Oxidative desulfurization of thiophene derivatives with H2O2 in the presence of catalysts based on MoO3/Al2O3 under mild conditions

Article abstract of DOI:10.1134/S0023158417010086

The catalysts based on MoO₃/Al₂O₃ were synthesized and tested using aqueous hydrogen peroxide as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO₃–WO₃)/Al₂O₃ prepared by a conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT, which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexadecyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reaction efficiently.

Full text of DOI:10.1134/S0023158417010086

ISSN 0023-1584, Kinetics and Catalysis, 2017, Vol. 58, No. 1, pp. 28–33. © Pleiades Publishing, Ltd., 2017.
Published in Russian in Kinetika i Kataliz, 2017, Vol. 58, No. 1, pp. 30–35.
Oxidative Desulfurization of Thiophene Derivatives
with H O in the Presence of Catalysts Based on MoO /Al O
2
2
3
2
3
1
under Mild Conditions
a
b, c
a,
b, c
b, c
a
b, c,
Y. Shen , X. Lu , X. Ma *, J. He , D. Zhang , H. Zhan , and Q. Xia **
a
Hubei Collaborative Innovation Center of Targeted Antitumor Drug, Jingchu University of Technology, Jingmen, P.R. China
b
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei University, Wuhan, P.R. China
c
Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University,
Wuhan, P.R. China
*e-mail: mxtjmhb@163.tom
*
*e-mail: xiaqh518@aliyun.com
Received March 11, 2016
Abstract—The catalysts based on MoO /Al O were synthesized and tested using aqueous hydrogen peroxide
3
2
3
as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene
(
DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO –WO )/Al O prepared by a
3 3 2 3
conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT,
which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexa-
decyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reac-
tion efficiently.
Keywords: MoO /Al O catalysts, catalytic oxidation, oxidative desulfurization, thiophenes, hydrogen peroxide
3
2
3
DOI: 10.1134/S0023158417010086
INTRODUCTION
deeply desulfurized diesel fuel. In the ODS process,
thiophene derivatives inclusive of thiophene, BT and
DBT are oxidized into the corresponding sulfones or
sulfoxides [7–9], which have higher polarity and can
be removed by organic extractants, such as acetonitrile
New processes for ultra-deep desulfurization are
needed stringently as sulfur in fuels or oils have greatly
contributed to the pollution of environment, such as
acid rain and air pollution [1]. Now many countries
have made new environment legislations to limit the
sulfur content of transportation fuels [2].
[10, 11], DMF [12, 13] and DMSO [14].
Obviously, H O has become a popular oxidant as
2
2
it does not pollute the environment and produces
water as the only byproduct. Usually, in the ODS pro-
cess hydrogen peroxide is used as the oxidizing
reagent. However, the reactions with H O always
The conventional process to remove sulfur in fuels
is known as catalytic hydrodesulfurization (HDS),
which is very effective for the removal of sulfur-con-
taining compounds, and has been applied worldwide
2
2
involve two or three phases, which more or less retards
the efficiency of ODS.
[
3, 4]. In this process, severe operating conditions
such as high temperature, pressure and hydrogen con-
sumption are required to achieve high-quality fuels
Several authors have reported the use of organic
acids or polyoxometallic acids and the salts in aqueous
solution as the catalysts in the oxidation of organosul-
fur compounds by H O to the corresponding sulfones
[
5]. Therefore, it is desirable to develop low energy-
consuming approaches producing deeply desulfurized
fuels. The oxidative desulfurization (ODS) has
attracted much attention owing to the advantages of
mild reaction conditions. In contrast to HDS, the pro-
cessing costs of ODS appear to be very low levels, rel-
atively linear with the degree of sulfur removal.
Another feature of ODS is that the refractory sulfur
2
2
[
15, 16]. On the other hand, it is known that homoge-
neous catalysts are difficult to be recycled, so that the
development of highly active heterogeneous catalysts
is very desirable for the ODS process [17–23].
Recently, researchers from BP Corporation have
compounds can be easily converted by oxidation [6]. reported that 100% of dibenzothiophene could be
Therefore, ODS has a great potential for producing converted to sulfones by using a phosphotungstic
acid−hydrogen peroxide system under mild condi-
tions [24]. The results suggest that highly substituted
1
The article is published in the original.
28

