Oxidative desulfurization of fuels at room temperature using ordered meso/macroporous H3PW12O40/SiO2 catalyst with high specific surface areas

Du Yue; Jiaheng Lei; Lina Zhou; Xiaodi Du; Zhenran Guo; Junsheng Li

doi:10.1016/j.arabjc.2018.06.017

View/Download PDF

Buy Reprints

PDF

Translate this page into:

Original article

13 (

); 2649-2658

doi:

10.1016/j.arabjc.2018.06.017

Oxidative desulfurization of fuels at room temperature using ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst with high specific surface areas

Du Yue^{^a}, Jiaheng Lei^{^b,⁎}, Lina Zhou^{^a}, Xiaodi Du^{^b}, Zhenran Guo^{^b}, Junsheng Li^{^b}

a School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, Hubei 430070, PR China

b Department of Chemistry, Wuhan University of Technology, Wuhan, Hubei 430070, PR China

⁎Corresponding author. 2187@whut.edu.cn (Jiaheng Lei)

Received: 2018-3-12, Accepted: 2018-6-27, Published: 2018-01-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ nanocomposites with high specific surface areas were prepared using cationic surfactant and monodispersed polystyrene spheres (PS) as dual-template. The characterization results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption, and small-angle XRD patterns confirmed the existence of ordered meso/macroporous structure and the wide-angle XRD patterns, Fourier transform infrared spectroscopy (FTIR), X-ray photoemission spectroscopy (XPS) measurements suggested the high dispersivity of the Keggin-type heteropolyacid (HPA) on silica matrix. There was an optimum value of cationic surfactant usage and proper calcination temperature of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst leading to ultra-high specific surface areas. Furthermore, the ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst was evaluated for ultra-deep oxidative desulfurization (ODS) of cyclic sulphur-containing compounds using hydrogen peroxide (H₂O₂) as oxidant. Under optimum reaction conditions, dibenzothiophene (DBT) could be removed within 100 min at 30 °C by meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst. The excellent catalytic activity should be attributed to the combination of ordered meso/macroporous architecture and high surface area of H₃PW₁₂O₄₀/SiO₂ catalyst which promoted the mass transport of reactants and products in the pore channel and provided more accessible catalytic active sites. In addition, the meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst showed good stability with only 1.9% efficiency decreased after 6 cycles.

Keywords

Ordered meso/macroporous structure

Phosphotungstic acid

Oxidative desulfurization

Room temperature

Show Related Articles from PubMed

1 Introduction

Desulfurization of fuel such as petroleum, gasoline, and diesel oil was an essential step on the petroleum refining process (Bhutto et al., 2016). Hydrodesulfurization (HDS), as the widely used approach in the petroleum refining industry, was efficient in eliminating aliphatic and acyclic sulfur-containing compounds such as thiols, sulfides, and disulfides (Mjalli et al., 2014). However, it was less effective to thiophene-type sulphide because of their steric hindrance (Te et al., 2001; Campos-Martin et al., 2004). In order to get rid of these sulphur-containing compounds such as benzothiophene (BT), dibenzothiophene (DBT) and its alkyl substituted derivatives, some alternative approaches such as, adsorption (ADS) (Ma et al., 2005), extraction (EDS) (Holbrey et al., 2008); biological (BDS) (Abro et al., 2014), and oxidative desulfurization technology (ODS) (Li et al., 2012) were developed recent years.

Since the high efficiency and mild reaction conditions (ambient pressure, <100 °C) of ODS technology on refractory heterocyclic S-compounds (Xun et al., 2014; Abdalla and Li, 2012); ODS was considered to be one of the most promising methods to accomplish clean fuel with ultra-low sulfur content. Various kinds of oxidants such as nitrogen dioxides (NO₂) (Kozhevnikov, 1997), O₃ (Zaykina et al., 2004), t-BuOOH (Ishihara et al., 2005), molecular oxygen (Lü et al., 2007), and H₂O₂ (Ishii et al., 1988) had been applied in ODS process. Among these oxidants, H₂O₂ was extensively investigated because of its high activity, environmental compatibility, affordable cost, and commercial availability (Bhutto et al., 2016). Besides, the ODS of thiophene derivatives with H₂O₂ can be proceed effectively under the presence of catalyst such as organic acid (Zannikos et al., 1995), titanium molecular sieves (Hulea et al., 2001), vanadium pentoxide (Ceden-Caero et al., 2008); polyoxometalates (POMs) (Duncan et al., 1995) or ionic liquids (IL) (Li et al., 2009). In the ODS process, the sulfur species could be selectively oxidized to corresponding sulfoxide and sulfone by the electrophilic addition reaction of oxygen atoms (Li et al., 2012). Combined with extraction process, the hexavalent sulfur of sulfones was then removed by polar solvent (Ishii et al., 1988).

Among these systems, H₂O₂/polyoxometalates systems have attracted the most attention from researchers because of its pseudo-liquid phase behaviour and unique catalytic properties (Yan et al., 2013). However, polyoxometalates was high solubility in the polar media and difficult reclamation from heterogeneous catalytic system, various kinds of porous solid materials such as SiO₂ (Qiu et al., 2015; Qi et al., 2015; Xiong et al., 2014 ); TiO₂ (Fraile et al., 2016); γ-Al₂O₃ (Garcia-Gutierrez et al., 2006), activated carbon (Arcibar-Orozco et al., 2013), and metal-organic framework (MOF) (Long et al., 2014) had been developed as carriers. These HPA-supported catalysts showed excellent ODS catalytic activity of thiophene and its derivative owing to its relatively high surface area and pore volume. In our previous study, several kinds of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalysts have been prepared by evaporation-induced self-assembly (EISA) and colloidal template method (Yang et al., 2016; Yue et al., 2018; Yue et al., 2017 ); the meso/macroporous catalysts displayed better catalytic activity of ODS than corresponding mesoporous H₃PW₁₂O₄₀/SiO₂ catalysts. The enhanced catalytic activity could be attributed to the interconnected meso/macroporous structure of catalyst, which facilitated the mass transfer of reactants and products in the pore channel, increased the availability of the internal surface. However, the specific surface areas of these supported meso/macroporous structured HPW catalyst was no more than 500 m²/g which limited the ODS capacity of hierarchical porous supported heteropoly acid catalysts.

In this work, a series of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalysts with high specific surface areas was prepared in one step using cationic surfactant and monodispersed polystyrene spheres (PS) as dual-template and the feasibility of its application as ODS catalysts was studied. Moreover, the influence of cationic surfactant usage and calcination temperature effects on catalytic activity of ordered meso/macroporous HPW/SiO₂ were further investigated. Under optimum conditions, the as-synthesized ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst showed excellent catalytic performance at room temperature in ODS process, which could be attributed to the combined action of ordered meso/macroporous architecture and ultra-high surface area of the catalyst.

2 Experimental section

2.1

2.1 Materials

Tetraethyl orthosilioate (TEOS), absolute ethanol, concentrated hydrochloric acid, styrene, potassium persulfate (K₂S₂O₈), petroleum ether (90–120 °C), and hydrogen peroxide (30%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Phosphotungstic acid (H₃PW₁₂O₄₀), stearyltrimethylammoniumbromide (STAB), dibenzothiophene (DBT), benzothiophene (BT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were marketed by Aladdin Chemistry. All the chemicals received were used directly without further purification.

