Heteropolyacid Ionic Liquid-Based MCF: An Efficient Heterogeneous Catalyst for Oxidative Desulfurization of Fuel

A new type of catalyst was synthesized by immobilizing heteropolyacid on ionic liquid-modified mesostructured cellular silica foam (denoted as MCF) and applied to the oxidative desulfurization of fuel. The surface morphology and structure of the catalyst were characterized by XRD, TEM, N2 adsorption–desorption, FT-IR, EDS and XPS analysis. The catalyst exhibited good stability and desulfurization for various sulfur-containing compounds in oxidative desulfurization. Heteropolyacid ionic liquid-based MCF solved the shortage of the amount of ionic liquid and difficult separation in the process of oxidative desulfurization. Meanwhile, MCF had a special three-dimensional structure that was not only highly conducive to mass transfer but also greatly increased catalytic active sites and significantly improved catalytic efficiency. Accordingly, the prepared catalyst of 1-butyl-3-methyl imidazolium phosphomolybdic acid-based MCF (denoted as [BMIM]3PMo12O40-based MCF) exhibited high desulfurization activity in an oxidative desulfurization system. The removal of dibenzothiophene could achieve levels of 100% in 90 min. Additionally, four sulfur-containing compounds could be removed completely under mild conditions. Due to the stability of the structure, sulfur removal efficiency still reached 99.8% after the catalyst was recycled six times.


Introduction
With the increasing demand for fuel consumption worldwide, environmental legislation implemented by various countries is increasingly strict, including the requirements for sulfur content [1,2]. Therefore, the study of ultra-deep desulfurization attracted increasing research attention [3][4][5] and many efficient desulfurization techniques have been developed. These include hydrodesulfurization (HDS) [6][7][8], extractive desulfurization (EDS) [9][10][11], adsorption desulfurization (ADS) [12][13][14][15] and oxidative desulfurization [16][17][18][19]. Hydrodesulfurization technologies are effective on most sulfides but have obvious disadvantages such as high temperature and pressure, and difficulty in removing aromatic sulfur compounds. These shortcomings can be solved by oxidative desulfurization technologies. Oxidative desulfurization not only requires mild operating conditions but is also effective in the removal of aromatic sulfur compounds. Oxidative desulfurization is regarded as a green and efficient deep desulfurization technology and has great development prospects.
High-efficiency catalysts are the key factor affecting the efficiency of the removal of sulfur compounds. Accordingly, increasing research has been focused on catalyst development. To date, catalysts widely used in oxidative desulfurization include polyoxometalates [20][21][22][23][24], ionic liquids [25][26][27][28], organic acid [29][30][31] and carbon materials [32,33]. In particular, polyoxometalates have received increasing attention as functional catalysts in organic reaction systems [34,35]. Due to their unique properties, polyoxometalates have advantages including good selectivity, high hydrothermal stability, oxidation-reduction ability, and strong acidity in oxidative desulfurization. However, due to the small specific surface area of heteropolyacids, which is not conducive to promoting catalytic reactions, their catalytic performance is greatly limited; this affects their application value in catalysis. Therefore, to address this shortcoming, it is of great significance to design and synthesize catalysts with more catalytic active sites by selecting a suitable support with a higher specific surface area.
Homogeneous catalysts usually show high catalytic activity in oxidative desulfurization but their separation and regeneration are difficult. Compared with homogeneous catalysts, heterogeneous catalysts have the advantages including ease of separation and regeneration but the catalytic active sites are less exposed to the reactants. Therefore, there is an urgent need to develop a method for preparing efficient catalysts for oxidative desulfurization that can not only be readily separated and regenerated but also have the high catalytic activity of heterogeneous catalysts.
Mesostructured cellular silica foam (MCF) [36][37][38] can be widely used in sensor, separation, adsorption, electronic insulation and other fields due to its large specific surface area, ordered pore structure and high hydrothermal stability. In contrast to other mesoporous materials, MCF is a kind of mesoporous silica with an open three-dimensional pore structure and large pore size, so it is often regarded as an excellent support. MCF as a heterogeneous catalyst support greatly increases the surface area, providing many sites for the reaction to take place. However, MCF has some drawbacks as a catalyst: the acid concentration on its surface is low and the acidity is weak. Furthermore, the weak interaction between active species and MCF can readily lead to the shedding of active substances.
In this study, to overcome these problems, heteropolyacid ionic liquids supported on MCF were designed and synthesized to improve mass transfer and increase catalytic activity sites. The resulting heteropolyacid ionic liquid-modified MCF catalyst was applied to the extractive and catalytic oxidative desulfurization (ECODS) system, wherein it proved to have the dual functional advantages of MCF and the heteropolyacid ionic liquids. The catalyst showed excellent desulfurization performance, could be recycled many times and was easy to recover and reuse. The excellent performance of the catalyst makes it very promising for industrial applications, across multiple fields.  (3-chloropropyl) trimethoxysilane, n-octane, hydrochloric acid, 30 wt% hydrogen peroxide, thiophene (T) and toluene were provided by Sinopharm Chemical Reagent Co., Ltd. and were of analytical grade. Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123), benzothiophene (BT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and dibenzothiophene (DBT) were obtained from Sigma-Aldrich. 1,3,5-trimethylbenzene (TMB) and ethyl silicate (TEOS) were purchased from Aladdin Chemistry. Ionic liquid [BMIM]BF 4 was synthesized according to a published procedure [39,40].

