Supported ionic liquid [Bmim]FeCl4/Am TiO2 as an efficient catalyst for the catalytic oxidative desulfurization of fuels

Article abstract of DOI:10.1039/c5ra00999e

High activity oxidation of sulfur compounds to sulfones in extraction coupled with catalytic oxidative desulfurization (ECODS) system catalyzed by supported ionic liquid [Bmim]FeCl₄/Am TiO₂ was reported. The catalysts were analyzed by thermogravimetric (TG) analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). It was found that [Bmim]FeCl₄ and Am TiO₂ had a synergistic effect on the desulfurization system. Effects of calcination temperature of the catalyst and various reaction conditions on the catalytic activity of desulfurization were investigated. Moreover, GC-MS analyses were employed to prove the process of the desulfurization. As a solid catalyst, the supported ionic liquid could be separated from the reaction easily. The recycling tests showed that the desulfurization efficiency remained 100% after reusing it for 25 times. Therefore, the ECODS system has excellent reusability and is promising for industrial applications for catalytic oxidative desulfurization.

Full text of DOI:10.1039/c5ra00999e

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Supported ionic liquid [Bmim]FeCl4/Am TiO2 as an efficient catalyst for
catalytic oxidative desulfurization of fuels
Suhang Xuna, Wenshuai Zhua,*, Dan Zhenga, Hongping Lia, Wei Jiangb, Ming Zhangb, Yuejiao
Qina, Zhen Zhaoc, Huaming Lib,*
a School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, 212013, P. R.
China
b Energy and Powder Engineering, Jiangsu University, Zhenjiang, 212013, P. R. China
c
State Key Laboratory of Heavy Oil Processing, Faculty of Science, China University of
Petroleum, Beijing, 102249, P. R. China
*Corresponding author: Tel.:+86ꢀ511ꢀ88791800; Fax: +86ꢀ511ꢀ88791708;
Eꢀmail address: zhuws@ujs.edu.cn (W. S. Zhu)，lhm@ujs.edu.cn (H. M. Li)
Abstract
High activity oxidation of sulfur compounds to sulfones in extractive coupled
with catalytic oxidative desulfurization (ECODS) system catalyzed by supported ionic
liquid [Bmim]FeCl4/Am TiO2 was reported. The catalysts were analyzed by
thermogravimetric (TG), Xꢀray diffraction (XRD), Fourier transform infrared
spectroscopy (FTꢀIR) and Xꢀray photoelectron spectroscopy (XPS). It was found that
[Bmim]FeCl4 and Am TiO2 had a synergistic effect on the desulfurization system.
Effects of calcination temperature of the catalyst and various reaction conditions on
the catalytic activity of desulfurization were investigated. Meanwhile, GCꢀMS
analysis were employed to prove the process of the desulfurization. As a solid catalyst,
the supported ionic liquid could be separated from the reaction easily. The recycling
tests showed that the desulfurization efficiency still remained 100% after 25 times
reused. Therefore, the ECODS system has excellent reusability and is promising for
industrial application on catalytic oxidative desulfurization.
Keywords: supported ionic liquid catalyst; desulfurization; Am TiO2;
dibenzothiophene; catalytic oxidation.

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1. Introduction
Sulfur compounds in fuel is converted to SOx during combustion, which not only
causes serious environmental pollution, but also irreversibly poisons the metal
catalysts in automobiles. Consequently, many countries have legislated more stringent
environmental regulations to restrict the sulfur content of fuels.1ꢀ2 As sulfur
compounds in fuels have greatly contribution to the air pollution of the environment,
much attention has been given to the desulfurization of fuel in the past few decades.
In the petroleum refining industry, hydrodesulfurization (HDS) is a conventional
method for the removal of sulfur compounds such as thiols, sulfides and disulfides.
However, it is difficult to remove some aromatic sulfur containing compounds such as
benzothiophene (BT), dibenzothiophene (DBT), 4,6ꢀdimethyl dibenzothiophene
(4,6ꢀDMDBT) and their derivatives under mild conditions. To achieve the purpose of
deep desulfurization, the conditions of high temperature and pressure as well as
highly active catalysts are used in HDS, resulting in a significant increase in the
expense. Therefore, various desulfurization technologies have attracted widely
attention, such as adsorption3ꢀ8, extraction9ꢀ11, bioprocess12 and oxidation13ꢀ20. Among
these methods, oxidative desulfurization (ODS) is regarded as a promising strategy to
achieve low sulfur content fuel under mild conditions. The oxidants used in ODS
include molecular oxygen21ꢀ23, ozone24, organic peroxide25 and hydrogen peroxide
(H2O2)13ꢀ16, 26, 27. Among these oxidants, H2O2 has been extensively used because of
its high activity and the only production water after reaction. Many approaches have
been used in combination of ODS, such as photocatalytic oxidation28, microwave
catalytic oxidation29, solvent extraction and oxidation30, 31 and so on.
Room temperature ionic liquids (ILs) have been traditionally employed as good
solvents and extractants in desulfurization of fuels.11, 26, 32 Due to the unique physical
and chemical properties such as nonꢀvolatility, good thermal stability, negligible vapor
pressure and good solubility characteristics, the ILs received particular interests as
novel catalysts in homogeneous system.33ꢀ36 Recently, there has been an increasing
attention on supported ILs to structure heterogeneous catalytic systems.37ꢀ39 The
supported ILs exhibit similar or enhanced chemical properties and have the advantage

