Porous cobalt-containing poly(ionic liquid) catalyst for tandem desulfurization and selective catalytic oxidation

Abstract

This study describes the synthesis of a porous polyvinyl imidazole cobalt chloride catalyst (denoted herein as pore-poly-[BVIM]CoCl₃) and its subsequent application in a two-step extraction-catalytic oxidation process for the desulfurization of octane. The catalyst synthesis process employed a porogen (P123) and low stirring speeds, which significantly increased the specific surface area of the catalyst from 78.5 m²/g (no P123) to 1196 m²/g and provided an average pore size of 26.46 nm. The pore-poly-[BVIM]CoCl₃ catalyst possessed uniformly distributed pores with cobalt ions dispersed throughout. The average molecular weight of the catalyst was 4090 g/mol, corresponding to 44 units of 3-butyl-1-vinylimidazolium cobalt chloride. Octane containing 500 ppm dibenzothiophene (DBT) was desulfurized in a two-step process, which involved the extraction of DBT into acetonitrile followed by the catalytic oxidation of DBT using the pore-poly-[BVIM]CoCl₃ catalyst with peroxymonosulfate (PMS) as the oxidant. The desulfurization experiment was optimally performed using 20 mg of catalyst, 0.6 g of 20 wt% PMS solution, 2 g of acetonitrile (extraction solvent), a reaction temperature of 30 °C, and an initial sulfur content of 500 ppm. Under these conditions, >99 % desulfurization was achieved in 15 min. Moreover, the porous catalyst maintained a desulfurization rate of > 90 % after 7 cycles of use, demonstrating excellent durability and reusability. The oxidation mechanism of DBT was determined through GC–MS analysis and density functional theory (DFT) calculations: DBT is first oxidized by a sulfate radical to dibenzothiophene oxide (DBTO), which is then further oxidized by hydroxyl radicals to dibenzothiophene sulfone (DBTO₂). The radical scavenger tert-butyl alcohol (TBA) inhibited hydroxyl radical attack in the second step, thereby stabilizing DBTO. This study’s findings demonstrate the potential of octane desulfurization and the mild catalytic oxidative synthesis of sulfur-containing organic compounds in the pharmaceutical sector.