Incorporation of tungsten oxide in mesoporous silica: Catalytic epoxidation of olefins using sodium-bi-carbonate as co-catalyst

Article abstract of DOI:10.1016/j.ica.2011.12.003

Tungsten oxide incorporated mesoporous molecular sieve (WO ₃-SBA-15) composite was successfully synthesized via one-step hydrothermal process using tetraethylorthosilicate (TEOS) as the silica source, sodium tungstate as the tungsten precursor,

Full text of DOI:10.1016/j.ica.2011.12.003

Inorganica Chimica Acta 384 (2012) 233–238
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Incorporation of tungsten oxide in mesoporous silica: Catalytic epoxidation
of olefins using sodium-bi-carbonate as co-catalyst
⇑
Rajesh Bera, Subratanath Koner
Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Tungsten oxide incorporated mesoporous molecular sieve (WO –SBA-15) composite was successfully
3
Received 11 February 2011
Received in revised form 1 December 2011
Accepted 3 December 2011
Available online 11 December 2011
synthesized via one-step hydrothermal process using tetraethylorthosilicate (TEOS) as the silica source,
sodium tungstate as the tungsten precursor, and pluronic P123 triblock polymer (EO20PO70EO20, Mav
=
(
5800) as a structure-directing agent. The material was characterized by small angle X-ray diffraction
SAX), transmission electron microscopy (TEM), nitrogen sorption measurement and Fourier transform
infrared spectroscopy. The catalyst showed excellent catalytic efficiency in epoxidation reactions with
various olefinic compounds using H as oxidant and NaHCO as co-catalyst. The solid catalyst can be
Keywords:
2
O
2
3
Tungsten oxide
Mesoporous silica
Epoxidation
recovered after reaction and can be reused for several times in catalytic reactions without any significant
loss of activity.
Ó 2011 Elsevier B.V. All rights reserved.
Olefin
Heterogeneous catalysis
1
. Introduction
quinolinolato Mo(VI) [15], polymer supported Mo(CO)
hexa-thiocyanatorhenate [17] in the presence of H /NaHCO
Many tungsten-based homogeneous catalytic systems have been
used in the activation of H [18–26]. Althoughthese systemsshow
high activity and selectivity of epoxides, the industrial application of
such systems are limited due to the problems associated with cata-
lyst recovery and easy product separation. Consequently, a number
of heterogeneous tungsten based catalyst for epoxidation with using
6
[16] and
2
O
2
3
.
The epoxidation of alkenes constitutes one of the most useful
reactions in organic synthesis as the epoxide formation is a crucial
step in the oxyfunctionalization of many molecules. Epoxides are
commercially important intermediates used in the synthesis of a
wide variety of fine chemicals [1–4]. Although many catalytic
epoxidation methods, including asymmetric epoxidation, have
been developed, selective epoxidation of alkenes using heteroge-
neous catalysts and clean oxidants under mild conditions is still
2 2
O
2
H O
2
as oxidant has been developed [27–31].
Tungsten oxides are a versatile catalytic material which has
been extensively used as catalysts for different reactions. Koo
et al. have used MCM-48-supported WO catalyst in selective het-
a challenge [5,6]. H
to economical and environmental grounds [7–9]. H
2
O
2
is the best terminal oxidant with respect
has the
2
O
2
3
largest content of active oxygen among the other known oxidants
besides dioxygen, but it is a slow oxidizing agent in the absence of
activators. Yao and Richardson described the epoxidation of
erogeneous catalytic oxidation of olefins, sulfides and cyclic
ketones [32]. Prasetyoko et al. reported the epoxidation of 1-octene
catalyzed by tungsten oxide impregnated titanium silicalite using
alkenes by H
2
O
2
/NaHCO
3
system in CH
3
CN/D
2
O where the reaction
H
2
O
2
as an oxidant. In this method a considerable amount of diol
was produced along with epoxide [33]. Recently, single-site meso-
porous WO materials were synthesized by Gao et al. and the mate-
rial was found to be highly active in the epoxidation of cycloocta-
1,5-diene with aqueous H [34]. Bolsoni et al. demonstrated that
meso-lamellar xerogel tungsten oxide phase (WO /CTAB/HDA)
time is high (24 h) and conversion of styrene is only 40% [10]. Ho
et al. reported the epoxidation of alkenes using Mn2 as the catalyst
+
3
2 2
where H O is electrogenerated in-situ in aqueous bicarbonate
solutions [11]. There are several other reports of epoxidation of
alkenes using catalysts such as manganese(III) meso-tetraphenyl-
2 2
O
3
porphyrin complex [12], MnSO
num(VI) complex [MoO(O (salox)] (salox = salicylaldoxime)
14], mesoporous silica incorporated oxodiperoxo-8-hydroxy-
4
[13], oxodiperoxo molybde-
(CTAB = cetyltrimethylammonium bromide, HDA = n-hexadecyl-
amine) displays good catalytic activity for epoxidation reactions
with different oxidants [35]. However, reports of epoxidation of al-
kenes catalyzed by mesoporous silica supported tungsten oxide are
still scanty.