Catalyst Characterization
The surface morphology of the ionic liquid-based MCF was analyzed by transmission electron microscopy (TEM; JEM-2100; JEOL HITACHI; Japan) at 100 kV. Powder X-ray diffraction (XRD; Bruker; Germany) analysis was carried out on a Bruker instrument with high-intensity Cu Ka radiation (λ = 1.54 Å). N 2 adsorption-desorption isotherms were investigated by surface area analyzer. FTIR spectrophotometry (PerkinElmer; USA) was performed using a KBr disc. Surface element analysis was performed by X-ray photoelectron spectroscopy (XPS; Thermo Scientific ESCALAB250; Waltham; USA). The removal of sulfur-containing compounds were determined using high-performance liquid chromatography (HPLC; LC-20A Prominence; Japan). The mobile phases of HPLC was methanol in water. The parameters of 4,6-DMDBT, DBT, BT and T were set as 90%, 90%, 80% and 70% with a flow rate of 1 mL/min, respectively.

Preparation of Model Oil and Desulfurization
The model oil containing DBT was made up by dissolving DBT (0.588 g) in n-butane (100 mL), giving with a corresponding sulfur concentration of 1000 ppm. The model oils of T, BT, and 4, 6-DBT were prepared using the same method with n-octane as the solvent.
Taking [BMIM] 3 PW 12 O 40 -based MCF as an example, each desulfurization experiment was conducted in a 10 mL round bottom flask, to which ionic liquid [BMIM]BF 4 (3 mL) and a portion of the catalyst were added and dispersed uniformly at room temperature by stirring for 40 min. Then, hydrogen peroxide (30 wt%) and model oil (5 mL) were added, sequentially. The desulfurization experiment was carried out in an oil bath at the reaction temperature of the extractive catalytic oxidation. While the experiment was in process, the upper phase containing the model oil was sampled and the sulfur concentration was measured by HPLC every 30 min.
At the end of one desulfurization experiment, the upper oil phase was separated by decantation. The lower ionic liquid and catalyst were washed with diethyl ether and dried for reuse, while fresh hydrogen peroxide oxidant and model oil were injected for the next run of desulfurization experiment.

Morphological Characterization of Heteropolyacid Ionic Liquids-Based MCF
The wide-angle XRD pattern of the MCF and heteropolyacid ionic liquid-based MCF is shown in Figure 1 Notable peaks corresponding to phosphomolybdic acid and phosphotungstic acid were also observed in the wide-angle XRD patterns, indicating that the heteropolyacids were successfully supported on MCF.

