A novel heteropolyanion-based amino-containing cross-linked ionic copolymer catalyst for epoxidation of alkenes with H2O2

Article abstract of DOI:10.1016/j.apcata.2012.08.040

A heteropolyanion-based cross-linked ionic copolymer was prepared by the anion-exchange of a newly task-specific designed amino-containing ionic copolymer with a Keggin heteropolyacid, and characterized by FT-IR, SEM, TG, XRD, UV-vis, ESR, ¹H NMR, and elemental analysis. Its catalytic activity was evaluated in the epoxidation of alkenes with aqueous H ₂O₂. The resultant heteropolyanion-based ionic copolymer is revealed to be a highly efficient heterogeneous catalyst for epoxidation of alkenes with H₂O₂, adding the advantages of convenient recovery and steady reuse.

Full text of DOI:10.1016/j.apcata.2012.08.040

Applied Catalysis A: General 445–446 (2012) 306–311
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
A novel heteropolyanion-based amino-containing cross-linked ionic copolymer
catalyst for epoxidation of alkenes with H2O2
Yan Lenga,∗, Weijie Zhanga, Jun Wangb, Pingping Jianga
a The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China
b State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2012
Received in revised form 26 August 2012
Accepted 27 August 2012
Available online 11 September 2012
A heteropolyanion-based cross-linked ionic copolymer was prepared by the anion-exchange of a newly
task-specific designed amino-containing ionic copolymer with a Keggin heteropolyacid, and character-
ized by FT-IR, SEM, TG, XRD, UV–vis, ESR, 1H NMR, and elemental analysis. Its catalytic activity was
evaluated in the epoxidation of alkenes with aqueous H2O2. The resultant heteropolyanion-based ionic
copolymer is revealed to be a highly efficient heterogeneous catalyst for epoxidation of alkenes with
H2O2, adding the advantages of convenient recovery and steady reuse.
Keywords:
Heteropolyacid
© 2012 Elsevier B.V. All rights reserved.
Cross-linked copolymer
Ionic liquid
Epoxidation of alkenes
Heterogeneous catalysis
1. Introduction
application of HPA-based ionic liquid (IL) hybrids as the catalysts for
organic syntheses [14], and some thermal/solvent-responsive HPA-
Epoxidation of alkenes with H2O2 has been extensively inves-
tigated over the catalysts of heteroatomic molecular sieves [1],
transition metal compounds [2], organometallic complexes [3],
and polyoxometalates (POMs) [4,5]. Heterpolyacids (HPAs) are
based IL hybrids have been reported [15,16]. We recently prepared
a series of HPA-based ionic hybrids by combining organic IL cations
with Keggin heteropolyanions, and the resulting ionic solids turned
out to be effective and recyclable catalysts for acid-catalyzed or
oxidative organic transformations [17,18].
a family of POMs, and the tungsten-containing HPAs, typically
3−
the Venturello-Ishii {PO4[WO(O2)2]4}
species, have attracted
More recent studies have shown that ionic copolymers contain-
ing IL units are capable of acting the bifunctions of both ILs and
polymers [19–21]. Moreover, owing to the features of high ther-
mal stability, easily shaping, corrosion resistance, and the variety
of structures available, polymer matrices are excellent supports to
entrap POMs for applications in heterogeneous catalysis [22]. For
example, poly(nisopropylacrylamide) polymer with a quaternary
ammonium and phosphotungstate anion (PW12O403−) can be used
as a temperature-responsive catalyst for the oxidation of alcohols,
causing thermoregulated formation of stable emulsion species at
90 ◦C in water [23]. Water-soluble HPA-conjugated chitosan matrix
was revealed to be an effective catalyst for the triphase epoxidation
of allylic alcohols [24]. Also noticeably, the amino groups tethered
to IL cations have been demonstrated to be the catalytic promoters
for HPA active sites in epoxidations due to the electron transfer
from aminos to HPA frameworks [18]. Accordingly, it is rational to
design and prepare a HPA-based amino-containing ionic copoly-
mer catalyst for epoxidation of alkenes with hydrogen peroxide by
combining amino-functionalized IL copolymers with HPAs with a
more structural stability, because of the involvement of a polymeric
framework in the catalyst.
much attention for a long time as the effective catalysts for the
H2O2-based epoxidation of alkenes [6]. However, HPAs always
cause homogeneous reactions because of their good solubility in
polar/oxidative media, resulting in the difficulty of catalyst isola-
tion. Thus, heterogeneous HPA catalysts are a promising option,
and various strategies, including attaching HPAs to porous supports
[7–9], biphasic technology and phase-transfer catalysis [10,11],
have been developed. Though good activity was achieved in those
cases, most of them still bear some drawbacks like the slow reac-
tion speed, leaching of active species, low catalyst recovery rate, or
high cost. A new strategy for catalyst preparation to overcome the
above problems is therefore highly desirable.
