Continuous flow oxidation of HMF using supported AuPd-alloy

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 continous oxidation of HMF. Air served as green oxidant, water as non-toxic solvent, and Na2CO3 as 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 molFDCA molM-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 of 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.