Morphological Characterization of Heteropolyacid Ionic Liquids-Based MCF
The wide-angle XRD pattern of the MCF and heteropolyacid ionic liquid-based MCF is shown in Figure 1. The results showed that the [BMIM]3PMo12O40-based MCF and [BMIM]3PW12O40-based MCF had corresponding characteristic peaks of heteropolyacids. Notable peaks corresponding to phosphomolybdic acid and phosphotungstic acid were also observed in the wide-angle XRD patterns, indicating that the heteropolyacids were successfully supported on MCF. The surface morphology and structure of MCF modified with different heteropolyacid ionic liquids were characterized by TEM. As shown in Figure 2a Figure 3 shows the N2 adsorption-desorption isotherms of MCF and the heteropolyacid ionic liquid-based MCF. All adsorption-desorption isotherms showed a typical IV-type curve with an H1-type hysteresis ring, which is characteristic of mesoporous samples. With the introduction of the heteropolyacid ionic liquids, the capillary condensation height decreased, indicating that the heteropolyacid ionic liquids were successfully supported on MCF. The BET surface areas of MCF and the heteropolyacid ionic liquid-based MCF samples were 510.78 and 365.83 m 2 ·g −1 . The decrease in the BET surface  curve with an H1-type hysteresis ring, which is characteristic of mesoporous samples. With the introduction of the heteropolyacid ionic liquids, the capillary condensation height decreased, indicating that the heteropolyacid ionic liquids were successfully supported on MCF. The BET surface areas of MCF and the heteropolyacid ionic liquid-based MCF samples were 510.78 and 365.83 m 2 ·g −1 . The decrease in the BET surface area suggested that the heteropolyacid ionic liquids were successfully grafted onto MCF.  Figure 3 shows the N2 adsorption-desorption isotherms of MCF and the heteropolyacid ionic liquid-based MCF. All adsorption-desorption isotherms showed a typical IV-type curve with an H1-type hysteresis ring, which is characteristic of mesoporous samples. With the introduction of the heteropolyacid ionic liquids, the capillary condensation height decreased, indicating that the heteropolyacid ionic liquids were successfully supported on MCF. The BET surface areas of MCF and the heteropolyacid ionic liquid-based MCF samples were 510.78 and 365.83 m 2 ·g −1 . The decrease in the BET surface area suggested that the heteropolyacid ionic liquids were successfully grafted onto MCF.

Composition and Elemental Analysis of Heteropolyacid Ionic Liquid-Based MCF
The different fabrication of heteropolyacid ionic liquid-modified MCF obtained by the ionic exchange reaction between the [BMIM]Cl-based MCF and HPA were characterized by FTIR spectroscopy (Figure 4), the image on the right is an enlarged image of

Composition and Elemental Analysis of Heteropolyacid Ionic Liquid-Based MCF
The different fabrication of heteropolyacid ionic liquid-modified MCF obtained by the ionic exchange reaction between the [BMIM]Cl-based MCF and HPA were characterized by FTIR spectroscopy (Figure 4 peaks caused by vibrations of P-O, W=O and W-Oe-W in the [BMIM]3PW12O40-based MCF. In curve e, the absorption peak at 1094 cm -1 was attributed to Si-O stretching vibrations, while the band at 978 cm -1 was attributed to the anti-symmetric stretching vibrations of W=O and the bands located at 926 and 804 cm -1 were attributed to the absorption peak caused by the anti-symmetric stretching vibrations of W-O-W [44]. Based on the above analysis, it was concluded that the presence of heteropolyacid anion groups confirmed the heteropolyacids were successfully supported on [BMIM]Cl-based MCF.

Influence of Different Catalyst on Sulfur Removal of DBT
The catalytic oxidative desulfurization activity of MCF modified with diff eropolyacid ionic liquids was compared under the same desulfurization react tions for the removal of DBT (Figure 7). The desulfurization efficiency of thre catalysts supported by different heteropolyacids increased over time. The desul efficiency with DBT increased at different rates until equilibrium was reached. tive charge of heteropolyanion depended first on electron reducibility. Comp