The organic–HPA hybrids, obtained by the modification of HPAs
with organic blocks, have attracted great research interest due to
their diverse chemical structures and improved catalytic behaviors
[12,13]. A topic of recent interest in this context is the design and
∗
Corresponding author. Tel.: +86 510 85917090; fax: +86 510 85917763.
E-mail address: lengyan1114@126.com (Y. Leng).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.08.040

Y. Leng et al. / Applied Catalysis A: General 445–446 (2012) 306–311
307
Scheme 1. Synthesis of the ionic hybrid AM–BM–PW.
In this study, we synthesize a task-specific cross-linked ionic
copolymer via the radical copolymerization of a dicationic IL
with an amine-functionalized IL. Then the ionic copolymer is
anion-exchanged with phosphotungstic acid H3PW12O40 (PW) to
provide the new HPA-based amino-containing ionic copolymer cat-
alyst that is designated as AM–BM–PW (Scheme 1). The obtained
hybrid catalyst leads to a liquid–solid heterogeneous epoxidation
of alkenes with aqueous H2O2, showing high conversion and selec-
tivity, easy recovery, and very steady reuse.
[1,1ꢀ-(Butane-1,4-diyl)-bis(3-vinylimidazolium)]Br2
([BVIM]Br2): [BVIM]Br2 was prepared according to the previ-
ous report [26]. N-vinylimidazole (18.84 g, 0.20 mol) and 1,4
dibromobutane (0.10 mol) were dissolved in isopropanol (50 mL)
at 80 ◦C for 24 h under nitrogen atmosphere. On completion, the
white solid of [BVIM]Br2 was obtained after the removing of
solvent and washing with THF (yield: 90%). 1H NMR (300 MHz,
D2O, TMS) ı (ppm) = 2.00 (s, 2H, CH2), 4.34 (s, 2H, CH2), 5.44 (d,
1H, CH), 5.86 (d, 1H, CH), 7.18 (m, 1H, CH), 7.63 (s, 1H, CH),
7.81 (s, 1H, CH), 9.11 (s, 1H, CH).
2. Experimental
2.2.2. Preparation of ionic liquid copolymer AM–BM
The procedure for the synthesis of amino containing cross-
linked IL polymer (AM–BM) was similar to that for the
copolymerization of ILs and divinylbenzene (DVB) [27]. The
obtained IL [AVIM]Br·HBr (1.0 g), [BVIM]Br2 (1.0 g), and azo-
bisisobutyronitrile (AIBN) (0.03 g) were dissolved in methanol
(10 mL) under nitrogen. The mixture was refluxed at 60 ◦C with
stirring. After 24 h, the white solid formed was filtrated and was
washed with ethanol and water (1.65 g solid was obtained). AM–BM
was obtained by the addition of KOH (0.168 g, 3.0 mmol) into the
aqueous solution of the above solid for neutralization of HBr, fol-
lowed by filtration and dried in vacuum at 60 ◦C for 12 h. According
to the amount of KOH consumed in the neutralization of HBr, the
composition of the ionic copolymer AM–BM was calculated to be
AM1.6–BM. The cross-linked IL polymers (BM) of [BVIM]Br2 was
prepared accordingly, without using the amino-functionalized IL
[AVIM]Br·HBr. The 1H NMR data for the copolymer AM–BM is not
provided because it is insoluble in various solvents, such as H2O,
CHCl3, DMF, DMSO, and CH3OH.
2.1. Materials and methods
All chemicals were analytical grade and used as received. FT-
IR spectra were recorded on a Nicolet 360 FT-IR instrument (KBr
discs) in the 4000–400 cm−1 region. 1H NMR spectra were mea-
sured with a Bruker DPX 300 spectrometer at ambient temperature
in D2O using TMS as internal reference. Elemental analyses were
performed on a CHN elemental analyzer (FlashEA 1112). ESR spec-
tra were recorded on a Bruker EMX-10/12 spectrometer at X-band.