2.2

2.2 Catalysts preparation

350 nm alcohol-dispersed monodispersed polystyrene spheres (PS) solution was prepared according to the previous report (Holland et al., 1999). A detailed procedure for the preparation of PS spheres was described in the Supporting Information.

Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.arabjc.2018.06.017.

Supporting information

Download

A typical synthesis of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst was carried out as follows: 2.83 g of TEOS was added to a clear solution containing 3.1 mL of ethanol, 0.15 g of hydrochloric acid, and 0.44 g of distilled water. Subsequently, a certain amount of HPW (20 wt% of the silica) was added to the solution. After vigorous stirring of the mixture for 0.5 h, ethanol solution of STAB (1 mmol, 3 mmol, 5 mmol, 7 mmol, or 9 mmol dissolved in 30 mL ethanol) was added to the solution by drop-wise addition and subjected to another 2 h stirring. Then, alcohol-dispersed PS solution (3 g PS powder dispersed in 30 mL ethanol) was added to the above-described precursor solution and maintained stirring for 5 h at room temperature. The homogeneous solution was poured into Petri dishes (diameter 200 mm) and kept in an oven at 40 °C for 2 days and 60 °C for another day without additional humidity control. The as-made product was calcined at different temperature (300 °C, 350 °C, 400 °C, 450 °C, or 500 °C) for 10 h in air. The ramping rate was fixed at 1 °C. The obtained ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalysts was labeled as HPW/SiO₂-x-y, where x and y stand for STAB usage and the final calcination temperature, respectively.

2.3

2.3 Characterization

Scanning electron microscope images and transmission electron microscopy was taken with a Hitachi S-4800 microscope operating at 20 kV and a JEM 2100F electron microscope operating at 200 kV, respectively. X-ray diffraction (XRD) patterns were tested in a Rigaku Ru-200B diffractometer with a Cu Κα radiation (λ = 1.5406 Å) operating at 40 kV, 40 mA. The N₂ adsorption-desorption data were recorded by Micromeritics TriStar II 3020 analyzer, the specific surface areas (S_BET) of catalysts were calculated by BET method using adsorption data in a relative pressure range from 0.1 to 0.30. The surface area of micropores (S_mi) was calculated using the t-plot method, the t values were calculated as a function of the relative pressure (P/P₀) ranging from 0.2 to 0.5 using the de Bore equation, t (Å) = [13.99/(log(P₀/P) + 0.0340)]^1/2 (Liu et al., 2013). The pore size distributions (PSDs) were calculated based on the adsorption branches data of the isotherms using the Barrett-Joyner-Halenda (BJH) method. The total pore volumes (V_t) were estimated on the basis of the amount adsorbed at a relative pressure of ∼0.95. The X-ray photoemission spectroscopy (XPS) was recorded on a VG MultiLab 2000 system with a monochromatic Mg-Ka source operated at 20 kV. Fourier transform infrared (FT-IR) spectra were recorded on a Digilab-FTS60 spectrometer in the transmission mode using KBr method. TG/DSC analysis of the catalyst was measured on a Netzsch STA 409 PC thermal analysis instruments. The catalyst was heated from 20 to 600 °C at a speed of 5 °C/min under air atmospheres. HPW content in sample was also done by using inductively coupled plasma (ICP, Perkin-Elmer 3300DV).

2.4

2.4 Oxidative desulfurization of model fuel

Model fuel oils with sulfur content of 500 mg/L (S) were prepared by dissolving DBT, BT, or 4,6-DMDBT in petroleum ether, respectively. Tests of catalytic oxidative desulfurization were performed in a 50 mL two-neck flask equipped with stirrer and a water-circulated condenser column. 10 mL of model fuel oil, 10 mL of acetonitrile, and 0.1 g of catalyst was add into the reactor and heated to 30 °C. And then, 63 μl of 30 wt% aqueous H₂O₂ put into the mixture to initiate the reaction. The dosage of oxidant was marked as O/S (the molar ratio of H₂O₂ to sulfur). After reaction, the catalyst was recovered by centrifugation, washed with methanol, dried at 100 °C for 12 h, and subjected to the next ODS process. Oxidized model fuel oil was withdrawn and the sulfur content was analyzed by a high performance liquid chromatography (HPLC). The HPLC system was LC-20A (Shimadzu, Japan), instrument with a SPD 20A ultraviolet detector, LC-20AT pumps and a SinoChrom ODS-BP column (4.6 mm × 200 mm, 5 μm).

3 Results and discussion

3.1

3.1 Characterization of the samples

The meso/macroporous morphology of HPW/SiO₂-5 catalyst was examined by SEM and TEM. As shown in Fig. 1A and B, the macroporous structure of catalyst was preserved throughout the entire area and the macropores was tended to accumulate and arranged periodicity. As presented in Fig. 1C, the uniform pore sizes, windows and wall thicknesses of the macroporous structure can be easily observed. Moreover, the macropores and porous walls of next layer were clearly displayed in Fig. 1C which suggested that partial structure of catalyst was an open ordered macroporous network interconnected by small window pores (Yu et al., 2015; Yang et al., 2014). The average macroporous diameter of catalyst was estimated to be 250 nm, which was much smaller than the monodispersed PS spheres. This was the combined impact of SiO₂ framework contraction and shrinkage of PS microspheres during the calcination process (Yang et al., 2016). Furthermore, TEM image further elucidated the inner ordered macro-mesoporous architecture of catalyst, highly ordered stripe-like arrays of channels existed between the close-packed macroporous wall Fig. 1E and F). The mesoporous diameter calculated from the TEM was about 3 nm.

SEM (A–C) and TEM (D–F) images of meso/macroporous HPW/SiO2-5 catalyst.

Textural properties of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂catalysts were further characterized by N₂ adsorption-desorption measurement. As presented in Fig. 2A, The N₂ sorption isotherm of catalysts presented a type IV isotherm, among which HPW/SiO₂-5 sample showed a clear capillary condensation step at P/P₀ = 0.4–0.8 suggesting the existence of uniform mesopores (Qiu et al., 2015). Moreover, the additional step at a high relative pressure could be attributed to the textural macorpore in sample (Liu et al., 2013; Dhainaut et al., 2010). The corresponding BJH PSDs curves of meso/macroporous H₃PW₁₂O₄₀/SiO₂ samples exhibited regular variations between 2.4 and 4.3 nm with the additional STAB usage Table 1). However, the BET surface areas of catalysts increased firstly but declined afterward with the enhanced STAB concentrations. The increasing BET surface areas were caused by the higher ordered mesoporous silicon spheres concentrations originated from the STAB (Liu et al., 2013). The decreased S_BET of HPW/SiO₂-7 and HPW/SiO₂-9 might be attributed to the instability of ordered mesoporous silicon spheres caused by the excessive cationic surfactant. Furthermore, the mesostructural ordering of meso/macroporous H₃PW₁₂O₄₀/SiO₂catalyst was characterized by small-angle XRD patterns Fig. 2C). With proper STAB usage, HPW/SiO₂-5 showed obvious characteristic diffraction peak at approximately 2θ = 2.5° compared with other samples, which indicated the existence of well-ordered mesoporous structure in HPW/SiO₂-5 sample (Qiu et al., 2015; Thompson et al., 2014), in consistence with the TEM result. In addition, the wide-angle XRD pattern of HPW/SiO₂-5 sample was presented in Fig. 2D, the broad and wild diffraction peaks at 2θ = 24.3° could be assigned to amorphous silica (Abdalla et al., 2009). No typical diffraction peaks of Keggin type of heteropoly acids could be observed in the amorphous silica, indicating the high dispersivity of the non-crystal HPW species on the SiO₂ framework (Yan et al., 2013; Yang et al., 2016).