2 2
)
[
In the course of our continuing investigation in different organic
reactions using ordered mesoporous silica materials as heteroge-
neous catalytic support we have found that the hybrid material
⇑
Corresponding author. Tel.: +91 33 2414 6666x2778; fax. +91 33 2414 6414.
E-mail addresses: snkoner@chemistry.jdvu.ac.in, skoner55@hotmail.com (S.
Koner).
0
020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.12.003

2
34
R. Bera, S. Koner / Inorganica Chimica Acta 384 (2012) 233–238
demonstrates desirable catalytic efficacy [36–39]. Herein we report
the synthesis and characterization of tungsten oxide incorporated
of the epoxidation reactions were collected at different time inter-
vals and were identified and quantified by gas chromatography.
3
mesoporous molecular sieve (WO –SBA-15) and its catalytic activ-
ity under moderate reaction condition. The catalyst show high
activity and selectivity towards the epoxidation of alkenes than
the other similar type of tungsten-based catalyst reported before.
3
. Results and discussion
3.1. Catalyst characterization
2
. Experimental
The small angle XRD patterns of SBA-15 and WO
3
–SBA-15 are
–SBA-15 dis-
plays three well-resolved peaks at low angle at a 2h in the range of
.5°–5°. These lines can be indexed to (100), (110) and (200)
shown in Fig. 1. The small angle XRD pattern of WO
3
2.1. Materials
0
The solvents used were purchased from Merck (India) and were
reflections in the hexagonal space group p6mm, which are typical
for mesoporous silica SBA-15 matrix (Fig. 1a). The strongest peak
for d100 = 9.4 nm appears in the region 2h ꢁ 0.937°. The pore center
2 2 3
distilled and dried before use. 30% H O and NaHCO was pur-
chased from Merck (India). Alkenes and EO20PO70EO20 were pur-
chased from Aldrich and were used as received.
to pore center distance (a) is 10.85 nm, which is calculated by the
2
3
equation, a ¼
p
ffiffi d100. The high angle XRD pattern (Fig. 2) shows
2.2. Catalyst preparation
peaks at 23.13°, 23.55°, 24.35°, 26.39°, 28.65°, 33.33°, 41.60°,
9.92° and 55.73° (2h) which are characteristic of WO
4
3
(monoclinic
Mesoporous hexagonally ordered tungsten oxide incorporated
(P21/n), JCPDS # 72-0677) [40].
3
The nitrogen adsorption–desorption isotherm of WO –SBA-15
are shown in Fig. 3. The isotherm shows typical type IV feature
with a clear H1 type hysteresis loop which is typical of mesoporous
materials [41,42]. The volume of adsorbate shows a sharp increase
SBA-15 was synthesized hydrothermally using tetraethylorthosili-
cate (TEOS) as the silica source and poly(ethylene oxide)-block-
poly(propylene oxide)-block-poly-(ethylene oxide) triblock copoly-
mer (average MW 5800, EO20PO70EO20, P123) as a structure-direct-
ing agent. Typically, 2 g of P123 triblock copolymer was dissolved in
1
5 g of water with stirring and 3 ml of aqueous sodium tungstate
solution (Na WO O, 0.5 M) was quickly added into the mixture
2
4
ꢀ2H
2
with vigorous stirring. After 2 h, 60 g of 2 M HCl and 4.5 g of TEOS
was added with and the stirring was continued for 24 h at 40 °C.