The measurements were done at 155 K in a frozen solution provided
by a liquid/gas nitrogen temperature regulation system controlled
by a thermocouple located at the bottom of the microwave cavity
within a Dewar insert. Solid UV–vis spectra were measured with a
PE Lambda 950 spectrometer, and BaSO4 was used as an internal
standard. XRD patterns were collected on the Bruker D8 Advance
powder diffractometer using Ni-filtered Cu K␣ radiation source at
40 kV and 20 mA, from 5 to 80◦ with a scan rate of 4◦/min. SEM
image was performed on a HITACHI S-4800 field-emission scanning
electron microscope. TG analysis was carried out with a STA409
instrument in dry air at a heating rate of 10 ◦C/min.
2.2.3. Preparation of the HPA-based polymeric hybrid
AM–BM–PW
AM–BM(0.3 g) was dissolvedin 30 mL deionizedwater with stir-
ring to form a transparent gel. The aqueous solution containing 2 g
of H3PW12O40 (PW) was added to the above solution of AM–BM,
and the resulting slurry was stirred at room temperature for 24 h.
The thus obtained solid catalyst (AM–BM–PW) was filtered and
washed with water for three times, followed by drying in a vac-
uum. Elemental analysis, found: C: 8.24%, N: 3.71% and H: 1.30%.
BM–PW was synthesized by reacting BM and H3PW12O40 with the
monomer molar ratio of 1.5:1.
2.2. Catalyst preparation
2.2.1. Preparation of [AVIM]Br·HBr and [BVIM]Br2
[3-Aminoethyl-1-vinylimidazolium]Br·HBr
([AVIM]Br·HBr):
The amino-containing ionic liquid (IL) monomer [AMIM]Br·HBr
was prepared according to the literature [25]. N-vinylimidazole
(9.42 g, 0.10 mol) and 2-bromoethylamine hydrobromide (20.49 g,
0.10 mol) were dissolved in acetonitrile (50 mL) at 80 ◦C for 12 h
under nitrogen atmosphere with stirring. On completion, the liquid
was poured out and the solid was washed with anhydrous ethanol
three times to remove the unreacted starting materials. After dry-
ing under vacuum, [3-aminoethyl-1-vinylimidazolium]Br·HBr was
obtained (yield: 85%). 1H NMR (300 MHz, D2O, TMS) ı (ppm) = 3.47
(m, 2H, CH2), 4.58 (m, 2H, CH2), 5.40 (dd, 1H, CH), 5.81 (dd,
1H, CH), 7.13 (m, 1H, CH), 7.66 (s, 1H, CH), 7.81 (s, 1H, CH),
9.18 (s, 1H, CH).
2.3. Catalytic test
Cyclooctene (10 mmol), CH3CN (10 mL), and AM–BM–PW (0.1 g)
were added to a 25 mL flask. The reaction started after the
addition of aqueous H2O2 (30 wt.%, 4 mmol) at 70 ◦C within
10 min under vigorous stirring. After reaction, the product

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Y. Leng et al. / Applied Catalysis A: General 445–446 (2012) 306–311
100
95
90
a
b
85
80
100 200 300 400 500 600 700 800
Temperature (OC)
10
20
30
40
50
60
70
80
2 Theta / degrees
Fig. 1. TG pattern of AM–BM–PW.
Fig. 2. XRD patterns of (a) H3PW12O40 and (b) AM–BM–PW.
mixture was analyzed by gas chromatography (GC). Conver-
sion = 100% × (mol epoxide product + mol byproducts)/mol initial
H2O2. Selectivity = 100% × mol epoxide product/(mol epoxide prod-
uct + mol byproducts). The concentration of H2O2 in the reacted
mixture was determined by the titration with sodium thiosulfate
(starch as the indicator) in the presence of potassium iodide, sul-
furic acid and ammonium molybdate. No remaining H2O2 was
detected due to the self-decomposition of H2O2 accompanying
with the oxidation of the alkene. In this case, the conversion of
the substrate based on H2O2 calculated by the formula above also
reflects the H2O2 utilization efficiency. Other alkene substrates
were tested accordingly. For a three-run operation of the epoxida-
tion of cyclooctene to test the catalytic stability of AM–BM–PW, the
catalyst was recovered by a filtration immediately after reaction,
followed with washing with ethanol and vacuum drying.
amino-containing cross-linked hybrid AM–BM–PW and various
control catalysts are listed in Table 1. AM–BM–PW caused a
liquid–solid heterogeneous epoxidation system, and exhibited a
98.5% conversion with 100% selectivity (entry 1). On the other
hand, the amino-free cross-linked counterpart BM–PW (entry 2),
another desirable heterogeneous catalyst, showed a low conver-
sion of 17.3%, implying that the amino groups in the IL copolymer
are indispensable for the high epoxidation activity of AM–BM–PW.
