China Petroleum Processing and Petrochemical Technology
Scientific Research
2014, Vol. 16, No. 3, pp 26-32
September 30, 2014
Solvothermal Synthesis of V2O3 Catalysts for Oxidative
Desulfurization of Dibenzothiophene
Liu Ni; Zhang Minghui; Wang Danhong
(Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai
University, Tianjin 300071)
Abstract: V2O3 nanoparticles with high surface area have been successfully prepared by a new solvothermal method without using any surfactant and template. The size of V2O3 nanoparticles is mostly equal to 10 nm-30 nm. The highest surface
area of obtained V2O3 nanoparticles reaches 49 m2/g. Several kinds of V2O3 catalysts were prepared by different methods.
All these V2O3 catalysts obtained thereby showed high catalytic activity for oxidative desulfurization (ODS) reaction by using tert-butyl hydroperoxide as the oxidant. The V2O3 catalyst with a highest ODS activity was obtained under the following
conditions: The catalyst was prepared upon using V2O5 as the vanadium source, methanol as the solvent, and oxalic acid as
the complexing reagent at a V2O5/oxalic acid molar ratio of 1:2. The process for ODS of dibenzothiophene was carried out
under mild conditions (under atmospheric pressure and at a relatively low temperature). The highest ODS activity of the obtained V2O3 nanoparticles can be attributed to their highest surface area.
Key words: vanadium sesquioxide; nanoparticles; oxidative desulfurization; solvothermal; dibenzothiophene
1　Introduction
oxidized to sulfoxides and sulfones. The chemical and
Nowadays, sulfur content in the fuel oil is being continu-
physical properties of sulfoxides and sulfones are very
ously regulated to lower levels due to environmental requirements[1-2]. Hydrodesulfurization (HDS) is a currently
adopted technology for sulfur removal in the petroleum
and petrochemical industries. HDS is highly efficient for
the removal of thiols, sulfides, and disulfides. However,
it is difficult to reduce refractory sulfur compounds such
as dibenzothiophene (DBT). The HDS process requires
high temperature and H2 pressure, making HDS a very
expensive pathway for deep desulfurization[3-4]. In recent
years, a lot of researchers have explored several alternative technologies to remove these refractory sulfur compounds, such as adsorption[5], extraction[6], oxidation[7]
and bioprocesses[8]. Among them, the ODS process seems
to be very promising and is receiving increasing attention, because the sulfur compounds (DBTs) that are the
most difficult to be removed by HDS are the most reac-
different from other hydrocarbons contained in fuel oil.
They can be removed by distillation, solvent extraction,
or adsorption. The DBTs are easily oxidized under mild
reaction conditions (under atmospheric pressure and at
a relatively low temperature) without using expensive
hydrogen[9-12].
Lots of catalysts for ODS have been discussed in previous publications[13-16]. Recently, the supported vanadiumcontaining compounds have been researched in the ODS
reaction[17-21]. For instance, V2O5/Al2O3, V2O5/TiO2 and
V2O5/SiO2-Al2O3 catalysts were introduced in oxidative
desulfurization process. V2O5 catalyst is well known for
its catalytic activity in the ODS process. But the catalytic
activity of other vanadium oxides is still rarely studied.
Actually there are plenty of publications about other
vanadium oxides, such as V2O3, and VO2. Most of these
tive in the ODS process. Moreover, the ODS process can
be carried out under very mild conditions compared with
[9]
Received date: 2014-03-24; Accepted date: 2014-08-05.
severe conditions used in HDS process . During the oxi-
Corresponding Author: Dr. Wang Danhong, Telephone: +86-
dative desulfurization process, sulfur compounds can be
22-23507730; E-mail: [email protected].
