High conversion of CO2 into cyclic carbonates under solvent free and ambient pressure conditions by a Fe-cyanide complex

Article abstract of DOI:10.1039/c9nj04058g

Methods of converting carbon dioxide into valuable chemicals are of great demand but their development is still challenging. Herein, we developed an efficient, green and facile synthetic method for the preparation of a Fe-cyanide complex. The target catalyst showed high catalytic activity for the cyclic reaction of carbon dioxide and epoxide under solvent free conditions and ambient pressure. Meanwhile, the effects of morphology of different catalysts on their catalytic activities were also investigated by the kinetic and thermodynamic studies. In addition, the catalyst could be recycled and reused for at least five successive cycles without significant decrease in the catalytic activity. This target catalyst thus represents one of the efficient and recyclable systems reported for the cyclic reaction in industry.

Full text of DOI:10.1039/c9nj04058g

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High conversion of CO2 into cyclic carbonates
under solvent free and ambient pressure
conditions by a Fe-cyanide complex†
Cite this: New J. Chem., 2019,
43, 17211
Pengbo Jiang,‡ Lei Ma,‡ Kaizhi Wang, Kai Lan, Zhenzhen Zhan, Anam Iqbal,
Fang Niu and Rong Li
*
Methods of converting carbon dioxide into valuable chemicals are of great demand but their development is
still challenging. Herein, we developed an efficient, green and facile synthetic method for the preparation of
a Fe-cyanide complex. The target catalyst showed high catalytic activity for the cyclic reaction of carbon
dioxide and epoxide under solvent free conditions and ambient pressure. Meanwhile, the effects of
morphology of different catalysts on their catalytic activities were also investigated by the kinetic and
thermodynamic studies. In addition, the catalyst could be recycled and reused for at least five successive
cycles without significant decrease in the catalytic activity. This target catalyst thus represents one of the
efficient and recyclable systems reported for the cyclic reaction in industry.
Received 5th August 2019,
Accepted 15th September 2019
DOI: 10.1039/c9nj04058g
rsc.li/njc
metal–organic frameworks.25–29 Homogeneous catalysts suffer
from high operating costs and cannot be separated easily from
1. Introduction
Carbon dioxide (CO2) is regarded as a greenhouse gas and is mainly the reaction media. However, heterogeneous catalysts could
produced by the combustion of fossil fuels. In recent years, the overcome these shortcomings well.
increasing content of CO2 in the atmosphere is causing global
Double metal cyanide (DMC) was first discovered for synthe-
warming. In response, the utilization of carbon dioxide has attracted sizing cyclic carbonates from CO2 and epoxides in 1966.30 DMC
considerable research interest in different areas.1–9 However, in comprises a metal ion (M1 being an oxophilic metal), which
addition to its greenhouse effect, CO2 also offers a number of forms a strong bond with oxygen and another metal (M2 is a
advantages: (1) it is inexpensive, (2) easily available and (3) from the transition metal) cyanide salt, e.g.,[M1]n[M2(CN)6]m. Later on,
carbon-chemical point of view, the carbon in carbon dioxide is various DMC polytypes were developed as the catalyst for
renewable.10,11 Hereby, CO2 can be used as a raw material to synthesizing cyclic carbonates.31–36 However, for most DMC,
synthesize a variety of highly valuable products such as form- the M2 is Co and such types of DMC as the catalyst for the
amides,12 methanol,13 formic acid14 and cyclic carbonates.15,16 synthesis of cyclic carbonates require a higher CO2 pressure,
Cyclic carbonates have been widely applied in the fields of aprotic longer reaction times or higher reaction temperatures.36
polar solvents, synthesis of plastics, medicines etc.17–19 The synth-
Herein, we report the synthesis of a Fe-cyanide complex from
esis of cyclic carbonates from CO2 and epoxides has been widely inexpensive potassium ferricyanide and other metal ions (Fe2+, Zn2+,
popular among researchers because of the high atom efficiency Ni2+, and Co2+) by a simple and green method. The catalyst shows a
(100%) of the cyclic reaction.20 As a consequence, a number of high catalytic activity and selectivity (99%) under mild conditions
catalysts including ionic liquids, onium salts and phosphines (solvent free, at 100 1C). Moreover, the effect of the morphology of
have been reported.10,21–24 Furthermore, a variety of hetero- the catalyst on its catalytic activity and the effect of the co-catalyst on
geneous catalysts have been investigated for the reaction of the cyclic reaction were investigated by kinetic and thermodynamic
CO2 and epoxides, such as metal salts, metallic oxides and studies. Finally, it was found that the catalyst can be recycled for at
least five times without significant decrease in activity.
