Metal silicotungstate salts as catalysts in furfural oxidation reactions with hydrogen peroxide

In this work, metal cations exchanged silicotungstic acid salts were synthesized and evaluated as catalysts in furfural oxidative esterification reactions with hydrogen peroxide in alkyl alcohols solution. The protons of silicotungstic acid were totally exchanged with Co2+, Cu2+, Ni2+, Al3+, and Fe3+ cations, generating catalysts that were characterized by infrared spectroscopy, X-rays diffraction patterns, energy dispersive spectroscopy, scan electronic microscopy images, and thermal analyses. Isotherms of adsorption/desorption of nitrogen provided the surface area, distribution, volume, and pores diameter. The strength and amount of the acid sites were determined by potentiometric titration curves. Noticeably, the oxidation of furfural proceeded without opening the furan ring. Furoic acid and alkyl furoate were the main reaction products, with the formation of the furfural acetal as a secondary product. The effect of main reaction parameters such as the H2O2: furfural molar ratio, the catalyst amount, and the temperature were studied. The reactivity of the furfural with other alkyl alcohols was also assessed. The solid, active, and easily synthesizable catalyst, and the use of an inexpensive and environmentally benign oxidant are positive aspects of this selective process for oxidative esterification of furfural.