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of being a solid catalyst, which make the catalysts separate from the reaction mixtures
conveniently. Another advantage of supported ILs is that loading the ILs on a suitable
carrier could increase the dispersion and number of active sites.37 This process
reduces not only the amount of ILs but also the costs. Consequently, various supports
have been researched such as layered materials40, porous glasses41, mesoporous
materials42, 43, silica gel44 and metallic oxide45. In addition, titanium dioxide (TiO2) as
a
good carrier has versatile applications in photocatalysis28 and
photoelectrochemistry46. For example, Chen et. al reported a oneꢀpot solꢀgel method
for the synthesis of Ag/TiO2 catalyst with highly dispersed Ag on the surface of TiO2
carrier.47 The TiO2ꢀsupported Ag catalyst displayed excellent catalytic activity in the
reduction of methylene blue in the aqueous phase. Meanwhile, taskꢀspecific basic
ionic liquid was prepared and successively immobilized on mesoporous silicas of
MCMꢀ41 and SBAꢀ15 by Yin and the cooperators.48 The supported ionic liquid
catalyst showed high catalytic performance and good reusability for Knoevenagel
condensation in aqueous media. In view of the characters of TiO2 carrier and
supported ionic liquid, this work focused on the supported ILs with the carrier of Am
TiO2 and applied in thermocatalytic oxidative desulfurization system.
The [Bmim]FeCl4 IL has been used in the desulfurization system, however, a
large amount of [Bmim]FeCl4 was used and it was difficult to be separated and
recycled after the reaction.49, 50 In this work, [Bmim]FeCl4 was loaded on Am TiO2
first, and then the supported ionic liquid was employed as catalyst in the extractive
coupled with catalytic oxidative desulfurization (ECODS) system. Compared to the
previous literature, the asꢀprepared supported catalyst is superior to most of the
traditional heterogeneous solid catalysts on the removal of DBT (Table S1 in
Supporting Information). The amount of [Bmim]FeCl4 used in the desulfurization
system is very low and it could be separated from the extractant easily after the
reaction. The defective sites on the surface of Am TiO2 have a strong adsorption to
atom with lone pair electrons51, 52, which makes Am TiO2 an ideal carrier in the
supported ionic liquid. The desulfurization efficiency of the supported IL improved
significantly compared with the simple mixing of the two substances, indicating that

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[Bmim]FeCl4 and Am TiO2 had a synergistic effect on the desulfurization system. In
addition, the ECODS system had an excellent reused performance with an extremely
low amount of catalyst. The desulfurization efficiency still remain 100% after
recycling for 25 times, this result is far superior to the reported literature.43, 53 It will
be conducive to catalytic oxidative desulfurization research for industrial application.
2. Experimental section
2.1 materials
BT, DBT and 4,6ꢀDMDBT were purchased from SigmaꢀAldrich. Tetradecane
was purchased from Aladdin. Tetrabutyl titanate, absolute ethyl alcohol, 30 wt.%
H2O2, Iron (III) chloride anhydrous (FeCl3) and nꢀoctane were purchased from
Sinopharm Chemical Reagent Co., Ltd. The conventional ionic liquids
1ꢀbutylꢀ3ꢀmethylimidazolium
1ꢀnꢀoctylꢀ3ꢀmethylimidazolium
1ꢀbutylꢀ3ꢀmethylimidazolium
tetrafluoroborate
tetrafluoroborate
([Bmim]BF4),
([Omim]BF4),
([Bmim]PF6),
hexafluorophosphate
1ꢀnꢀoctylꢀ3ꢀmethylimidazolium hexafluorophosphate ([Omim]PF6) and the
1ꢀbutylꢀ3ꢀmethylimidazolium chloride ([Bmim]Cl) were purchased from Shanghai
Chengjie Chemical Co., Ltd. Nꢀoctane was of chemical pure, other chemicals used in
the experiments were of analytical reagent grade without further purification.
2.2 Preparation of [Bmim]FeCl4/Am TiO2 catalyst
The [Bmim]FeCl4 was prepared based on the previous work.49 The supported
ionic liquid catalyst was carried out via the following steps (scheme 1). First, 4.6
mmol tetrabutyl titanate was dissolved in 10 mL absolute ethyl alcohol under stirring,
then 0.9 mL deionized water was added to form solution A. Next, 0.5 mmol
[Bmim]FeCl4 was dissolved in 10 mL absolute ethyl alcohol to form solution B.
Solution A was magnetically stirred for 0.5 h at room temperature, and then solution B
filled slowly and stirred for another 2 h to form a homogeneous mixed solution. The
mixed solution was aged overnight, and then drying at 60oC and 100oC to obtain a
powder. Finally, the powder was calcined in muffle furnace from room temperature to

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250oC under air atmosphere with a heating rate of 5oC/min and then kept at 250oC for
180 min before cooling. Am TiO2 and other samples with different metalꢀbased ionic
liquids and treated temperatures were prepared with the similar method above.
2.3 Characterization of the catalysts
Thermogravimetric (TG) analysis was done on STAꢀ449C Jupiter (NETZSCH
Corporation, Germany). The sample was tested from room temperature to 600oC
under air atmosphere with a heating rate of 10oC/min. The powder Xꢀray diffraction
(XRD) analysis was carried out on a Bruker D8 diffractometer with highꢀintensity
CuꢀKα radiation. Fourier Transform Infrared Spectroscopy (FTꢀIR) were performed
on a Nicolet FTꢀIR spectrophotometer (Nexus 470, Thermo Electron Corporation)
using KBr pellets at room temperature. Xꢀray photoelectron spectroscopy (XPS) was
measured on a PHI5300 with a monochromatic Mgꢀ Kα source to explore the
elements on the surface. The GCꢀMS analysis was measured on Agilent
7890/5975CꢀGC/MSD (HPꢀ5 MS column, 30 m × 250 µm i.d. × 0.25 µm;
temperature program: 100ºCꢀtemperature rising 15ºC/min ꢀ 200ºC for 10 min) to
characterize the oxidized sulfur compounds after the desulfurization reaction.
2.4 Oxidative desulfurization procedure
In a typical reaction run, 5 mg [Bmim]FeCl4/Am TiO2, 1 mL conventional IL and
5 mL model oil with DBT were added into a flask. Then 32 ꢁL H2O2 was added, and
the mixture was stirred vigorously to complete the desulfurization reaction. After the
reaction, the remained sulfurꢀcontaining compounds in model oil were analyzed by
GCꢀFID (Agilent 7890A; HPꢀ5, 30 m × 0.32 mm i.d. × 0.25 µm; FID: Agilent). The
conversion of DBT in the model oil was used to calculate the removal of sulfur
compounds. Model oils were prepared by dissolving DBT, BT and 4,6ꢀDMDBT in
nꢀoctane with a corresponding Sꢀcontent of 500 ppm, 250 ppm, and 250 ppm,
respectively. The internal standard was tetradecane.
3. Results and discussion