Influence of Different Catalyst on Sulfur Removal of DBT
The catalytic oxidative desulfurization activity of MCF modified with different heteropolyacid ionic liquids was compared under the same desulfurization reaction conditions for the removal of DBT (Figure 7). The desulfurization efficiency of three kinds of catalysts supported by different heteropolyacids increased over time. The desulfurization efficiency with DBT increased at different rates until equilibrium was reached. The negative charge of heteropolyanion depended first on electron reducibility. Compared with [PMo 12 Figure 8 shows the effect of the amount of catalyst on sulfur removal efficiency, us ing DBT. It can be seen that, under the same conditions, sulfur removal was continuousl promoted, accompanying the catalyst dosage increase from 15 to 40 mg within 3 h. It wa evident that the number of catalytic sites contributed to the increase in catalyst dosage leading to significant positive impacts on the desulfurization efficiency of the system When the desulfurization reaction was carried out for 2 h with 30 mg, the DBT in th model oil was completely removed. There was no significant difference in the desulfur zation performance at 30 and 40 mg dosages. Thus, to optimize material efficiency, th optimal dosage amount of [BMIM]3PMo12O40-based MCF was determined to be 30 mg.  Figure 8 shows the effect of the amount of catalyst on sulfur removal efficiency, using DBT. It can be seen that, under the same conditions, sulfur removal was continuously promoted, accompanying the catalyst dosage increase from 15 to 40 mg within 3 h. It was evident that the number of catalytic sites contributed to the increase in catalyst dosage, leading to significant positive impacts on the desulfurization efficiency of the system. When the desulfurization reaction was carried out for 2 h with 30 mg, the DBT in the model oil was completely removed. There was no significant difference in the desulfurization performance at 30 and 40 mg dosages. Thus, to optimize material efficiency, the optimal dosage amount of [BMIM] 3 PMo 12 O 40 -based MCF was determined to be 30 mg. evident that the number of catalytic sites contributed to the increase in catalyst dosage leading to significant positive impacts on the desulfurization efficiency of the system When the desulfurization reaction was carried out for 2 h with 30 mg, the DBT in th model oil was completely removed. There was no significant difference in the desulfur zation performance at 30 and 40 mg dosages. Thus, to optimize material efficiency, th optimal dosage amount of [BMIM]3PMo12O40-based MCF was determined to be 30 mg.

Influence of O/S Ratio on Sulfur Removal
Due to its superiority, hydrogen peroxide plays an important role as an oxidant i the process of oxidative desulfurization. Stoichiometrically, 2 mol of hydrogen peroxid is required for the oxidation of sulfur components to the corresponding sulfones [46 However, a higher oxygen/sulfur ratio (O/S) is needed in practice because of the compe tition between the oxidation of DBT and the self-decomposition reaction of hydroge peroxide. Accordingly, Figure 9 shows the effect of the O/S ratio on sulfur removal usin

Influence of O/S Ratio on Sulfur Removal
Due to its superiority, hydrogen peroxide plays an important role as an oxidant in the process of oxidative desulfurization. Stoichiometrically, 2 mol of hydrogen peroxide is required for the oxidation of sulfur components to the corresponding sulfones [46]. However, a higher oxygen/sulfur ratio (O/S) is needed in practice because of the competition between the oxidation of DBT and the self-decomposition reaction of hydrogen peroxide. Accordingly, Figure 9 shows the effect of the O/S ratio on sulfur removal using DBT. When the molar ratio of O/S increased from 2 to 6, sulfur removal efficiency markedly increased from 78% to 100% in 1.5 h. There was no evident change in sulfur removal as the molar ratio H 2 O 2 /DBT gradually increased up to 10. These results revealed that the amount of oxidant required in the system had reached saturation at an O/S ratio of 6. Therefore, considering the reality of the reaction system, a molar ratio H 2 O 2 /DBT of 6 was regarded as the most suitable value in the oxidative desulfurization system. DBT. When the molar ratio of O/S increased from 2 to 6, sulfur removal efficiency markedly increased from 78% to 100% in 1.5 h. There was no evident change in sulfur removal as the molar ratio H2O2/DBT gradually increased up to 10. These results revealed that the amount of oxidant required in the system had reached saturation at an O/S ratio of 6. Therefore, considering the reality of the reaction system, a molar ratio H2O2/DBT of 6 was regarded as the most suitable value in the oxidative desulfurization system.

Sulfur Removal of Different Temperatures
The influence of temperature on the desulfurization efficiency is shown in Figure 10. The experimental conditions were as follows: O/S = 6, VDBT = 5 mL, VIL = 3 mL, m = 30 mg, and t = 180 min. When the reaction temperature increased from 20 to 60 °C, the rate of desulfurization increased markedly from 69.3% to 100% within 2 h. Under the same ex-

Sulfur Removal of Different Temperatures
The influence of temperature on the desulfurization efficiency is shown in Figure 10. The experimental conditions were as follows: O/S = 6, V DBT = 5 mL, V IL = 3 mL, m = 30 mg, and t = 180 min. When the reaction temperature increased from 20 to 60 • C, the rate of desulfurization increased markedly from 69.3% to 100% within 2 h. Under the same experimental conditions, 60 • C was the lowest temperature at which a sulfur removal rate of 100% was achieved. Higher temperatures promote the desulfurization process but higher temperatures mean higher costs of production. Accordingly, 60 • C was selected as the optimal reaction temperature for sulfur removal using DBT under the experimental conditions.

