Zeolitic imidazolate framework as efficient heterogeneous catalyst for the synthesis of ethyl methyl carbonate

Article abstract of DOI:10.1016/j.molcata.2012.09.006

A zeolitic imidazolate framework (ZIF-8) was developed as a novel efficient heterogeneous catalyst for the synthesis of ethyl methyl carbonate from dimethyl carbonate and diethyl carbonate. ZIF-8 was characterized by element analysis, X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), temperature programmed desorption (TPD), N₂ adsorption-desorption and thermogravimetric analysis. The effects of catalyst amount, temperature and reaction time on the yield of ethyl methyl carbonate were also tested. The results showed that ZIF-8 performed excellent activity, selectivity and reusability under mild reaction conditions.

Full text of DOI:10.1016/j.molcata.2012.09.006

Journal of Molecular Catalysis A: Chemical 366 (2013) 43–47
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Zeolitic imidazolate framework as efficient heterogeneous catalyst for the
synthesis of ethyl methyl carbonate
Xi Zhoua,b, Hong Ping Zhanga, Gong Ying Wangb,∗, Zhi Gang Yaoa, Ying Ran Tanga, Shan Shan Zhenga
a Department of Biological and Chemical Engineering, Shaoyang University, Shaoyang 422000, Hunan, PR China
b Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, Sichuan, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 July 2012
Received in revised form 3 September 2012
Accepted 4 September 2012
Available online 11 September 2012
A zeolitic imidazolate framework (ZIF-8) was developed as a novel efficient heterogeneous catalyst for the
synthesis of ethyl methyl carbonate from dimethyl carbonate and diethyl carbonate. ZIF-8 was character-
ized by element analysis, X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), temperature
programmed desorption (TPD), N2 adsorption–desorption and thermogravimetric analysis. The effects
of catalyst amount, temperature and reaction time on the yield of ethyl methyl carbonate were also
tested. The results showed that ZIF-8 performed excellent activity, selectivity and reusability under mild
reaction conditions.
Keywords:
Ethyl methyl carbonate
Heterogeneous
© 2012 Published by Elsevier B.V.
Dimethyl carbonate
Diethyl carbonate
Zeolitic imidazolate framework
1. Introduction
catalytic activity of several metal oxides, and found that MgO is the
most active catalyst due to its basic property. Jia et al. [6] reported
Ethyl methyl carbonate (EMC) can be utilized as a co-solvent
in a nonaqueous electrolyte to improve the energy density and
discharge capacity of the lithium ion cells. Several methods have
been reported for EMC synthesis. Traditionally, EMC is prepared by
esterification of chloroformate with ethanol in the presence of basic
catalyst [1]. However, this route is not an environmentally benign
process since methyl chloroformate is highly toxic. Another method
to synthesis EMC is the transesterification of dimethyl carbonate
(DMC) with ethanol [2]. This route has the drawback of formation
of three binary azeotropes, causing a serious difficulty in separa-
tion. EMC can also be prepared by the transesterification of DMC
with diethyl carbonate (DEC) [3–8]. Because all the reaction mix-
tures (DEC, DMC and EMC) can be used as solvent in a nonaqueous
electrolyte, the separation step can be avoided in this method. In
addition, the composition of the reaction mixture can be adjusted
by controlling the raw material ration and the conversion.
that carbon-supported MgO (MgO/NC-2) catalysts prepared by a
wet impregnation technique are efficient heterogeneous catalysts
for the reaction. Palani et al. [7] reported that high yield of EMC can
be obtained with Al-MCM-41 or Al-Zn-MCM-41 as catalyst under
175–200 ◦C. Recently, Jia et al. [8] found that amorphous meso-
porous aluminophosphate (AlPO) shows remarkably higher activity
than other solid catalysts. 47.7% conversion of DEC was achieved
under desired reaction conditions (catalyst 4.8 wt%, 366 K, 0.5 h).