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3.1 Characterization of the catalysts
In order to investigate the correlation between structure and properties of the
catalysts, various of characteristics were taken. TG analysis of TiO2 and
[Bmim]FeCl4/TiO2 under air atmosphere were first taken to study the calcining
process of the samples. Then Am TiO2 and the catalysts calcined under different
temperatures were characterized by wideꢀangle powder XRD, FTꢀIR and XPS. As
shown in Fig. 1(A), when the catalyst and TiO2 were calcined at 250oC, the weight
loss of TiO2 was 3.8% more than [Bmim]FeCl4/TiO2. Since there was no obvious loss
of [Bmim]FeCl4 when the temperature was below 290oC [Fig. 1(B)], this difference of
loss was caused by the decomposition of Ti(OH)4 and the desorption of water on the
catalyst. As could be seen in Fig. 2, no typical diffraction was detected in the samples
calcined at 250oC [Fig. 2(a) and (b)], indicating that the synthesized TiO2 might
present in an amorphous structure. As for TiO2, the FTꢀIR spectra characteristic peaks
around 633 cmꢀ1, 1400 cmꢀ1 and 1548 cmꢀ1 were observed in Fig. 3(a). The peak at
1400 cmꢀ1 were attributed to TiꢀO bond, which came from Ti(OH)4.54 When the
calcination temperatures up to 400oC, since the [Bmim]FeCl4 decompose violently,
the difference of the loss between the two samples reached 6.9% [Fig. 1(A)]. Finally,
calcination temperatures at 550oC, the weight loss of [Bmim]FeCl4/TiO2 was 8.3%
more than TiO2 [Fig. 1(A)]. The decomposition of [Bmim]FeCl4 would result in the
decrease of catalytic activity in the ECODS system. As the catalysts calcined at 400
and 550oC, the diffraction peaks were observed and became stronger with the
increasing of calcination temperature [Fig. 2 (c) and (d)]. The peaks at 25.36o (101),
38.02 o (111), 48.12 o (200) and 55.12 o (211) were clearly representative of the anatase
phase TiO2 (JSPDF NO.84ꢀ1285). As displayed in Fig. 3, The peaks at 1400 cmꢀ1
turned weak when the calcination temperatures increased from 250oC to 550oC,
meaning the Ti(OH)4 had broken down into TiO2 and H2O. The absorption peak of
C=N in the imidazole ring was around 1591 cmꢀ1, however, there was no obvious
peaks found from the curves in Fig. 3(b)ꢀ(d), that’s because the peak was covered by
TiO2 around 1548 cmꢀ1. Meantime, as shown in the Fig. 3(B) (the catalyst calcination
temperatures at 250oC), the ring stretching vibrations of the imidazole ring around

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1164 cmꢀ1 and 1107 cmꢀ1 could be detected55. The results proved that [Bmim]FeCl4
has been loaded on Am TiO2 and intact.
The XPS analysis provided further information for the evaluation of the purity
and surface composition of the [Bmim]FeCl4/Am TiO2 catalyst calcined at 250oC. The
survey XPS spectrum in Fig. 4(A) demonstrated that the main elements on the surface
of the catalyst are C, O, N, Cl, Ti and Fe. The C 1s peak shown in Fig. 4(B) with two
peaks around 284.9 eV and 288.5 eV could be assigned to the sp2 hybridization of
carbon atoms 56. As can be seen from Fig. 4(C), the N 1s peak is located at 399.8 eV,
which could be ascribed to sp2ꢀhybridized nitrogen (C=NꢀC)56. The highꢀresolution
spectrum [Fig. 4(D)] showed that the peak binding energies of 529.9 eV was assigned
57
to O 1s 54. The peak binding energy of 198.1 eV is ascribed to Cl 2p [Fig. 4(E)]
.
The Ti 2p region displayed in Fig. 4(F) with the characteristic peaks at 458.4 and
464.0 eV was ascribed to Ti 2p3/2 and Ti 2p1/2 respectively54. The result of XPS further
confirmed the existence of [Bmim]FeCl4 and Am TiO2 in the [Bmim]FeCl4/Am TiO2
composites, which is consistent with the result of FTꢀIR analysis.
3.2 Effects of the calcination temperatures on sulfur removal
To investigate the effect of calcination temperatures of the catalysts on sulfur
removal58, three temperatures of 250oC, 400oC and 550oC were taken on
[Bmim]FeCl4/TiO2. The results of various calcination temperatures catalysts with
different reaction times were shown in Fig. 5. The results indicated that sulfur
removal decreased from 99.6% to 31.3% in 1 h with the increasing temperatures from
250oC to 550oC. There is no significant increase in sulfur removal when prolonging
the reaction time for another 30 min. Based on the results of TG analysis (Fig. 1),
[Bmim]FeCl4 remained stable at 250oC and began to decompose at 290oC, meaning
that the catalyst calcined at 250oC presents the highest desulfurization efficiency
among the three calcination temperatures. However, as the carrier Am TiO2
transformed from amorphous to anatase phase at 400 and 550oC, the defective sites on
the surface reduced, and it weakened the performance of attracting DBT. Both of the
two factors resulted in the higher calcination temperatures, the lower sulfur removal