Sulfur Removal of Different Temperatures
The influence of temperature on the desulfurization efficiency is shown in Figure 10 The experimental conditions were as follows: O/S = 6, VDBT = 5 mL, VIL = 3 mL, m = 30 mg and t = 180 min. When the reaction temperature increased from 20 to 60 °C, the rate o desulfurization increased markedly from 69.3% to 100% within 2 h. Under the same ex perimental conditions, 60 °C was the lowest temperature at which a sulfur removal rat of 100% was achieved. Higher temperatures promote the desulfurization process bu higher temperatures mean higher costs of production. Accordingly, 60 °C was selected a the optimal reaction temperature for sulfur removal using DBT under the experimenta conditions.

Sulfur Removal of Different Sulfur-Containing Compounds
Different sulfur-containing compounds T, BT, DBT and 4,6-DMDBT were used in the model oil as representatives to investigate the desulfurization efficiency of the ECODS system under the optimal experimental conditions. As the desulfurization process progressed, the sulfur content of the different model oils gradually decreased. The removal of T eventually was up to 74% within 3 h, while the removal of BT, DBT and 4,6-DMDBT reached 99.63%, 100% and 99.75%, respectively. As can be seen from Figure 11, sulfur removal efficiency decreased as follows: DBT > 4,6-DMDBT > BT > T. At the same time, the electron density and steric hindrance of the sulfur atom were two critical factors for desulfurization efficiency. It is known that a higher electron density and lower steric hindrance contribute to a higher desulfurization efficiency in desulfurization systems. The electron densities of the sulfur atoms in 4,6-DMDBT, DBT, BT and T are 5.760, 5.758, 5.739 and 5.696, respectively; thus, the desulfurization rates using T, BT and DBT were affected by the electron density [47]. However, 4,6-DMDBT was unfavorable for its interactions with the catalytic centers because of the steric hindrance imposed by the methyl group, with the effect that the sulfur removal rate of 4,6-DMDBT was lower than that of DBT.
The electron densities of the sulfur atoms in 4,6-DMDBT, DBT, BT and T are 5.760, 5.75 5.739 and 5.696, respectively; thus, the desulfurization rates using T, BT and DBT wer affected by the electron density [47]. However, 4,6-DMDBT was unfavorable for its in teractions with the catalytic centers because of the steric hindrance imposed by the me thyl group, with the effect that the sulfur removal rate of 4,6-DMDBT was lower than tha of DBT.

Sulfur Removal of Different Desulfurization Systems
After optimizing the experimental conditions, sulfur removal of different desulfu rization systems was compared in Figure 12. As shown in curve b, when the desulfuriza tion reaction was carried out for 120 min, the individual extractive desulfurization effi ciency of pure ionic liquid [BMIM]BF4 without any catalyst was only 28.11%. As shown i curve c, when [BMIM]Cl-based MCF as a non-catalytic carrier was added to ionic liqui [BMIM]BF4, the desulfurization efficiency was 33.89%. This result was similar to the ex tractive desulfurization system alone, indicating that [BMIM]Cl-based MCF had no ca alytic function to improve the sulfur removal rate. For the extractive and catalytic oxida tive desulfurization (ECODS) model, pure H3PMo12O40 was used as the catalyst wit [BMIM]BF4 as the extractant (curve d), resulting in a sulfur removal rate of 72.6%. Th indicated that the desulfurization efficiency was promoted in the pure acidic cataly system. However, as it can be seen from curve e with the [BMIM]3PMo12O40-based MC as the catalyst, the desulfurization rate was 100% within 90 min. Therefore, under th optimal experimental conditions, the ECODS system with [BMIM]3PMo12O40-based MC as the catalyst produced the best desulfurization performance. This was ascribed to th dual advantages of [BMIM]3PMo12O40-based MCF-the structural advantages of MC

Sulfur Removal of Different Desulfurization Systems
After optimizing the experimental conditions, sulfur removal of different desulfurization systems was compared in Figure 12. As shown in curve b, when the desulfurization reaction was carried out for 120 min, the individual extractive desulfurization efficiency of pure ionic liquid [BMIM]BF 4 without any catalyst was only 28 and the catalytic properties of the heteropolyacids; in tandem, these characteristics increased the contact between the catalytic active sites and the fuel system.