Then the gel was transferred into a Teflon lined autoclave and kept
at 100 °C under static condition for two days. The solid product was
recovered by filtration, washed several times with water and etha-
nol, and dried in air. The collected product was then calcined at
5
60 °C for 8 h in stream of air to remove the template. The sample
was designated as WO –SBA-15. Atomic absorption result showed
tungsten content of the catalyst was ca. 0.84% (wt). 2WO –SBA-
5 and 4WO –SBA-15 were prepared by following the same proce-
3
3
1
3
dure as above, adding 6 ml and 9 ml of aqueous sodium tungstate
solution, respectively. The tungsten content of the catalysts
2
3 3
WO –SBA-15 and 4WO –SBA-15 were ca. 2.12 and 4.42% (wt),
respectively.
2.3. Catalyst characterization
Fig. 1. Small angle X-ray diffraction (XRD) patterns of SBA-15 (a) and WO
b).
3
–SBA-15
The powder X-ray diffraction (XRD) patterns of the samples
(
were recorded with a Philips X’Pert PRO PANalytical diffractometer
using Cu K -radiation. N sorption measurements were undertaken
a
2
on a Quantachrome Autosorb Automated Gas Sorption system.
Infrared spectra were measured on Shimadzu S-8400 Fourier trans-
form infrared (FTIR) spectrophotometer. Transmission electron
microscopic (TEM) measurements were performed on a JEOL JEM
2
100 instrument. The products of the catalytic reactions were iden-
tified and quantified by a Varian CP-3800 gas chromatograph using
a CP-Sil 8 CB capillary column and yields were determined by inte-
gration relative to an alkane internal standard. The tungsten con-
tent of the sample was estimated on a Varian Techtron AA-ABQ
atomic absorption spectrometer.
2.4. Catalytic reactions
The catalytic reactions were carried out according to the follow-
ing procedure. An acetonitrile (8 ml) solution of a given substrate
10 mmol), NaHCO (2 mmol) and the catalyst (50 mg) were mixed
(
3
in a flat-bottom two-neck reaction flask where one neck fitted with
a reflux condenser to check evaporation. After addition of 30%
2
H O
2
, the reaction was stirred continuously at 30 °C. The products
3
Fig. 2. High angle X-ray diffraction (XRD) patterns of WO –SBA-15.

R. Bera, S. Koner / Inorganica Chimica Acta 384 (2012) 233–238
235
TEM images of WO
3
–SBA-15 shows the hexagonally ordered
porous structure of SBA-15 is retained after the formation of tung-
sten oxide species (Fig. 4). The tungsten oxide species are not visible
in the HRTEM images which reveal that no extra framework tung-
sten oxide species are present outside the mesoporous structure
and are present inside the mesochannels of SBA-15. The distance
between two consecutive centers of hexagonal pores estimated
from the TEM image is around 11 nm, which is in well agreement
with the position of the first peak in the small angle XRD pattern.
The average thickness of the wall is 4.55 nm, and the pore diameter
is around 6–7 nm which is consistent with the small angle XRD and
the nitrogen adsorption–desorption measurement
3.2. Catalytic activities
3
The results of the catalytic performance of WO –SBA-15 in epox-
idation of aromatic and aliphatic alkenes are shown in Table 1. The
catalyst shows excellent yield of corresponding epoxides in aceto-
nitrile medium using H O as oxidant and NaHCO as co-catalyst.
2 2 3
3
Fig. 3. Nitrogen adsorption–desorption isotherm of WO –SBA-15.
A detailed study of the epoxidation of cyclooctene with various re-
agents was carried out to optimize the conditions (Table 2). All
at a (P/P
densation of nitrogen within the uniform mesoporous structure
of WO –SBA-15. The BET surface area, pore volume and pore diam-
0
) of approximately 0.7 which arises from capillary con-
reactions were carried out with 5 mmol of cyclooctene in CH
for 3 h at room temperature. Controlled experiments without using
catalyst or NaHCO failed to produce the desired product. The con-
version of cyclooctene was only 9% with NaHCO and H in the
absence of catalyst. The conversion was increased to 94% with
WO –SBA-15/NaHCO /H . Clearly the oxidation reaction occurs
in a very slow pace in presence of H –NaHCO . Yao and Richard-
son [10] showed that H and bicarbonate react in an equilibrium
process to produce peroxymonocarbonate (Eq. (1)) which is a more
3
CN
3
2
ꢂ1
3 ꢂ1
eter are 396 m g , 0.20 cm g and 6.3 nm, respectively (Fig. 3).