(A) N2 sorption isotherms and (B) the corresponding BJH PSD curves of meso/macroporous HPW/SiO2 catalysts with different STAB usage; (C) The small-angle XRD patterns of (a) HPW/SiO2-1, (b) HPW/SiO2-3, (c) HPW/SiO2-5, (d) HPW/SiO2-7, and (e) HPW/SiO2-9; (D) The wide-angle XRD patterns of HPW/SiO2-5 catalyst.

Table 1 Structure parameters and sulfur removal activities of catalysts.

Catalysts	HPW dosage^a (%)	S_BET^b (m²/g)	S_mi^c (m²/g)	D^d (nm)	V_t^e (cm³/g)	DBT removal^f (%)
HPW/SiO₂-1	19.8	623.9	400.9	2.4	0.33	92.1
HPW/SiO₂-3	19.6	1184.4	786.1	2.6	0.31	96.4
HPW/SiO₂-5	19.8	1457.7	1244.5	2.7	0.33	100
HPW/SiO₂-7	19.9	1047.4	900.2	3.2	0.72	93.2
HPW/SiO₂-9	19.6	833.6	658.3	4.3	0.79	83.5
HPW/SiO₂-5-300	19.8	554.9	340.1	2.7	0.34	71.4
HPW/SiO₂-5-350	19.7	627.7	421.5	2.8	0.41	80.2
HPW/SiO₂-5-400	19.7	1354.4	1031.7	2.8	0.94	92.3
HPW/SiO₂-5-500	19.7	1434.3	1189.4	2.7	0.92	76.5

a HPW dosage in catalysts, calculated from the mass percentage of element W and P in the catalyst.

b S_BET BET specific surface area.

c S_mi micropore surface area, was calculated from t-plot method.

d D mesopore diameter at the maxima of BJH pore size distribution curve.

e V_t total pore volume.

f Reaction conditions: catalyst dosage = 0.1 g, T = 30 °C, O/S = 4 and t = 100 min.

Chemical states of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂catalysts were investigated by XPS and FT-IR analysis. As shown in Fig. 3A, the survey scan XPS spectrum of HPW/SiO₂-5 suggested elements composition of sample (Si, O, C, P, and W). The Si 2p XPS spectrum and O 1s peak in 533.2 eV of catalyst exhibited in Fig. 2C and D confirmed the existence of SiO₂ in the sample (Xiong et al., 2014). Moreover, Fig. 2E and F displayed the high resolution P 2p and W 4f XPS spectra indicated the introduction of HPW in catalyst. In addition, the FT-IR analysis was used to further illustrate the structure of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂catalysts. As shown in Fig. 4, Keggin type of phosphotungstic acid exhibited four main spectra between 700 and 1200 cm⁻¹ (1080 cm⁻¹ for v_as(P-O), 980 cm⁻¹ for v_as(W = O), 890 cm⁻¹ for v_as(W-O_b-W), and 800 cm⁻¹ for v_as(W-O_c-W)) (Zheng et al., 2013), which overlapped with the typical absorption peaks of amorphous silica at 805 cm⁻¹, 960 cm⁻¹, and 1060–1250 cm⁻¹ (Wu et al., 2014). While, there were still two weak typical absorption peaks of H₃PW₁₂O₄₀ could be observed at 980 and 890 cm⁻¹, suggested that the H₃PW₁₂O₄₀ incorporated in the SiO₂ framework maintained its Keggin structure, in consistence with XPS result (Yang et al., 2016).

XPS spectra of the meso/macroporous HPW/SiO2-5 catalyst (A) Survey of the sample; (B) C 1s; (C) Si 2p; (D) O 1s; (E) P 2p; (F) W 4f.

FT-IR spectra of HPW and meso/macroporous HPW/SiO2 catalysts prepared with different dosage of STAB (a) HPW/SiO2-1, (b) HPW/SiO2-3, (c) HPW/SiO2-5, (d) HPW/SiO2-7, and (e) HPW/SiO2-9.

The calcination temperature of catalyst played a major role which was related to the BET surface areas and the total pore volume of catalyst. Templates of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ composite such as quaternary ammonium salt and monodispersed PS spheres could be removed successfully under proper calcination temperature, without decomposition of Keggin structure of H₃PW₁₂O₄₀ and destruction of the porous structure (Qiu et al., 2015). As shown in Fig. 5A and B, the N₂ sorption isotherm of ordered meso/macroporous HPW/SiO₂-5catalyst calcined under 300 °C, 350 °C, 400 °C, 450 °C, and 500 °C exhibited a typical type of IV isotherm with an H1 like hysteresis loop, suggesting the existence of large numbers of mesopores. Moreover, the additional adsorption step appeared at P/P₀ > 0.9, indicated the coexistence of macroporous structure (Yue et al., 2018). The corresponding BJH PSD of each catalyst showed similar mesoporous diameter, with a mean value of 2.7 nm Fig. 5B). As showed in Table 1, the micropore surface area of these catalysts were increased with the raised calcination temperatures, which suggested that the development of micropores was closely connected with the BET surface areas of catalysts (Liu et al., 2011). Meanwhile, the total pore volume of these catalysts became larger when the calcination temperature was less than 400 °C, contributing to different shrinkage level of catalyst structure (Liu et al., 2012). However, a decreasing trend of catalyst pore volume appeared at 500 °C Table 1, which could contribute to the decomposition of H₃PW₁₂O₄₀ and partially disrupting of porous structure under high calcination temperature. Furthermore, Fig. 5C displayed simultaneous TG/DSC curves of HPW/SiO₂-5composite under air atmosphere. Two DSC endothermic peaks at 110 and 232 °C could be ascribed to the melting of polystyrene microspheres and decomposition of organic radicals, respectively (Cho et al., 2011). Two major weight losses over 300 °C corresponded well with two exothermic peaks at 350 and 490 °C, which was mainly contributed to the desorption of PS spheres and H₃PW₁₂O₄₀ (Sen et al., 2004). The DSC measurements showed that the calcination temperature of ordered meso/macroporous HPW/SiO₂-5catalyst should not go below 350 °C or above 490 °C. Moreover, FT-IR spectra of HPW/SiO₂-5calcined under different temperature suggested that the Keggin-type H₃PW₁₂O₄₀ structure could be preserved under 450 °C, while, there were no typical absorption peaks of H₃PW₁₂O₄₀ could be observed at 500 °C. Taking the BET surface areas, pore volume, and the decomposition of H₃PW₁₂O₄₀ into account, 450 °C was selected to be the optimal calcination temperature of HPW/SiO₂-5catalyst.

(A) N2 sorption isotherms and (B) the corresponding BJH PSD curves of meso/macroporous HPW/SiO2-5 catalyst calcined under different temperature; (C) TG curves for meso/macroporous HPW/SiO2-5 composites under an air atmosphere; (D) FT-IR spectra of meso/macroporous HPW/SiO2-5 calcined at different temperature (a) HPW/SiO2-5-300, (b) HPW/SiO2-5-350, (c) HPW/SiO2-5-400, (d) HPW/SiO2-5-450, and (e) HPW/SiO2-5-500.