Reusability of [BMIM]3PMo12O40-Based MCF
The reusability and stability of catalysts are significant requirements for its industrial application. Under the optimal experimental conditions, the regeneration of catalysts in the ECODS system was investigated (Figure 13). In the extractive catalytic oxidation process, the sulfide in the oil phase was first extracted by the ionic liquid phase and then the extracted sulfide was further oxidized into the polar sulfone in the presence of [BMIM]3PMo12O40-based MCF and hydrogen peroxide. The first removal and conversion of DBT was completed in fuel. After the first recycling reaction of oxidative desulfurization, the upper oil phase was decanted from the reaction system. The catalyst was isolated from the lower phase by centrifugal separation, then washed with diethyl ether and heated before the next reaction was commenced using fresh model oil and fresh hydrogen peroxide [48]. Sulfur removal efficiency still reached 99.8% after the [BMIM]3PMo12O40-based MCF was recycled six times. Thus, the [BMIM]3PMo12O40-based MCF showed an excellent recycling capability, which was attributed to its structural stability.

Reusability of [BMIM] 3 PMo 12 O 40 -Based MCF
The reusability and stability of catalysts are significant requirements for its industrial application. Under the optimal experimental conditions, the regeneration of catalysts in the ECODS system was investigated (Figure 13). In the extractive catalytic oxidation process, the sulfide in the oil phase was first extracted by the ionic liquid phase and then the extracted sulfide was further oxidized into the polar sulfone in the presence of [BMIM] 3 PMo 12 O 40 -based MCF and hydrogen peroxide. The first removal and conversion of DBT was completed in fuel. After the first recycling reaction of oxidative desulfurization, the upper oil phase was decanted from the reaction system. The catalyst was isolated from the lower phase by centrifugal separation, then washed with diethyl ether and heated before the next reaction was commenced using fresh model oil and fresh hydrogen peroxide [48]. Sulfur removal efficiency still reached 99.8% after the [BMIM] 3 PMo 12 O 40 -based MCF was recycled six times. Thus, the [BMIM] 3 PMo 12 O 40 -based MCF showed an excellent recycling capability, which was attributed to its structural stability. and the catalytic properties of the heteropolyacids; in tandem, these characteristics in creased the contact between the catalytic active sites and the fuel system.

Reusability of [BMIM]3PMo12O40-Based MCF
The reusability and stability of catalysts are significant requirements for its indu trial application. Under the optimal experimental conditions, the regeneration of cata lysts in the ECODS system was investigated ( Figure 13). In the extractive catalytic oxida tion process, the sulfide in the oil phase was first extracted by the ionic liquid phase an then the extracted sulfide was further oxidized into the polar sulfone in the presence o [BMIM]3PMo12O40-based MCF and hydrogen peroxide. The first removal and conversio of DBT was completed in fuel. After the first recycling reaction of oxidative desulfuriza tion, the upper oil phase was decanted from the reaction system. The catalyst was iso lated from the lower phase by centrifugal separation, then washed with diethyl ether an heated before the next reaction was commenced using fresh model oil and fresh hydro gen peroxide [48]. Sulfur removal efficiency still reached 99.8% after th [BMIM]3PMo12O40-based MCF was recycled six times. Thus, the [BMIM]3PMo12O40-base MCF showed an excellent recycling capability, which was attributed to its structural sta bility.

Conclusions
In this paper, MCF modified with heteropolyacid ionic liquids was successfully designed and synthesized. The surface morphology and structure of samples were characterized by XRD, N 2 adsorption-desorption and TEM, indicating that MCF modified with different heteropolyacid ionic liquids maintains the mesoporous structure of MCF. Because of advantages in structure, heteropolyacid ionic liquid-based MCF was not only highly conducive to mass transfer, but also greatly increased catalytic active sites to improve catalytic efficiency. Simultaneously, heteropolyacid ionic liquid-based MCF solved the difficult separation in the process of oxidative desulfurization. By comparison, [BMIM] 3 PMo 12 O 40based MCF exhibited the highest catalytic activity, which also led to the most optimal performance in terms of sulfur removal efficiency in the extractive catalytic oxidation desulfurization system. The removal of dibenzothiophene could achieve levels of 100% in 90 min. Additionally, four sulfur-containing compounds could be removed completely under mild conditions. After the desulfurization process of extractive catalytic oxidation desulfurization system was completed, the regeneration of [BMIM] 3