Nowadays, it is still important and challenging to develop highly
efficient heterogeneous catalyst for the synthesis of EMC from DMC
and DEC under mild reaction conditions.
Metal–organic frameworks (MOFs), also known as porous coor-
dination polymers, consist of metallic nodes bonded by organic
linkers. In the past decades, MOFs have received much attention
due to their special properties, such as ultrahigh surface area com-
bined with a high crystallinity [9–11]. They have been widely
used in gas storage and separation [12], magnetism [13], chem-
ical sensing [14], drug delivery [15], and catalysis [16–18]. The
use of MOFs as heterogeneous catalyst is interesting, since the
pose size and functionality of framework can be easily tuned
over a wide range for different catalytic reactions. Recently, Zhou
et al. [19] reported that MOF-5 [Zn4O(BDC)3] (BDC = benzene-1,4-
dicarboxylate) is an active catalyst for the transesterification of
DMC and DEC. And high EMC yield (50.1%) is obtained. However,
MOF-5 is unstable exposing to air [20], which limits its applica-
tion. Herein, a zeolitic imidazolate framework (ZIF-8) [Zn(MeIm)2]
For the transesterification of DMC with DEC, Ti(OBu)4 and
Bu2SnO were found to be active homogeneous catalysts [3]. How-
ever, the separation of catalysts from product is difficult. Gan et al.
[4] reported that lithium diethyl amide and lithiated carbon per-
formed high activity for the reaction. But these catalysts are very
expensive, which limits their application. Shen et al. [5] tested the
∗
Corresponding author. Tel.: +86 28 85215405; fax: +86 28 85220713.
E-mail address: gywang@cioc.ac.cn (G.Y. Wang).
1381-1169/$ – see front matter © 2012 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.molcata.2012.09.006

44
X. Zhou et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 43–47
(MeIm = 2-methylimidazole) which shows high surface area,
exceptional chemical and thermal stability was developed as highly
efficient heterogeneous catalyst for the synthesis of EMC from DMC
and DEC.
2. Experimental
2.1. Catalyst preparation
ZIF-8 was prepared according to the literature reported by
Chizallet et al. [21]. A solution consisting of 2-methylimidazole
(3.220 g) dissolved in 100 mL of methanol was slowly added
(30 min) to a solution of Zn(OH)2 (1.951 g) in aqueous ammonia
(25–28% (v/v), 250 mL). The white solid began to produce immedi-
ately. Preparation was done under room temperature with gentle
steering in 2 days. And the prepared white solid was collected by
filtration, then washed 3 times with 100 mL of H2O/MeOH (1:1, v/v)
solution and dried in oven at 100 ◦C.
2.2. Catalyst characterization
Fig. 1. XRD patterns of ZIF-8: (A) simulated and (B) synthesized in this work.
The X-ray diffraction patterns were collected on X-ray
of 1368 m2/g (calculated by BET), which was similar with that in
the previous literature (about 1400 m2/g) [22,23]. In the TG result
for ZIF-8, there was little weight loss while the temperature was
lower than 400 ◦C, indicating that ZIF-8 was stable up to 400 ◦C. It
was also verified by the DTA result for ZIF-8 (Fig. 3). The thermal
stability of ZIF-8 in this work was agreed well with that reported
in the literature [22–24]. According to the results of CO2-TPD and
NH3-TPD, both acid and base active centers were existed on the
surface of ZIF-8 (Figs. 4 and 5).
diffractometer (XPERT PRO) using a Cu K␣ radiation source
˚
(ꢀ = 1.54056 A), operating at 40 kV and 45 mA. FT-IR spectra were
obtained by Nicolet 560 in KBr pellets. A continuous mode was
used for collecting data at a scanning speed of 0.02◦/s. Low tem-
perature nitrogen adsorption and desorption measurements were
conducted using a TriStar II 3020 (Micromeritics Instrument Corpo-
ration). The content of Zn in filtration was detected by TS IRIS 1000
ICP-AES instrument. Thermogravimetric analysis was conducted
on a HCT-2 thermo-analyzer (Beijing Scientific Instrument Factory)
with a heating rate of 10 ◦C/min. The surface acid–base properties of
ZIF-8 were characterized by temperature programmed desorption
of CO2 (CO2-TPD) and NH3 (NH3-TPD). The sample was pretreated
at 200 ◦C in argon atmosphere for 1 h, and the desorption temper-
ature was between room temperature and 450 ◦C with a heating
rate of 10 ◦C/min.