3
ꢂ1
FTIR spectra of WO
3
–SBA-15 show typical bands at 1075 cm
3
2 2
O
ꢂ1
with a shoulder at 1225 cm due to asymmetric Si–O–Si stretching
modes and symmetric stretch at 804 cm . An additional band at
54 cm is observed which is widely assigned the presence of tran-
ꢂ1
3
3
2 2
O
ꢂ1
9
2
O
2
3
sition metal atoms near the silica framework as the stretching Si–O
vibration mode perturbed by the neighboring transition metal ions.
2 2
O
3
Fig. 4. TEM images showing pores of WO –SBA-15.
Table 1
3 2 2 3 3
Heterogeneous alkene epoxidation catalyzed by WO –SBA-15 with 30% H O and NaHCO at room temperature (30 °C) in CH CN.
Alkenes
Reaction Time (h)
Conversion (wt%)
% Yield of products
Epoxide
cTOF (hꢂ1
)
Others
Styrene
Cyclohexene
Cyclooctene
8
3
3
3
3
3
88
91
94
82
78
58
81
91
94
82
78
58
7a
–
–
–
459
1319
1362
1188
1130
841
1
-Octene
Trans-b-methylstyrene
cis-Stilbene
–
Traceb
Reaction conditions: alkene (10 mmol); catalyst (50 mg); 30% H
2
O
2
(4–5 ml); NaHCO
3
(10 mg); CH
3
CN (8 ml).
a
Benzaldehyde.
Other product.
b
c
Turn over frequency = moles converted/mol of active site/time.

2
36
R. Bera, S. Koner / Inorganica Chimica Acta 384 (2012) 233–238
Table 2
Control experiments in epoxidation of cyclooctene with 30% H
2 2
O .
Run
Catalyst
WO –SBA-15
None
WO –SBA-15
Co-catalyst
None
Reaction time (h)
Conversion (wt%)
% yield of epoxide
1
2
3
3
3
3
3
2
9
94
2
9
94
NaHCO
NaHCO
3
3
3
2 2 3 3
Reaction condition: alkene (5 mmol), catalyst (25 mg), 30% H O (2 ml), NaHCO (5 mg); CH CN (4 ml).
active nucleophile than H
epoxidation reaction:
2 2
O , and causes enhancement of speed of
Table 4
Cyclooctene epoxidation catalyzed by different tungsten oxide content WO
3
–SBA-15
catalysts at 30 °C.
ꢂ
ꢂ
ꢂ1
HCO3 þ H
2
O
2
¼ HCO þ H
2
O
ð1Þ
Sample
WO –SBA-15
WO
3
(wt%)
% Yield of cyclooctene oxide
TOF (h
)
4
3
0.84
2.12
4.42
94
82
78
1362
471
217
Maiti et al. demonstrated homogeneous epoxidation of olefins
using oxo-diperoxo tungsten(VI) complex with NaHCO
24]. They showed that the H
or diperoxo complex and such peroxo complexes subsequently
epoxidize the olefin. Thereby monoperoxo or diperoxo complex
2 2 4
revert to the oxo complexes which again react with H O /HCO
2
4
WO
WO
3
–SBA-15
–SBA-15
3
and H
2
O
2
3
ꢂ
[
2
O
2
/HCO
4
generates a monoperoxo
Reaction conditions: alkene (10 mmol); catalyst (50 mg); 30%
NaHCO (10 mg); CH CN (8 ml).
2 2
H O (4–5 ml);
3
3
ꢂ
to regain the catalytic properties and so on. We propose a similar
kind of mechanism in our present case.
Tungsten–phosphoramide-grafted MCM-41 also used as cata-
lyst for cyclooctene epoxidation that gives a 70% epoxide yield
with >95% selectivity [27] (Table 3). Briot et al. reported 98% con-
version of cyclooctene with 100% epoxide selectivity in 24 h using
MCM-41 supported tungsten oxide catalyst and H
et al. studied the cyclooctene epoxidation over a SiO
tungsten-based polyoxometalate ( -1,2-H SiV
that gives a yield of >99% with 81% of olefin conversion in 24 h [30]
Table 3). In our present study, no allylic C–H oxidation product
2
O
2
[43]. Kasai
-immobilized
40) with H
2
c
2
W
2 10
O
2 2
O
(
was observed.
