized a series of cesium-exchanged acid-redox bifunctional polyoxometalates (POMs) and evaluated their performance as catalysts for the depolymerization of birch lignin into low molecular weight aromatic compounds. The Cs3H2PMOV2O40 catalyst exhibited the highest activity, resulting in a monomer yield of approximately 13.6 %. Gel permeation chromatography (GPC), heteronuclear single quantum coherence (HSQC) spectroscopy, and gas chromatography-mass spectrometry (GC-MS) analysis confirmed the effective cleavage of β-O-4, β-5, and β-β linkages in the lignin polymer. The proposed reaction mechanism for the lignin depolymerization over cesium-exchanged POMs was also discussed. Our results demonstrate the potential of cesium-exchanged POMs as effective catalysts for the conversion of lignin into value-added chemicals, thereby contributing to the complete sustainable utilization of lignocellulose.