3.2. Catalytic performance
The activity of different catalysts for the transesterification of
DMC with DEC to synthesis EMC was tested, and the results were
summarized in Table 1. Obviously, the reaction could not proceed
without catalyst (Entry 1), which is in accord with the result
reported by literature [8,19]. In the presence of ZIF-8, 50.7% yield
of EMC was obtained (Entry 2), which is very close to the equilib-
rium yield of this reaction [8,19]. It is noteworthy that byproducts
were not detected by GC–MS. In order to compare ZIF-8 with other
2.3. Catalytic reactions
Typical procedure for the synthesis of EMC: 9.000 g (0.1 mol)
DMC, 11.800 g (0.1 mol) DEC and 0.208 g (1 wt%) catalyst were
charged into a 50 mL flask equipped with a magnetic stirring and a
reflux condenser. The reaction mixture was then heated to 100 ◦C
with continuous stirring. After 3 h, the mixture was cooled to room
temperature. And the product analyzed by GC (Shandong Lunan
Ruihong Co. SP-6890). The structure of the product was defined by
GC–MS (HP 6890/5973). In the experiment to test the reusability of
catalyst, ZIF-8 was separated by filtration, washed using ethanol.
After drying in oven, ZIF-8 was reused for the next time.
3. Results and discussion
3.1. Characterization
The catalyst ZIF-8 was characterized by X-ray powder diffraction
(XRD), N2 adsorption–desorption and thermogravimetric analysis.
As shown in Fig. 1, the XRD patterns of ZIF-8 in this work were agree
well with patterns simulated from single crystal structure in the
Cambridge Structural Database. There was a very sharp pattern at
2ꢁ = 7.2◦ in the XRD pattern of ZIF-8, indicating that the crystallinity
of ZIF in this work was relatively high. N2 adsorption–desorption
isotherms and pore size distribution of ZIF-8 were summarized in
Fig. 2. The pore structure of ZIF-8 was mainly micropore, and the
pore size was about 1.0–1.2 nm. ZIF-8 exhibited a high surface area
Fig. 2. N2 adsorption–desorption isotherms and pore size distribution (inset) of
ZIF-8.

X. Zhou et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 43–47
45
Table 1
Transesterification of DMC with DEC in the presence of different catalysts.a
Entry
Catalyst
Reacted mixture (mol%)
Yieldb (%)
Selectivity (%)
TOFc (mmol g−1 h−1
)
DMC
DEC
EMC
1
–
50.0
33.0
36.7
41.0
49.9
49.9
49.9
58.1
14.6
50.0
33.0
36.7
41.0
49.9
49.9
49.9
16.2
57.3
–
Trace
50.7
42.0
30.5
0.1
0.2
0.2
30.6
65.7
–
∼100
∼100
∼100
∼100
∼100
∼100
∼100
∼100
–
81.3
67.3
48.9
0.2
0.3
0.3
49.0
105.3
2
ZIF-8
MOF-5
MgO
Zn(OH)2
2-Methylimidazole
Zn(OH)2 + 2-methylimidazole
ZIF-8
ZIF-8
34.0
26.4
18.0
0.05
0.1
0.1
25.6
28.0
3d
4
5
6
7
8e
9f
a
Reaction conditions: DMC (0.1 mol), DEC (0.1 mol), catalyst (0.208 g), 100 ◦C and 3 h.
Determined by GC, calculated in terms of DMC (moles of EMC/2 × moles of DMC).