3.2

3.2 The catalytic performance of samples

Characterization results of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalysts showed that the proper usage of STAB led to larger S_BET, S_mi, and mesopore diameter of catalyst. In order to illustrate the influence of the STAB usage of catalyst on ODS process, the DBT removal of HPW/SiO₂-1, HPW/SiO₂-3, HPW/SiO₂-5, HPW/SiO₂-7, and HPW/SiO₂-9 was tested under the same test conditions (catalyst dosage = 0.1 g, T = 30 °C, O/S = 4). As shown in Fig. 6, DBT removal of catalysts enhanced with the increasing BET surface areas and mesopore diameter of HPW/SiO₂-1, HPW/SiO₂-3, and HPW/SiO₂-5. However, DBT removal of catalysts decreased when the STAB usage increased to 7 or 9 mmol. This was caused by an excessive dose of STAB which led to the partial collapse of the porous structure. It was in consistent with the N₂ adsorption-desorption results. The superior activity of HPW/SiO₂-5 was the combined effects of ordered meso/macroporous structure and high specific surface areas of catalyst which further facilitated the mass transfer of sulphur containing compounds, increased the availability of the catalytic active sites, and elevated the desulphurization efficiency of catalyst.

The DBT removal of meso/macroporous HPW/SiO2-1, HPW/SiO2-3, HPW/SiO2-5, HPW/SiO2-7, and HPW/SiO2-9, catalyst dosage = 0.1 g, T = 30 °C, O/S = 4.

Effects of oxidant amount, catalyst usage, and reaction temperature on the DBT removal of HPW/SiO₂-5 was studied systematically. As shown in Fig. 7A, at the value of stoichiometry of the reactions (O/S = 2), 93.9% of DBT could be removed within 2 h which indicated that there was only 6.1% of H₂O₂ unreacted with DBT because of decomposition (Collins et al., 1997). The high utilization of H₂O₂ should be attributed to the low reaction temperature (30 °C) of the ODS system. When the O/S molar ratio reached up to 4 or 8, the DBT removal rate of catalyst enhanced with the increasing production quantity of catalytic activity species (Fraile et al., 2016). However, there was a significant downswing appeared when the O/S molar ratio up to 12. This was because of the increasing concentration of H⁺ in the catalytic system which facilitated the attack of the H⁺ on the P = O species and restrained the reaction of H₂O₂ with the P = O species form the catalytic active intermediate species, such as {PO₄[WO(O₂)₂]₄} (Qiu et al., 2015). Hence, O/S molar ratio of 4 was considered to be the optimal conditions.

The DBT removal of meso/macroporous HPW/SiO2-5 catalyst with (A) different O/S, (B) different catalyst usage, (C) different reaction temperature, and (D) the sulfur removal of meso/macroporous HPW/SiO2-5 with different substrates, catalyst dosage = 0.1 g, T = 30 °C, O/S = 4.

The effect of catalyst amount on DBT removal was shown in Fig. 7B. It can be seen that the DBT removal of catalyst enhanced when the catalyst usage increased from 0.03 g to 0.2 g, which should be attributed to the more catalytic active sites provided by the increased catalyst dosage (Yang et al., 2016). When the catalyst dosage was 0.1 g, the desulfurization rates of DBT got up to 96.8% within 1 h at 30 °C, which indicated that 0.1 g of catalyst had provided enough catalytic active sites for the ODS.

Temperature also played an important role in the ODS system. As shown in Fig. 7C, The desulfurization reaction might be limited by the kinetics at low temperatures such as 25, 30, and 35 °C, DBT removal of catalyst increased obviously with the temperature (Zhang et al., 2011). However, DBT removal showed no significant increase at 40 °C, this result might be closely related to the increasing decomposition of hydrogen peroxide (Tang et al., 2013). Hence, the optimal temperature of ODS was determined to be 30 °C under the current reaction conditions.

Apart from DBT, desulphurization efficiency of cyclic sulphur-containing substrates such as BT and 4,6-DMDBT was carried out under selected conditions. Fig. 7D displayed that the sulfur removal of BT, DBT, and 4,6-DMDBT reached 87.7, 100, and 96.9% within 2 h, respectively, consistent with the order of DBT ＞ 4,6-DMDBT ＞ BT (Yue et al., 2018). The result was linked to the both effects of electron density on the sulfur atoms and steric hindrance of sulfur compounds (Zhang et al., 2014). The oxidation rate constants of polyaromatic sulfur-containing compounds were increased with the electron density on the sulfur atoms, which were 5.739, 5.758, and 5.760 for BT, DBT, and 4,6-DMDBT, respectively (Zhang et al., 2011). The lowest removal rate of BT than DBT and 4;6-DMDBT was contributed to its lowest electron density on the sulfur atoms. The lower removal rate of 4,6-DMDBT than DBT was due to the methyl groups at the position 4 and 6 of DBT rings hindered the adsorption of the sulfur atom on the catalytic active site (Lorencon et al., 2014).

Fig. 8 showed the effect of calcination temperature on the BET surface area and catalytic efficiency of HPW/SiO₂-5 catalyst. The DBT removal of catalyst increased obviously with the calcination temperature, when the calcination temperature was lower than 450 °C. This could be contributed to the change in the pore structure and increased BET surface area during the calcination of catalyst (Qiu et al., 2015). When the calcination temperature exceeded the thermal decomposition temperature of H₃PW₁₂O₄₀ (470 °C) such as 500 °C (Sen et al., 2004), the decline of DBT removal of HPW/SiO₂-5-500 catalyst was mainly caused by the serious decomposition of Keggin-type H₃PW₁₂O₄₀ structure with no obvious lose BET surface area.

Effect of calcination temperature on BET surface area and DBT removal of meso/macroporous HPW/SiO2-5 catalyst, catalyst dosage = 0.1 g, T = 30 °C, O/S = 4.

Moreover, the recycle of the catalyst HPW/SiO₂-5 was carried out in the oxidation of DBT. Even after 6 cycles, there were only 1.9% of efficiency was decreased than the fresh catalyst. HPW content on the spent catalyst was recorded by ICP, which dropped from 19.8% to 19.0% after six cycles. In addition, Fig. 9B showed the FT-IR spectra of fresh catalyst and spent catalyst which further confirmed the stability of Keggin-type H₃PW₁₂O₄₀ structure on HPW/SiO₂-5 catalyst under operating conditions.

(A) Effect of the recycles on the conversion of DBT with HPW/SiO2-5 as catalyst, catalyst dosage = 0.1 g, T = 30 °C, O/S = 4, t = 2 h and (B) FT-IR spectra of fresh catalyst and spent catalyst.