State Key Laboratory of Applied Organic Chemistry (SKLAOC), the Key Laboratory
of Catalytic Engineering of Gansu Province, College of Chemistry and Chemical
Engineering, Lanzhou University, Lanzhou, Gansu, 730000, P. R. China.
2. Experiment
2.1 Reagents and chemicals
E-mail: liyirong@lzu.edu.cn; Fax: +86-931-8912582; Tel: +86-18919803060
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9nj04058g
All the reagents and solvents used in the synthesis of the
catalyst were purchased from commercial sources and used
‡ These authors contributed equally to this work and should be considered
co-first authors.
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without further purification. Ferric(III) nitrate nonahydrate were carried out to investigate the morphology. Nitrogen
(Fe(NO3)3ꢀ9H2O, 98.5%), nickel(II) nitrate hexahydrate (Ni(NO3)2ꢀ physisorption isotherms were carried out on a TriStar II 3020
6H2O, 98.0%), zinc(II) chloride (ZnCl2, 99.0%) and potassium V1.04 instrument. The specific surface area was calculated
hexacyanoferrate(II) trihydrate (K4[Fe(CN)6]ꢀ3H2O) were purchased by the Brunauer–Emmett–Teller method. X-ray photoelectron
from Chengdu Kelong Chemical Reagents Co., Ltd. Cobalt(II) spectroscopy (XPS) was performed on PHI-5702 instruments.
nitrate hexahydrate (Co(NO3)2ꢀ6H2O, 98.5%) was purchased from
2.4 Catalytic conversion of CO2 to cyclic carbonates
Shanghai Zhongqin Chemical Reagents Co., Ltd. Ferrous chloride
tetrahydrate (FeCl2ꢀ4H2O, 98.5%) was purchased from Xilong
Science Chemical Reagents Co., Ltd. Potassium hexacyano-
ferrate(III) hexahydrate (K3[Fe(CN)6]ꢀ6H2O) was purchased from
Tianjin Guangfu Chemical Reagents Co., Ltd.
The conversion of CO2 to a cyclic carbonate was carried out in a
25 mL three-necked round bottom flask under reflux and CO2
bubbling. Epoxide (5 mmol), catalyst (10 mg) and co-catalyst
(Bu4NBr or others) 2.5 mol% were mixed in a three-necked
round bottom flask and the reaction mixture was kept in a n oil
bath and stirred (600 rpm) for 0.25–5 h. Samples were collected
and filtered after the completion of the reaction and the
conversion, selectivity and product yield were detected by gas
chromatography-mass spectrometry (GC-MS, Agilent 6890N/5937N)
and 1H NMR spectroscopy (Varian Inova 400, 400 MHz using CDCl3
as a solvent).
The activities of the catalysts were calculated as follows:
conversion % = 100 ꢁ ([C0 ꢂ C1]/[C0]), selectivity % = 100 ꢁ [C0]/
[C0 ꢂ C1] and yield % = 100 ꢁ [C0]/[C0], where, [C0] is the initial
concentration of the substrate, [C1] is the concentration of the
substrate at the end of the reaction, and [C0] is the concen-
tration of the target product at the end of the reaction.
2.2 Preparation of the catalyst
For the synthesis of the FeI4II(Fe(CN)6)3, FeCl2ꢀ4H2O (1 mmol)
and K3[Fe(CN)6]ꢀ6H2O (0.5 mmol) were dissolved in 20 mL of
distilled water, separately. The two solutions were mixed with
magnetic stirring and the mixture was transferred to a Teflon-
lined stainless steel autoclave and heated at 80 1C for 12 h. The
resultant solid was collected by centrifugation and washed
3 times with water and dried at 80 1C overnight.
The detailed preparation process of other catalysts (except
the Prussian blue micro-cubes) is similar to the above process.
Prussian blue micro-cube, FeI4II(Fe(CN)6)3, was prepared by a
reported method.37 Briefly, 0.5 mmol of K4Fe(CN)6ꢀ3H2O was
added to a HCl solution (0.1 M, 50 mL) under constant
magnetic stirring. After stirring for 10 min, a clear solution
was obtained. Then, the mixture was transferred to a Teflon-
lined stainless steel autoclave and heated at 80 1C for 12 h. The
resultant solid was collected by centrifugation and washed
3 times with ultra-pure water and then dried at 80 1C overnight.