Moles of DMC converted per gram of catalyst in 1 h.
b
c
d
e
f
Cited by literature [19], DMC (0.02 mol), DEC (0.02 mol), MOF-5 (1 wt%, based on the total mass of DMC and DEC), 100 ◦C and 3 h.
DMC (0.2 mol), DEC (0.1 mol).
DMC (0.1 mol), DEC (0.2 mol).
Fig. 5. NH3-TPD analysis of ZIF-8.
Fig. 3. TG-DTA analysis of ZIF-8.
addition, ZIF-8 performs exceptional chemical and thermal stabil-
ity while the framework of MOF-5 is unstable exposing to air, which
has been reported by Yaghi et al. [20,24]. Among base metal oxides,
MgO is the most active catalyst for the transesterification [5]. How-
ever, the activity of MgO is much lower than that of ZIF-8. Moreover,
the activity of raw materials of synthesis ZIF-8, Zn(OH)2 and 2-
methylimidazole, were also tested (Entries 5 and 6). The result
showed that they perform almost no catalytic activity for the syn-
thesis of EMC. Note that the yield of EMC was also very low with
the mixture of Zn(OH)2 and 2-methylimidazole as catalyst (Entry
7).
heterogeneous catalyst, the activity of MOF-5, MgO was examined
or cited by literature (Entries 3 and 4). As shown in Table 1, ZIF-
8 showed higher activity than another metal–organic framework
MOF-5 under the same reaction conditions (1 wt%, 100 ◦C, 3 h). In
Jia et al. demonstrated the relationship between acid–base pairs
and the high catalytic activity of catalyst for the transesterification
of DMC with DEC [8]. There are ZnII species as acid sites, combined
with N− moieties and OH groups as basic sites in the framework of
ZIF-8 [21]. CO2-TPD and NH3-TPD results in this work also revealed
that there are acid and base active centers on the surface of ZIF-8
(Figs. 4 and 5). According to that, ZIF-8 is an acid–basic bifunctional
catalyst, which may be one of reasons for high catalytic activity
in the transesterification. Another reason may be the high surface
area of ZIF-8 (1368 m2/g). Chizallet et al. [21] studied the trans-
esterification of vegetable oil with alcohols with ZIF-8 as catalyst,
and demonstrated that acid–basic catalytic sites are located at the
external surface, but not in the micropores. However, they also
pointed out that smaller reactants could enter the micropore and
showed higher activity due to the confinement effect. Note that
Fig. 4. CO2-TPD analysis of ZIF-8.

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X. Zhou et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 43–47
Fig. 6. Effect of reaction time on the yield of EMC with different amount of ZIF-8.
Fig. 8. Leaching test for ZIF-8 in the transesterification of DMC with DEC (ꢀ: with
ZIF-8; ᭹: reaction after removing ZIF-8 by filtration at 1 h). Reaction conditions:
DMC (9.000 g, 0.1 mol), DEC (11.800 g, 0.1 mol), ZIF-8 (0.208 g, 1 wt%) and 100 ◦C.
Reaction conditions: DMC (9.000 g, 0.1 mol), DEC (11.800 g, 0.1 mol) and 100 ◦C.
molecular size of DMC and DEC was much smaller than that of
vegetable oil.
the number of catalytic active center in the framework of ZIF-8 is
relatively high causing by the high surface area.
It is well known that all the reaction mixtures including DMC,
DEC and EMC can be used as solvent in a nonaqueous electrolyte.
According to practical requirement, the composition of reaction
mixture needs to be changed. As shown in Table 1, the composition
of reaction mixture (DMC, DEC and EMC) was changed remarkably
through adjusting the molar ratio of raw material (DMC and DEC)
from 1:2 to 2:1 (Entries 2, 8 and 9).
