Immobilized Multifunctional Ionic Liquids for Highly Efficient Oxidation of Sulfur-Containing Compounds in Model Fuels

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 H2O2/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.