·
26 ·
Liu Ni, et al. Solvothermal Synthesis of V2O3 Catalysts for Oxidative Desulfurization of Dibenzothiophene
publications have paid attention to the technological applications except for their catalytic property
[22-24]
. Over
two decades, many techniques and different methods
have been reported to synthesize V2O3 powder. For example, the sphere-like V2O3 particles were prepared by
using O2-H2 flame fusion of V2O5 at 2 273 K. Spherelike V2O3 particles were synthesized by reduction of V2O5
in H2 atmosphere at 1 123 K for 6 h. In addition, V2O3
powders were formed by pyrolyzing the hydrazine containing vanadium salt and reducing the V2O5 gel under H2
atmosphere[25]. There are some other synthetic methods,
such as the laser-induced vapor-phase reaction and ultrashort pulsed deposition of vanadium oxides[26]. However,
2　Experimental
2.1　Materials
In this synthesis procedure, we use V2O5 as the source of
vanadium. In a typical synthesis procedure, V2O5 powder
and oxalic acid in a definite proportion was added to 30
mL of aqueous solution under stirring, until the color
of the solution changed from yellow to dark blue. This
procedure was carried out in about 3 hours. The mixture
was transferred into a teflon-lined autoclave. The autoclave was sealed and heated to 453 K for 16 hours. Then
the autoclave was cooled to room temperature and the
precipitate was separated by filtration, and then washed
with deionized water and ethanol. The product was dried
there are several disadvantages in these systems, such as
in a vacuum oven at 333 K for 3 h. The obtained black
complicated process, high temperature, unavailability to
powder precursor was proved to be metastable VO2 (B).
dispersed nanoparticles, and expensive production costs.
The monoclinic VO2 (M) was obtained by crystallizing
Only micrometer-scale powders are obtained by these
the precursor at 773 K for 4 h in the Ar atmosphere[27-29].
methods. Few preparation methods of the V2O3 nanopar-
When the precursor was crystallized at 873 K for 4 h in
ticles have been reported.
the Ar atmosphere, V2O3 was formed. As shown in Table 1,
In this paper, our group has developed a simple solvothermal approach for synthesis of V2O3 nanoparticles by using
V2O5, methanol and oxalic acid as reaction reagents. The
application of this reaction is particularly attractive and
the obtained V2O3 nanoparticles are phase-pure. Besides,
the process is rather simple and the reaction temperature is relatively low, which would make it much easier
to achieve large-scale production. The obtained V 2O 3
nanoparticles showed very high catalytic activity in oxi-
we marked this V2O3 product as V2O3 (1). In a typical synthesis process, one gram of V2O5 was directly added into a
teflon-lined autoclave with the addition of excess methanol. The autoclave was sealed and heated to 453 K for 12
hours. Next steps were similar to those for preparation of
V2O3 (1). Similarly, V2O3 was formed when the precursor
was crystallized at 873 K for 4 h in the Ar atmosphere. As
shown in Table 1, we marked this V2O3 product as V2O3 (2).
V2O3 nanoparticles can be directly synthesized by the solvothermal method. V2O5 powder and oxalic acid in a defi-
dative desulfurization process. In addition, there was no
nite proportion with excess methanol being added into a
contamination during the production with other inorganic
teflon-lined autoclave. The autoclave was sealed and heat-
compounds, such as halides or alkaline ions.
ed to 453 K for 12 hours. Then the autoclave was cooled
Table 1　Different experimental conditions for synthesis of V2O3 particles
Catalysts
Vanadium source
V2O5:H2C2O4 molar ratio
Solvent
Crystallization temperature, K
Total time needed, h
V2O3 (1)
V2O5
1:2
Purified water
873
26
V2O3 (2)
V2O5
Methanol
873
19
V2O3 (3)
V2O5
1:1
Methanol
673
19
V2O3 (4)
V2O5
1:2
Methanol
673
19
V2O3 (5)
V2O5
1:3
Methanol
673
19
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China Petroleum Processing and Petrochemical Technology
2014,16(3):26-32
to room temperature. The precipitate was separated by
adsorption–desorption analysis was carried out at 77 K
filtration and washed with deionized water and ethanol.
on a Micromeritics TriStar 3000 apparatus. Transmission
The V2O3 was formed when the precursor was crystallized
electron microscopy (TEM) experiments were carried
at 673 K for 4 h in the Ar atmosphere. As shown in Table
out on a JEM-100CXII transmission electron microscope
1, we marked the obtained V2O3 product as V2O3 (3) when
with an accelerating voltage of 100 kV. Scanning electron
the molar ratio of V2O5 to oxalic acid was 1:1. Likewise,
microscopy (SEM) images were collected by employing a
we marked the obtained V2O3 product as V2O3 (4) when
Quanta 200 scanning electron microscope operated at 30
the molar ratio of V2O5 to oxalic acid was 1:2 and labeled
kV. Oxidation products were analyzed by a gas chromato-
the product as V2O3 (5) when the V2O5/oxalic acid molar
graph, which was equipped with a SGE AC10 capillary
ratio was equal to 1:3.
