Catalytic oxidative desulfurization of diesel oil by Co/Mn/Al₂O₃ catalysts—tert-butyl hydroperoxide (TBHP) system: preparation, characterization, reaction, and mechanism

The hydrodesulfurization (HDS) technique available is no longer suitable for the purpose of achieving ultra-low sulfur diesel. Therefore, in this study, the catalytic oxidative desulfurization of model diesel was carried out using tert-butyl hydroperoxide along with inexpensive alumina-supported manganese-based oxide catalysts, and later, the oxidized sulfur compounds were extracted by dimethylformamide, a polar solvent. The effect of dopant ratio, calcination temperature, reaction time, and reaction temperature were investigated in detail. The oxidation reactivity of different substrates was in the following order: DBT > Th > 4,6-DMDBT. The best desulfurization efficiency of model diesel, under mild reaction conditions, was 85.3 % thiophene, 85.0 % dibenzothiophene, and 74.5 % 4,6-dimethyldibenzothiophene using the 2.14 %Co/13.17 %Mn/Al₂O₃ catalyst calcined at 400 °C. Besides, this catalyst retained a high conversion of sulfur after three rounds of reaction cycles and can be used as a reusable active catalyst in ODS treatment. Under the optimal conditions, the S-content in the commercial diesel could be decreased from 415 to less than 10 ppmw. The oxidation mechanism was studied in detail, and TBHP-Co/Mn catalyst was the main active oxidizing species on the oxidation of DBT.