The aerobic oxidation of 5-hydroxymethylfurfural, a versatile biomass-derived chemical, is examined in water with a titania-supported gold-nanoparticle catalyst at ambient temperature (30 °C). The selectivity of the reaction towards 2,5-furandicarboxylic acid and the intermediate oxidation product 5-hydroxymethyl-2-furancarboxylic acid is found to depend on the amount of added base and the oxygen pressure, suggesting that the reaction proceeds via initial oxidation of the aldehyde moiety followed by oxidation of the hydroxymethyl group of 5-hydroxymethylfurfural. Under optimized reaction conditions, a 71% yield of 2,5-furandicarboxylic acid is obtained at full 5-hydroxymethylfurfural conversion in the presence of excess base.
Wine into vinegar: It is possible to selectively oxidize ethanol into acetic acid in aqueous solution with air as the oxidant and a heterogeneous gold catalyst (see TEM image of supported gold particles) at temperatures of about 423 K and O2 pressures of 0.6 MPa. This reaction proceeds readily in aqueous acidic media with yields of up to 90 % and CO2 as the only major by‐product.
The catalytic performance of zeolite‐supported vanadia catalysts was examined for the aerobic oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) in organic solvents such as N,N‐dimethylformamide (DMF), methyl isobutyl ketone, toluene, trifluorotoluene and DMSO. Catalysts based on the four different zeolite supports H‐beta, H‐Y, H‐mordenite, and H‐ZSM‐5 with 1–10 wt % vanadia loading were prepared and characterized by nitrogen physisorption, X‐ray powder diffraction, scanning electron microscopy, ammonia temperature‐programmed desorption, Raman spectroscopy and UV/Vis spectrophotometry. The H‐beta zeolite catalysts were found to contain highly dispersed vanadium oxide species at all loadings, and provided the highest reaction selectivity towards DFF and the lowest metal leaching of the examined systems. In particular, 1 wt % V2O5/H‐beta was found to be a stable, recyclable, and non‐leaching catalyst for the production of DFF under mild conditions in DMF as solvent, although with low DFF yield. To increase the yield, oxidation of HMF at elevated pressures was also investigated with this catalyst. Under optimized conditions, a reaction selectivity towards DFF of >99 % at 84 % HMF conversion was obtained, albeit with some contribution from lixiviated species to the total catalyst activity.
Heterogeneous ruthenium-based catalysts were applied in the selective, aerobic oxidation of 5-hydroxymethylfurfural, a versatile biomass-derived chemical, to form 2,5-furandicarboxylic acid. The oxidation reactions were performed in water with dioxygen as the oxidant at different pressures without added base. Catalysts were prepared by depositing catalytically active Ru(OH) x species on a number of different supports, such as titanium-, aluminum-, cerium-, zirconium-, magnesium-and lanthanum oxides, magnetite, spinel, hydrotalcite and hydroxyapatite. All the catalysts were found to be active in the oxidation reactions, and the choice of support was demonstrated to be important for the catalytic performance.
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