Cr-Promoted Pt@Fe_2–<i>x</i>Cr_<i>x</i>O₃ Hematite-Type Catalysts for Efficient Base-Free HMF Oxidation under Mild Conditions

The catalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) offers a sustainable pathway for biomass valorization; however, achieving base-free, efficient, and recyclable catalysis remains challenging. Herein, we report the rational design of chromium-modified Pt@Fe2–xCrxO3 nanocatalysts, synthesized via ethanolamine-assisted coprecipitation followed by platinum nanoparticle (≈2.6 nm) deposition, for the aerobic oxidation of HMF under mild conditions. The isovalent substitution of Fe3+ with Cr3+ enhanced the oxygen vacancy concentration and surface acidity while strengthening the Pt–O interactions. The optimized [email protected] catalyst achieved nearly 100% HMF conversion with a 78.7% FDCA yield at 120 °C and 1 bar O2 within 12 h, compared to only 41% yield over Pt@Fe2O3. Kinetic studies revealed first-order behavior with activation energies of 67.9 kJ mol–1 for HMF conversion and 36.3 kJ mol–1 for FDCA formation. The catalyst retained >90% of its activity after five consecutive cycles, demonstrating its excellent recyclability. Density functional theory calculations further confirmed that Cr doping increased the HMF adsorption energy (−67.0 vs −56.6 kcal mol–1) and raised the Pt d-band center, thereby promoting the generation of reactive oxygen species. This study establishes a quantitative and generalizable strategy for designing robust and recyclable catalysts for sustainable biomass conversion.