4 Conclusions

Ordered meso/macroporous structured H₃PW₁₂O₄₀/SiO₂ catalyst with high specific surface areas was successfully synthesised in one step using STAB and monodisperse PS spheres as templates. Influences of STAB usage and calcination temperature on the ordered meso/macroporous structure were further investigated in the preparation process. With proper STAB usage, ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ material with ultra-high mesoporous specific surface areas 1457.7 m²/g could be obtained. The Keggin-type H₃PW₁₂O₄₀ were highly dispersed on silica matrix. The catalyst with 5 mmol STAB usage calcined at 450 °C was found to exhibit the highest desulfurization performance of thiophenic sulfur than other samples. Under selected reaction conditions, DBT could be totally removed within 100 min at 30 °C and the low reaction temperature effectively increased the utilization of oxidant H₂O₂. Superior ODS activity could be attributed to the high specific surface area of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst, resulting in a higher amount of accessible active sites. In addition, the ordered meso/macroporous structure of catalyst allowed the oxidation of aromatic sulfides to sulfones without significant diffusion limitations. The catalyst also exhibited good regeneration ability with only 1.9% of conversions of decreasing even after 6 cycles. The as-synthesized ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ catalyst can be an attractive alternative for ODS of fuel.

Acknowledgements

This work was supported by the National Nature Science Foundation of China (Grant No. 21476177, 51502218).