column, 0.25 mm in diameter and 30 m in length. The
2.2　Catalysts preparation
A mixture of 0.20 g of V2O3 black powder and 0.80 g of
macroporous silica gel was ground, pressed, crushed, and
screened. 0.10 g of sieved catalyst with a grain size of
40—60 mesh was used for oxidative desulfurization process.
2.3　Catalytic performance test
products were identified by checking the retention time
with standard materials.
3　Results and Discussion
3.1　Characterization of V2O3 nanoparticles
Crystal structure of the as-synthesized V2O 3 samples
prepared at different temperatures was characterized by
The obtained vanadium sesquioxide particles were used as
wide-angle XRD as shown in Figure 1. V 2O3 (1) was
the catalyst for oxidative desulfurization of dibenzothio-
obtained using deionized water as the solvent and was
phene. Oxidative desulfurization of DBT was carried out
crystallized in the Ar atmosphere at 873 K. VO2 (M) was
in a fixed-bed reactor. A simulated model diesel (MD500)
obtained at 773 K and VO2 (B) was obtained either with-
was prepared as follows: 0.05 g of DBT was dissolved in
out crystallization or through crystallization at 673 K. As
99.95 g of decalin to obtain a solution containing 500 mg/g of
shown in Figure 2, V2O3 (2) was obtained using methanol
DBT. Since the molar mass of DBT is about 3 times that of
as the solvent and was crystallized in the Ar atmosphere at
TBHP, so 0.112 8 g of 65% TBHP was dissolved in 99.9 g of
873 K. VO2 (M) was obtained at 773 K and a mixture of
decalin to obtain a solution containing 500 mg/g of TBHP.
VO2 (B) and VO2 (M) was obtained either without crystal-
A typical oxidative desulfurization process was carried
lization or through crystallization at 673 K. Figure 3 shows
out in a stainless steel and temperature-controlled fixed-
the XRD patterns of V2O3 samples synthesized under dif-
bed reactor (with an i. d. of 3 mm). 0.10 g of sieved catalyst was loaded in the reactor and heated up to a specified
temperature. Then the feed (MD500) was introduced by a
peristaltic pump under atmospheric pressure at a WHSV
of 40 h-1. After the effluent was maintained at each temperature for one hour, the reaction solution at that temperature was collected for half an hour to be analyzed by
a gas chromatograph (GC-FID).
2.4　Characterization methods
Powder X-ray diffraction (XRD) patterns were obtained
on a Rigaku D MAX diffractometer using CuKα radiation
(at a tube voltage of 40 kV and a tube current of 100 mA)
from 10° to 80° (2θ) with a scanning rate of 12(°)/min. N2
·
28 ·
Figure 1　XRD patterns of vanadium oxides synthesized
by using deionized water as the solvent and crystallized at
different temperatures at a V2O5/H2C2O4 molar ratio of 1:3
(a) —Without crystallization; (b) —673 K; (c)— 773 K; (d)— 873 K
Liu Ni, et al. Solvothermal Synthesis of V2O3 Catalysts for Oxidative Desulfurization of Dibenzothiophene
ever, the obtained product V2O3 (5) was not pure when the
V2O5/oxalic acid molar ratio was 1:3, because diffraction
peaks of VO2 (M) were identified, indicating that excessive amount of oxalic acid inhibited the reduction of V2O5
to V2O3. Except for V2O3 (5), all of the diffraction peaks
can be assigned to the Karelianite phase of V2O3, which
is consistent with the values given in the standard card
(JCPDS no. 34-0187). No peaks of any other phases were
detected, indicating to the excellent purity of the products.
