Continuous flow oxidation of HMF using a supported AuPd-alloy

Abstract

The oxidation of 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) holds significant promise for replacing fossil-based monomers. Continuous flow operation enhances the process in terms of green chemistry by improving heat and mass transfer, enabling easier scalability of the reaction and ensuring higher safety with a smaller reactor volume. In this study, we investigated the use of heterogeneous catalysts in a fixed-bed reactor for the continuous oxidation of HMF. Air served as a green oxidant, water as a non-toxic solvent, and Na₂CO₃ as a mild base. An AuPd-alloy-based catalyst supported on activated carbon demonstrated remarkable performance, yielding 81% FDCA at a liquid hourly space velocity of 31.4 h⁻¹. This corresponds to a productivity of 68 mol_FDCA mol_AuPd⁻¹ h⁻¹, which is, to our knowledge, one order of magnitude higher than typically reported for the heterogeneously catalyzed continuous oxidation of HMF. In addition, the catalyst showed a good stability over 90 h time on stream without any detectable deactivation. The formation of humins led to a progressive catalyst deactivation. The developed catalytic system and continuous process offer a more sustainable and efficient approach to future production of the renewable monomer FDCA.