OXIDATIVE DESULFURIZATION OF THIOPHENE DERIVATIVES
29
dibenzothiophenes be the most readily oxidized spe- into thin wafers. The scanning range was from 4000 to
−
1
−1
cies containing a thiophenic nucleus. Huang et al. [25, 400 cm , with a resolution of 2 cm .
26] employed quaternary ammonium salts and phos-
UV-Vis spectra were recorded on a Shimadzu
UV-2550 spectrometer. For the diffuse reflectance
mode (solid), the powdered sample was loaded into a
holder, and the spectra were collected in the range of
photungstic acid in the reaction system to realize the
deep desulfurization. Dolbear and co-workers reported
that the refractory sulfur compounds could be effec-
tively removed using appropriate oxidants and catalysts
at near-ambient temperature and pressure [27–29].
2
00–800 nm, referenced to BaSO .
4
X-ray diffraction (XRD) patterns of solid samples
In our present work, catalysts based on MoO /Al O
3
2
3
were recorded on a Rigaku D/MAX−IIIC diffractom-
were synthesized and used in the ODS process with
hydrogen peroxide as the oxidant. In n-octane solvent,
thiophene, benzothiophene (BT) and dibenzothio-
phene (DBT) were oxidized into the corresponding
sulfones on MoO /Al O catalysts with hexadecil-
eter with CuK (λ = 1.54184 Å) radiation operating at
α
3
0 kV and 25 mA. The scanning range was 2θ from 5°
to 65° with a scanning speed of 2 deg/min.
The average crystal sizes were estimated from
images, which were observed using a JEOL JSM 6500F
scanning electron microscope (SEM) operating at an
3
2
3
trimethil ammonium bromide (CTAB) as the phase-
transfer reagent:
accelerating voltage of 25 kV and a tube current of
6
1
00 μA under a vacuum of 10− mbar.
(
DBTO2)
(DBT)
Oxidative Desulfurization Over Catalysts
Substrates (thiophene, BT or DBT) were respec-
tively dissolved in n-octane to get model fuels with the
sulfur concentration of 1500 ppm (l.5 g/L). A mixture
of the catalyst (10 mg), model fuel (15 mL), CTAB
S
S
(
99.2% conversion)
O
O
H O
2
2
(
3 mg) and deionized water was added into three-
necked flask equipped with a cryogenic-liquid con-
denser and an air pump. The mixture was vigorously
stirred by a magnetic stirrer and heated to the desired
temperature, and then H O was added into the bot-
WO MoO WO MoO WO MoO
3
3
3
3
3
3
2
2
Al O
2
3
tom of the reactor. After the completion of the reac-
tion, the reaction mixture was cooled down to room
temperature and the catalyst was filtered off. The fil-
trate was quantitatively analyzed by gas chromato-
graph-atomic emission detection (GC-AED).
It is found that the sulfur level in model fuel can be
lowered down from 1500 ppm to < 10 ppm.
EXPERIMENTAL SECTION
Preparation of Catalysts
RESULTS AND DISCUSSION
All the catalysts based on MoO /Al O were pre-
Characterizations of Catalysts
3
2
3
pared by a conventional impregnation method. For
example, appropriate amount of boehmite powder was
immersed in an aqueous solution containing a certain
amount of mixed metal salts (ammonium tungstate and
molybdate) (with 1 : 1 molar ratio) at 353 K for 24 h, and
then excess water was evaporated off at 353 K, followed
by drying at 353 K overnight and calcination at 823 K for
Figure 1 shows the FT-IR spectra of composite
catalysts calcined at 823K for 8 h. FT-IR spectra of
1
5%MoO /Al O sample show characteristic twin
3 2 3
−
1
bands at 900 and 613 cm , which are assigned to the
vibrations of Mo–O–Mo [30]. Two bands appearing
–
1
at 900 and 646 cm
from the spectra of
1
5%WO /Al O nanoparticles can be assigned to the
3 2 3
8
h in the flowing air at a heating rate of 2.0 K/min. The
vibrations of W–O–W. IR absorption bands near 812
resultant catalyst was designated as 15%(WO –
3
−
1
and 636 cm are observed from the spectra of
MoO )/Al O , where 15% is the weight percent of met-
3
2
3
1
5%(WO –MoO )/Al O , ascribable to Mo–O–
3 3 2 3
als in the catalyst. The catalysts 15%WO /Al O ,
3
2
3
Mo, W–O–W and Mo–O–W bands.
1
5% MoO /Al O and 15%MnO /Al O (with the metal
3 2 3 2 2 3
Figures 2 and 3 show the UV-Vis spectra and the
powder wide-angle XRD patterns for different cata-
lysts. These results indicate that the uniform struc-
ture of Al O is still retained. The absence of MoO
3
salt of hydrated manganese acetate) were prepared using
the method similar to that described above.
2
3
Characterization of Catalyst
and WO peaks indicates that all the samples do not
3
contain detectable amount of aggregated metal
IR spectra were recorded on a Shimadzu IR Pres-
tige-21 Fourier Transform Infrared spectrophotome-
oxides, meaning the high dispersion of MoO and
3
ter. The samples were ground with KBr and pressed WO
as oxides on the surface of Al O .
2 3
3
KINETICS AND CATALYSIS Vol. 58 No. 1 2017

