Effect of transition metal oxides catalysts on oxidative desulfurization of model diesel

In this paper, model diesel is used to study the performance of oxidative desulfurization (ODS) system compared to hydrodesulfurization (HDS) process. A detailed parametric experimental study was performed to select the best technique for sulfur removal. The effects of solvent, oxidant, bimetallic oxide catalyst, dopant, dopant ratio and calcination temperature were investigated. Dimethylformamide (DMF) and tert-butyl hydroperoxide (TBHP) were found to be the best solvent and oxidizing agent for the removal of sulfur compounds in model diesel. Both solvent and oxidant were then applied to explore the applicability of various catalysts, such as iron, manganese, molybdenum, tin, zinc and cobalt in model diesel. The results showed that the catalytic activity was decreased in the order: Mo > Mn > Sn > Fe ≈ Co > Zn. Further investigation of doped molybdenum revealed that 4.35% WO3/16.52% MoO3/Al2O3 in the ratio of 10:90 with calcination temperature at 500 °C was assigned as the best catalyst in this research. Under mild reaction condition, this catalyst showed high conversion with appreciable stability until 150 hours and can be used as a reusable active catalyst in ODS treatment. Additionally, on the basis results obtained, a mechanistic proposal for this reaction was postulated, as an oxidation mechanism by nucleophilic attack of the sulfur atom on peroxo species of WO3/MoO3/Al2O3.