3. Results and discussion
3.1 Characterization of the catalyst
The XRD pattern is shown in Fig. 1a, which shows the crystal-
linity of catalysts. The XRD curves of catalysts show eight
observable peaks at 17.31, 24.61, 35.21, 39.41, 43.41, 50.51,
53.91 and 57.01 corresponding to the lattice planes of (200),
2.3 Characterization of the catalysts
The XRD patterns of the catalysts were recorded by an X-ray (220), (400), (420), (422), (440), (600) and (620) ( JCPDS no. 73-0687),
diffractometer (XRD) Rigaku D/max-2400. The metal content respectively.38 The Raman spectrum is shown in Fig. 1b with two
was measured by inductively coupled plasma optical emission strong peaks at 2091 and 2130 cmꢂ1, indicating the stretching
spectrometry (ICP-OES), which is carried out on a PerkinElmer vibration of the carbon nitrogen triple bond.39 Furthermore, the
(Optima-4300DV) instrument. Scanning electron microscopy bands at 264 and 534 cmꢂ1 could be assigned to the stretching and
(SEM) was performed on a MIRA3 TESCAN instrument. The trans- bending modes of Fe–CRN–Fe.40
mission electron microscopy (TEM), high-resolution transmission
The morphologies and microstructures of the prepared
electron microscopy (HR-TEM), and high angle annular dark field- samples were characterized by TEM. TEM images of FeI4II(Fe(CN)6)3
scanning transmission electron microscopy (HAADF-STEM) (Fig. 2a) show that the synthesized FeI4II(Fe(CN)6)3 does not have
Fig. 1 (a) XRD pattern and (b) Raman spectra of FeI4II(Fe(CN)6)3.
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Fig. 2 (a) The TEM image of FeI4II(Fe(CN)6)3, (b) the EDX spectrum of FeI4II(Fe(CN)6)3, (c) the TEM image of FeI4II(Fe(CN)6)3-cube, (d) HAADF-STEM image of
FeI4II(Fe(CN)6)3, (e–h) elemental mapping of FeI4II(Fe(CN)6)3.
a regular structure. To study the elemental distribution of The surface area and pore volume of the FeI4II(Fe(CN)6)3-cube
FeI4II(Fe(CN)6)3, high angle annular dark field scanning trans- was 10.0 m2 gꢂ1 and 0.018 cm3 gꢂ1, respectively. The Fe4III(Fe(CN)6)3-
mission electron microscopy (HAADF-STEM) was performed cube catalyst has a solid core cube and this structure is not
(Fig. 2d). The energy dispersive X-ray (EDX) elemental mapping conducive for active sites contacting with the substrate.
(Fig. 2b) analysis indicates a uniform distribution of C, N, K
XPS measurements were carried out to further investigate
and Fe throughout the entire region. In addition, the data of the surface composition and chemical state of the as-prepared
EDX also provides the molar fraction of elements (C 83.55%, catalyst. All the binding energies obtained in the XPS analysis
N 10.50%, K 0.33% and Fe 3.39%) in the catalyst. Fig. 2c shows were calibrated using the C1s peak at 284.6 eV. The wide-range
the cubic structure of FeI4II(Fe(CN)6)3-cube. Furthermore, the XPS spectrum (Fig. 4a) clearly shows that the C1s (284.6 eV),
SEM images of the catalyst are shown in Fig. S1 (ESI†) and we N1s (397.9 eV) and Fe2p (708.5 and 721.8 eV) elements are
found that most of the catalysts have massive structures except present on the surface of the catalyst.44 The high-resolution
the FeI4II(Fe(CN)6)3-cube.
spectrum of Fe2p (Fig. 4b) shows four main peaks with the
Nitrogen adsorption–desorption isotherms of the prepared binding energy of 708.5, 711.5, 721.4 and 724.3 eV. The peaks
catalysts were also measured. The isotherms reveal a type-IV located at 708.5 and 724.3 eV correspond to Fe2p3/2 and Fe2p1/2
adsorption isotherm with the H1 and H3 type hysteresis loop at of [FeII(CN)6],4–45 while the binding energy of 711.5 and 721.4 eV
a high relative pressure (Fig. 3a), indicating a uniform filling of can be assigned to FeIII2p3/2 and FeIII2p1/2 in the Fe4III(Fe(CN)6)3
the pores.41 Furthermore, the surface area and pore volume catalyst, respectively.38,44
of FeI4II(Fe(CN)6)3 was found to be 296.3 m2 gꢂ1 and 0.23 cm3 gꢂ1
,
3.2 Evaluation of catalysts
respectively. Large surface area and pore volume are responsible
for the high catalytic activity of the catalyst.42,43 The hysteresis
loops in the high-pressure region of FeI4II(Fe(CN)6)3-cube
exhibits that the catalyst does not have a mesoporous structure.