3
0
SHEN et al.
1
5%(MoO –WO )/Al O
3 3 2 3
1
5%WO /Al O
3 2 3
MoO3
1
5%MoO /Al O
3 2 3
WO3
MoO –WO (1 : 1)
3
3
1
5%WO /Al O
3 2 3
1
5%(MoO –WO )/Al O
3
3
2
3
1
5%MoO /Al O
3900 3400 2900 2400 1900 1400 900 400
3
2
3
ν, cm–1
5
15
25
35
45
55
65
75
2θ, deg
Fig. 1. FT-IR spectra of samples.
Fig. 3. XRD patterns of samples.
SEM was used to observe the morphology of
5%MoO /Al O (a), 15%WO /Al O (b) and
Catalyzed Oxidative Desulfurization
1
3
2
3
3
2
3
Comparison of the catalytic activity of different cat-
alysts. The reaction system was composed of catalysts,
H O and model diesel fuel. Observed from the reac-
tions, four catalysts were neither soluble in model die-
sel nor hydrogen peroxide (Fig. 5). While stirring con-
tinuously, emulsion system was formed in the reaction
process, which was composed of catalysts, H O and
1
5%(MoO –WO )/Al O (c) (calcined at 823 K for 8 h),
3 3 2 3
as presented in Fig. 4. Very clearly, the crystal sizes of
2
2
15%(MoO –WO )/Al O , 15%MoO /Al O , and
3
3
2
3
3
2
3
1
5%WO /Al O are detected to be 0.5–3.0, 0.2–4.0
3 2 3
and 0.2–4.0 μm, correspondently.
2
2
oil according to the literature before [31]. When the
reaction finished, catalysts can be removed from the
model fuel by demulsification, which was benefit for
catalysts’ reuse. Quaternary ammonium cations of
catalysts served as the phase-transfer agent in the reac-
MoO –WO (1 : 1)
3
3
tion, transferring H O into oil phase, leading to a
1
5%(MoO –WO )/Al O
2
2
3
3
2
3
good mixing between oxidant and model fuel, as well
as to get a high sulfur removal.
WO3
The ODS results of the model diesels containing
thiophene, BT or DBT with H O over different cata-
WO /Al O
3
3
2
2
2
lysts are shown in Fig. 5. When using 15%MnO /Al O
3
2
2
MoO3
as the catalyst, only 36.5% of thiophene, 32.0% of BT
or 32.3% of DBT is converted into the corresponding
oxidation products. When only MoO –WO oxide
MoO /Al O
3
2
3
3
3
(
with 1 : 1 molar ratio) is added (the added amount
corresponds to 30% of 15%MoO –WO /Al O
3
Al O
2
3
3
3
2
amount), only 48.1% of thiophene, 46.5% of BT or
4
1
5.6% of DBT is converted. However, over
210
310
410
510
610
710
5%MoO –WO /Al O catalyst, 99.4% of thiophene,
3
3
2
3
Wavelength (nm)
9
9.3% of BT or 99.2% of DBT can be converted.
Clearly, the catalytic activity of those catalysts gradually
decreases in the sequence of 15%MoO –WO /Al O >
Fig. 2. UV-Vis spectra of samples.
3
3
2
3
KINETICS AND CATALYSIS
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No. 1
2017