As shown in Fig. 6, the time of reaching reaction equilibrium
could be shortened from 4 h to less than 2 h increasing the amount
of ZIF-8 from 0.5% to 2%. In addition, it is worth noting that the
reaction time had no effect on the selectivity of EMC. And EMC
selectivity kept nearly 100% even if the reaction occurred contin-
uously after reaching equilibrium. The results revealed that ZIF-8
performed excellent catalytic activity and selectivity for the trans-
esterification of DMC with DEC.
For the transesterification of DMC with DEC, temperature has
remarkably effect on the reaction rate and the equilibrium yield.
So the effect of temperature on the yield of EMC was also stud-
ied, and the results were summarized in Fig. 7. The yield of EMC
increased from 5.5% to 50.7% with rising the reaction temperature
from 80 ◦C to 100 ◦C. Because the reaction reached the equilib-
rium under 100 ◦C, EMC yield had no viewable change with further
increasing temperature. It must be pointed out that the reflux
temperature of the reaction mixture is 102 ◦C under atmospheric
pressure. As a result, the reaction temperature could not over 102 ◦C
even though the oil bath temperature increased to 110 ◦C.
3.3. Effect of reaction conditions on the EMC yield
Effect of the amount of ZIF-8 on the yield of EMC was shown
in Fig. 6. The yield of EMC increased with increasing the amount
of ZIF-8 when it is lower than 2% (based on the total mass of raw
materials), and then kept almost constant with further increasing
the amount of ZIF-8. It must be pointed out that relatively high yield
of EMC (40.1%) was obtained even though in the presence of a small
amount of ZIF-8 (0.5%) within 3 h. One of the reasons may be that
Fig. 7. Effect of temperature on EMC yield. Reaction conditions: DMC (9.000 g,
0.1 mol), DEC (11.800 g, 0.1 mol), ZIF-8 (0.208 g, 1 wt%) and 3 h.
Fig. 9. Reusability of ZIF-8 for the synthesis of EMC. Reaction conditions: DMC
(9.000 g, 0.1 mol), DEC (11.800 g, 0.1 mol), ZIF-8 (0.104 g, 0.5 wt%), 100 ◦C and 3 h.

X. Zhou et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 43–47
47
3.5. Reusability test
The reusability of ZIF-8 was also examined, and the reusabil-
ity test was carried out with 0.5% ZIF-8 as catalyst at 100 ◦C in
3 h. After the completion of the reaction, the catalyst was filtered,
washed with ethanol, dried in oven, and used for the next time. As
shown in Fig. 9, ZIF-8 could be reused for the transesterification of
DMC with DEC in 3 runs without viewable change of its catalytic
activity, indicating that ZIF-8 performed well reusability. Fig. 10
shows the XRD pattern of the recovered catalyst matched well that
of the fresh one. And there was almost no difference in terms of IR
spectrum between the fresh and recovered ZIF-8 (Fig. 11). Above
results demonstrated that the framework of ZIF-8 was well retained
after being used 4 times in this reaction system.
4. Conclusion
The zeolitic imidazolate framework (ZIF-8) showed excellent
activity, selectivity and reusability for the synthesis of EMC from
DMC and DEC. Under optimal reaction conditions, high EMC yield
(50.7%) was obtained. After simple separation, ZIF-8 can be reused
at least 3 times without viewable loss of activity. Due to the excel-
lent catalytic property, easy preparation and low cost, ZIF-8 has the
potential application in the synthesis of EMC.
Fig. 10. XRD patterns of ZIF-8: (A) fresh and (B) reused.
Acknowledgment
This work was supported by Aid Program for Science and Tech-
nology Innovative Research Team of Shaoyang University.
References
[1] P. Tundo, F. Trotta, G. Moraglio, F. Ligorati, Ind. Eng. Chem. Res. 27 (1988) 1565.
[2] I. Zielinska-Nadolska, K. Warmuzinski, J. Richter, Catal. Today 114 (2006) 226.
[3] S.Z. Zhuo, G.L. Jiang, J.X. Zhen, Chinese J. Catal. 25 (2004) 171.
[4] H. Gan, M.J. Palazzo, E.S. Takeuchi, U.S. Patent 6,057,062, (2000).