Initially, the cycloaddition of styrene oxide with CO2 (1 atm) to
produce styrene carbonate was carried out as the model reaction
to test the activity of various catalysts in the presence of TBAB
Fig. 3 (a) N2 adsorption–desorption isotherm of Fe4III(Fe(CN)6)3 and FeI4II(Fe(CN)6)3-cube, (b) pore volume of FeI4II(Fe(CN)6)3 and Fe4III(Fe(CN)6)3-cube.
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Fig. 4 (a) XPS survey spectrum of all elements present in Fe4III(Fe(CN)6)3, (b) the corresponding high-resolution XPS spectra of Fe.
Table 1 The consequence of the reaction of styrene oxide and CO2 with different catalystsa
Entry
Catalysts
Co-catalyst
Temperature (1C)
Conversion (%)
Selectivity (%)
Yieldb (%)
1
2
3
4
5
6
7
8
FeI4II(Fe(CN)6)3
—
—
100
100
100
100
100
100
100
100
100
90
0
10
99
85
90
80
65
97
98
90
76
71
60
0
95
99
93
96
96
51
95
96
92
89
70
52
0
9.5
99
79
86
76
33
92
94
83
67
49
31
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAC
TBAI
TBAB
TBAB
TBAB
TBAB
FeI4II(Fe(CN)6)3
FeI4II(Fe(CN)6)3-cube
KNi4(FeIII(CN)6)3
KZn4(FeIII(CN)6)3
KCo4(FeIII(CN)6)3
FeI4II(Fe(CN)6)3
FeI4II(Fe(CN)6)3
FeI4II(Fe(CN)6)3
FeI4II(Fe(CN)6)3
FeI4II(Fe(CN)6)3
FeI4II(Fe(CN)6)3
9
10
11
12
13
80
70
60
a
Reaction conditions: styrene oxide (5 mmol), 2.5 mol% co-catalyst, catalyst (10 mg), CO2 pressure (1 atm), reaction time (3 h), conversion and
b
selectivity were determined by GC-MS. The product of styrene carbonate.
(TBAC or TBAI) as co-catalyst, and the results are listed in Table 1.
Negligible amounts of the products were detected when the
a
Table 2 Cycloaddition reaction of epoxides and CO2
reaction was performed without a co-catalyst (Table 1, entry 1)
Entry Substrate
1
Product
Conversion (%) Selectivity (%)
or when only TBAB (Table 1, entry 2) was used at 100 1C and 1 atm
CO2 pressure. This process indicates that the catalyst and
co-catalyst both are essential for the cycloaddition reaction.
Entries 3–9 show that different types of catalysts have different
catalytic activities. The Fe4III(Fe(CN)6)3 catalyst (entry 3) can cata-
lyze the reaction of styrene oxide and CO2 in the presence of the
co-catalyst (TBAB) to attain 99% conversion and 99% selectivity
for styrene carbonate. With the TBAC (entry 8) or TBAI (entry 9) as
99
99
99
99
2
3
99
94
4
99
90
99
89
5b
6
99
99
a
Reaction conditions: epoxides (5 mmol), 2.5 mol% co-catalyst, catalyst
(10 mg), CO2 pressure (1 atm), reaction time (3 h), conversion and
b
selectivity were determined by GC-MS. Reaction time (5 h).
Scheme 1 Possible reaction of the by-product.
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the co-catalyst, none of the morphology of FeI4II(Fe(CN)6)3 resulted
The differences between three types of co-catalysts are the halide
in lower conversion and selectivity. Hence, the collaboration of ions; therefore, the performances of the co-catalyst towards the
the Lewis acid and nucleophilic agent is necessary to achieve high cycloaddition reaction are influenced by the halide anions.
conversion for this reaction.46 Furthermore, Table S2 (ESI†) shows The activity decreased in the order of TBAB 4 TBAI 4 TBAC.
a detailed comparison with different reported metal cyanides as The nucleophilic property (Clꢂ 4 Brꢂ 4 Iꢂ) and leaving ability
high-efficiency catalyst for the cycloaddition reaction.
