Sonocatalytic epoxidation of alkenes by vanadium-containing polyphosphomolybdate immobilized on multi-wall carbon nanotubes

Article abstract of DOI:10.1016/j.ultsonch.2009.09.011

A Keggin type polyoxometalate (POM) has been immobilized in the unique network structure of multi-wall carbon nanotubes (CNTs). The vanadium-containing polyphosphomolybdate (PVMo) supported on CNTs, which was prepared by a one-step solid-state reaction, was characterized by FT-IR, XRD, SEM and elemental analyses. These uniform nanoparticles have an average size 20-30 nm. Furthermore, due to the chemical interaction between PVMo and carboxylic acid groups, PVMo nanoparticles were successfully immobilized on the CNTs. Moreover, the obtained composite was found as an efficient catalyst for oxidation of hydrocarbons under reflux and ultrasonic irradiation (US) conditions.

Full text of DOI:10.1016/j.ultsonch.2009.09.011

Ultrasonics Sonochemistry 17 (2010) 453–459
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Sonocatalytic epoxidation of alkenes by vanadium-containing
polyphosphomolybdate immobilized on multi-wall
carbon nanotubes
Hossein Salavati a, , Shahram Tangestaninejad , Majid Moghadam , Valiollah Mirkhani ,
b
b
b
*
b
Iraj Mohammadpoor-Baltork
a
Department of Chemistry, Payame Noor University (PNU), 81395-671 Isfahan, Iran
Department of Chemistry, Catalysis Division, University of Isfahan, 81746-73441 Isfahan, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 May 2009
Received in revised form 10 September
A Keggin type polyoxometalate (POM) has been immobilized in the unique network structure of multi-
wall carbon nanotubes (CNTs). The vanadium-containing polyphosphomolybdate (PVMo) supported on
CNTs, which was prepared by a one-step solid-state reaction, was characterized by FT-IR, XRD, SEM
and elemental analyses. These uniform nanoparticles have an average size 20–30 nm. Furthermore,
due to the chemical interaction between PVMo and carboxylic acid groups, PVMo nanoparticles were suc-
cessfully immobilized on the CNTs. Moreover, the obtained composite was found as an efficient catalyst
for oxidation of hydrocarbons under reflux and ultrasonic irradiation (US) conditions.
Ó 2009 Elsevier B.V. All rights reserved.
2
009
Accepted 25 September 2009
Available online 2 October 2009
Keywords:
Polyoxometalate
Alkene epoxidation
Multi-wall carbon nanotube
Ultrasonic irradiation
1
. Introduction
Nanosystems, with characteristic lengths (1–100 nm), have be-
the immobilization of POMs on carbon nanotube by direct syn-
thesis of these molecules in the CNTs [6].
In this work, the chemical modification of CNTs by PVMo nano-
particles is reported. Based on the novel properties of both PVMo
and CNTs, such structures may find a wide field of applications
[6]. Recently, various efficient catalytic systems have been reported
come one of the most attractive subjects in materials science,
chemistry, physics and biology. Therefore, the exploration of new
nanostructure materials for various applications is still the first
and one of the most significant challenges in nano science [2]. In
the last decade, carbon nanotubes (CNTs) have attracted wide
interest because of their unique physical properties and many po-
tential applications such as one dimension quantum wires, optical
switches, nano-transistors and other essential electronic compo-
nents [1].
2 2
for epoxidation of alkenes with H O using homogeneous or heter-
ogeneous polyoxometalates as catalyst [7–12]. However, an impor-
tant disadvantage associated with heterogeneous catalytic systems
is their lower catalytic activity in comparison with homogeneous
counterparts. In most cases the use of ultrasonic (US) wave (sonoc-
atalysis) is recommended for solving this problem.
Polyoxometalates (POM) can also be practically used as solid
catalysts if they could be physically immobilized on solid sup-
ports. Recently, Müller et al. have reported the synthesis of many
POMs with nanometer size, including novel kinks, of large rings
and wheel-shaped systems with 176 or even more Mo atoms
In general US has chemical and mechanical effects. The chemi-
cal effects of ultrasound do not derive from a direct coupling of the
acoustic field with chemical species on a molecular level. Instead,
sonochemistry and sonoluminescence derive principally from
acoustic cavitation: the formation, growth and implosive collapse
of bubbles in liquids irradiated with high-intensity ultrasound.