Also without amino groups, pure H3PW12O40 (entry 3), though as
a homogeneous catalyst, only gave a 12.9% conversion with 82.3%
selectivity. This implies that the featured cross-linked polymeric
framework of AM–BM–PW endows the catalyst with an insoluble
nature in the reaction media.
In order to investigate the scope of the AM–BM–PW cata-
lyst for epoxidation reactions, the substrates such as cyclohexene,
1-octene, and 1-hexene were also investigated on the catalysts
AM–BM–PW, BM–PW, and H3PW12O40, with the results shown in
entries 4–12 of Table 1. It can be seen that the present cross-linked
polymeric hybrid AM–BM–PW could be applied to the epoxidation
of various alkenes using H2O2, and good to excellent activities and
selectivity were obtained in all cases. However, amino-free hybrid
BM–PW and H3PW12O40 were inactive or exhibit very low catalytic
activities for all those substrates, which further confirms the pro-
motional role of amino groups for the high epoxidation activity of
AM–BM–PW.
3. Results and discussion
3.1. Characterization of AM–BM–PW
The TG profile in Fig. 1 shows that AM–BM–PW was quite stable
up to 280 ◦C. The weight loss of nearly 7% in the range 280–400 ◦C
was due to the elimination of the amino-functionalized ILs AM [27].
The further weight loss of 8% in 400–600 ◦C was attributed to the
decomposition of dicationic IL BM. Thus, estimatively, the molar
ratio of AM to BM was 1.6/1, which is consistent with that calcu-
lated from the amount of KOH consumed for the neutralization of
HBr in the synthesis of AM–BM. Moreover, the elemental analy-
sis for the catalyst AM–BM–PW showed 8.24 wt.% for the weight
percentage of C, 3.71 wt.% for N, and 1.30 wt.% for H, which is very
near to the theoretical values of C: 7.93%, N: 3.25%, and H: 1.01%,
demonstrating that AM–BM–PW has the structure illustrated in
Scheme 1.
3.3. Understanding of the catalytic behavior of AM–BM–PW
To investigate the promotional effects of the amino groups in the
polymeric AM–BM–PW catalyst on epoxidations, the UV–vis pro-
files of AM–BM–PW and amino-free hybrid BM–PW are compared
in Fig. 4. AM–BM–PW showed a absorption band in the range of
600–800 nm that is assignable to the intramolecular charge trans-
fer from the amino-tethered cations to PW anions [28], but the band
was undetectable for the amino-free counterpart BM–PW, suggest-
ing the reduction of W6+ in AM–BM–PW by amino groups. The ESR
signals at ca. 3500 G in Fig. 5 also confirms the existence of low
valent W5+ species for AM–BM–PW. Therefore, these observations
suggest that the redox property of W species might be significantly
tuned through the intramolecular charge transfer from the amino
groups to HPA frameworks.
The neat HPA and the polymeric hybrid AM–BM–PW were
characterized by the IR spectra in Fig. 6. The four characteristic
bands for the Keggin structure of neat H3PW12O40 appeared at
the wavenumbers of 1080 (P Oa), 982 (W Od), 889 (W Ob W),
and 804 cm−1 (W Oc W) (curve a). However, for the polymeric
hybrid AM–BM–PW (curve b), the P Oa band at 1080 cm−1 split-
ted into two bands at 1080 and 1049 cm−1, due to the formation of
The XRD pattern in Fig. 2 displayed the featured diffraction
peaks for the secondary crystal structure of the neat H3PW12O40
.
However, all these peaks disappeared in the case of AM–BM–PW,
indicating definitely a noncrystal structure of the hybrid. It is thus
suggested that the hybrid catalyst largely inherits the amorphous
structure of the ionic copolymer after the introduction of Keggin
anions into the copolymer matrix by the anion-exchange, rather
than retains the HPA crystal structure. The unsharp profiles for
the micrometer sized particles of the IL copolymer AM–BM and
the hybrid AM–BM–PW in the SEM image (Fig. 3) also confirms an
amorphous structure for them.
