Catalytic Oxidation of 5‑Hydroxymethylfurfural to 2,5-Furandicarboxylic acid over Ru/Al₂O₃ in a Trickle-Bed Reactor

Oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) was carried out over Ru/Al2O3 using O2 aqueous alkaline solutions in a trickle-bed reactor. HMF was completely converted at 140 °C, 30 bar O2, resulting in 98% FDCA selectivity (pH 11, GHSV = 900 h–1, WHSV = 1 h–1). At 140 °C, FDCA was the main product under all conditions. Alkali (nature and concentration) played a significant role in oxidation or degradation of HMF. The selectivity to oxidized compounds was favored using Na2CO3 by accelerating oxidation steps, principally to the aldehyde group maintaining an appropriate pH for the reaction. The estimated kinetic parameters obtained were statistically significant, suggesting an accurate representation of the system. The effects of parameters such as temperature, GHSV, WHSV, and oxygen pressure on product distribution and HMF conversion were evaluated. The catalyst showed high stability, retaining activity after 12 cycles, being reactivated by a simple hydrothermal treatment