(Iꢂ 4 Brꢂ 4 Clꢂ) of halide anions make TBAB a good co-catalyst.47
Fig. 5 The reaction rate constant at each temperature (a, FeI4II(Fe(CN)6)3), (c, FeI4II(Fe(CN)6)3-cube), (e, KNi4(FeIII(CN)6)3), (g, KZn4(FeIII(CN)6)3) vs. the
activation energy of catalysts (b, FeI4II(Fe(CN)6)3), (d, FeI4II(Fe(CN)6)3-cube), (f, KNi4(FeIII(CN)6)3), (h, KZn4(FeIII(CN)6)3). Reaction conditions: epoxides
(5 mmol), 2.5 mol% co-catalyst, catalyst (10 mg), CO2 pressure (1 atm), conversion was determined by GC-MS.
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From the entries (3 and 10–13), we found that the cyclo-
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addition reaction is sensitive towards temperature. When the
temperature was decreased from 100 1C to 80 1C, the conversion
and selectivity both were found to decrease. The lowest conversion
and selectivity was observed when the temperature was 60 1C. A
lower reaction temperature produced more by-products with the
epoxide ring-opening reaction when the iron cyanide complex was
used as a catalyst. Therefore, we can conclude that CO2 needs
a higher temperature. Therefore, it can be concluded that when
FeI4II(Fe(CN)6)3 is used as the catalyst, a lower reaction temperature
is not suitable for the cycloaddition reaction.
For this reaction, the possible by-products are hyacinthin
and 1-phenyl-1,2-ethanediol (Scheme 1). Hyacinthin is produced
by the isomerization of styrene oxide and 1-phenyl-1,2-ethanediol
is produced by the hydrolysis of styrene oxide. For the cycloaddi-
tion reaction of styrene oxide with CO2, the catalyst is an
important factor to retard the production of the by-product.48,49
Fig. 7 Reusability of FeI4II(Fe(CN)6)3. (Reaction conditions: styrene oxide
(5 mmol), 2.5 mol% co-catalyst, catalyst (10 mg), CO2 pressure (1 atm),
reaction time (3 h), conversion and selectivity were determined by GC-MS.)
So, a high activity of the catalyst is beneficial for the cycloaddition CO2 are not changed, so it can have a change with expression
reaction. Table 1 shows that FeI4II(Fe(CN)6)3 as the catalyst and the K = k[CO2]a, so eqn (1) can be simplified to eqn (2). Based on the
100 1C as the reaction temperature is the best reaction condition reported literarure, the reaction of styrene oxide and CO2 is first
for cycloaddition reaction.
order.52,53 So we can hypothesize that the reaction is a first
To investigate the compatibility of the catalyst, different order reaction, which modifies eqn (2) to eqn (3). According to
types of epoxides were chosen for the cycloaddition reaction the Arrhenius equation (eqn (4)) and eqn (5), it can be seen that
under 1 atm pressure and 100 1C. Different types of epoxides if the rate constant is known at different temperatures, the
were converted to relevant products with good conversion and activation energy can be calculated, where K is the apparent
selectivity. In the presence of TBAB as catalyst, the epichloro- rate constant of the reaction, A is the pre-exponential factor,
hydrin showed a high yield of 99%, probably attributed to the Eact is the activation energy, R is the ideal gas constant
electron-withdrawing ability of the chlorine atom.50 The conversion (8.314 J molꢂ1
of cyclohexane oxide was lower, which may have resulted from the
steric hindrance (Table 2).51
K
ꢂ1) and T is the reaction temperature.
d½Sꢃ
a
b
ꢂ
¼ k½CO2ꢃ ½Sꢃ
(1)
(2)
dt
3.3 Kinetic study
d½Sꢃ
b
ꢂ
¼ k0½Sꢃ
To understand the mechanism of the reaction and further
investigate the impact of the co-catalyst in the cycloaddition
reaction, a kinetic study was carried out for the reaction
between styrene oxide and CO2. The reaction rate is defined
as per eqn (1), where, [S] and [Cat] are the concentrations of the
substrate and catalysts, k represents the rate constant, and a
and b are the series of [CO2] and [S], respectively. In the process
of reaction, the concentration of catalysts and the pressure of
dt
ln[S]t = ꢂKt + ln[S]0
(3)
(4)
Eact
RT
K ¼ Aeꢂ
ꢀ ꢁ
Eact
R
1
ln K ¼ ln A ꢂ
(5)
T
Fig. 6 Conversion (a) and selectivity (b) using different catalysts. Reaction conditions: epoxides (5 mmol), 2.5 mol% co-catalyst, catalyst (10 mg), CO2
pressure (1 atm), conversion and selectivity were determined by GC-MS.
