Basic ionic liquid supported on mesoporous SBA-15: An efficient heterogeneous catalyst for epoxidation of olefins with H2O 2 as oxidant

Article abstract of DOI:10.1016/j.catcom.2012.03.003

Basic ionic liquid functionalized mesoporous silica SBA-15 was prepared and characterized by XRD, N₂ adsorption-desorption, FT-IR and TEM. The catalyst demonstrated to be an efficient heterogeneous catalyst for olefin epoxidation using H₂O₂ as oxidant. The catalyst could be recycled at least five times without appreciable loss of catalytic activity.

Full text of DOI:10.1016/j.catcom.2012.03.003

Catalysis Communications 24 (2012) 56–60
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Catalysis Communications
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Short Communication
Basic ionic liquid supported on mesoporous SBA-15: An efficient heterogeneous
catalyst for epoxidation of olefins with H2O2 as oxidant
Chengyuan Yuan a,b, Zhiwei Huang a, Jing Chen a,
⁎
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 73000, PR China
b
Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Basic ionic liquid functionalized mesoporous silica SBA-15 was prepared and characterized by XRD, N2 adsorption–
desorption, FT-IR and TEM. The catalyst demonstrated to be an efficient heterogeneous catalyst for olefin epoxida-
tion using H2O2 as oxidant. The catalyst could be recycled at least five times without appreciable loss of catalytic
activity.
Received 9 December 2011
Received in revised form 27 February 2012
Accepted 1 March 2012
Available online 10 March 2012
© 2012 Published by Elsevier B.V.
Keywords:
Epoxidation
Basic ionic liquid
Mesoporous SBA-15
Hydrogen peroxide
1. Introduction
exhibited more advantages such as high catalytic efficiency and easy
catalyst recycling for some base-catalyzed processes [22–24]. Up to
The epoxidation of olefins is of great interest due to the impor-
tance of epoxides in the manufacture of fine chemicals [1,2]. For the
economic and environmental reasons, hydrogen peroxide (H2O2) is
an ideal oxidant for epoxidation of olefins because of its ease of
handling and high active oxygen content, as well as the fact that
water is the only byproduct [3–5]. Epoxidation of olefins with H2O2
has been extensively studied over the last two decades using various
of catalysts such as Ti [6], Mn [7], W [8], and Re [9]. A major drawback
of the processes mentioned above is the using transition metals as
catalytically active components. Alternatively, epoxidation of olefins
is usually performed under strongly alkaline conditions using bases
such as NaOH, Na2CO3 or KOH with H2O2 as the oxidant. However,
using these strong bases has numerous disadvantages such as large
production of industrial waste, severe corrosion and difficulty in
catalyst recovery [10]. To solve the problems mentioned above, various
solid basic catalysts such as hydrotalcites [11–13], hydroxyapatites
[14,15] and basic metal oxides [16] have been used for epoxidation of
olefins using H2O2.
now, basic ionic liquids have been successfully introduced as catalysts
to catalyze various reactions such as Heck reaction [25], Michael addi-
tion [26] and Markovnikov addition [27].
Although the catalytic ability of basic IL has been successfully dem-
onstrated in many reactions, the chemical industry still prefers to use
heterogeneous catalysts due to the easy separation. Furthermore, it
has been reported that supported ILs led to more improvements in effi-
ciency than homogenous ionic liquids [28,29]. Therefore, it is highly
desirable to supported basic ILs onto solid supports. Our group has suc-
cessfully used supported basic ILs to catalyze hydrolysis of propylene
carbonate reaction [30] and Knoevenagel condensation reaction [31].
Herein, we report a catalytic system based on SBA-15 molecular
sieves supported basic ILs, which proved to be efficient for epoxida-
tion of olefins using H2O2 as oxidant.
2. Experimental
2.1. Catalysts preparation
In recent years, ionic liquids (IL) have received increasing interest
in the area of green chemistry [17]. Initially, ionic liquids were usually
used as alternative reaction solvents, but today they have been
employed as catalysts for different reactions [18–21]. Among them,
basic ionic liquids have attracted unprecedented attention, because
compared to the combination of inorganic base and ionic liquid they
Mesoporous SBA-15 was prepared according to the reported
method [32]. The preparation of chloropropyltriethoxysilane modi-
fied SBA-15 molecular sieves was carried out as follows. 2.0 g of
SBA-15 was dispersed in 50 ml dry toluene and to this suspension
3 ml chloropropyltriethoxysilane (CPTES) was added. The resulting
mixture was refluxed under N2 protection for 24 h. After cooling to
room temperature, the solid was separated by filtration and washed
in a Soxhlet apparatus with dichloromethane for 24 h. After filtration,
the solid was dried at 60 °C under reduced pressure to give the
⁎
Corresponding author.
E-mail address: chenj@licp.cas.cn (J. Chen).
1566-7367/$ – see front matter © 2012 Published by Elsevier B.V.
doi:10.1016/j.catcom.2012.03.003

