Surface Hydroxyl Steered Adsorption Configuration for Efficient Photocatalysis Coupling Hydrogen Evolution and 5-Hydroxymethylfurfural Selective Oxidation Toward 2,5-Furandicarboxylic Acid Production

Photocatalytic coupling water reduction reaction and 5-hydroxymethylfurfural (HMF) selective oxidation toward 2,5-furandicarboxylic acid (FDCA) offers a promising route for co-production of green hydrogen and value-added bio-based platform chemicals, but limited by low FDCA selectivity and yield. Herein, an Al-doped SrTiO₃ (STO) photocatalyst integrated with RhCrO_x and Co₃O₄ cocatalysts is investigated for HMF oxidation reaction (HMFOR) under neutral and alkaline conditions. While alkaline conditions markedly improve the FDCA production, the accelerated HMF self-degradation and competing Cannizzaro side-reaction compromise the hole utilization efficiency. Spectral and theoretical investigations reveal that surface-bonded hydroxyl (─OH) species on Co₃O₄ under alkaline conditions steer HMF adsorption from vertical to a tilted configuration, which facilitates the rate-determining step of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) to 5-formyl-2-furancarboxylic acid (FFCA) conversion. Building upon this mechanistic insight, Co₃O₄ is substituted with a ─OH terminated Co(OH)₂ oxidation cocatalyst, which sustains the favorable flat HMF adsorption configuration even under neutral and oxygen-free conditions. The obtained RhCrO_x/STO/Co(OH)₂ achieves a FDCA selectivity of 72.7% and a yield of 49.0% for HMFOR, together with hydrogen evolution rate of 626 µmol g⁻¹ h⁻¹. This study demonstrates that steering reactant adsorption configuration via surface ─OH species offers an effective strategy for efficient solar-driven photocatalysis coupling biomass valorization and hydrogen production.