Bubble collapse during cavitation serves as an effective means of
concentrating the diffuse energy of sound: compression of a gas
generates heat. When the compression of bubbles occurs during
cavitation, heating is more rapid than thermal transport, creating
a short lived localized hot spot. There is a nearly universal consen-
sus that this hot spot is the source of homogeneous sonochemistry
[13,14].
[
4 3 40
3]. In another work, the growing process of [(NH ) PW12O ]
nanoparticles has been reported [4]. Due to the unique properties
of POMs, the preparation of POMs nanocrystals and nano/micro-
systems is of great interest [5]. Kang and co-workers reported
*
Corresponding author. Tel.: +98 311 7380003; fax: +98 311 7381002.
E-mail address: hosseinsalavati@pnu.ac.ir (H. Salavati).
1
350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.09.011

4
54
H. Salavati et al. / Ultrasonics Sonochemistry 17 (2010) 453–459
The most successful applications of ultrasound have been found
obtained as potassium bromide pellets in the range 400–
4000 cm with Nicolet-Impact 400D instrument. Scanning elec-
tron micrographs of the catalyst and support were taken on SEM
Philips XL 30. Powder X-ray diffraction data were obtained on a
8
D Advanced Bruker using Cu Ka radiation (2h = 5–70°). Gas chro-
À1
in the field of heterogeneous chemistry involving solids and met-
als. This is due to the mechanical impact of ultrasound on solid sur-
faces. In conventional chemistry there are several problems
associated with reactions involving solids or metals: small surface
area of the solid/metal may limit reactivity, penetration of reac-
tants into deeper areas is not possible, oxide layers or impurities
can cover the surface, reactants/products have to diffuse onto
and from the surface and reaction products can act as deposit on
the surface and prevent further reactions.
The mechanical effects of ultrasound offer an opportunity to
overcome the following types of problem associated with conven-
tional solid/metal reactions: break up of the surface structure al-
lows penetration of reactants and/or release of materials from
surface, degradation of large solid particles due to shear forces in-
duced by shock waves and microstreaming leads to reduction of
particle size and increase of surface area and accelerated motion
of suspended particles leads to better mass transfer [15].
matography experiments (GC) were performed on a Shimadzu GC-
16A instrument using a 2 m column packed with silicon DC-200 or
1
Carbowax 20 m. H NMR spectra were recorded on a Bruker-Ara-
nce AQS 300 MHz. Conversions and yields were obtained by GC
experiments and the products were identified after isolation and
purification.
The Na
the literature [16].
5
[PV
2
Mo10
O
2
40]Á14H O salt was prepared as described in
2.1. Preparation and characterization of PVMo–CNTs composite
The unmodified carbon nanotubes (multi-wall carbon nano-
tubes with diameters between 20 and 30 nm) were purchased
from Shenzen NTP Factory and modified. Multi-wall carbon nano-
tubes containing carboxylic acid groups were the predominant
groups expected to be acquired [17]. Subsequently, the CNTs were
dispersed in N,N-dimethylformamine (DMF), yielding a black–
brown suspension.
Recently, we reported the sonocatalytic oxidation of organic
compounds catalyzed by vanadium-containing polyphosphomo-
lybdate supported on MCM-41 and TiO
paper, we wish to report the sonocatalytic oxidation of alkenes
with H catalyzed by Na PV 40 (PVMo) supported on mul-
2
nanoparticles [7,8]. In this
2
O
2
5
2
Mo10O
ti-wall carbon nanotubes (CNTs). The effect of US irradiation on the
catalytic activity of this catalyst was also investigated (Scheme 1).
The typical preparation of PVMo/CNTs nanoparticles is as fol-
lows: PVMo (0.1 g) and CNTs (0.4 g) were put into an agate mortar
and the surfactant Triton-X-100 (0.5 ml) was added drop-wise to
the mixture. The mixture was thoroughly ground for 20 min,
washed in a supersonic washing machine using absolute alcohol
as dispersant, and centrifuged. The washing and centrifugalizing
processes were repeated five times. The wet nanoparticles of
PVMo–CNTs obtained and were dried in vacuum drying oven for
5 h (60–80 °C).