The epoxidation of styrene gives styrene oxide in 81% yield
(
selectivity ꢃ94%). Along with this, a small amount of benzalde-
hyde (7%) is also detected. Upon hydrolysis of the epoxide and sub-
sequent oxidative C–C cleavage benzaldehyde is produced via
formation of trans diol. A turnover frequency of ꢃ459 has been
attained in the styrene epoxidation reaction. There are a few re-
ports of epoxidation of styrene by tungsten-based catalysts under
heterogeneous condition. Gelbard et al. reported the epoxidation
3 3
Fig. 5. Cyclooctene epoxidation by WO –SBA-15 catalysts with different WO
loadings at 30 °C.
of styrene with H
peroxotungstic acid which gives only 10% yield of styrene oxide
28]. Polyoxotungstate catalyst supported on chemically modified
hydrophobic mesoporous silica gel was studied for styrene epoxi-
dation reaction that gives a yield of 90% styrene epoxide with
2 2
O by silica-grafted phosphoramide immobilized
Linear alkene such as 1-octene was also successfully converted
to epoxide with 100% selectivity (conversion 82%) with WO -SBA-
5. Prasetyoko et al. reported the epoxidation of 1-octene using
tungsten oxides-containing titanium silicalite using H at 70 °C
in acetone solvent, where diol is also formed as a side-product
33]. Trans-b-methylstyrene also effectively converted to epoxide
[
3
1
2 2
O
1
[
5% H
44].
The oxidation of cyclohexene proceeds smoothly, showing an
2 2
O as oxidant, but high temperature (90 °C) was required
[
with high yield (conversion 78%, selectivity 100%).
excellent conversion of 91% to form cyclohexene oxide as a sole
product. Epoxide of cyclohexene could be isolated (ꢃ91%) from
the reaction mixture. Only 28% conversion of cyclohexene with
Epoxidation of cyclooctene is tested by different loading of WO
3
in SBA-15. The results are given in Table 4. It is found that with in-
crease in the amount of WO , the conversion of cyclooctene as well
as TOF value decreased (Fig. 5). This is probably occurs due to site-
isolation of active WO centers as percentage of tungsten oxide de-
creases in the catalysts.
8
5% epoxide selectivity has been obtained using tungsten–phos-
phoramide-grafted MCM-41 catalysts using H at 50 °C in
CH CN where pyridine was added to minimize the formation of
3
2 2
O
3
3
diol [27].
Table 3
2 2
Epoxidation of cyclooctene with H O catalyzed by a variety of tungsten-based heterogeneous catalysts.
Catalyst
Conversion (wt%)
Reaction time (h)
Reaction temperature (°C)
Epoxide selectivity (%)
Reference
WO
PW–MCM-41
3
–SBA-15/NaHCO
3
94
70
11
98
91
3
12
-
24
12
30
50
60
25
40
100
>95
100
100
91
this study
[27]
[35]
[43]
[32]
WO
WO
3
/CTAB/HDA
–MCM-41
–MCM-48
x
Nano WO
3

R. Bera, S. Koner / Inorganica Chimica Acta 384 (2012) 233–238
237
Table 5
Comparison of styrene conversion between heterogeneous WO
3
–SBA-15 and homogeneous tungstic acid at 30 °C.
Sample
Catalyst amount(mg)
Conversion (wt%)
% Yield of products
Styrene oxide
Benzaldehyde
WO
Tungstic acid
3
–SBA-15
50
4.2
69
28
69
22
–
6
2 2 3
Reaction conditions: alkene (10 mmol); 30% H O (4–5 ml); NaHCO (10 mg).
reactions. The solid catalyst was recovered from the reaction mix-
ture and has been reused successively three times under the same
reaction conditions. After each reaction, the catalyst has been
washed with CH CN. The recovered catalyst was found to exhibit
3
almost same catalytic activity for cyclooctene epoxidation reaction
in every run: first run, conversion = 93%, second run, conver-
3
sion = 91%, third run, conversion = 93%. WO based catalysts can
be activated by different oxidants (Table 6) in olefin epoxidation
2 2
reactions, however, H O being eco-friendly reagent it attracts in-
creased attention.
4
. Conclusion
In summary, we have successfully synthesized the tungsten
oxide containing mesoporous SBA-15 catalyst by hydrothermal
synthetic method. The material has high surface area, uniform hex-
agonal channel and the tungsten oxide was highly dispersed in the
Fig. 6. Comparison of styrene conversion between heterogeneous WO
homogeneous tungstic acid at 30 °C.
3
–SBA-15 and
mesochannels of SBA-15. The WO
catalytic efficiency towards the epoxidation of alkenes using
as oxidant and NaHCO as co-catalyst.
