Polyoxometalate-based ionic liquid hybrid materials with a pyridinium cation, containing Brönsted acid sites, were synthesized and used as catalysts for the oxidation of model and real diesel fuels. Keggin-type polyoxometalates with the formulae [PMo12O40]3−, [PVMo11O40]4−, [PV2Mo10O40]4−, [PW12O40]3− were used as anions. It was shown that increasing the acid site strength leads to an increase of dibenzothiophene conversion to the corresponding sulfone. The best results were obtained in the presence of a catalyst, containing a nicotinic acid derivative as cation and phosphomolybdate as anion. The main factors affecting the process consisting of catalyst dosage, temperature, reaction time, oxidant dosage were investigated in detail. Under optimal conditions full oxidation of dibenzothiophene and more than a 90% desulfurization degree of real diesel fuel (initial sulfur content of 2050 ppm) were obtained (the oxidation conditions: NK-1 catalyst, molar ratio H2O2:S 10:1, molar ratio S:Mo 8:1, 1 mL MeCN, 70 °C, 1 h). The synthesized catalysts could be used five times with a slight decrease in activity.
New highly efficient heterogeneous catalysts based on an immobilized Anderson-type polyoxometalate supported on the functionalized SBA-15 surface have been successfully synthesized and characterized by FT-IR, XRD, N 2 adsorption−desorption isotherms, BET, SEM, TEM, EDX, and XPS analyses. The catalytic activity was investigated in the aerobic oxidative desulfurization of a model fuel. Heterogeneous catalysts were synthesized by various methods of immobilization using organic fragments of different natures. An efficient method of immobilization based on the grafting of N-methylimidazole as a cation-forming agent has been shown. The effect of temperature, dosage, and active phase loading on the conversion of dibenzothiophene (DBT) was studied. The highest activity was shown by the CoMo-0.5IL-SBA catalyst (IL = 1-methyl-3-(trimethoxysilylpropyl)-imidazolium cation), in the presence of which 100% DBT removal is achieved within 90 min at 120 °C at a catalyst amount of 0.2 wt %. Moreover, the immobilized catalyst could be recycled 5 times without a significant loss of catalytic activity.
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