2
. Experimental
All chemicals were of analytical grade and were used without
further purification. Elemental analysis was performed on a Per-
kin–Elmer 2400 instrument. Atomic absorption analysis was car-
ried out on
reflectance spectra were recorded on a Shimadzu UV-265 instru-
ment using optical grade BaSO as reference. FT-IR spectra were
a
Shimadzu 120 spectrophotometer. Diffuse
2.2. General procedure for oxidation reactions with H
conditions
2 2
O under reflux
4
Reactions were carried out in a 50 ml thermostated glass reac-
tor equipped with a magnetic stirrer. In a typical experiment, the
reaction vessel was loaded with the supported catalysts (30 mg,
O
PVMo-CNTs
CH CN/ H O
2
3
2
containing 2.86
acetonitrile (5 ml). H
was refluxed. The progress of the reaction was monitored by GC.
At the end of the reaction, the mixture was diluted with Et
l
mol of PVMo), alkene or alkane (0.8 mmol) in
Reflux or.) )
2 2
O
(1 ml, 30%) was added and the mixture
)
)
Scheme 1.
2
O
Fig. 1. XRD patterns of (A) CNTs and (B) PVMo–CNTs composite.

H. Salavati et al. / Ultrasonics Sonochemistry 17 (2010) 453–459
455
Fig. 2. FT-IR spectrum of PVMo–CNTs composite.
Fig. 3. SEM images of (A) CNTs and (B) PVMo–CNTs composite.

4
56
H. Salavati et al. / Ultrasonics Sonochemistry 17 (2010) 453–459
(
20 ml) and filtered. The catalyst was thoroughly washed with Et
2
O
PVMo–CNTs. However, PVMo–CNTs pattern indicated that PVMo
was introduced in the substitutional position of CNTs.
and combined washings and filtrates were purified on a silica gel
plate or a silica gel column. IR and HNMR spectral data confirmed
the identities of the products.
1
The FT-IR spectrum of the prepared catalyst in the range 700–
À1
À1
1100 cm
7
showed absorption bands at 1045, 943, 858 and
83 cm , corresponding to the four typical skeletal vibrations of
the Keggin polyoxoanions, which indicated that PVMo has been
supported on CNTs (Fig. 2). These peaks could be attributed to
2
.3. General procedure for oxidation reactions with H
2 2
O under US
irradiation
m(P@O
a
),
m
(Mo@O
t
),
m
b c
(Mo–O –Mo) and m(Mo–O –Mo), respectively
(
O
t
= terminal oxygen, O
b
= bridged oxygen of two octahedral shar-
A UP 400S ultrasonic processor equipped with a 3 mm wide and
40 mm long probe, which was immersed directly into the reac-
tion mixture, was used for sonication. The operating frequency
was 24 kHz and the output power was 0–400 W through manual
adjustment. The final volume of solution was 6 ml. The tempera-
ture of the solution reached to 60 °C during sonication.
ing a corner and O
c
= bridged oxygen sharing an edge) [18]. IR
1
À1
spectra show a peak at about 1578 cm , corresponding to the IR
active phonon mode of CNTs [19]. The IR spectra indicated that
the structure of the polyoxometalate retain upon impregnation.
It is reported that supporting of PVMo nanoparticles on CNTs is
due to the chemical adsorption between carboxylic acid groups
on CNTs and PVMo nanoparticles, in which PVMo nanoparticles
tend to be preferably attached to the ends, the curves, and the con-
nection points of CNTs [6].
Fig. 3 shows SEM images of nanoparticles. The morphologies
and microstructure of the nanoparticles are approximately spheri-
cal. Some nanoparticles are importantly aggregated. Assuming that
a nanoparticle is spherical, the average diameter of nanoparticles is
estimated to be about 20–30 nm by averaging its diameters mea-
sured in several directions in the SEM images. A clear change in
the morphology of catalysts indicated that the PVMo has been sup-
ported on the CNTs.
