Porous aromatic frameworks modified by sulfonic groups were synthesized and, for the first time, applied for the oxidative desulfurization of a model and a real fuel. The main factors affecting the process including the catalyst dosage, temperature, reaction time, oxidant dosage, and hydrogen peroxide concentration were investigated in detail. Under optimal conditions, dibenzothiophene (DBT) was removed completely. It was shown that the synthesized catalysts reduced the sulfur content in the straight-run gasoline fraction up to ultra-low values (7 ppm). Fuel fractions and their oxidation products were analyzed by two-dimensional gas chromatography with time-of-flight mass spectrometry detection. No byproducts of hydrocarbon oxidation were found, which confirms the high selectivity of oxidation in the presence of synthesized catalysts. These catalysts retain their activity in DBT oxidation for at least five cycles.

Oxidative desulfurization is a promising method to produce clean fuels with an ultralow sulfur content at mild conditions. Herein, for the first time, we present multifunctional ionic liquid catalysts immobilized on mesoporous SBA-15 for highly efficient oxidation of dibenzothiophene. A combination of two active catalytic sites (phosphomolybdic acid fragment and carboxylic group) allows us to achieve complete oxidation of the most intractable dibenzothiophene to the corresponding sulfone in 5 min at 80 °C and H 2 O 2 /S = 6:1 molar ratio. The support and catalyst structures were investigated by low-temperature nitrogen adsorption/ desorption, Fourier transform infrared spectroscopy, X-ray fluorescence analysis, CHN analysis, and transmission electron microscopy techniques. Nicotinic acid fragments, bonded with the support and phosphomolybdic acid anion via covalent and ionic bonds, respectively, prevent active site leaching, thus retaining the catalyst activity for at least 10 reaction runs with preliminary regeneration. These catalysts are considered as promising systems for clean fuel production.

In this work, new heterogeneous Mo-containing catalysts based on sulfonic titanium dioxide were developed for the oxidation of sulfur-containing model feed. The synergistic effect of molybdenum and sulfonic group modifiers allows for enhancing catalytic activity in dibenzothiophene oxidative transformation, and a strong interaction between support and active component for thus obtained catalysts provides increased stability for leaching. For the selected optimal conditions, the Mo/TiO2-SO3H catalyst exhibited 100% DBT conversion for 10 min (1 wt % catalyst, molar ratio of H2O2:DBT, 2:1; 80 °C). Complete oxidation of DBT in the presence of the synthesized catalyst is achieved when using a stoichiometric amount of oxidizing agent, which indicates its high selectivity. The enhanced stability for metal leaching was proved in recycling tests, where the catalyst was operated for seven oxidation cycles without regeneration with retainable activity in DBT-containing model feed oxidation with hydrogen peroxide under mild reaction conditions. In 30 min of the reaction (H2O2:S = 2:1 (mol), 0.5% catalyst, 5 mL of acetonitrile, 80 °C), it was possible to reduce the content of sulfur compounds in the diesel fraction by 88% (from 5600 to 600 ppm).

A new heterogeneous catalyst containing two types of active sites, sulfo group and ammonium heptamolybdate, on ASKG silica gel support was synthesized. The influence of oxidation conditions (temperature, reactant ratio, reaction time) on the conversion of a model substrate, dibenzothiophene (DBT), was examined. Conditions were found for exhaustive oxidation of DBT. The catalyst synthesized is stable under the oxidation conditions and preserves its activity in five oxidation cycles. The combination of two types of active sites not only considerably enhances the catalyst performance but also reduces to a minimum the possible washout of molybdenum compounds from the support surface.

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