3
–SBA-15 catalyst showed high
2
H O
2
3
Table 6
Acknowledgements
Epoxidation of cyclooctene with various oxygen sources catalyzed by different WO
based catalysts.
3
We acknowledge the Department of Science and Technology,
Government of India for funding a project (to S.K.) (SR/S1/IC-01/
Catalyst
Oxidant Reaction
Epoxide
Reference
temperature (°C) selectivity (%)
2
009). We also acknowledge the Department of Science and Tech-
WO
WO
WO
WO
WO
3
/CTAB/HDA
3
/CTAB/HDA
3
/CTAB/HDA
3
/CTAB/HDA
3
–SBA-15/NaHCO
t-BOOHa 25
6
69
88
79
100
[35]
[35]
[35]
[35]
nology, Government of India for financial assistance to procure a
Gas Chromatograph in another project (to S.K.) (SR/S1/IC-23/
2003). We are grateful to CIF, IIT Kharagpur for allowing us to avail
TEM facility (on a chargeable basis).
t-BOOH 60
b
m-CPBA 25
m-CPBA 60
3
H
2
O
2
30
[this study]
a
tert-Butyl hydroperoxide.
m-Chloroperbenzoic acid.
b
References
[
[
1] S. Ulmann, Encyclopedia of Industrial Chemistry, sixth ed., Wiley, VCH, New
York, Weinheim, 1998.
2] K.A. Jørgenson, Chem. Rev. 89 (1989) 431.
Epoxidation of cis-stilbene affords mainly cis-Stilbene oxide in
8% yield and a trace amount (<1%) of other product is detected,
suggesting that radical intermediates are not involved (Table 3).
On the other hand in homogeneous condition cis-stilbene affords
a yield of 21% of cis-epoxide and 3% of trans-epoxide using tungstic
acid as catalyst.
5
[3] S. Bhattacharjee, J.A. Anderson, J. Mol. Catal. A Chem. 249 (2006) 103.
[
[
[
4] S.K. Samantaray, K. Parida, Catal. Commun. 6 (2005) 578.
5] J.M. Fraile, J. Garcia, J.I. Mayoral, E. Vispe, J. Catal. 189 (2000) 40.
6] D.E. de Vos, P.A. Jacobs, Catal. Today 57 (2000) 105.
[7] M. Ziolek, Catal. Today 90 (2004) 145.
[
[
10] H. Yao, D.E. Richardson, J. Am. Chem. Soc. 122 (2000) 3220.
[11] K.-P. Ho, T.H. Chan, K.-Y. Wong, Green Chem. 8 (2006) 900.
8] W.R. Sanderson, Pure Appl. Chem. 72 (2000) 1289.
9] G. Grigoropoulou, J.H. Clark, J.A. Elings, Green Chem. 5 (2003) 1.
In order to compare the efficiency of heterogeneous WO
3
–SBA-
[
1
5 catalyst, epoxidation of styrene is studied in homogeneous con-
dition using tungstic acid as catalyst. The results are shown in Ta-
ble 5. In case of homogeneous reaction, the conversion is only 28%
[12] H.H. Monfared, V. Aghapoor, M. Ghorbanloo, P. Mayer, Appl. Catal. A Gen. 372
(
2010) 209.
[
[
13] B.S. Lane, K. Burgess, J. Am. Chem. Soc. 123 (2001) 2933.
14] N. Gharah, S. Chakraborty, A.K. Mukherjee, R. Bhattacharyya, Chem. Commun.
(2004) 2630.
compared to 69% conversion of heterogeneous WO
Fig. 6). Along with 22% styrene oxide, 6% benzaldehyde is also de-
tected in homogeneous reaction. However, in case of WO –SBA-15
no side product was obtained in 3 h. Notably, the catalytic reac-
3
–SBA-15 in 3 h
(
[
[
[
[
15] S.K. Maiti, S. Dinda, M. Nandi, A. Bhaumik, R. Bhattacharyya, J. Mol. Catal. A
Chem. 287 (2008) 135.
16] S. Tangestaninejad, V. Mirkhani, M. Moghadam, G. Grivani, Catal. Commun. 8
(2007) 839.
17] S. Dinda, S.R. Chowdhury, K.M. Abdul Malik, R. Bhattacharyya, Tetrahedron
Lett. 46 (2005) 339.
18] K. Kamata, R. Ishimoto, T. Hirano, S. Kuzuya, K. Uehara, N. Mizuno, Inorg.