To a mixture of alkene or alkane (0.8 mmol) and the supported
catalysts (30 mg, containing 2.86
lmol of PVMo) in acetonitrile
(
5 ml) was added hydrogen peroxide (1 ml, 30%) and the mixture
was exposed to US irradiation. The reaction was monitored by
GC. After the reaction was completed, the reaction mixture was di-
luted with Et
washed with Et
2
O (20 ml) and filtered. The catalyst was thoroughly
O and combined washings and filtrates were puri-
2
1
fied on a silica gel plates or a silica gel column. IR and HNMR spec-
tral data confirmed the identities of the products.
3
. Results and discussion
3.1. Preparation and characterization of PVMo–CNTs composite
3.2. Catalytic activity
Since heteropolyanions of the Keggin structure have molecular
diameters of ꢀ12 Å, it is feasible to support polyoxometalates such
Since heterogeneous catalysts are recoverable, hence, heteroge-
nization of homogenous catalysts is of great interest. Therefore, we
as PVMo on CNTs. Fig. 1 shows the XRD patterns of CNTs and
Table 1
Epoxidation olefins with H
catalyzed by PVMo–CNTs under reflux conditions.a
Products
2
O
2
Entry
1
Substrate
Time (h)
10
Conversion (%)b,c
80
Epoxide selectivity (%)
100
TOF (h
22.4
À1
)
O
2
3
10
10
72
47
96
20.2
13.2
O
58d
O
O
H
4
5
O
10
10
57
70
70e
62f
15.9
19.6
O
CH3
O
O
OH
6
7
1-Dodecene
1-Octene
O
10
10
31
44
73g
67h
8.7
OH
O
12.3
OH
a
b
c
Reaction conditions: olefin (0.8 mmol), catalyst (2.86
Based on the starting olefin.
GC yield.
lmol), H
2
O
2
3
(1 ml), CH CN (5 ml).
d
e
f
2
1
1
8
1
0% benzaldehyde was produced.
7% acetophenone was detected as by product.
7% verbenone and 10% verbenol were produced.
% alcohol was produced.
g
h
4.5% alcohol was detected.

H. Salavati et al. / Ultrasonics Sonochemistry 17 (2010) 453–459
457
decided to immobilize PVMo on CNTs nanoparticles, and investi-
gate its catalytic activity in the epoxidation of alkenes with H
under agitation with magnetic stirring and under US irradiation.
120
Epoxide Selectivity (%)
Conversion (%)
2 2
O
1
00
3
.2.1. Alkene epoxidation with H
reflux conditions
First, the ability of the prepared catalyst, PVMo–CNTs, was
investigated in the epoxidation of cyclooctene with H in aceto-
2 2
O catalyzed by PVMo–CNTs under
8
0
2
O
2
60
nitrile. The reactions were continued until no further progress was
observed. The results (Table 1) showed that the conversion was
4
0
8
0% with 100% epoxide selectivity. Epoxidation of cyclohexene
with 72% conversion and 96% epoxide selectivity, and only small
amounts of allylic oxidation products (cyclohexene-1-one and
cyclohexene-1-ol) were detected in the reaction mixture. In the
20
0
case of styrene and
were obtained in 47% and 57% epoxide selectivity. In the oxidation
of -pinene, the major product was -pineneoxide, while verbe-
a-methyl styrene, the corresponding epoxides
20
40
60
80
100
a
a
Ultrasound intensity
none and verbenol were produced as minor products. Oxidation
of linear alkenes such as 1-octene and 1-dodecene was accompa-
nied by allylic oxidation. A blank experiment in the absence of
the catalyst showed only small amounts of products in the oxida-
Fig. 4. The effect of ultrasonic irradiation intensity on the oxidation of cyclooctene
with H catalyzed by PVMo–CNTs.
2 2
O
2 2
tion of cyclooctene with H O .
As shown in Table 2, application of US waves in this catalytic
system has reduced the reaction times and improved the yields
and product selectivities. The system under US irradiation showed
a good catalytic activity in the oxidation of linear alkenes such as
1-octene and 1-dodecene.