C. Yuan et al. / Catalysis Communications 24 (2012) 56–60
57
imidazolium hydrogen carbonate (BIL) was supported on SBA-15 by
ion exchange. Solid potassium hydrogen carbonate and SCIL were
added to 50 ml distilled water, and the mixture was stirred vigorously
at room temperature for 24 h. Then the mixture was filtrated and
washed with distilled water until neutral, followed by drying at 70 °C
under reduced pressure for 24 h to give the product which was desig-
nated SBIL (Scheme 1 step III).
2.2. Catalysts characterization
X-ray powder diffraction (XRD) experiments were carried out on
a PANalytical X'pert Pro diffractometer. The N2 adsorption/desorption
isotherms were measured using a Micromeritics ASAP 2010 instru-
ment at liquid N2 temperature. Fourier transform infrared (FT-IR)
measurements were carried out using a Bruker IFS 120HR FT-IR
sepectrometer and KBr pellets. Transmission electron microscopy
(TEM) images were obtained on a Hitachi H-600 electron microscope.
Scheme 1. Preparation of the SBA-15 supported basic ionic liquid.
2.3. Catalytic performance
A typical procedure of the epoxidation of cyclohexene was as
follow: A mixture of cyclohexene (4 mmol), SBIL (100 mg), benzoni-
trile (10 mmol), 30% aq. H2O2 (2.4 ml, 24 mmol) and MeOH (10 ml)
was stirred at 60 °C for 24 h. The catalysts were separated by filtration
and the filtrate was treated with MnO2 and anhydrous MgSO4 for GC
analyses. The used catalysts were washed with MeOH and then dried
under reduced pressure for recycle. Qualitative analysis was con-
ducted with a HP 6890/5973 GCMS with chemstation containing a
NIST Mass Spectral Database. Quantitative analysis was conducted
with an Agilent 6820 GC equipped with a FID using an internal stan-
dard method.
(100)
(b)
(110)
(200)
(a)
1
2
3
4
5
2θ (o)
3. Results and discussion
Fig. 1. Small angle XRD patterns of (a) SBA-15 and (b) SBIL.
3.1. Catalysts characterization
product of CPTES/SBA-15 (Scheme 1 step I). Grafting IL of 1-methyl-
3-(chloropropyltriethoxysilane) imidazolium chloride (CIL) on SBA-15
was as follow: a mixture of CPTES/SBA-15 (2.0 g) and 1-methyl imidaz-
ole in 50 ml dry toluene was refluxed for 24 h under N2 protection. After
cooling to room temperature, the reaction mixture was filtered, and the
resulting solid was washed with toluene and methanol, followed by
drying at 60 °C under reduced pressure for 24 h. The obtained product
was designated SCIL (Scheme 1 step II). The loading of the IL was
obtained to be 0.39 mmol/g according to the results of elementary
analysis. Finally, basic IL of 1-methyl-3-(chloropropyltriethoxysilane)
Low-angle powder X-ray diffraction patterns of SBA-15 and SBIL
are depicted in Fig. 1. SBA-15 patterns showed an intense peak
assigned to reflections at (100) and two low-intensity peaks at
(110) and (200), indicating a significant degree of long-range order-
ing in the structure and a well-formed hexagonal lattice [32]. The
sample of SBIL also exhibited three clear diffraction peaks in low
angle region, which indicated that the mesoporous structure of the
support remained intact under the conditions used for functionaliza-
tion. Compared with pure SBA-15, the intensity of reflections of (100)
a
b
1100
(b)
(a)
1000
900
800
700
600
500
400
300
200
100
0
(a)
(b)
0
10
20
30
40
50
60
70
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P0)
Pore diameter (nm)
Fig. 2. N2 adsorption–desorption isotherms and pore diameter distributions of (a) SBA-15 and (b) SBIL.