Figure 2　XRD patterns of samples synthesized by using
The XRD peaks are strong and narrow, indicating to the
methanol as the solvent and crystallized at different
good crystallinity of the as-synthesized V2O3. The synthe-
temperatures without oxalic acid
(a)—without crystallization; (b)—673 K; (c)—773 K; (d)—873 K
sized V2O3 samples were characterized by the BET method using N2 adsorption/desorption technique. As shown in
Table 1 and Table 2, the BET surface area, pore size and
pore volume of the synthesized V2O3 samples increased
with the increase in molar ratio of V2O5 to H2C2O4 in the
methanol solvothermal systems. The obtained V2O3 (4)
sample showed a highest surface area of 48.7 m2/g. The
morphology of the V2O3 samples was examined by SEM.
As shown in Figure 4, the synthesized V2O3 seemed to be
stacked with V2O3 flakes. The size of V2O3 flakes increased
with an increasing amount of oxalic acid in the methanol
Figure 3　The XRD pattern of V2O3 samples obtained under
different experimental conditions
ferent experimental conditions. V2O3 (3) was synthesized
using methanol as the solvent and oxalic acid as the complexing agent (with the molar ratio of V2O5 and oxalic
acid equating to 1:1), and was crystallized in the Ar atmosphere at 673 K consequently. The addition of oxalic acid
obviously decreased the reduction temperature upon comparing the conditions for synthesis of V2O3 (3) with those
of V2O3 (2). Similarly, V2O3 (4) was obtained at 673 K
when the molar ratio of V2O5/oxalic acid was 1:2. How-
solvothermal systems. The TEM image of V2O3 (4) sample
revealed that the size of V2O3 nanoparticles was mostly
around 10—30 nm as shown in Figure 5.
Table 2　Textural properties of these synthesized catalysts
Catalysts
BET area, m2/g
Pore size, nm
Pore volume, cm3/g
V2O3 (1)
29.9
156
0.117
V2O3 (2)
10.8
51.2
0.013 8
V2O3 (3)
19.5
102
0.050 1
V2O3 (4)
48.7
158
0.192
V2O3 (5)
48.6
103
0.125
Figure 4　SEM images of synthesized V2O3 samples
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2014,16(3):26-32
China Petroleum Processing and Petrochemical Technology
BET area leads to higher ODS catalytic activity. It is obvious that the appropriate molar ratio of V2O5 to H2C2O4
for the methanol solvothermal system is 1:2.
Figure 6　ODS of DBT under different temperature on V2O3
catalysts
■—V2O3 (1); ●—V2O3 (2); ▲—V2O3 (3); ▼—V2O3 (4);
—V2O3 (5)
3.3　Reaction mechanism of V2O3 catalyst
Figure 5　TEM images(a), HRTEM images(b) and
particle size distribution graph(c) of V2O3 (4) sample
The chemical reactions involved in the methanol solvothermal processes are briefly proposed as follows:
V2O5+3H2C2O4→2VO2++2C2O42−+2CO2+3H2O
2+
3.2　Catalytic performance
The ODS activity of the synthesized V2O3 catalysts is
summarized in Figure 6. All V2O3 catalysts showed high
DBT conversion, which decreased at 343 K in the following order: V2O3 (4)>V2O3 (3)>V2O3 (2)>V2O3 (1)>V2O3
(5). The activity of V2O3 (4),V2O3 (3) and V2O3 (2) is obviously higher than that of V2O3 (1). The reason is that they
were synthesized by using different solvents as shown
in Table 1. In addition, methanol as the solvent could
significantly reduce the crystallization temperature upon
comparing the synthesis of V2O3 (1) with that of V2O3 (4).