[5] Z.L. Shen, X.Z. Jiang, W.J. Zhao, Catal. Lett. 91 (2003) 63.
[6] G.M. Zhao, J.H. Shi, G. Liu, Y. Liu, Z.L. Wang, W.X. Zhang, M.J. Jia, J. Mol. Catal. A:
Chem. 327 (2010) 32.
[7] A. Palani, N. Gokulakrishnan, M. Palanichamy, A. Pandurangan, Appl. Catal. A:
Gen. 304 (2006) 152.
[8] J.H. Shi, G. Liu, Z.Q. Fan, L.Y. Nie, Z.H. Zhang, W.X. Zhang, Q.S. Huo, W.F. Yan, M.J.
Jia, Catal. Commun. 12 (2011) 721.
[9] J.R. Long, O.M. Yaghi, Chem. Soc. Rev. 38 (2009) 1213.
[10] N. Stock, S. Biswas, Chem. Rev. 112 (2012) 933.
[11] H.C. Zhou, J.R. Long, O.M. Yaghi, Chem. Rev. 112 (2012) 673.
[12] S.Q. Ma, H.C. Zhou, Chem. Commun. 46 (2010) 44.
[13] M. Kurmoo, Chem. Soc. Rev. 38 (2009) 1353.
[14] L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P. Van Duyne, J.T. Hupp, Chem.
Commun. 112 (2012) 1105.
Fig. 11. FT-IR patterns of fresh and reused ZIF-8.
[15] P. Horcajada, R. Gref, T. Baati, P.K. Allan, G. Maurin, P. Couvreur, G. Ferey, R.E.
Morris, C. Serre, Chem. Commun. 112 (2012) 1232.
3.4. Leaching test
[16] J.Y. Lee, O.K. Farha, J. Roberts, K.A. Scheidt, S.T. Nguyen, J.T. Hupp, Chem. Soc.
Rev. 38 (2009) 1450.
[17] A. Corma, H. Garcia, F.X.L. Xamena, Chem. Rev. 110 (2010) 4606.
[18] M. Ranocchiari, J.A.V. Bokhoven, Phys. Chem. Chem. Phys. 13 (2011) 6388.
[19] Y.X. Zhou, J.L. Song, S.G. Liang, S.Q. Hu, H.Z. Liu, T. Jiang, B.X. Han, J. Mol. Catal.
A: Chem. 308 (2009) 68.
[20] S.S. Kaye, A. Dailly, O.M. Yaghi, J.R. Long, J. Am. Chem. Soc. 129 (2007) 14176.
[21] C. Chizallet, S. Lazare, D. Bazer-Bachi, F. Bonnier, V. Lecocq, E. Soyer, A.A.
Quoineaud, N. Bats, J. Am. Chem. Soc. 132 (2010) 12365.
[22] A. Phan, C.J. Doonan, F.J. Uribe-romo, C.B. Knobler, M. O’keeffe, O.M. Yaghi, Acc.
Chem. Res. 43 (2010) 58.
[23] X.C. Huang, Y.Y. Lin, J.P. Zhang, X.M. Chen, Angew Chem. Int. Ed. 45 (2006) 1557.
[24] K.S. Park, Z. Ni, A. Côté, J.Y. Choi, R. Huang, F.J. Uribe-romo, H.K. Chae, M. O’keeffe,
O.M. Yaghi, PNAS 103 (2006) 10186.
A hot leaching test was performed to investigate whether the
transesterification takes place homogeneously or heterogeneously,
and the result was summarized in Fig. 8. After removing the cat-
alyst by filtration at 1 h, the yield of EMC had almost no change
in the filtrated solution even prolonging the reaction time to 4 h.
It indicated that the ZIF-8 is a well-defined heterogeneous cat-
alyst for the transesterification of DMC with DEC. In addition,
the subsequent analysis of filtrate by ICP-AES showed that only
3 ppm of Zn content was leached, which is agree well with above
results.