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was obtained in the ECODS system. Thus, the catalyst calcined at 250oC and reaction
for 1 h were chosen as the optimal conditions in the desulfurization system.
3.3 Effect of different desulfurization system on sulfur removal
The desulfurization systems had great effect on sulfur removal 59, 60, the results
of various systems contained different catalysts are shown in Fig. 6. As can be seen,
the sulfur removal was only 32.3% without catalyst. The sulfur removal reached
82.1% when the [Bmim]FeCl4 and Am TiO2 were employed only by simple mix
together. If the [Bmim]FeCl4 was loaded on Am TiO2 first, and then used as catalyst
in the ECODS system, the sulfur removal increased evidently and reached 99.6%.
These results indicated that [Bmim]FeCl4 and Am TiO2 had a synergistic effect after
loading, which could improve the desulfurization efficiency greatly. However, sulfur
removal in desulfurization systems containing other supported ionic liquid, for
example, [Bmim]CuCl3/Am TiO2, [Bmim]ZnCl3/Am TiO2 and [Bmim]CoCl3/Am
TiO2, were below 65%. It’s obvious that [Bmim]FeCl4/Am TiO2 had the best catalytic
ability among different supported ionic liquid catalysts. Further research was focused
on studying the desulfurization system catalyzed by [Bmim]FeCl4/Am TiO2.
3.4 Effect of the amount of catalyst on sulfur removal
Fig. 7 shows the effect of catalyst amount on sulfur removal, and sulfur removal
increased with the increasing of catalyst amount. When the amount of the catalyst was
increased from 1 mg to 5 mg, the sulfur removal increased from 86.2% to 99.6% in 1
h. Compared with the previous research, this work greatly reduced the amount of
[Bmim]FeCl4 to achieve ultra deep desulfurization.49 However, when 7.5 mg catalyst
was used, the sulfur removal was only reached 98.4%, which is due to [Bmim]FeCl4
might increase the decomposition of H2O2, resulting in reduced efficiency of the
oxidant.37 Therefore, 5 mg catalyst was chosen as the most suitable amount in the
following investigation.
3.5 The effect of different reaction temperature on sulfur removal

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The reaction temperature is an important parameters in the desulfurization
system, the sulfur removal at different reaction temperatures and times were displayed
in Fig. 8. With the increase of the temperature from 40 to 60oC, a continuous increase
in the removal of DBT was observed. When the desulfurization system was reacted
for 1 h, the sulfur removal was 47.4%, 79.6% and 99.6% at 40, 50 and 60oC,
respectively. However, the sulfur removal appeared to be unsatisfactory at 30oC,
mainly owing to the catalyst and oxidant cannot work efficiently at a low reaction
temperature.61 Based on the above results, the reaction temperature of 60oC was
recommended.
3.6 The effect of different n(H2O2)/n(DBT) on sulfur removal
To investigate the amount of H2O2 on the removal of DBT, the desulfurization
reaction was carried out under various molar ratios of H2O2 and DBT (O/S) at 60oC.
According to the stoichiometric reaction, 2 mol of H2O2 are consumed for oxidation
of 1 mol DBT to DBTO2. However, as shown in Fig. 9, the sulfur removal was only
62.3% when the O/S was 2 within 1 h. The reason for this was that there existed two
parallel reactions in the oxidation, one was the oxidation of DBT and the other was
the selfꢀdecomposition of H2O2. When the O/S rose to 4, sulfur removal reached
99.6% in 1 h. Thus, the O/S of 4 was chosen as the optimal ratio.
3.7 Effects of different extractants on sulfur removal
In the ECODS system, one of the main factors was the kind of extractants. To
investigate the influence of different extractants on desulfurization, four conventional
ILs [Bmim]BF4, [Omim]BF4, [Bmim]PF6 and [Omim]PF6 were used in ECODS
system. [Bmim]FeCl4/Am TiO2 was insoluble in the ILs, which made the catalyst easy
to be separated and recovered after reaction. In addition, neither the catalyst nor the
ILs could dissolution in the model oil. The results in Table 1 showed the sulfur
removal in ECODS system with the four ILs were 75.8%, 99.6%, 17.9% and 32.2%,
respectively, while the sulfur removal in the extractive desulfurization (EDS) system
were 17.2%, 29.3%, 15.1% and 26.5%, respectively.61 Therefore, [Omim]BF4 was

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chosen as the suitable extractant in the desulfurization experiments.
3.8 Effects of the nature of the substrates on sulfur removal
The nature of the substrates is a crucial factor to influence the sulfur removal in
the desulfurization system. Besides DBT, two other representatives BT and
4,6ꢀDMDBT were chosen to investigate the desulfurization efficiency. As shown in
Fig. 10, the sulfur removal decreased in the order DBT > BT > 4,6ꢀDMDBT under the
corresponding reaction conditions. The sulfur removal of DBT and BT increased over
time obviously, and the sulfur removal of DBT could reach deep desulfurization
within 1 h, while the sulfur removal of BT increased from 56.2% in 1 h to 81.3% in 2
h. However, what’s unexpected is that the removal of 4,6ꢀDMDBT in the
desulfurization system is poor, the sulfur removal was only 28.9% in 1 h and
increased slightly in another hour (35%). For DBT and BT, the result could be
attributed to the different electron density of the sulfur atoms62, the electron density of
BT (5.739) is lower than DBT (5.758), which led to the low desulfurization efficiency.
Though 4,6ꢀDMDBT had the highest electron density (5.760) of the three sulfur
containing compounds, the two methyl groups on the benzene ring brought great
steric hindrance, which became the main difficulties and caused the lowest sulfur
removal in the ECODS system.59, 60
3.9 Recycling performance of the ECODS system
Recycling ability and multiphase reaction are two important factors in industrial
application. The recycling performance of the ECODS system was investigated on the
removal of DBT in model oil. Judging from the results reported in literatures43, 50, 53
,
the stability and recycle ability of the ECODS system in this work was more
outstanding than other desulfurization systems. Since the catalyst and IL were
immiscible in the model oil, the model oil could be transferred from the system by
decanting and drying easily, then new model oil containing DBT was added for next
run. There was some white DBT sulfone residue in the system after oxidation. Though
the amount of DBT sulfones increased over reaction times, it has no effect on the