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Fig. 8 (a) FTIR spectra of FeI4II(Fe(CN)6)3 and pyridine adsorbed Fe4III(Fe(CN)6)3, (b) proposed mechanism of the cycloaddition reaction.
The apparent rate constant of different types of catalysts centrifugation as well as experimental errors in the recycling
at different temperatures and their activation energy are experiments.
elaborated in Fig. 5. All the catalysts follow first order reaction.
3.5 Proposed Mechanism
The rate constants of different catalysts at different reaction tem-
peratures are shown in Tables S2–S5 (ESI†). Moreover, it can be
found from Fig. 5 that the activation energies of KNi4(FeIII(CN)6)3,
Fe4III(Fe(CN)6)3, Fe4III(Fe(CN)6)3-cube and KZn4(FeIII(CN)6)3 were
To determine the acid type of the catalyst, infrared spectroscopy
(IR) was performed on Fe4III(Fe(CN)6)3 and pyridine adsorbed
FeI4II(Fe(CN)6)3. The pyridine adsorbed FeI4II(Fe(CN)6)3 was pre-
pared by mixing 3 mL pyridine and 50 mg FeI4II(Fe(CN)6)3 in a
round-bottom flask under magnetic stirring for 5 h at room
temperature. Then, the catalyst was collected by distillation and
dried at 80 1C overnight. The result of the acid type of the
catalyst is shown in Fig. 7a. After adsorbing pyridine, a peak
was observed at 1450 cmꢂ1, indicating that the catalyst was a
Lewis acid.
The catalytic mechanism of the catalyst can be explained by
the following steps. First, the epoxide reacts with the Lewis acid
followed by a nucleophilic attack on epoxide by TBAB to form a
metal alkoxide intermediate.36,54 After that, CO2 and the inter-
mediate form an acyclic carbonate. Finally, the cyclic carbonate
was produced when the catalyst left the intermediate.55 From
the above mechanism, it could be seen that the Lewis acid and
nucleophile work together for this reaction and are necessary
for this cycloaddition reaction (Fig. 8).
39.49 kJ molꢂ1, 56.03 kJ molꢂ1, 61.05 kJ molꢂ1 and 78.34 kJ molꢂ1
,
respectively.
Moreover, the conversion efficiency of the catalyst was
further evaluated by a thermodynamic study (Fig. 6); the con-
version of KNi4(FeIII(CN)6)3, FeI4II(Fe(CN)6)3, FeI4II(Fe(CN)6)3-cube
and KZn4(FeIII(CN)6)3 are 36%, 28%, 25% and 24%, respec-
tively, with the reaction time being 40 min. Furthermore, the
result showed that the data conformed well to the kinetic
study: the catalyst with lower activation energy had the higher
conversion at the same time. Fig. 6b shows the selectivity
of several catalysts, indicating that the selectivity increases
with the increase in reaction time. This is because at the
beginning of the reaction time, a mass of by-products was
produced, and at the end, the product consists mainly of the
target product.
3.4 Catalyst recycling
4. Conclusion
The as-prepared catalyst not only has good catalytic activity but
also has good recyclability and reusability.48 After the reaction,
the catalyst was collected with centrifugation and washed with
alcohol for three times, and then dried in vacuum. The
recycled catalyst was reused for the next reactions. Therefore,
a variety of CO2 and styrene oxide reactions were conducted
under solvent free condition at 100 1C and 1 atm pressure.
TBAB as the co-catalyst was used during the recyclability and
reusability study of the catalyst. The recycling ability of the
catalyst is shown in Fig. 7, which shows that after five recycling
cycles, the conversion and selectivity decreased only slightly.
This result shows that the catalyst has good recyclability and
reusability. Finally, after recycling the catalyst for five times, we
analyzed the catalyst with ICP and found that the content of
In summary, we report a green and facile method to synthesize
a highly active catalyst to catalyze the cyclic reaction between
carbon dioxide and epoxides. After the screening of the reaction
conditions (CO2 at atmospheric pressure, solvent free, 100 1C),
satisfactory conversion (99%) and selectivity (99%) were obtained.
Moreover, the mechanism of the reaction was investigated by
kinetic study. In addition, the recyclability test of the catalyst
indicates that it could be reused for 5 times without a significant
decrease in activity.
Conflicts of interest
Fe reduced from 37.39% to 33.92%, which may be due to There are no conflicts to declare.
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