## 3 Result and Discussion
### Oxidative Desulfurization of the Model Oil  
To probe the oxidation performance, DBT, BT, and 4.6-DMDBT fuel oil oxidation desulfurization experiments were performed with the catalyst. Figure 5 shows the effect of the \(m(\text{catalyst})/m(\text{model oil})\) on the desulfurization rate of 10 mL DBT, BT, and 4.6-DMDBT fuel oil. In Figure 5 it is shown that the desulfurization rate of the DBT, BT, and 4.6-DMDBT fuel oils gradually increased when the \(m(\text{catalyst})/m(\text{fuel oil})\) increased, and finally tended to be flat. When the \(m(\text{catalyst})/m(\text{fuel oil})\) was 0.018%, the desulfurization rate of DBT and 4.6-DMDBT could be close to 100%, and with BT this rate could be close to 80%.  
Figure 6 shows the effect of \(v(\text{H}_{2}\text{O}_{2})/v(\text{fuel oil})\) on the desulfurization rate of 10 mL DBT, BT, and 4.6-DMDBT fuel oil. In Figure 6 it is shown that the desulfurization rate of the DBT, BT, and 4.6-DMDBT fuel oils first increased then decreased as the \(v(\text{H}_{2}\text{O}_{2})/v(\text{model oil})\) increased; when \(v(\text{H}_{2}\text{O}_{2})/v(\text{fuel oil})\) was 0.3%, the desulfurization rate of all the DBT, BT, and 4.6-DMDBT fuel oils reached the maximum. Within a certain range, the amount of peroxopolymetallic compound increased with the amount of the oxidant \(\text{H}_{2}\text{O}_{2}\), which formed by combining with the active center of ammonium molybdate, thereby speeding up the reaction rate. When the amount exceeded the optimal amount, the water generated by the \(\text{H}_{2}\text{O}_{2}\) reaction led to the production of a two-phase system, which may have reduced the catalyst's dispersion in the oil phase, causing a decrease in the reaction rate [28].  
Figure 7 shows the effect of reaction temperature and reaction time on the desulfurization rate of DBT, BT, and 4,6-DMDBT. At the same reaction temperature, the desulfurization rate of DBT, BT, and 4,6-DMDBT fuel oils gradually increased while the reaction time increased. Simultaneously, the desulfurization rate of DBT, BT, and 4,6-DMDBT fuel oils steadily increased with the increase of reaction temperature. When the reaction temperature increased, the thermal motion between molecules was increased [29]. At the same time, the number of metal peroxides generated by \(\text{MoO}_{3}\) and \(\text{H}_{2}\text{O}_{2}\) in the fuel oil was increased while the reaction time increased, which provided more catalytic activity sites, thereby accelerating the reaction rate [30]. At 60 \({}^{\circ}\)C, the desulfurization rate of DBT was close to 100% at 5 min, the desulfurization rate of 4,6-DMDBT was close to 100% at 6 min, and the desulfurization rate of BT was close to 100% at 12 min. Under the same reaction conditions, the oxidation performance of the sulfur compounds decreased in the order of DBT \(>\) 4,6-DMDBT \(>\) BT. Due to the electron cloud density of sulfur atoms on BT being smaller than on DBT and 4,6-DMDBT, BT was more challenging to remove than DBT and 4,6-DMDBT [31]. Although the electron cloud density of 4,6-DMDBT was bigger than DBT,  
Figure 5: Effect of catalyst/ fuel oil on dibenzothiophene (DBT), benzothiophene (BT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) desulfurization. Reaction conditions for DBT desulfurization: \(v(\text{H}_{2}\text{O}_{2})/v\) (fuel oil) = 0.30%, 50 \({}^{\circ}\)C, 5 min. Reaction conditions for BT desulfurization: \(v(\text{H}_{2}\text{O}_{2})/v\) (fuel oil) = 0.30%, 50 \({}^{\circ}\)C, 8 min. Reaction conditions for 4,6-DMDBT desulfurization: \(v(\text{H}_{2}\text{O}_{2})/v\) (fuel oil) = 0.30%, 50 \({}^{\circ}\)C, 5 min.