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sulfur removal ability in the ECODS system. The results in Fig. 11 showed that the
ECODS system had an excellent recycling performance, the sulfur removal could still
reach 100% after recycling for 25 times. This result also showed that [Bmim]FeCl4
did not leak from the carrier after the reaction, since the sulfur removal was only
82.1% when the [Bmim]FeCl4 and Am TiO2 were employed with simple mixed
together (Fig. 6). Supported ionic liquid has unique advantages compared with other
ionic liquid catalysts. The excellent cycling performance would promote the ECODS
system applied to industrial application of catalytic oxidative desulfurization.
3.10 The proposed reaction process of ECODS system
In order to research the mechanism of the ECODS system, sulfur compounds in
model oil phase and IL phase were measured by GCꢀMS. During the reaction, DBT
was first extracted into ionic liquid phase from oil phase under rigorous stirring, then
it was oxidized by H2O2 with catalyst. After reaction, the model oil was in the upper
layer while the others were in the lower layer. The model oil was withdrawn and
analyzed by GCꢀMS directly after reaction for 30 min, 60 min and recycled for 25
times, the results were shown in Fig. 12(A). There was a strong peak belong to DBT
(m/z = 184.0) 53, 63 in the oil phase with the sulfur removal of 74.2% after reaction for
30 min. The peak of DBT was not obvious after reaction for 60 min because the sulfur
removal reached 99.6%. There was no peak of DBT to be found in the oil phase since
the sulfur removal remained 100% after 25 times recycled. The results of IL phase
was shown in Fig. 12(B), the ionic liquid phase was first reꢀextracted by
tetrachloromethane, and then detected by GCꢀMS. The peak of DBTO2 (m/z = 216.0)
53, 63
could be detected in ionic liquid phase, meaning DBTO2 was the final oxidizing
product of DBT. Based on the results above, apart from the ultra low content of DBT,
there was no other sulfur containing compounds detected in the oil phase after
reaction, meaning clean oil was obtained after catalytic oxidative desulfurization.
Conclusions
In conclusion, a supported ionic liquid catalyst [Bmim]FeCl4/Am TiO2 was

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synthesized and investigated in this work. The catalyst had high desulfurization
efficiency in the removal of DBT in ECODS system. The most appropriate conditions,
catalyst calcination temperature of 250oC, amount of the catalyst of 5 mg, temperature
of 60oC, O/S of 4, extractant of 1 mL, reaction time of 1 h were obtained. GCꢀMS
analysis was employed to detect the sulfur containing compounds after the reaction
and to investigate the process of the ECODS system. The ECODS system presents an
excellent recycling performance with extremely low amount of supported ionic liquid,
the desulfurization efficiency still remain 100% after recycling for 25 times.
Therefore, the supported ionic liquid catalyst is promising for catalytic oxidation
desulfurization in industrial application.
Acknowledgements
This work was financially supported by the National Nature Science Foundation
of China (Nos. 21276117, 21376111, 21406092), Doctoral Innovation Fund of Jiangsu
Province (KYLX_1066), Six Big Talent Peak in Jiangsu province (JNHBꢀ004) and
State Key Laboratory of Heavy Oil Processing (No. SKLOP201402004).
References
1 J. Zhang, D. S. Zhao, L. Y. Yang and Y. B. Li, Chem. Eng. J., 2010, 156, 528ꢀ531.
2 B. B. Shao, L. Shi and X. Meng, Ind. Eng. Chem. Res., 2014, 53, 6655ꢀ6663.
3 W. L. Li, Q. F. Liu, J. M. Xing, H. S. Gao, X. C. Xiong, Y. G. Li, X. Li and H. Z. Liu, AIChE J.,
2007, 53, 3263ꢀ3268.
4 Y. L. Zhang, Y. X. Yang, H. X. Han, M. Yang, L. Wang, Y. N. Zhang, Z. X. Jiang and C. Li,
Appl. Catal., B, 2012, 119, 13ꢀ19.
5 J. M. Palomino, D. T. Tran, J. L. Hauser, H. Dong and S. R. J. Oliver, J. Mater. Chem. A, 2014,
2, 14890ꢀ14895.
6 J. Xiao, X. X. Wang, Y. S. Chen, M. Fujii and C. S. Song, Ind. Eng. Chem. Res., 2013, 52,
15746ꢀ15755.
7 J. Xiao, X. X. Wang, M. Fujii, Q. J. Yang and C. S. Song, AIChE J., 2013, 59, 1441ꢀ1445.
8 J. Xiong, W. S. Zhu, H. P. Li, W. J. Ding, Y. H. Chao, P. W. Wu, S. H. Xun, M. Zhang and H.
M. Li, Green Chem., 2015, 17, 1647ꢀ1656.
9 A. Bosmann, L. Datsevich, A. Jess, A. Lauter, C. Schmitz and P. Wasserscheid, Chem.
Commun., 2001, 2494ꢀ2495.

