Merging Cu₂O Photo‐Thermo‐Catalyst with Lignosulfonate‐Supported Tempo for Aerobic Oxidation of 5‐Hydroxymethylfurfural into 2,5‐Diformylfuran

The selective oxidation of 5‐hydroxymethylfurfural (HMF) into 2,5‐diformylfuran (DFF) represents a critical step in the sustainable synthesis of high‐value chemicals from renewable biomass. A significant challenge in achieving this transformation lies in developing an effective visible light‐driven heterogeneous photocatalytic method that excludes the use of dye‐based sensitizers. While solar energy presents an exceptionally promising renewable energy source for extensive future applications, its overall utilization remains suboptimal. To address these challenges, we introduce an innovative photo‐thermo‐catalyst system comprising octahedral Cu 2 O particles, which, when combined with lignosulfonate (LS)‐supported 2,2,6,6‐tetramethylpiperidinyloxyl (TEMPO), demonstrates decent catalytic performance for the selective oxidation of HMF into DFF under the illumination of a 400 nm light‐emitting diode light. This system achieves a remarkable 95% DFF yield at 60 °C under ambient oxygen conditions. This study successfully demonstrates the effective integration of a non‐noble metal photo‐thermo‐catalyst with a supported TEMPO system, which enables the efficient HMF‐to‐DFF transformation driven by visible light, eliminating the need for dye sensitizers in the process.