OXIDATIVE DESULFURIZATION OF THIOPHENE DERIVATIVES
31
5
μm
2 μm
(а)
(b)
5
μm
(c)
Fig. 4. SEM images of 15%MoO /Al O (a), 15%WO /Al O (b), and 15%(MoO –WO )/Al O (c).
3
2
3
3
2
3
3
3
2
3
1
00
9
0
0
0
0
0
0
0
0
(а)
(b)
(c)
8
7
6
5
4
3
2
1
0
0
1
2
3
4
1
2
3
4
1
2
3
4
Catalyst
Fig. 5. Oxidative desulfurizations of thiophene (a), BT (b), and DBT (c) catalyzed by 15%MnO /Al O (1), 15%MoO /Al O (2),
2
2
3
3
2 3
1
5%WO /Al O (3), and 15%(MoO –WO )/Al O (4). Reaction conditions: model fuel 15 mL, catalyst 10 mg, H O 0.5 mL, H O
3
2
3
3
3
2
3
2
2
2
3
.0 mL, CTAB 3.0 mg, temperature 333 K, time 4 h.
1
00
1
00
100
80
60
40
20
0
(а)
(b)
(c)
8
0
9
5
0
5
0
9
8
8
60
40
20
0
7
5
3
20
330
340
350
305 312 319 326 333 340
Temperature, К
290 299 309 317 326 335
Fig. 6. Effect of temperature on the ODS catalyzed by 15%(MoO –WO )/Al O : (a) thiophene, (b) BT, (c) DBT. Reaction con-
3
3
2 3
ditions: model fuel 15 mL, catalyst 10 mg, H O 0.5 mL, H O 3.0 mL, CTAB 3.0 mg, time 4 h.
2
2
2
KINETICS AND CATALYSIS Vol. 58 No. 1 2017