Page 13 of 30
RSC Advances
View Article Online
DOI: 10.1039/C5RA00999E
10 Y. Nie, C. X. Li, A. J. Sun, H. Meng and Z. H. Wang, Energy Fuels, 2006, 20, 2083ꢀ2087.
11 C. P. Li, D. Li, S. S. Zou, Z. Li, J. M. Yin, A. L. Wang, Y. N. Cui, Z. L. Yao and Q. Zhao,
Green Chem., 2013, 15, 2793ꢀ2799.
12 S. Guchhait, D. Biswas, P. Bhattacharya and R. Chowdhury, Chem. Eng. J., 2005, 112,
145ꢀ151.
13 D. Huang, Z. Zhai, Y. C. Lu, L. M. Yang and G. S. Luo, Ind. Eng. Chem. Res., 2007, 46,
1447ꢀ1451.
14 C. Komintarachat and W. Trakarnpruk, Ind. Eng. Chem. Res., 2006, 45, 1853ꢀ1856.
15 J. T. Sampanthar, H. Xiao, H. Dou, T. Y. Nah, X. Rong and W. P. Kwan, Appl. Catal., B, 2006,
63, 85ꢀ93.
16 B. Y. Zhang, Z. X. Jiang, J. Li, Y. N. Zhang, F. Lin, Y. Liu and C. Li, J. Catal., 2012, 287, 5ꢀ12.
17 Y. Lu, Y. Wang, L. D. Gao, J. C. Chen, J. P. Mao, Q. S. Xue, Y. Liu, H. H. Wu, G. H. Gao and
M. Y. He, ChemSusChem, 2008, 1, 302ꢀ306.
18 J. H. Xu, S. Zhao, W. Chen, M. Wang and Y. F. Song, Chem. Eur. J., 2012, 18, 4775ꢀ4781.
19 C. Li, Z. X. Jiang, J. B. Gao, Y. X. Yang, S. J. Wang, F. P. Tian, F. X. Sun, X. P. Sun, P. L. Ying
and C. R. Han, Chem. Eur. J., 2004, 10, 2277ꢀ2280.
20 Y. S. Chi, C. P. Li, Q. Z. Jiao, Q. S. Liu, P. F. Yan, X. M. Liu and U. WelzꢀBiermann, Green
Chem., 2011, 13, 1224ꢀ1229.
21 H. Y. Lü, J. B. Gao, Z. X. Jiang, Y. X. Yang, B. Song and C. Li, Chem. Commun., 2007,
150ꢀ152.
22 W. Zhang, H. Zhang, J. Xiao, Z. X. Zhao, M. X. Yu and Z. Li, Green Chem., 2014, 16,
211ꢀ220.
23 J. Wang, Q. Guo, C. Zhang and K. Li, RSC Adv., 2014, 4, 59885ꢀ59889.
24 C. H. Ma, B. Dai, P. Liu, N. Zhou, A. J. Shi, L. L. Ban and H. W. Chen, J. Ind. Eng. Chem.,
2014, 20, 2769ꢀ2774.
25 A. Chica, A. Corma and M. E. Domine, J. Catal., 2006, 242, 299ꢀ308.
26 F. T. Li, C. G. Kou, Z. M. Sun, Y. J. Hao, R. H. Liu and D. S. Zhao, J. Hazard. Mater., 2012,
205, 164ꢀ170.
27 D. S. Zhao, J. L. Wang and E. Zhou, Green Chem., 2007, 9, 1219ꢀ1222.
28W. S. Zhu, C. Wang, H. P. Li, P. W. Wu, S. H. Xun, W. Jiang, Z. G. Chen, Z. Zhao and H. M. Li,
Green Chem., 2015, 17, 2464ꢀ2472.
29 M. Ibe, S. Gomez, K. A. Malinger, P. Fanson and S. L. Suib, Appl. Catal., B, 2007, 69,
235ꢀ239.
30 H. S. Gao, C. Guo, J. M. Xing, J. M. Zhao and H. Z. Liu, Green Chem., 2010, 12, 1220ꢀ1224.
31 H. Y. Lü, S. N. Wang, C. L. Deng, W. Z. Ren and B. C. Guo, J. Hazard. Mater., 2014, 279,
220ꢀ225.
32 J. H. Xu, S. Zhao, Y. C. Ji and Y. F. Song, Chem. Eur. J., 2013, 19, 708ꢀ714.
33 P. S. Kulkarni and C. A. M. Afonso, Green Chem., 2010, 12, 1139ꢀ1149.
34 D. A. Vicic and W. D. Jones, J. Am. Chem. Soc., 1997, 119, 10855ꢀ10856.
35 E. Lissner, W. F. de Souza, B. Ferrera and J. Dupont, ChemSusChem, 2009, 2, 962ꢀ964.
36 F. L. Yu, Y. Y. Wang, C. Y. Liu, C. X. Xie and S. T. Yu, Chem. Eng. J., 2014, 255, 372ꢀ376.
37 J. Zhang, A. J. Wang, X. Li and X. H. Ma, J. Catal., 2011, 279, 269ꢀ275.
38 Y. Chen, S. Zhao and Y. F. Song, Appl. Catal., A, 2013, 466, 307ꢀ314.
39 H. Li, P. S. Bhadury, B. Song and S. Yang, RSC Adv., 2012, 2, 12525ꢀ12551.

