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

Lignocellulosic biomass, consisting of lignin, cellulose, and hemicellulose, represents a major renewable resource, and its efficient utilization 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 provides a comprehensive overview of recent advances in POM-catalyzed lignocellulosic biomass conversion, with particular emphasis on lignin depolymerization and the selective conversion of hemicellulose- and cellulose-derived platform molecules, namely furfural (FF) and 5-hydroxymethylfurfural (HMF). For lignin depolymerization, the catalytic roles of different POM families are systematically discussed. For the valorization of FF and HMF, particular attention is devoted to their selective oxidative and reductive transformations. This review encompasses a broad range of POM catalysts, including classical POMs and their cation-modified derivatives, supported POM materials, and structurally novel POM architectures, and highlights how their intrinsic properties govern reaction pathways, product selectivity, and reaction mechanisms under thermal, photocatalytic, and electrocatalytic conditions. Finally, current challenges and future opportunities for biomass valorization using POM-based catalytic systems are discussed.