3
2
SHEN et al.
1
00
to 76.6% at 328 K, to 88.1% at 333 K, and to the max-
imum of 99.3% at 338 K. The conversion of DBT can
be increased from 12.2% at 298 K to the maximum of
9
9.2% at 328 K. This indicates that an appropriate
9
5
0
5
0
reaction temperature facilitates the ODS of fuels.
From the data in Fig. 6 (at 328 K), the oxidation
reactivity shows a decrease in the sequence DBT
(
99.2%) > thiophene (82.5%) > BT (76.6%). The
9
8
8
reactivity of sulfur-containing substrates may be
related with electron density and steric hindrance
around the sulfur atoms [14]. The higher electron den-
sity on the sulfur atoms is, the more reactive com-
pounds are. Among thiophene, BT and DBT, the
electron density on the sulfur atom of BT is signifi-
cantly lower than others, so its reactivity is the lowest.
For thiophene and DBT, a slight difference in sulfur
electron density leads to the dominant influence of
steric hindrance on the reactivity.
0
1
2
3
4
5
Time, h
Effect of reaction conditions on the ODS of diben-
zothiophene. The table shows the effect of different
reaction conditions on DBT conversion. When no cat-
alyst is added, the conversion of DBT is only 30.9%.
CTAB as a phase-transfer reagent can effectively pro-
mote the ODS reaction [25], for which no addition of
CTAB will lead to a low DBT conversion of 39.2%. At
the same time, a certain amount of water is needed.
When no water is added, the conversion of DBT is
Fig. 7. Effect of reaction time on the DBT oxidation cata-
lyzed by 15%(MoO –WO )/Al O . Reaction conditions:
3
3
2 3
model fuel 15 ml, catalyst 10 mg, H O 0.5 mL, H O 3.0 mL,
2
2
2
CTAB 3.0 mg, temperature 333 K.
1
5%WO /Al O > 15%MoO /Al O > 15%MnO /Al O .
3 2 3 3 2 3 2 2 3
Above results suggest that the interaction of tungsten
and molybdenum enhance the catalytic activity, which
has been confirmed by the corresponding infrared
spectrum characterization.
only 73.2%. However, once catalyst, CTAB and H O
2
in certain amounts are added into the catalytic system,
the conversion of DBT is largely elevated to 99.2%.
The results indicate the concerted effect of catalyst,
CTAB and water in the ODS reaction.
Effect of reaction temperature in the process over
1
5%(MoO –WO )/Al O . The impact of reaction
3 3 2 3
temperature on the ODS of thiophene, BT or DBT
over 15%(MoO –WO )/Al O is shown in Fig. 6. Dis-
Figure 7 clearly shows the effect of time on the
3
3
2
3
ODS efficiency of DBT over 15%(MoO –WO )/Al O
3
3
2
3
tinctly, the conversions exhibit an increase with the
reaction temperature from 328 to 333 K for thiophene,
catalyst at 333 K. The DBT conversion in model fuel
is 84.0% in only 0.5 h, slowly increased to 85.6% in
3
08 to 338 K for BT and 298 to 328 K for DBT. The
1
.5 h, and then rapidly to 94.4% in 2.0 h, and to 99.2%
ODS conversion of thiophene is 82.5% at 328 K, rap-
idly risen to 99.4% at 333 K. The ODS of BT and DBT
also displays the similar regularity. For example, below
in 3.0 h. After 3 h, a continuous increase of reaction
time exerts little effect on the DBT conversion. There-
fore, the reaction time of 3.0 h and temperature of
3
23 K 43.4% of BT and 64.5% of DBT are converted
3
33 K are the optimal conditions for the ODS of DBT.
into oxidation products. With increasing the reaction
temperature, the conversion of BT is quickly increased
CONCLUSIONS
Catalysts containing MO /Al O were synthesized
Effect of reaction conditions on the ODS of DBT over
3
2
3
15%(MoO –WO )/Al O
and used in the oxidative desulfurization. In the process
of ODS with CTAB as the phase-transfer reagent and
hydrogen peroxide as the oxidant, thiophene, ben-
zothiophene and dibenzothiophene were oxidized into
the corresponding sulfones. Among tested catalysts, the
3
3
2
3
DBT
conversion
Catalyst (mg) CTAB (mg) H O (mL)
2
(
%)
1
5%(MoO –WO )/Al O prepared by a conventional
3 3 2 3
no
0.0
0.0
0.0
3.0
no
3.0
3.0
no
30.9
39.2
73.2
99.2
impregnation method was relatively active for the oxi-
dative desulfurization of model diesel, with the highest
1
9
9.2% conversion of DBT at low reaction temperature
1
3.0
3.0
of ≤338 K, superior to other catalysts. The results
showed that many factors could affect the performance
of the catalysts, such as the loading of metal, the reac-
tion system, the reaction temperature and time, etc.
1
3.0
Reaction conditions: model fuel 15 mL, H O 0.5 mL, tempera-
2
2
ture 333 K, time 4 h
KINETICS AND CATALYSIS
Vol. 58
No. 1
2017

OXIDATIVE DESULFURIZATION OF THIOPHENE DERIVATIVES
33
ACKNOWLEDGMENTS
15. March, J., Advanced Organic Chemistry, New York:
Wiley–Interscience, 1992.
This work was supported by National Natural Sci-
ence Foundation of China (21273064, 21503074,
1
6. Te, M., Fairbridge, C., and Ring, Z., Appl. Catal., A,
001, vol. 219, p. 267.
7. Palomeque, J., Clacens, J.M., and Figueras, F., J. Catal.,
002, vol. 211, p. 103.
2
2
1673069), by the Natural Science Fund for Creative
1
Research Groups of Hubei Province of China
2014CFA015), by the 2014 Sci-tech Support Project
2
(
of the Science and Technology Department of Hubei 18. Shiraishi, Y., Naito, T., and Hirai, T., Ind. Eng. Chem.
Res., 2003, vol. 42, p. 6034.
Province of China (2014BAA098).
1
9. Javadli, R. and Klerk, A.D., Energy Fuels, 2012, vol. 26,
p. 594.
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