Microwave-Assisted Oxidation of Hydroxymethyl Furfural to Added-Value Compounds over a Ruthenium-Based Catalyst

Oxidation of 5-hydroxymethylfurfural (HMF) toward 2,5-furandicarboxylic acid (FDCA) was successfully performed under microwave (MW)-assisted heating using hydrogen peroxide (H₂O₂) as an oxidant. Various Ru-based materials as catalytic systems have been investigated. Particularly, commercial 5% Ru/C achieved an impressive FDCA yield of 88% in only 30 min under microwave batch conditions. Various reaction parameters such as the reaction time, type of base, base amount, temperature, catalyst loading, and hydrogen peroxide concentration have been optimized. The optimum conditions were employed under an air atmosphere, exhibiting an 84% FDCA yield in 22 h. Noticeably, a microwave continuous flow approach was also investigated using the optimum conditions, displaying full HMF conversion with 38% FFCA and 47% FDCA yields. Reusability studies revealed the reason for catalyst deactivation to be most likely associated with the deteriorated textural properties after MW batch and continuous flow reactions. Ru leaching was found to be more severe under continuous flow (8%) as compared to batch conditions (2%). The present study provided a promising pathway for FDCA synthesis using commercially available and environmentally benign catalysts.