Polyoxometalate catalysts for the selective transformation of lignocellulosic biomass: Lignin depolymerization and furan derivative valorization

Efficient utilization of lignocellulosic biomass, which consists of lignin, cellulose, and hemicellulose and is a major renewable resource, is central to green and sustainable chemistry. Polyoxometalates (POMs) have emerged as versatile catalysts for biomass valorization owing to their tunable Brønsted acidity/basicity, redox properties, and unique electron/proton storage capability. This review highlights recent advances in POM-catalyzed lignocellulosic biomass conversion, focusing on lignin depolymerization and the selective conversion of hemicellulose- and cellulose-derived platform compounds, namely furfural (FF) and 5-hydroxymethylfurfural (HMF). We systematically discuss the catalytic roles of different POM families (classical POMs and their cation-modified derivatives, supported POM materials, and structurally novel POM architectures) in lignin depolymerization and examine the selective redox transformations involved in FF and HMF valorization. Moreover, we show how the properties of POM catalysts govern reaction pathways, product selectivity, and reaction mechanisms under thermal, photocatalytic, and electrocatalytic conditions and discuss the challenges and future opportunities for biomass valorization using POM-based catalytic systems.