RSC Advances
Page 14 of 30
View Article Online
DOI: 10.1039/C5RA00999E
40 W. S. Zhu, B. L. Dai, P. W. Wu, Y. H. Chao, J. Xiong, S. H. Xun, H. P. Li and H. M. Li, ACS
Sustainable Chem. Eng., 2015, 3, 186ꢀ194.
41 M. Haumann, K. Dentler, J. Joni, A. Riisager and P. Wasserscheid, Adv. Synth. Catal., 2007,
349, 425ꢀ431.
42 X. Wang, X. Zhang, H. Liu, K. L. Yeung and J. Wang, Chem. Eng. J., 2010, 156, 562ꢀ570.
43L. Zhang, Y. D. Cui, C. P. Zhang, L. Wang, H. Wan and G. F. Guan, Ind. Eng. Chem. Res., 2012,
51, 16590ꢀ16596.
44 M. Y. Zhu, G. Q. Luo, L. H. Kang and B. Dai, RSC Adv., 2014, 4, 16769ꢀ16776.
45 T. Selvam, A. Machoke and W. Schwieger, Appl. Catal., A, 2012, 445, 92ꢀ101.
46 K. C. Goddeti, S. M. Kim, Y. K. Lee, S. H. Kim and J. Y. Park, Catal. Lett., 2014, 144,
1411ꢀ1417.
47 H. J. Zhang, X. Y. Li and G. H. Chen, J. Mater. Chem., 2009, 19, 8223ꢀ8231.
48 H. H. Zhao, N. Y. Yu, Y. Ding, R. Tan, C. Liu, D. H. Yin, H. Y. Qiu and D. L. Yin, Micropor.
Mesopor. Mat., 2010, 136, 10ꢀ17.
49 H. M. Li, W. S. Zhu, Y. Wang, J. T. Zhang, J. D. Lu and Y. S. Yan, Green Chem., 2009, 11,
810ꢀ815.
50 S. H. Xun, W. S. Zhu, D. Zheng, L. Zhang, H. Liu, S. Yin, M. Zhang and H. M. Li, Fuel, 2014,
136, 358ꢀ365.
51 U. Terranova and D. R. Bowler, J. Phys. Chem. C, 2010, 114, 6491ꢀ6495.
52 G. Liu, J. A. Rodriguez, Z. Chang, J. Hrbek and L. Gonzalez, J. Phys. Chem. B, 2002, 106,
9883ꢀ9891.
53 W. S. Zhu, P. W. Wu, L. Yang, Y. H. Chang, Y. H. Chao, H. M. Li, Y. Q. Jiang, W. Jiang and S.
H. Xun, Chem. Eng. J., 2013, 229, 250ꢀ256.
54 C. Wang, W. S. Zhu, Y. H. Xu, H. Xu, M. Zhang, Y. H. Chao, S. Yin, H. M. Li and J. G. Wang,
Ceram. Int., 2014, 40, 11627ꢀ11635.
55 F. Wang, Z. Q. Zhang, J. Yang, L. P. Wang, Y. Lin and Y. Wei, Fuel, 2013, 107, 394ꢀ399.
56 Q. J. Xiang, J. G. Yu and M. Jaroniec, Chem. Soc. Rev., 2012, 41, 782ꢀ796.
57 J. Di, J. Xia, S. Yin, H. Xu, L. Xu, Y. Xu, M. He and H. Li, RSC Adv., 2014, 4, 14281ꢀ14290.
58 Z. Hasan, J. Jeon and S. H. Jhung, J. Hazard. Mater., 2012, 205, 216ꢀ221.
59 Y. Q. Jiang, W. S. Zhu, H. M. Li, S. Yin, H. Liu and Q. J. Xie, ChemSusChem, 2011, 4,
399ꢀ403.
60 J. T. Zhang, W. S. Zhu, H. M. Li, W. Jiang, Y. Q. Jiang, W. L. Huang and Y. S. Yan, Green
Chem., 2009, 11, 1801ꢀ1807.
61 Y. X. Ding, W. S. Zhu, H. M. Li, W. Jiang, M. Zhang, Y. Q. Duan and Y. H. Chang, Green
Chem., 2011, 13, 1210ꢀ1216.
62 S. Otsuki, T. Nonaka, N. Takashima, W. H. Qian, A. Ishihara, T. Imai and T. Kabe, Energy
Fuels, 2000, 14, 1232ꢀ1239.
63 W. Jiang, W. S. Zhu, Y. H. Chang, Y. H. Chao, S. Yin, H. Liu, F. X. Zhu and H. M. Li, Chem.
Eng. J., 2014, 250, 48ꢀ54.

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Figures captions
Fig. 1. TG analysis of (A): (a) Am TiO2, (b) [Bmim]FeCl4/Am TiO2 and (B):
[Bmim]FeCl4.
o
Fig. 2. Wide angle XRD patterns at different calcination temperatures of (a) 250 C
o
o
o
TiO2, (b) 250 C [Bmim]FeCl4/TiO2, (c) 400 C [Bmim]FeCl4/TiO2 and (d) 550 C
[Bmim]FeCl4/TiO2.
o
o
o
Fig. 3. FT-IR spectra of (a) 250 C TiO2, (b) 250 C [Bmim]FeCl4/TiO2, (c) 400 C
[Bmim]FeCl4/TiO2 and (d) 550 oC [Bmim]FeCl4/TiO2.
Fig. 4. XPS spectra of [Bmim]FeCl4/Am TiO2. (A) survey of the catalyst; (B) C 1s;
(C) N 1s; (D) O 1s; (E) Cl 2p and (F) Ti 2p3.
Fig. 5. The effects of different calcination temperatures on removal of DBT.
Fig. 6. The effect of different desulfurization systems on removal of DBT.
Fig. 7. The effect of the amount of catalyst on removal of DBT.
Fig. 8. The effects of different reaction temperatures on removal of DBT.
Fig. 9. The effect of H2O2/DBT (molar ratio) on removal of DBT.
Fig. 10. Removal of different substrates in the desulfurization system.
Fig. 11. The recycle performance of the desulfurization system.
Fig. 12. The GC-MS of main compounds of the oil phase (A) and ionic liquid phase
(B).
Scheme 1. Preparation of the supported ionic liquid catalyst [Bmim]FeCl4/Am TiO2
Scheme 2. The suggested process of the ECODS system.
1

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Figures
100
95
90
85
80
75
70
65
60
250 oC
(A)
400 oC
100
90
80
70
60
50
40
30
[Bmim]FeCl
4
(B)
550 oC
(a)
(b)
100
200
300
400
500
600
Temperature / o
C
100
200
300
400
500
600
Temperature / oC
Fig. 1. TG analysis of (A): (a) Am TiO2, (b) [Bmim]FeCl4/Am TiO2 and (B):
[Bmim]FeCl4.
2