The US processor used in this study works at low frequency and
it is well known that low frequency does not produce important
radicals. Radicals can come from the reactions at the surface of
the catalyst. In this case, it seems that this is the ‘‘ultrasonic
3.2.2. Alkene epoxidation with H
2 2
O catalyzed by PVMo–CNTs under
US irradiation
As mentioned in the previous works, US irradiation can be used
as an efficient tool to influence the product yield and selectivity
[
7,8]. Therefore, we decided to investigate the effect of US waves
on the epoxidation of different alkenes with H
PVMo–CNTs.
2 2
O catalyzed by
Table 2
Epoxidation of olefins with H
2
O
2
catalyzed by PVMo–CNTs under ultrasonic irradiation.a
Products
Entry
1
Substrate
Time (min)
40
Conversion (%)b,c
95
Epoxide selectivity (%)
100
TOF (h
402.6
À1
)
O
2
3
40
40
88
71
95
373.0
301.0
O
60d
O
O
H
4
5
O
40
40
78
82
82e
62f
330.6
347.5
O
CH3
O
O
OH
6
7
1-Dodecene
1-Octene
O
40
40
48
64
82g
62h
203.4
271.2
OH
O
OH
a
b
c
Reaction conditions: olefin (0.8 mmol), catalyst (2.86
Based on the starting olefin.
GC yield.
lmol), H
2
O
2
(1 ml), CH
3
CN (5 ml).
d
e
f
2
1
2
9
2
8% benzaldehyde was produced.
4% acetophenone was detected as by product.
0% verbenone and 11% verbenol were produced.
% alcohol was produced.
g
h
4% alcohol was detected.

4
58
H. Salavati et al. / Ultrasonics Sonochemistry 17 (2010) 453–459
mechanical effect” which is involved. Shock waves induce by the
collapsing bubble conduct to strong movement in the liquid and
to particles collision. This will reduce particles size; it also in-
creases the mass transfer and reduces the diffusion layer at the
surface of the particles [13–15]. On the other hand, collapse of
the produced bubbles results in generation of high temperatures.
As the reaction under mechanical stirring requires a temperature
of about 80 °C, therefore, the reaction can be also accelerated under
US irradiation. To confirm the influence of the mechanical effects in
breaking up the agglomerates and reducing the particles size dur-
ing the oxidation reactions, a sample of catalyst was exposed to US
waves and then used for oxidation of cyclooctene under reflux con-
ditions. The results showed that the reaction time reduced from 10
to 7 h. These observations showed that both chemical and mechan-
ical effects of US are effective in the acceleration the reaction.
The power of ultrasound is a very important parameter and also
has a great influence on the phenomena of acoustic cavitation and
efficiency of ultrasound treatment. Fig. 4 shows the effect of irradi-
ation power on the epoxidation of cyclooctene, which indicates
that increasing of ultrasound power will improve the extent of oxi-
dation and the highest conversion was observed at a power of
400 W.
Fig. 5 comprises systems under US irradiation and under agita-
tion with magnetic stirring, which indicating that the catalytic
activity of PVMo–CNTs catalyst has been enhanced by US
irradiation.
The blank experiments in the absence of catalyst showed that
US irradiation has poor ability to epoxidize the alkenes with hydro-
gen peroxide.
In order to show the effect of supporting on the catalytic activ-
ity, all reactions were repeated in the presence of homogeneous
PVMo catalyst and under the same reaction conditions. It is clear
from Tables 1 and 3 that the catalytic activity of PVMo–CNTs
was much higher than that of unsupported heteropolyanion. The
conversions, selectivities and TOFs are higher for heterogeneous
PVMo–CNTs in comparison with the homogeneous one. Therefore,
the catalytic activity increases by dispersing of the catalyst on the
nanotubes. On the other hand, the ability of CNTs, as catalyst, was
1
00
US
MS
8
6
4
2
0
0
0
0
0
checked in the oxidation of cyclooctene with H
2 2
O . The obtained
results showed that CNTs has poor ability to catalyze the epoxida-
tion of cyclooctene and the amount of epoxide was less than 3%.
3.2.3. Catalyst reuse and stability
0
10
20
30
40
200
400
600
The stability of the supported catalyst was monitored using
Time (min)
multiple sequential oxidation of cyclooctene with hydrogen perox-
ide under reflux or US irradiation. For each of the repeated reac-
tions, the catalyst was recovered, washed thoroughly with
Fig. 5. Comparison of ultrasonic irradiation and magnetic agitation in the oxidation
of cyclooctene with H O catalyzed by PVMo–CNTs.
