Desulfurization of model diesel by extraction/oxidation using a zinc-substituted polyoxometalate as catalyst under homogeneous and heterogeneous (MIL-101 (Cr) encapsulated) conditions

Abstract

A composite material comprising the chromium terephthalate metal organic framework MIL 101 and the tetrabutylammonium(TBA) salt of a zinc substituted polyoxotungstate anion, TBA4.2H0.8[PW11Zn(H2O)O39] (denoted PW11Zn), has been prepared by an impregnation method and characterized by powder X ray diffraction, scanning electron microscopy, N2 adsorption/desorption, thermogravimetric analysis, FT IR, FT Raman and 31P magic angle spinning (MAS) NMR spectroscopies. The characterization data reveal that the polyoxometalate was homogeneously encapsulated within the cages of the support without affecting its crystalline structure and morphology. Both the homogeneous catalyst PW11Zn and the composite material PW11Zn@MIL 101 exhibit high activity in the extractive and catalytic oxidative desulfurization of a model oil containing dibenzothiophene, 1 benzothiophene and 4,6 dimethyldibenzothiophene. Complete desulfurization of the model oil could be achieved within 2 h by using the ionic liquid (IL) 1 butyl 3 methylimidazolium hexafluorophosphate as extraction solvent, aqueous 30% H2O2 as oxidant and a reaction temperature of 50 °C. When acetonitrile was used as extraction solvent instead of the IL, the heterogeneous catalyst PW11Zn@MIL 101 could be easily recovered and reused several times without leaching or loss of activity.