References

Abdalla Z., Li B.S., . Preparation of MCM-41 supported (Bu₄N)₍₄₎H₃(PW₁₁O₃₉) catalyst and its performance in oxidative desulfurization. Chem. Eng. J.. 2012;200:113-121.
[Google Scholar]
Abdalla Z., Li B.S., Tufail A., . Direct synthesis of mesoporous (C₁₉H₄₂N)₄H₃(PW₁₁O₃₉)/SiO₂ and its catalytic performance in oxidative desulfurization. Colloid. Surface. A. 2009;341:86-92.
[Google Scholar]
Abro R., Abdeltawab A.A., Al-Deyab S.S., Yu G.R., Qazi A.B., Gao S.R., Chen X.C., . A review of extractive desulfurization of fuel oils using ionic liquids. RSC Adv.. 2014;4:35302-35317.
[Google Scholar]
Arcibar-Orozco J.A., Rene Range-Mendez J., Bandosz T.J., . Desulfurization of model diesel fuel on activated carbon modified with iron oxyhydroxide nanoparticles: effect of tert-butylbenzene and naphthalene concentrations. Energ. Fuel. 2013;27:5380-5387.
[Google Scholar]
Bhutto A.W., Abro R., Gao S., Abbas T., Chen X., Yu G., . Oxidative desulfurization of fuel oils using ionic liquids: a review. J. Taiwan Inst. Chem. E.. 2016;62:84-97.
[Google Scholar]
Campos-Martin J.M., Capel-Sanchez M.C., Fierro J., . Highly efficient deep desulfurization of fuels by chemical oxidation. Green Chem.. 2004;6:557-562.
[Google Scholar]
Ceden-Caero L., Gomez-Bernal H., Fraustro-Cuevas A., Guerra-Gomez H.D., Cuevas-Garcia R., . Oxidative desulfurization of synthetic diesel using supported catalysts Part III. Support effect on vanadium-based catalysts. Catal. Today. 2008;133:244-254.
[Google Scholar]
Cho W.H., Lee C.T., Yu C.C., Kei C.C., Liu D.R., Lee C.C., . Microstructure and optical properties of Al₂O₃ prepared by oblique deposition using microsphere shell templates. Appl. Opt.. 2011;9:246-249.
[Google Scholar]
Collins F.M., Lucy A.R., Sharp C., . Oxidative desulphurisation of oils via hydrogen peroxide and heteropolyanion catalysis. J. Mol. Catal. A 1997:397-403.
[Google Scholar]
Dhainaut J., Dacquin J., Lee A.F., Wilson K., . Hierarchical macroporous – mesoporous SBA-15 sulfonic acid catalysts for biodiesel synthesis. Green Chem.. 2010;12:296-303.
[Google Scholar]
Duncan D.C., Chambers R.C., Hecht E., Hill C.L., . Mechanism and dynamics in the H₃[PW₁₂O₄₀]-catalyzed selective epoxidation of terminal olefins by H₂O₂. Formation, reactivity, and stability of {PO₄[WO(O₂)₂]₄}³⁻. J. Am. Chem. Soc.. 1995;2:681-691.
[Google Scholar]
Fraile J.M., Gil C., Mayoral J.A., Muel B., Roldán L., Vispe E., Calderón S., Puente F., . Heterogeneous titanium catalysts for oxidation of dibenzothiophene in hydrocarbon solutions with hydrogen peroxide: On the road to oxidative desulfurization. Appl. Catal. B. 2016;180:680-686.
[Google Scholar]
Garcia-Gutierrez J.L., Fuentes G.A., Hernandez-Teran M.E., Murrieta F., Navarrete J., Jimenez-Cruz F., . Ultra-deep oxidative desulfurization of diesel fuel with H₂O₂ catalyzed under mild conditions by polymolybdates supported on Al₂O₃. Appl. Catal. A.. 2006;305:15-20.
[Google Scholar]
Holbrey J.D., Lopez-Martin I., Rothenberg G., Seddon K.R., Silvero G., Zheng X., . Desulfurisation of oils using ionic liquids: selection of cationic and anionic components to enhance extraction efficiency. Green Chem.. 2008;10:87-92.
[Google Scholar]
Holland B.T., Blanford C.F., Do T., Stein A., . Synthesis of highly ordered, three-dimensional, macroporous structures of amorphous or crystalline inorganic oxides, phosphates, and hybrid composites. Chem. Mater.. 1999;11:795-805.
[Google Scholar]
Hulea V., Fajula F., Bousquet J., . Mild oxidation with H₂O₂ over Ti-containing molecular sieves – a very efficient method for removing aromatic sulfur compounds from fuels. J. Catal.. 2001;198:179-186.
[Google Scholar]
Ishihara A., Wang D., Dumeignil F., Amano H., Qian E.W., Kabe T., . Oxidative desulfurization and denitrogenation of a light gas oil using an oxidation/adsorption continuous flow process. Appl. Catal. A. 2005;279:279-287.
[Google Scholar]
Ishii Y., Yamawaki K., Ura T., Yamada H., Yoshida T., Ogawa M., . Hydrogen peroxide oxidation catalyzed by heteropoly acids combined with cetylpyridinium chloride. Epoxidation of olefins and allylic alcohols, ketonization of alcohols and diols, and oxidative cleavage of 1, 2-diols and olefins. J. Org. Chem.. 1988;53:3587-3593.
[Google Scholar]
Kozhevnikov I.V., . Catalysis by heteropoly acids and multicomponent polyoxometalates in liquid-phase reactions. Chem. Rev.. 1997;98:171-198.
[Google Scholar]
Li H.M., He L.N., Lu J.D., Zhu W.S., Jiang X., Wang Y., Yan Y.S., . Deep oxidative desulfurization of fuels catalyzed by phosphotungstic acid in ionic liquids at room temperature. Energ. Fuel. 2009;23:1354-1357.
[Google Scholar]
Li B., Liu Z., Han C., Ma W., Zhao S., . In situ synthesis, characterization, and catalytic performance of tungstophosphoric acid encapsulated into the framework of mesoporous silica pillared clay. J. Colloid Interf. Sci.. 2012;377:334-341.
[Google Scholar]
Liu D., Lei J., Guo L., Deng K., . Simple hydrothermal synthesis of ordered mesoporous carbons from resorcinol and hexamine. Carbon. 2011;49:2113-2119.
[Google Scholar]
Liu D., Lei J.H., Guo L.P., Qu D.Y., Li Y., Su B.L., . One-pot aqueous route to synthesize highly ordered cubic and hexagonal mesoporous carbons from resorcinol and hexamine. Carbon. 2012;50:476-487.
[Google Scholar]
Liu D., Xia L., Qu D., Lei J., Li Y., Su B., . Synthesis of hierarchical fiberlike ordered mesoporous carbons with excellent electrochemical capacitance performance by a strongly acidic aqueous cooperative assembly route. J. Mater. Chem. A. 2013;48:15447-15458.
[Google Scholar]
Long Z.Y., Yang C.P., Zeng G.M., Peng L.Y., Dai C.H., He H.J., . Catalytic oxidative desulfurization of dibenzothiophene using catalyst of tungsten supported on resin D152. Fuel. 2014;130:19-24.
[Google Scholar]
Lorencon E., Alves D., Krambrock K., Avila E.S., Resende R.R., Ferlauto A.S., Lago R.M., . Oxidative desulfurization of dibenzothiophene over titanate nanotubes. Fuel. 2014;132:53-61.
[Google Scholar]
Lü H., Gao J., Jiang Z., Yang Y., Song B., Li C., . Oxidative desulfurization of dibenzothiophene with molecular oxygen using emulsion catalysis. Chem. Commun.. 2007;150–152
[Google Scholar]
Ma X., Velu S., Kim J.H., Song C., . Deep desulfurization of gasoline by selective adsorption over solid adsorbents and impact of analytical methods on ppm-level sulfur quantification for fuel cell applications. Appl. Catal. B. 2005;56:137-147.
[Google Scholar]
Mjalli F.S., Ahmed O.U., Al-Wahaibi T., Al-Wahaibi Y., Al-Nashef I.M., . Deep oxidative desulfurization of liquid fuels. Rev. Chem. Eng.. 2014;30:337-378.
[Google Scholar]
Qi H.X., Zhai S.R., Zhang W., Zhai B., An Q.D., . Recyclable HPW/PEHA/ZrSBA-15 toward efficient oxidative desulfurization of DBT with hydrogen peroxide. Catal. Commun. 2015:53-56.
[Google Scholar]
Qiu J.H., Wang G.H., Zhang Y.Q., Zeng D.L., Chen Y., . Direct synthesis of mesoporous H₃PMo₁₂O₄₀/SiO₂ and its catalytic performance in oxidative desulfurization of fuel oil. Fuel. 2015;147:195-202.
[Google Scholar]
Sen T., Tiddy G., Casci J.L., . Synthesis and characterization of hierarchically ordered porous silica materials. Chem. Mater.. 2004;16:2044-2054.
[Google Scholar]
Tang L., Luo G., Zhu M., Kang L., Dai B., . Preparation, characterization and catalytic performance of HPW-TUD-1 catalyst on oxidative desulfurization. J. Ind. Eng. Chem.. 2013;19:620-626.
[Google Scholar]
Te M., Fairbridge C., Ring Z., . Oxidation reactivities of dibenzothiophenes in polyoxometalate/H₂O₂ and formic acid/H₂O₂ systems. Appl. Catal. A. 2001;219:267-280.
[Google Scholar]
Thompson D.J., Zhang Y., Ren T., . Polyoxometalate [γ-SiW₁₀O₃₄(H₂O)₂]⁴⁻ on MCM-41 as catalysts for sulfide oxygenation with hydrogen peroxide. J. Mol. Catal. A. 2014;392:188-193.
[Google Scholar]
Wu N., Li B., Liu Z., Han C., . Synthesis of Keggin-type lacunary 11-tungstophosphates encapsulated into mesoporous silica pillared in clay interlayer galleries and their catalytic performance in oxidative desulfurization. Catal. Commun.. 2014;46:156-160.
[Google Scholar]
Xiong J., Zhu W.S., Ding W.J., Yang L., Chao Y.H., Li H.P., Zhu F.X., Li H.M., . Phosphotungstic acid immobilized on ionic liquid-modified SBA-15: efficient hydrophobic heterogeneous catalyst for oxidative desulfurization in fuel. Ind. Eng. Chem. Res.. 2014;53:19895-19904.
[Google Scholar]
Xun S., Zhu W., Zheng D., Zhang L., Liu H., Yin S., Zhang M., Li H., . Synthesis of metal-based ionic liquid supported catalyst and its application in catalytic oxidative desulfurization of fuels. Fuel. 2014;136:358-365.
[Google Scholar]
Yan X.M., Mei P., Xiong L., Gao L., Yang Q.F., Gong L.J., . Mesoporous titania-silica-polyoxometalate nanocomposite materials for catalytic oxidation desulfurization of fuel oil. Catal. Sci. Technol.. 2013;3:1985-1992.
[Google Scholar]
Yang R.C., Yang L.J., Tao T.X., Ma F.Y., Xu M.D., Zhang Z.H., . Contrastive study of structure and photocatalytic performance with three-dimensionally ordered macroporous CuO-TiO₂ and CuO/TiO₂. Appl. Surf. Sci.. 2014;288:363-368.
[Google Scholar]
Yang P., Zhou S., Du Y., Li J., Lei J., . Synthesis of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ and its catalytic performance in oxidative desulfurization. RSC Adv.. 2016;6:53860-53866.
[Google Scholar]
Yu X., Zhao Z., Wei Y., Liu J., Li J., Duan A., Jiang G., . Three-dimensionally ordered macroporous SiO₂-supported transition metal oxide catalysts: Facile synthesis and high catalytic activity for diesel soot combustion. RSC Adv.. 2015;5:49780-49790.
[Google Scholar]
Yue D., Lei J., Peng Y., Li J., Du X., . Hierarchical ordered meso/macroporous H₃PW₁₂O_40/SiO₂ catalysts with superior oxidative desulfurization activity. J. Porous Mat. 2017
[CrossRef] [Google Scholar]
Yue D., Peng Y., Zhou S., Li J., Du X., Lei J., . Direct synthesis of ordered meso/macrostructured phosphotungstic acid/SiO₂ by EISA method and its catalytic performance of fuel oil. Mater. Res. Bull.. 2018;97:42-48.
[Google Scholar]
Zannikos F., Lois E., Stournas S., . Desulfurization of petroleum fractions by oxidation and solvent extraction. Fuel Process. Technol.. 1995;42:35-45.
[Google Scholar]
Zaykina R.F., Zaykin Y.A., Yagudin S.G., Fahruddinov I.M., . Specific approaches to radiation processing of high-sulfuric oil. Radiat. Phys. Chem.. 2004;71:467-470.
[Google Scholar]
Zhang J., Wang A.J., Li X., Ma X.H., . Oxidative desulfurization of dibenzothiophene and diesel over [Bmim]₍₃₎PMo₁₂O₄₀. J. Catal.. 2011;279:269-275.
[Google Scholar]
Zhang J., Wang A.J., Wang Y.J., Wang H.Y., Gui J.Z., . Heterogeneous oxidative desulfurization of diesel oil by hydrogen peroxide: Catalysis of an amphipathic hybrid material supported on SiO₂. Chem. Eng. J.. 2014;245:65-70.
[Google Scholar]
Zheng H., Sun Z., Chen X., Zhao Q., Wang X., Jiang Z., . A micro reaction-controlled phase-transfer catalyst for oxidative desulfurization based on polyoxometalate modified silica. Appl. Catal. A. 2013;467:26-32.
[Google Scholar]