3.2. Epoxidation of alkenes with H2O2 over AM–BM–PW and
various control catalysts
With the epoxidation of cyclooctene by aqueous H2O2 as
a
model reaction, catalytic performances of the HPA-based

Y. Leng et al. / Applied Catalysis A: General 445–446 (2012) 306–311
309
Fig. 3. SEM images of (a) AM–BM and (b) AM–BM–PW.
Table 1
Catalytic performance of various catalysts for the epoxidation of alkenes with H2O2.a
Entry
Substrate
Catalyst
Solubility in reaction
Conb (%)
Selc (%)
1
2
3
AM–BM–PW
BM–PW
H3PW12O40
Insoluble
Insoluble
Soluble
98.5
17.3
12.9
100
100
82.3
4
5
6
AM–BM–PW
BM–PW
H3PW12O40
Insoluble
Insoluble
Soluble
94.7
40.5
28.7
92.5
67.4
32.4
7
8
9
AM–BM–PW
BM–PW
H3PW12O40
Insoluble
Insoluble
Soluble
89.0
7.6
1.7
100
89.6
48.6
10
11
12
AM–BM–PW
BM–PW
H3PW12O40
Insoluble
Insoluble
Soluble
78.1
3.3
0
100
100
–
a
b
c
Reaction conditions: catalyst (0.1 g), substrate (10 mmol), 30% H2O2 (4 mmol), acetonitrile (10 mL), 70 ◦C for 4 h, 6 h for cyclohexene, 8 h for 1-octene and 1-hexene.
Conversion of the substrate based on H2O2.
Selectivity for the epoxide product; byproducts for entry 3: 2-cycloocten-1-ol and 2-cycloocten-1-one; entries 4–6: 2-cyclohexen-1-ol and 2-cyclohexen-1-one; 8 and
9: 2-octanone and octylaldehyde.
hydrogen bondings between the terminal oxygens of PW and the
amino groups of copolymer [29,30]. Moreover, a new peak at
951 cm−1 branched from 982 cm−1 for WVI O is assignable to the
reduced W5+ species due to the intramolecular charge transfer from
aminos to terminal oxygens [31,32]. This result consolidates the
evidence for the effective modification of the oxidation property of
W species in the polymeric hybrid by the tethered amino groups
in the cross-linked copolymer matrix, which relates to the good
performances in the epoxidation of alkenes.
mimics the practical reaction but in the absence of any olefin
substrates (curve c, Fig. 6). The intensities of the bands at 1049
and 951 cm−1 decreased significantly, which might be indicative
of the fadeaway of the intramolecular electron delocalization and
the hydrogen bonding interaction. The more noteworthy point is
that a new distinct peak at 840 cm−1 for the peroxo–oxygen band
v(O O) in peroxo–W species occurred, which has been known
as the active species for {PO4[WO(O2)2]4}3−-based epoxidations
[6,8,33]. However, it seems that the HPA polymeric hybrid with
amino-functional groups was easier to generate the peroxo–W
species, because the band at 840 cm−1 could not be observed for
the H2O2-treated amino-free hybrid BM–PW. This result clearly
More insight into the HPA-based polymeric hybrid-catalyzed
epoxidation was gained by the IR measurement of the AM–BM–PW
after reacting with 30% H2O2 in CH3CN at 70 ◦C for 10 min, which
a
b
400
600
800
1000
1200
3000
3500
4000
Wavelength (nm)
Magnetic field (G)
Fig. 4. UV–vis spectra of (a) AM–BM–PW and (b) BM–PW.
Fig. 5. ESR spectrum of AM–BM–PW.

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Y. Leng et al. / Applied Catalysis A: General 445–446 (2012) 306–311
1049
a
b
951
1080
982
889
804
c
d
840
1800 1600 1400 1200 1000 800 600
Wavenumbers (cm-1)
Scheme 2. Proposed mechanism for the heterogeneous epoxidation of alkenes with
H2O2 over the HPA-based ionic copolymer catalyst AM–BM–PW.
Fig. 6. FT-IR spectra of (a) H3PW12O40, (b) fresh AM–BM–PW, (c) H2O2 treated
AM–BM–PW, and (d) recycled AM–BM–PW.
had leached out during the first run of the reaction, which is
much higher than that of the present cross-linked polymeric hybrid
AM–BM–PW. This allows to draw that the hybrid HPA catalyst with
cross-linked polymeric cations is more structural stable, with a
great improvement of the leaching-resistance property.
indicate that peroxo–W species improved by the amino groups
were the possible intermediate active species, which may directly
associate with the high activity and selectivity of AM–BM–PW for
the epoxidation of alkenes.
