Novel palladium magnetic catalysts for 5-hydroxymethylfurfural oxidation

5-hydroxymethyl-2-furaldehyde (HMF) can be obtained from the hexose fraction of lignocellulosic biomass and its catalytic exploitation represents a big challenge for sustainability. Environmentally friendly oxidation of aqueous HMF to give 5-hydroxymethyl-2-furancarboxylic acid (HFCA) and 2,5-furandicarboxylic acid (FDCA) was now studied through heterogeneously catalyzed reactions, working in water under mild conditions. Pd-doped Fe3O4was synthesized adopting a novel MW-assisted solvothermal approach. This magnetic system resulted an easily recoverable and versatile catalyst able to reach up to 70% yields of HFCA when subjected to 1 atmosphere of O2and 40°C in the as-synthesized form. On the contrary, this catalyst can reach up to 71% FDCA yields when working at 40°C and atmospheric O2pressure in a mildly reduced form, as shown by XPS analysis. Biomass derived HMF raw liquors were also employed as substrate, and these novel catalysts were also tested in a cascade process of biomass valorization using raw hydrolysates derived from cellulose. These aqueous liquors contained HMF, furfural and small amounts of unreacted sugars. Quite good results were obtained from the cascade approach using Pd-doped Fe3O4leading to 81% yield of HFCA, 4% FDCA and 80% yield of furoic acid (furfural oxidation product).