Selective oxidation of 5-hydroxymethyl-2-furfural into 2,5-diformylfuran over VO2+ and Cu2+ ions immobilized on sulfonated carbon catalysts

Abstract

Immobilization of vanadyl (VO2+) and cupric (Cu2+) ions on sulfonated carbon and their catalytic activity toward the aerobic oxidation of 5-hydroxymethyl-2-furfural (HMF) are described. The carbon material (C) was derived from commercial ion exchange resin (Amberlyst-15) by performing carbonization process. Subsequently, sulfonated carbon (CS) was prepared by treating C with 98% sulfuric acid. Finally, VO2+ and/or Cu2+ ions were immobilized on CS by ion exchange technique. The synthesized catalysts were characterized by X-ray diffraction (XRD), elemental analysis, Raman spectroscopy, and transmission electron microscopy (TEM). Interestingly, in the catalytic oxidation of HMF using these catalysts, 2,5-diformylfuran (DFF), a high-value chemical is found to be the major product. The VO2+ ion-immobilized catalyst (V-CS) exhibits highly stable catalytic activity without the leaching of vanadyl ion during recycling tests, with low selectivity to DFF. The copper counterpart (Cu-CS), however, shows the opposite behavior, i.e., high selectivity to DFF and decreasing catalytic performance due to the leaching of copper component during recycling runs. The presence of copper in low concentrations in the vanadyl-exchanged catalyst (V-Cu-CS) leads to high selectivity to DFF and good re-usability. A catalyst with the composition 0.93%V–0.26%Cu-CS exhibits the best performance.