As compared to the use of purified water, methanol used
as the solvent has great advantages. In regard to V2O3(4),
V 2O 3 (3) and V 2O 3 (2) catalysts, the ODS activity decreased with a decreasing surface area. The highest ODS
activity of V2O3 (4) sample can be attributed to its highest
surface area. Despite the high surface area, V2O3 (5) catalyst showed low ODS activity, which could be attributed
to the existence of VO2 (M). For methanol solvothermal
system, the BET surface areas of synthesized V2O3 catalysts increased with the addition of oxalic acid. Larger
·
30 ·
2VO +CH3OH+H2O→V2O3+HCHO+4H
+
(1)
(2)
As described in Equation (1), VO2+ with a characteristic sapphire color was produced by reducing vanadium
pentaoxide with oxalic acid during the preparation of the
precursor (VOC2O4), which was consistent with the result
reported by Liu Xinghai[30]. Oxalic acid acts not only as a
reducing reagent but also as a complexing reagent in the
solvothermal process. VOC2O4 was suggested to be formed
in Eq. (1). It was reported[31] that hydroxide nanoflakes
were synthesized by hydrothermal reaction with divalent
cations (Ni2+, Co2+) and H2C2O4. The C2O42− ions acted as
a complexing reagent in the formation of two-dimensional
large plane and could control the reaction speed. Equation
(2) was the key step for preparing V2O3. It was reported
that ethanol can serve as the reducing reagent and aldehyde
was detected in the solvothermal process[32].
4　Conclusions
In summary, a simple, safe, and facile method to obtain
V2O3 nanoparticles with diameters ranging from 10 nm to
30 nm by the solvothermal reduction of V2O5 was studied.
Liu Ni, et al. Solvothermal Synthesis of V2O3 Catalysts for Oxidative Desulfurization of Dibenzothiophene
The obtained V2O3 nanoparticles show very high catalytic
activity in the oxidative desulfurization process. We believe
that the V2O3 nanoparticles catalyst would have a good application prospect in the oxidative desulfurization process.
dibenzothiophene and diesel over [Bmim]3PMo12O40[J]. J
Catal, 2011, 279(2): 269-275
[11] Wang D H, Qian E W H, Amano H, et al. Oxidative de　sulfurization of fuel oil - Part I. Oxidation of dibenzothiophenes using tert-butyl hydroperoxide[J]. Appl Catal A,
Acknowledgment: This work was supported by the National
Nature Science Foundation of China (21303088).
2003, 253(1): 91-99
[12] Ishihara A, Wang D H, Dumeignil F, et al. Oxidative de　sulfurization and denitrogenation of a light gas oil using
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1878-1880
Enlarged Scale of Domestic Syngas-to-EG Unit
The Shanghai Wuzheng Engineering Technology Limited
Liability Company in collaboration with China Huanqiu
Contracting and Engineering Corporation will provide
the technology and project design to the commercial and
engineering scale-up project for manufacture of ethylene
glycol (EG) from syngas launched by the Zhejiang Rongsheng Holding Group Company. Currently the project
design activity is being carried out successfully.
It is learned that this project will adopt the upgraded catalyst and novel plate reactor, with the production capacity
of a single reactor reaching 200 kt/a. The enlargement of
a single EG reactor can reduce the consumption of major
materials by 5% and the consumption of energy by over
10%, with the qualified rate of polyester grade EG exceeding 95%.
The carbonylation reactor and hydrotreating reactor comprising the commercial single series 200 kt/a—300 kt/a
EG production technology are all made of plate reactors
which can save the equipment investment cost by more
than 25% as compared to that of the connected in parallel multiple tubular reactors having the same throughput.
The enlarged size of equipment can avoid the bias flow
in reaction materials and temperature fluctuations during
·
32 ·
temperature rise which is characteristic of the connected
in parallel multiple tubular reactors along with setbacks
such as the worsening catalyst selectivity and low rate of
qualified polyester grade EG product.
The adoption of novel plate-type reactors can reduce
compression energy consumption by over 20% and the
investment in the associated system as compared to those
of the connected in parallel multiple tubular reactors with
the same production scale. The macroporous zeolite can
be used as the catalyst in the novel plate reactors and its
EG selectivity and hourly space yield can be significantly
increased after addition of the promoter. In order to abate
poisoning and inactivation of the catalyst the Shanghai
Wuzheng Engineering Technology Limited Liability
Company has innovatively introduced the prehydrotreating catalyst that can extend the service life of hydrotreating catalyst to two years. In the meantime, the adoption of
an on-line mass spectrometer can help to solve the tough
problem for quality control, because a mass spectrometer can concurrently monitor and measure multiple gas
streams at the ppb level. The tail gases, waste liquids and
waste solids are recycled in order to reduce the material
and energy consumption.