3.5. Catalysis mechanism
3.4. Catalyst reusability
The mechanism for the traditional H3PW12O40-catalyzed
epoxidations was demonstrated previously, involving derived
{PO4[WO(O2)2]4} from Keggin precursors in the presence H2O2,
As it is very convenient to recover the polymeric hybrid cata-
lyst by filtration or centrifugation after a reaction, the solid catalyst
could be readily reused for the next run. Table 2 displays the cat-
alytic recycling property for AM–BM–PW in the epoxidation of
cyclooctene with H2O2, the three-run test gave 100% selectivity
without significant loss of conversion, revealing a quite steady
reusability. ICP-AES elemental analysis for the reacted filtrates
indicates that less than 3 wt.% W of AM–BM–PW leached into the
reaction media during the first run, and in the followed runs, the
leaching is negligible. Furthermore, the IR spectrum for the recov-
ered AM–BM–PW in Fig. 6, curve (d) was well consistent with that
of the fresh one, which demonstrates a durable catalyst structure
and accounts for the steadily catalytic reuse.
In order to test the possible catalysis of the slightly leached
species in the reaction solution from the catalyst, an experiment
was carried out under the reaction conditions shown in Table 2.
The conversion 65.3% and selectivity 100% were obtained at the
reaction time 2 h. Then, the solid catalyst was hot-filtered and the
reaction proceeded for another 4 h with the homogeneous filtrate,
which resulted in almost unchanged conversion 65.7% and selec-
tivity 100%. This result strongly indicates the heterogeneous nature
of the present catalyst AM–BM–PW for the epoxidation reaction.
Our previous report [18] revealed that a HPA-based non-
polymeric ionic hybrid catalyst prepared by protonating and
anion-exchanging the 3-aminoethyl-1-methylimidazolium IL with
3−
with peroxo–W as the active centres [6,34]. In the present work, the
polymeric hybrid catalyst AM–BM–PW revealed a undegradable
solid nature in H2O2 attributed to the amino-containing cross-
linked polymeric cations, which allows to easily recover the used
solid catalyst and to provide the evidence for the peroxo–W active
species. Based on the above results, the reaction mechanism for
the epoxidation of alkenes with H2O2 over AM–BM–PW can be
described as in Scheme 2. The catalytic cycle starts from the reac-
tion of H2O2 with amino groups to form a quaternary ammonium
and a perhydroxyl. Simultaneously, the perhydroxyl reacts with the
amino-modified W sites in the HPA framework, leading to the gen-
eration of the peroxo–W complex that is supposed to be the active
site for epoxidation. Finally, the peroxo–W complex is resumed to
the original state of W O by inserting its oxygen into the alkene
reactant to produce an epoxide product.
4. Conclusion
In summary, we have developed and synthesized an
heteropolyanion-based amino-containing cross-linked ionic
copolymer catalyst for the liquid–solid heterogeneous epoxidation
of alkenes with H2O2. The new polymeric catalyst exhibits very
high conversions and selectivity, coupled wih convenient recovery
and steady reusability. The cross-linked structure of the copolymer
cations is responsible for the catalyst’s stable structure, and the
evidenced peroxo–W active sites in HPA frameworks promoted by
the amino groups in polymer matrix is revealed to account for the
catalyst’s excellent performances in epoxidation of alkenes with
H2O2.
H3PW12O40 offered
a high conversion of 95.7% with 100%
selectivity. However, 10.5% of the W in the monocationic hybrid
Table 2
Catalytic reusability of the polymeric hybrid catalyst AM–BM–PW for the epoxida-
tion of cyclooctene with H2O2.a
Run
1
2
3
Conb (%)
Selc (%)
98.5
100
98.0
100
97.2
100
Acknowledgments
a
Reaction conditions: catalyst (0.1 g), cyclooctene (10 mmol), 30% H2O2 (4 mmol),
acetonitrile (10 mL), 70 ◦C for 4 h.
The authors thank the financial support from National Natu-
ral Science Foundation of China (Nos. 21206052 and 21136005),
the National “Twelfth Five-Year” Plan for Science & Technology
b
Conversion of the substrate based on H2O2.
c
Selectivity for the epoxide product.

Y. Leng et al. / Applied Catalysis A: General 445–446 (2012) 306–311
311
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