58
C. Yuan et al. / Catalysis Communications 24 (2012) 56–60
Table 1
(a)
(b)
(c)
a
Epoxidation of cyclohexene under various reaction conditions
.
b
c
Entry
Catalyst
Conversion (%)
Yield (%)
d
1
2
3
4
5
6
7
None
18
18
19
65
20
87
14
13
16
53
2978
2928
d
SBA-15
e
d
CIL
BIL
e
d
1573
1630
d
960
SCIL
SBIL
SBIL
17
804
87
f
No reaction
–
3430
a
Reaction conditions: cyclohexene (4 mmol), benzonitrile (10 mmol), catalyst
(100 mg), MeOH (10 ml), 30% aq. H2O2 (2.4 ml, 24 mmol H2O2), 60 °C, 24 h.
1080
b
Conversion determined by GC.
Yields of epoxides were determined by GC analysis using internal standards (toluene),
c
1000 1500 2000 2500 3000 3500 4000
Wave number ( cm-1)
based on the olefins.
d
The byproduct of cyclohexane-1, 2-diol was found.
The amount was equivalent to the amount of basic IL on the surface of SBIL.
Benzonitrile was not added.
e
Fig. 3. FT-IR spectra of (a) SBA-15, (b) CPTES/SBA-15 and (c) SBIL.
f
peak of SBIL was slightly decreased, which could be mainly attributed
to the effect of pore-filling of organic components that reduced scat-
tering contrast between the pores and the framework of SBA-15 [33].
Furthermore, the (100) peak of SBIL shifted toward higher 2θ values,
implying the reduction of pore size due to the introduction of organic
components into the pore channel of SBA-15 [34].
comparison with the naked SBA-15, the bands at 2978 cm−1 and
2928 cm−1 for CPTES/SBA-15 and SBIL were due to C–H stretching
of CPTES. Additional band at 1574 cm−1 due to the C–C and C–N
stretching vibrations of imidazole ring [37] was observed for the sam-
ple of SBIL, confirming the functionalization of basic IL into the
material.
Fig. 4 shows TEM images of SBIL. It can be clearly seen that the
uniform mesoporous structure of SBA-15 was not destroyed after
functionalization with basic IL, which was in good agreement with
the results obtained from XRD and N2 adsorption–desorption.
Fig. 2 shows the N2 adsorption–desorption isotherms and pore di-
ameter distributions of SBA-15 and SBIL. BET surface areas and BJH
distributions were calculated using N2 adsorption at 77 K. Both of
samples displayed a type IV isotherm with HI hysteresis loop and a
sharp increase in pore volume adsorbed above P/P0 ~0.7, which is typ-
ical characteristic of highly ordered mesoporous materials [35]. The
textural properties of SBA-15 were substantially maintained over
basic ionic liquid functionalization. Functionalization of basic ionic
liquid significantly affected the surface area and pore distribution of
the modified samples. The parent SBA-15 sample showed a maximum
pore diameter at 8.7 nm and surface area of 574 m2/g. After functio-
nalization of basic IL, the maximum pore diameter and surface area
of the sample SBIL decreased to 6.3 nm and 361 m2/g, respectively.
In order to warrant the successful functionalization SBA-15 with
basic IL, FT-IR is employed to give detailed investigation of the
obtained SBIL (Fig. 3). For all samples, the bands at 1630 and
3430 cm−1 can be assigned to the O–H vibration of physisorbed
water. The bands due to Si–O–Si stretching of SBA-15 framework
3.2. Catalytic activity
Table 1 shows results of epoxidation of cyclohexene under various
reaction conditions. As it has been found, in the absence of a catalyst,
the cyclohexene conversion and epoxide yield were very low with
formation of byproduct of cyclohexane-1, 2-diol (entry 1). Since
SBA-15 and ionic liquid of CIL exhibited similar low catalytic activity
as that of no catalyst, SBA-15 and CIL were not active component of
the catalyst (entries 2 and 3). Using SCIL as catalyst did not increase
cyclohexene conversion and epoxide yield remarkably (entry 5), indi-
cating that SCIL was not effective. When only addition of ionic liquid
of BIL, the conversion and epoxide yield increased remarkably, dem-
onstrating that BIL was active for our epoxidation system (entry 4).
Compared with BIL, SBIL exhibited much higher catalytic activity
(entry 6). The cyclohexene conversion increased to 87%, and no
byproduct was detected so epoxide yield was also 87%. It has been
reported that basic reaction medium could effectively prevent ring
opening reaction in olefin epoxidation [38], so the excellent epoxide
were observed at 804 and 1080 cm−1
. A band was seen at
960 cm−1 aroused by O–H vibration of surface silanols. After functio-
nalization with CPTES and basic IL, the intensity of this band for the
samples of CPTES/SBA-15 and SBIL decreased significantly which
was caused by the occupation of surface O–H by CPTES and basic IL
[36], indicating the successful supporting of CPTES and basic IL. In
Fig. 4. TEM pictures of SBIL.