2 2
Table 3
Epoxidation of olefins with H
2
O
2
(30%) catalyzed by homogeneous PVMo.a
Products
Entry
1
Substrate
Time (h)
20
Conversion (%)b,c
78
Epoxide selectivity (%)
96
TOF (h
10.9
À1
)
O
2
3
20
20
70
43
85
49
9.8
6.0
O
O
O
H
4
5
O
20
20
27
20
29
28
3.8
2.8
O
CH3
O
O
OH
6
7
O
20
20
26
38
59
31
3.6
5.3
OH
O
OH
a
b
c
Reaction conditions: olefin (0.8 mmol), catalyst (2.86
Based on the starting olefin.
GC yield.
2 2 3
lmol), H O (1 ml), CH CN (5 ml).

H. Salavati et al. / Ultrasonics Sonochemistry 17 (2010) 453–459
459
Table 4
The results obtained from catalyst reuse and stability in the oxidation of cyclooctene with H
2 2
O by PVMo–CNTs under agitation with magnetic stirring and under ultrasonic
irradiation.a
Run
Time
Conversion (%)b,c
MS
Epoxide selectivity (%)
MS
V leaching (%)d
MS (h)
US (min)
US
US
MS
US
1
2
3
4
10
10
10
10
40
40
40
40
80
79
78
78
95
94
93
92
100
100
100
100
100
100
100
100
1.0
0.8
0.4
0.3
1.0
0.7
0.5
0.4
a
b
c
Reaction conditions: olefin (1 mmol), catalyst (2.86
Based on the starting olefin.
GC yield.
2 2 3
lmol), H O (1 ml), CH CN (10 ml).
d
Determined by ICP.
acetonitrile and 1,2-dichloroethane, successively, and dried before
being used with fresh cyclooctene and hydrogen peroxide. In both
cases, the catalysts were consecutively reused four times. Since the
vanadium-containing catalysts usually show the leaching phenom-
ena, the amounts of catalyst leaching after each run, was deter-
mined by ICP. In this manner the filtrates were collected after
each run and used for determining of the amounts of V leached (Ta-
ble 4). Addition of fresh alkene and oxidant to the filtrates showed
that the amount of epoxide is comparable to the blank experi-
ments. These results are in accordance with the leaching data.
The nature of the recovered catalyst was followed by IR. After reus-
ing the catalyst for several times, no change in the IR spectra was
observed.
[4] T. Ito, K. Inumaru, M. Misono, Epitaxially self-assembled aggregates of
polyoxotungstate nanocrystallites, (NH PW12 synthesis by
homogeneous precipitation using decomposition of urea, Chem. Mater. 13
2001) 824.
[5] Z.H. Kang, E.B. Wang, M. Jiang, S.Y. Lian, Y.G. Li, C.W. Hu, Convenient
controllable synthesis of inorganic 1D nanocrystals and 3D high-ordered
microtubes, Eur. J. Inorg. Chem. 2 (2003) 370.
)
4 3
40
O :
(
[
6] Z.H. Kang, Y. Wang, E. Wang, S. Lian, L. Gao, W. You, C. Hu, L. Xu,
Polyoxometalates nanoparticles: synthesis, characterization and carbon
nanotube modification, Solid State Commun. 129 (2004) 559.
[
7] S. Tangestaninejad, V. Mirkhani, M. Moghadam, I. Mohammadpoor-Baltork, E.
Shams, H. Salavati, Hydrocarbon oxidation catalyzed by vanadium
polyoxometalate supported on mesoporous MCM-41 under ultrasonic
irradiation, Ultrason. Sonochem. 15 (2008) 438.
[
[
8] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork, E.
Shams, H. Salavati, Olefin epoxidation with H O catalyzed by vanadium-
2 2
containing polyphosphomolybdates immobilized on TiO2 nanoparticles under
different conditions, Catal. Commun. 9 (2008) 1001.