Chem. 49 (2010) 2471.
3
tions undertaken in the air or under N
in conversion and product selectivity.
2
do not make a difference
To test the leaching of tungsten, the reaction mixture is filtered
after the reaction is over and the filtrate was subjected to atomic
absorption spectroscopic analysis. The analyses show the presence
of very little amount of tungsten (<0.5%). Besides, the filtrate
mixture did not show any catalytic activity towards epoxidation
[
[
[
19] G.B. Payne, P.H. Williams, J. Org. Chem. 24 (1959) 54.
20] C. Venturello, R. D’ Aloisio, J.C. Bart, M. Ricci, J. Mol. Catal. 32 (1985) 107.
21] K. Sato, M. Aoki, M. Ogawa, T. Hashimoto, D. Panyella, R. Noyori, Bull. Chem.
Soc. Jpn. 70 (1997) 905.

2
38
R. Bera, S. Koner / Inorganica Chimica Acta 384 (2012) 233–238
[
[
22] H. Mimoun, I.S. de Roch, L. Sajus, Tetrahedron 26 (1970) 37.
23] K. Kamata, K. Yonehara, Y. Sumida, K. Yamaguchi, S. Hikichi, N. Mizuno,
Science 300 (2003) 964.
24] S.K. Maiti, S. Dinda, N. Gharah, R. Bhattacharyya, New J. Chem. 30 (2006) 479.
25] P.U. Maheswari, P. de Hoog, R. Hage, P. Gamez, J. Reedijk, Adv. Synth. Catal. 347
[33] D. Prasetyoko, H. Fansuri, Z. Ramli, S. Endud, H. Nur, Catal. Lett. 128 (2009)
177.
[34] R. Gao, X. Yang, W. Dai, Y. Le, H. Li, K. Fan, J. Catal. 256 (2008) 259.
[35] A.T. Bolsoni, J.S. dos Santos, M.D. Assis, H.P. Oliveira, J. Non-Cryst. Solids 357
(2011) 3301.
[
[
(
2005) 1759.
26] K. Kamata, M. Kotani, K. Yamaguchi, S. Hikichi, N. Mizuno, Chem. Eur. J. 13
2007) 639.
27] D. Hoegaerts, B.F. Sels, D.E. de Vos, F. Verpoort, P.A. Jacobs, Catal. Today 60
2000) 209.
[36] S. Jana, B. Dutta, R. Bera, S. Koner, Langmuir 23 (2007) 2492.
[37] S. Jana, B. Dutta, R. Bera, S. Koner, Inorg. Chem. 47 (2008) 5512.
[38] S. Jana, S. Haldar, S. Koner, Tetrahedron Lett. 50 (2009) 4820.
[39] S. Bhunia, S. Koner, J. Porous Mater. 18 (2011) 399.
[40] L. Hu, S. Ji, Z. Jiang, H. Song, P. Wu, Q. Liu, J. Phys. Chem. C 111 (2007) 15173.
[41] K.S.W. Sing, D.H. Everett, R.A.W. Haul, L. Moscou, R.A. Pierotti, J. Rouquerol, T.
Siemieniewska, Pure Appl. Chem. 57 (1985) 603.
[
[
[
(
(
28] G. Gelbard, T. Gauducheau, E. Vidal, V.I. Parvulescu, A. Crosman, V.M. Pop, J.
Mol. Catal. A Chem. 182 (2002) 257.
[
[
29] A.L. Villa, B.F. Sels, D.E. de Vos, P.A. Jacobs, J. Org. Chem. 64 (1999) 7267.
30] J. Kasai, Y. Nakagawa, S. Uchida, K. Yamaguchi, N. Mizuno, Chem. Eur. J. 12
[42] M. Kruk, M. Jaroniec, Chem. Mater. 13 (2001) 3169.
[43] E. Briot, J.-Y. Piquemal, M. Vennat, J.-M. Brégeault, G. Chottard, J.-M. Manoli, J.
Mater. Chem. 10 (2000) 953.
(
2006) 4176.
[
[
31] D.E. de Vos, B.F. Sels, P.A. Jacobs, Adv. Synth. Catal. 345 (2003) 457.
32] D.H. Koo, M. Kim, S. Chang, Org. Lett. 7 (2005) 5015.
[44] T. Sakamoto, C. Pac, Tetrahedron Lett. 41 (2000) 10009.