Oxidation of 5-Hydroxymethylfurfural Using Ru Supported Mg-Fe Hydrotalcite Materials.

A series of hydrotalcite-derived bimetallic catalysts were prepared, and Ru was loaded by wet impregnation. The catalyst retained a layered structure even after reduction, which was confirmed by Fourier-transform infrared spectroscopy and powder X-ray diffraction analyses. Among the prepared catalysts, ruthenium on magnesium-iron (Ru/MgFe) showed the best activity for 5-hydroxymethylfurfural oxidation under mild conditions in an aqueous medium (98.3% conversion at 120 °C, 3 h, and 30 bar O2), with the formation of 2, 5- furandicarboxylic acid (61.5%) as a major product along with 5-formyl 2-furancarboxylic acid and 2,5-diformylfuran as minor products. The highly dispersed metallic ruthenium on the surface of HT favored better activity. In addition, from the solvent studies, green solvent water showed higher activity than the other organic solvents. The activity of the catalyst reduced after the first cycle but regained upon treatment under a CO2 atmosphere, which facilitated the regeneration of surface basicity and hence helped in the reactivation of the catalyst. Overall, this work demonstrates that finely dispersed ruthenium on MgFe hydrotalcite (MgFe-HT) facilitates the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The Ru-dispersed MgFe-HT exhibits a high surface area (61.5 m2/g) along with surface basicity and redox properties, which contribute to a high HMF conversion (>99%) and a moderate FDCA yield (73.3%).