Dodecatungstocobaltate supported over ZSM-5 zeolite as novel solid catalyst in selective sulfide oxidation

The catalytic behavior of a Keggin type potassium dodecatungstocobaltate (II) salt supported on ZSM-5 zeolite for wet peroxide oxidation of 2-(methylthio)benzothiazole, as a model organic sulfide, was thoroughly studied. Microporous ZSM-5 zeolite was obtained by the hydrothermal crystallization method. The Keggin salt was incorporated in the MFI zeolite matrix by the wet impregnation method followed by calcination at 350 °C. Catalysts were further characterized by X ray diffraction, UV–Vis diffuse reflectance spectroscopy and scanning electron microscopy-EDAX techniques. Supported and bulk Keggin dodecatungstocobaltate (II) were compared with pure H-ZSM-5 zeolite as catalysts for the sulfide oxidation. When the reaction was not catalyzed, just a 9 mol% of sulfide conversion was obtained. Reaction parameters, such as nature of the solvent, hydrogen peroxide concentration, reaction time, catalyst mass, substrate initial concentration and reaction temperature, were evaluated to reach the optimum reaction conditions, considering substrate conversion and sulfoxide and sulfone selectivities. Catalyst stability in several oxidation cycles was also examined.