9] N. Mizuno, K. Yamaguchi, K. Kamata, Epoxidation of olefins with hydrogen
peroxide catalyzed by polyoxometalates, Coord. Chem. Rev. 249 (2005)
4
. Conclusion
1944.
[
10] G. Suss-Fink, L. Gonzalez, G.B. Shalpin, Alkane oxidation with hydrogen peroxide
catalyzed homogeneously by vanadium-containing polyphosphomolybdates,
Appl. Catal. A: Gen. 217 (2001) 111.
Supporting of polyoxometalates on nanoparticle materials such
as CNTs gave a catalyst, which was recoverable and reusable in the
oxidation of alkenes with hydrogen peroxide. The use of US irradi-
ation increased the conversions and reduced the reaction times.
The results showed that good catalytic activity of the vanadium
polyoxometalate, especially under US irradiation; make them as
useful catalysts for further applications in the area of catalysis.
[11] M.M.Q. Simões, I.C.M.S. Santos, M.S.S. Balula, J.A.F. Gamelas, A.M.V. Cavaleiro,
M.G.P.M.S. Neves, J.A.S. Cavaleiro, Oxidation of cycloalkanes with hydrogen
peroxide in the presence of Keggin-type polyoxotungstates, Catal. Today 91–
92 (2004) 211.
[12] Y. Nakagawa, K. Kamata, M. Kotani, K. Yamaguchi, N. Mizuno,
Polyoxovanadometalate-catalyzed selective epoxidation of alkenes with
hydrogen peroxide, Angew. Chem. Int. Ed. 44 (2005) 5136.
[
13] L.A. Crum, Comments on the evolving field of sonochemistry by a cavitation
physicist, Ultrason. Sonochem. 2 (1995) S147.
14] K.S. Suslick, Y. Didenko, M.M. Fang, T. Hyeon, K.J. Kolbeck, W.B. Mc Namara III,
M.M. Mdleleni, M. Wong, Acoustic cavitation and its chemical consequences,
Philos. Trans. Roy. Soc. A 357 (1999) 335.
15] T. Mason, D. Peters, Practical Sonochemistry, second ed., Horwood Publishing,
Chichester, 2002, p. 17.
16] K. Nomiya, S. Matsuoka, T. Hasegawa, Y. Nemoto, Benzene hydroxylation with
hydrogen peroxide catalyzed by vanadium(V)-substituted polyoxomolybdates,
J. Mol. Catal. A: Chem. 156 (2000) 143.
Acknowledgement
[
The support of this work by, Catalysis Division of University of
Esfahan (CDUE) and Payame Noor University (PNU) are
acknowledged.
[
[
References
[
17] T. Osakai, S. Himeno, A. Saito, Voltammetric study of the transfer of Dawson-
type heteropolyanions across the nitrobenzene–water interface, J. Electroanal.
Chem. 332 (1992) 169.
[
[
[
1] G. Lu, B. Chang, H. Shen, Y. Chen, T. Wang, Z. Chen, H. Lu, K. Jin, Y. Zhou, G. Yang,
Large optical third-order nonlinearity of composite thin film of carbon
nanotubes and BaTiO
3
, Chem. Phys. Lett. 407 (2005) 397.
[18] Th. Ilkenhans, B. Herzag, Th. Braun, R. Schlogl, The nature of the active phase in
the heteropolyacid catalyst
PVMo11 used for the selective
40Á32H
oxidation of isobutyric acid, J. Catal. 153 (1995) 275.
[19] M.A. Hamon, H. Hu, P. Bhowmik, S. Niyogi, B. Zhao, M.E. Itkis, R.C. Haddon,
End-group and defect analysis of soluble single-walled carbon nanotubes,
Chem. Phys. Lett. 347 (2001) 8.
2] R.Y. Wang, J. Yang, Z.P. Zheng, M.D. Carducci, J. Jiao, S. Seraphin, Dendron-
controlled nucleation and growth of gold nanoparticles, Angew. Chem. Int. Ed.
H
4
O
2
O
4
0 (2001) 549.
3] A. Müller, S.Q.N. Shah, H. Bogge, M. Schmidtmann, Molecular growth from a
Mo176 to a Mo248 cluster, Nature 397 (1999) 48.