C. Yuan et al. / Catalysis Communications 24 (2012) 56–60
59
A series of catalytic cycles were run to investigate the constancy
of the catalyst activity. As it is displayed in Fig. 5, this catalyst can
be reusable for at least five times with slight loss of activity.
The SBIL catalyst can be used for the epoxidation of a wide range
of cyclic, linear and aromatic olefins, the results are summarized in
Table 2. Cyclic and aromatic olefins such as cyclopentene (entry 1),
cyclooctene (entry 2) and indene (entry 4) gave the corresponding
epoxides with good conversion and epoxide yield, respectively.
Besides epoxide product, byproduct of benzaldehyde was found for
epoxidation of styrene (entry 3). Compared with cyclic and aromatic
olefins, linear olefins such as 1-heptene and 1-dodecene showed
lower conversions and epoxide yields (entries 5 and 6).
Scheme 2. Possible mechanism.
80
60
40
20
0
4. Conclusions
In summary, mesoporous SBA-15 functionalized with basic IL was
synthesized, and used as an efficient heterogeneous catalyst for epoxi-
dation reaction of various olefins using a combined oxidant of aqueous
hydrogen peroxide and benzonitrile. The cyclic and aromatic olefins
were oxidized to corresponding epoxides with good yields, whereas
linear olefins were less reactive. The catalyst could be facilely separated
from the reaction mixture by filtration and could be reused at least five
times without significant degradation in activity.
1
2
3
4
5
Reaction cycle
Fig. 5. Reuse of the SBIL catalyst.
Acknowledgments
yield was probably due to the basicity provided by SBIL. Furthermore,
we found that no reaction happened without addition of benzonitrile
(entry 7), so benzonitrile was indispensable for our epoxidation sys-
tem. It has been reported that base-catalyzed epoxidation reaction
using H2O2 required the addition of nitrile [39]. The possible mecha-
nism is depicted in Scheme 2. In first step (StepI), a hydroperoxide
anion is formed from hydrogen peroxide in basic condition provided
by the catalyst of SBIL [39]. In the second Step (StepII), nitrile is oxi-
dated to peroxicarboximidic acid by hydroperoxide anion. Finally, in
the third step (StepIII), the peroxicarboximidic acid transfers oxygen
to the olefin to form epoxide.
The authors express their gratitude for the financial support of this
work provided by National Science Fund for Distinguished Young
Scholars of China (No. 20625308).
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a
Reaction conditions: olefin (4 mmol), benzonitrile (10 mmol), SBIL(100 mg),
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b
Conversion determined by GC.
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c
based on the olefins.
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