Introduction

Experimental section

Materials
Catalysts preparation
Characterization
Oxidative desulfurization of model fuel

Results and discussion

Characterization of the samples
The catalytic performance of samples

Conclusions

Fulltext Views
1,349

PDF downloads
879

View/Download PDF
Download Citations

BibTeX
RIS

Show Sections

[1] Abdalla Z., Li B.S., . Preparation of MCM-41 supported (Bu₄N)₍₄₎H₃(PW₁₁O₃₉) catalyst and its performance in oxidative desulfurization. Chem. Eng. J.. 2012;200:113-121.
[Google Scholar]

[2] Abdalla Z., Li B.S., Tufail A., . Direct synthesis of mesoporous (C₁₉H₄₂N)₄H₃(PW₁₁O₃₉)/SiO₂ and its catalytic performance in oxidative desulfurization. Colloid. Surface. A. 2009;341:86-92.
[Google Scholar]

[3] Abro R., Abdeltawab A.A., Al-Deyab S.S., Yu G.R., Qazi A.B., Gao S.R., Chen X.C., . A review of extractive desulfurization of fuel oils using ionic liquids. RSC Adv.. 2014;4:35302-35317.
[Google Scholar]

[4] Arcibar-Orozco J.A., Rene Range-Mendez J., Bandosz T.J., . Desulfurization of model diesel fuel on activated carbon modified with iron oxyhydroxide nanoparticles: effect of tert-butylbenzene and naphthalene concentrations. Energ. Fuel. 2013;27:5380-5387.
[Google Scholar]

[5] Bhutto A.W., Abro R., Gao S., Abbas T., Chen X., Yu G., . Oxidative desulfurization of fuel oils using ionic liquids: a review. J. Taiwan Inst. Chem. E.. 2016;62:84-97.
[Google Scholar]

[6] Campos-Martin J.M., Capel-Sanchez M.C., Fierro J., . Highly efficient deep desulfurization of fuels by chemical oxidation. Green Chem.. 2004;6:557-562.
[Google Scholar]

[7] Ceden-Caero L., Gomez-Bernal H., Fraustro-Cuevas A., Guerra-Gomez H.D., Cuevas-Garcia R., . Oxidative desulfurization of synthetic diesel using supported catalysts Part III. Support effect on vanadium-based catalysts. Catal. Today. 2008;133:244-254.
[Google Scholar]

[8] Cho W.H., Lee C.T., Yu C.C., Kei C.C., Liu D.R., Lee C.C., . Microstructure and optical properties of Al₂O₃ prepared by oblique deposition using microsphere shell templates. Appl. Opt.. 2011;9:246-249.
[Google Scholar]

[9] Collins F.M., Lucy A.R., Sharp C., . Oxidative desulphurisation of oils via hydrogen peroxide and heteropolyanion catalysis. J. Mol. Catal. A 1997:397-403.
[Google Scholar]

[10] Dhainaut J., Dacquin J., Lee A.F., Wilson K., . Hierarchical macroporous – mesoporous SBA-15 sulfonic acid catalysts for biodiesel synthesis. Green Chem.. 2010;12:296-303.
[Google Scholar]

[11] Duncan D.C., Chambers R.C., Hecht E., Hill C.L., . Mechanism and dynamics in the H₃[PW₁₂O₄₀]-catalyzed selective epoxidation of terminal olefins by H₂O₂. Formation, reactivity, and stability of {PO₄[WO(O₂)₂]₄}³⁻. J. Am. Chem. Soc.. 1995;2:681-691.
[Google Scholar]

[12] Fraile J.M., Gil C., Mayoral J.A., Muel B., Roldán L., Vispe E., Calderón S., Puente F., . Heterogeneous titanium catalysts for oxidation of dibenzothiophene in hydrocarbon solutions with hydrogen peroxide: On the road to oxidative desulfurization. Appl. Catal. B. 2016;180:680-686.
[Google Scholar]

[13] Garcia-Gutierrez J.L., Fuentes G.A., Hernandez-Teran M.E., Murrieta F., Navarrete J., Jimenez-Cruz F., . Ultra-deep oxidative desulfurization of diesel fuel with H₂O₂ catalyzed under mild conditions by polymolybdates supported on Al₂O₃. Appl. Catal. A.. 2006;305:15-20.
[Google Scholar]

[14] Holbrey J.D., Lopez-Martin I., Rothenberg G., Seddon K.R., Silvero G., Zheng X., . Desulfurisation of oils using ionic liquids: selection of cationic and anionic components to enhance extraction efficiency. Green Chem.. 2008;10:87-92.
[Google Scholar]

[15] Holland B.T., Blanford C.F., Do T., Stein A., . Synthesis of highly ordered, three-dimensional, macroporous structures of amorphous or crystalline inorganic oxides, phosphates, and hybrid composites. Chem. Mater.. 1999;11:795-805.
[Google Scholar]

[16] Hulea V., Fajula F., Bousquet J., . Mild oxidation with H₂O₂ over Ti-containing molecular sieves – a very efficient method for removing aromatic sulfur compounds from fuels. J. Catal.. 2001;198:179-186.
[Google Scholar]

[17] Ishihara A., Wang D., Dumeignil F., Amano H., Qian E.W., Kabe T., . Oxidative desulfurization and denitrogenation of a light gas oil using an oxidation/adsorption continuous flow process. Appl. Catal. A. 2005;279:279-287.
[Google Scholar]

[18] Ishii Y., Yamawaki K., Ura T., Yamada H., Yoshida T., Ogawa M., . Hydrogen peroxide oxidation catalyzed by heteropoly acids combined with cetylpyridinium chloride. Epoxidation of olefins and allylic alcohols, ketonization of alcohols and diols, and oxidative cleavage of 1, 2-diols and olefins. J. Org. Chem.. 1988;53:3587-3593.
[Google Scholar]

[19] Kozhevnikov I.V., . Catalysis by heteropoly acids and multicomponent polyoxometalates in liquid-phase reactions. Chem. Rev.. 1997;98:171-198.
[Google Scholar]

[20] Li H.M., He L.N., Lu J.D., Zhu W.S., Jiang X., Wang Y., Yan Y.S., . Deep oxidative desulfurization of fuels catalyzed by phosphotungstic acid in ionic liquids at room temperature. Energ. Fuel. 2009;23:1354-1357.
[Google Scholar]

[21] Li B., Liu Z., Han C., Ma W., Zhao S., . In situ synthesis, characterization, and catalytic performance of tungstophosphoric acid encapsulated into the framework of mesoporous silica pillared clay. J. Colloid Interf. Sci.. 2012;377:334-341.
[Google Scholar]

[22] Liu D., Lei J., Guo L., Deng K., . Simple hydrothermal synthesis of ordered mesoporous carbons from resorcinol and hexamine. Carbon. 2011;49:2113-2119.
[Google Scholar]

[23] Liu D., Lei J.H., Guo L.P., Qu D.Y., Li Y., Su B.L., . One-pot aqueous route to synthesize highly ordered cubic and hexagonal mesoporous carbons from resorcinol and hexamine. Carbon. 2012;50:476-487.
[Google Scholar]