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(d)
(c)
(b)
(a)
10
20
30
40
50
60
70
80
2 theta / degree
Fig. 2. Wide angle XRD patterns at different calcination temperatures of (a) 250 oC
TiO2, (b) 250 oC [Bmim]FeCl4/TiO2, (c) 400 oC [Bmim]FeCl4/TiO2 and (d) 550 oC
[Bmim]FeCl4/TiO2.
3

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(A)
(d)
(c)
(b)
(a)
(B)
1000
1800
1700
1600
1500
1400
1300
1200
1100
Wavenumber / cm-1
3500
3000
2500
2000
1500
1000
500
Wavenumber / cm-1
Fig. 3. FT-IR spectra of (a) 250 oC TiO2, (b) 250 oC [Bmim]FeCl4/TiO2, (c) 400 oC
[Bmim]FeCl4/TiO2 and (d) 550 oC [Bmim]FeCl4/TiO2.
4

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(A) survey
(B) C 1s
1200
1000
800
600
400
200
0
280
285
290
295
Binding energy / eV
Binding energy / eV
(D)
O 1s
(C)
N 1s
525
530
535
540
395
400
405
410
Binding energy / eV
Binding energy / eV
(F)
Ti 2p3
(E) Cl 2p
455
460
465
470
195
200
205
210
Binding energy / eV
Binding energy / eV
Fig. 4. XPS spectra of [Bmim]FeCl4/Am TiO2. (A) survey of the catalyst; (B) C 1s;
(C) N 1s; (D) O 1s; (E) Cl 2p and (F) Ti 2p3.
5

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100
90
80
70
60
50
40
30
250 oC
400 oC
550 oC
10
20
30
40
50
60
70
80
90
Time / min
Fig. 5. The effects of different calcination temperatures on removal of DBT.
Experiment conditions: m(catalyst) = 5 mg, T = 60 oC, n(H2O2)/n(DBT) = 4:1,
V([Omim]BF4) = 1 mL, V(model oil) = 5 mL.
6

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100
80
60
40
20
0
2
2
2
2
2
4
3
4
3
3
Fig. 6. The effect of different desulfurization systems on removal of DBT.
Experiment conditions: m(catalyst) = 5 mg, T = 60 oC, t = 1 h, n(H2O2)/n(DBT) = 4:1,
V([Omim]BF4) = 1 mL, V(model oil) = 5 mL;
Conditions of [Bmim]FeCl4 + Am TiO2: m([Bmim]FeCl4) = 1.6 mg, m(Am TiO2) =
3.4 mg.
7

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Fig. 7. The effect of the amount of catalyst on removal of DBT.
Experiment conditions: T = 60 oC, n(H2O2)/n(DBT) = 4:1, V([Omim]BF4) = 1 mL,
V(model oil) = 5 mL.
8

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100
90
80
70
60
50
40
30
60 oC
50 oC
40 oC
30 oC
10
20
30
40
50
60
70
80
90
Time / min
Fig. 8. The effects of different reaction temperatures on removal of DBT.
Experiment conditions: m(catalyst) = 5 mg, n(H2O2)/n(DBT) = 4:1, V([Omim]BF4) =
1 mL, V(model oil) = 5 mL.
9

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100
90
80
70
60
50
40
30
n(O/S) = 2
n(O/S) = 2.5
n(O/S) = 3
n(O/S) = 3.5
n(O/S) = 4
10
20
30
40
50
60
70
80
90
Time / min
Fig. 9. The effect of H2O2/DBT (molar ratio) on removal of DBT.
Experiment conditions: m(catalyst) = 5 mg, T = 60 oC, V([Omim]BF4) = 1 mL,
V(model oil) = 5 mL.
10

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100
90
80
70
60
50
40
30
20
DBTa
BTa
4,6-DMDBTb
20
40
60
80
100
120
Time / min
Fig. 10. Removal of different substrates in the desulfurization system.
Experiment conditions: T = 60 oC, V([Omim]BF4) = 1 mL, V(model oil) = 5 mL;
a: m(catalyst) = 5 mg, n(H2O2)/n(DBT) = 4:1; b: m(catalyst) = 10 mg, n(H2O2)/n(DBT)
= 8:1.
11

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1 0 0
8 0
6 0
4 0
2 0
0
2
4
6
8
1 0
1 2
1 4
1 6
1 8
2 0
2 2
2 4
R e c y c l e t i m e s
Fig. 11. The recycle performance of the desulfurization system.
Experiment conditions: m(catalyst) = 5 mg, T = 60 oC, t = 1 h, n(H2O2)/n(DBT) = 4:1,
V([Omim]BF4) = 1 mL, V(model oil) = 5 mL.
12

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216.0
184.1
184.0
(A)
(B)
S
Internal
Standard
S
O
O
187.0
168.0
S
139.1
115.0
120
139.1
79.1
80
152.0
69.0
92.0
60
80
100
120
140
160
180
60
100
140
160
180
200
220
139.1
140
m/z
m/z
92.0
152.0
69.0
113.1
DBTO
40
60
80
100
120
m/z
160
180
200
2
Internal
Standard
DBT
(reaction 30 min)
(reaction 60 min)
(recycle 25 times)
(reaction 60 min)
(
recycle 25 times)
4
6
8
10
12
14
16
4
6
8
10
12
14
16
Time / min
Time / min
Fig. 12. The GC-MS of main compounds of the oil phase (A) and ionic liquid phase
(B).
Experiment conditions: m(catalyst) = 5 mg, T = 60 oC, n(H2O2)/n(DBT) = 4:1,
V([Omim]BF4) = 1 mL, V(model oil) = 5 mL.
13

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Scheme 1. Preparation of the supported ionic liquid catalyst [Bmim]FeCl4/Am TiO2
14

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Scheme 2. The suggested process of the ECODS system.
15