[24] Liu D., Xia L., Qu D., Lei J., Li Y., Su B., . Synthesis of hierarchical fiberlike ordered mesoporous carbons with excellent electrochemical capacitance performance by a strongly acidic aqueous cooperative assembly route. J. Mater. Chem. A. 2013;48:15447-15458.
[Google Scholar]

[25] Long Z.Y., Yang C.P., Zeng G.M., Peng L.Y., Dai C.H., He H.J., . Catalytic oxidative desulfurization of dibenzothiophene using catalyst of tungsten supported on resin D152. Fuel. 2014;130:19-24.
[Google Scholar]

[26] Lorencon E., Alves D., Krambrock K., Avila E.S., Resende R.R., Ferlauto A.S., Lago R.M., . Oxidative desulfurization of dibenzothiophene over titanate nanotubes. Fuel. 2014;132:53-61.
[Google Scholar]

[27] Lü H., Gao J., Jiang Z., Yang Y., Song B., Li C., . Oxidative desulfurization of dibenzothiophene with molecular oxygen using emulsion catalysis. Chem. Commun.. 2007;150–152
[Google Scholar]

[28] Ma X., Velu S., Kim J.H., Song C., . Deep desulfurization of gasoline by selective adsorption over solid adsorbents and impact of analytical methods on ppm-level sulfur quantification for fuel cell applications. Appl. Catal. B. 2005;56:137-147.
[Google Scholar]

[29] Mjalli F.S., Ahmed O.U., Al-Wahaibi T., Al-Wahaibi Y., Al-Nashef I.M., . Deep oxidative desulfurization of liquid fuels. Rev. Chem. Eng.. 2014;30:337-378.
[Google Scholar]

[30] Qi H.X., Zhai S.R., Zhang W., Zhai B., An Q.D., . Recyclable HPW/PEHA/ZrSBA-15 toward efficient oxidative desulfurization of DBT with hydrogen peroxide. Catal. Commun. 2015:53-56.
[Google Scholar]

[31] Qiu J.H., Wang G.H., Zhang Y.Q., Zeng D.L., Chen Y., . Direct synthesis of mesoporous H₃PMo₁₂O₄₀/SiO₂ and its catalytic performance in oxidative desulfurization of fuel oil. Fuel. 2015;147:195-202.
[Google Scholar]

[32] Sen T., Tiddy G., Casci J.L., . Synthesis and characterization of hierarchically ordered porous silica materials. Chem. Mater.. 2004;16:2044-2054.
[Google Scholar]

[33] Tang L., Luo G., Zhu M., Kang L., Dai B., . Preparation, characterization and catalytic performance of HPW-TUD-1 catalyst on oxidative desulfurization. J. Ind. Eng. Chem.. 2013;19:620-626.
[Google Scholar]

[34] Te M., Fairbridge C., Ring Z., . Oxidation reactivities of dibenzothiophenes in polyoxometalate/H₂O₂ and formic acid/H₂O₂ systems. Appl. Catal. A. 2001;219:267-280.
[Google Scholar]

[35] Thompson D.J., Zhang Y., Ren T., . Polyoxometalate [γ-SiW₁₀O₃₄(H₂O)₂]⁴⁻ on MCM-41 as catalysts for sulfide oxygenation with hydrogen peroxide. J. Mol. Catal. A. 2014;392:188-193.
[Google Scholar]

[36] Wu N., Li B., Liu Z., Han C., . Synthesis of Keggin-type lacunary 11-tungstophosphates encapsulated into mesoporous silica pillared in clay interlayer galleries and their catalytic performance in oxidative desulfurization. Catal. Commun.. 2014;46:156-160.
[Google Scholar]

[37] Xiong J., Zhu W.S., Ding W.J., Yang L., Chao Y.H., Li H.P., Zhu F.X., Li H.M., . Phosphotungstic acid immobilized on ionic liquid-modified SBA-15: efficient hydrophobic heterogeneous catalyst for oxidative desulfurization in fuel. Ind. Eng. Chem. Res.. 2014;53:19895-19904.
[Google Scholar]

[38] Xun S., Zhu W., Zheng D., Zhang L., Liu H., Yin S., Zhang M., Li H., . Synthesis of metal-based ionic liquid supported catalyst and its application in catalytic oxidative desulfurization of fuels. Fuel. 2014;136:358-365.
[Google Scholar]

[39] Yan X.M., Mei P., Xiong L., Gao L., Yang Q.F., Gong L.J., . Mesoporous titania-silica-polyoxometalate nanocomposite materials for catalytic oxidation desulfurization of fuel oil. Catal. Sci. Technol.. 2013;3:1985-1992.
[Google Scholar]

[40] Yang R.C., Yang L.J., Tao T.X., Ma F.Y., Xu M.D., Zhang Z.H., . Contrastive study of structure and photocatalytic performance with three-dimensionally ordered macroporous CuO-TiO₂ and CuO/TiO₂. Appl. Surf. Sci.. 2014;288:363-368.
[Google Scholar]

[41] Yang P., Zhou S., Du Y., Li J., Lei J., . Synthesis of ordered meso/macroporous H₃PW₁₂O₄₀/SiO₂ and its catalytic performance in oxidative desulfurization. RSC Adv.. 2016;6:53860-53866.
[Google Scholar]

[42] Yu X., Zhao Z., Wei Y., Liu J., Li J., Duan A., Jiang G., . Three-dimensionally ordered macroporous SiO₂-supported transition metal oxide catalysts: Facile synthesis and high catalytic activity for diesel soot combustion. RSC Adv.. 2015;5:49780-49790.
[Google Scholar]

[43] Yue D., Lei J., Peng Y., Li J., Du X., . Hierarchical ordered meso/macroporous H₃PW₁₂O_40/SiO₂ catalysts with superior oxidative desulfurization activity. J. Porous Mat. 2017
[CrossRef] [Google Scholar]

[44] Yue D., Peng Y., Zhou S., Li J., Du X., Lei J., . Direct synthesis of ordered meso/macrostructured phosphotungstic acid/SiO₂ by EISA method and its catalytic performance of fuel oil. Mater. Res. Bull.. 2018;97:42-48.
[Google Scholar]

[45] Zannikos F., Lois E., Stournas S., . Desulfurization of petroleum fractions by oxidation and solvent extraction. Fuel Process. Technol.. 1995;42:35-45.
[Google Scholar]

[46] Zaykina R.F., Zaykin Y.A., Yagudin S.G., Fahruddinov I.M., . Specific approaches to radiation processing of high-sulfuric oil. Radiat. Phys. Chem.. 2004;71:467-470.
[Google Scholar]

[47] Zhang J., Wang A.J., Li X., Ma X.H., . Oxidative desulfurization of dibenzothiophene and diesel over [Bmim]₍₃₎PMo₁₂O₄₀. J. Catal.. 2011;279:269-275.
[Google Scholar]

[48] Zhang J., Wang A.J., Wang Y.J., Wang H.Y., Gui J.Z., . Heterogeneous oxidative desulfurization of diesel oil by hydrogen peroxide: Catalysis of an amphipathic hybrid material supported on SiO₂. Chem. Eng. J.. 2014;245:65-70.
[Google Scholar]

[49] Zheng H., Sun Z., Chen X., Zhao Q., Wang X., Jiang Z., . A micro reaction-controlled phase-transfer catalyst for oxidative desulfurization based on polyoxometalate modified silica. Appl. Catal. A. 2013;467:26-32.
[Google Scholar]