Amorphous mesoporous aluminophosphate as highly efficient heterogeneous catalysts for transesterification of diethyl carbonate with dimethyl carbonate

Article abstract of DOI:10.1016/j.catcom.2011.01.002

The catalytic performance of an amorphous mesoporous aluminophosphate (AlPO) was investigated for the transesterification of diethyl carbonate (DEC) with dimethyl carbonate (DMC) to synthesize ethyl methyl carbonate (EMC). Compared with other solid acid a

Full text of DOI:10.1016/j.catcom.2011.01.002

Catalysis Communications 12 (2011) 721–725
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Catalysis Communications
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Short Communication
Amorphous mesoporous aluminophosphate as highly efficient heterogeneous
catalysts for transesterification of diethyl carbonate with dimethyl carbonate
a
a
b
a
a
a
b
Jinghui Shi , Gang Liu , Zhiqiang Fan , Liying Nie , Zhihui Zhang , Wenxiang Zhang , Qisheng Huo ,
b
a,
Wenfu Yan , Mingjun Jia ⁎
a
State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, Changchun 130023, China
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 October 2010
Received in revised form 28 December 2010
Accepted 4 January 2011
Available online 8 January 2011
The catalytic performance of an amorphous mesoporous aluminophosphate (AlPO) was investigated for the
transesterification of diethyl carbonate (DEC) with dimethyl carbonate (DMC) to synthesize ethyl methyl
carbonate (EMC). Compared with other solid acid and/or base catalysts, the mesoporous AlPO showed
remarkably high activity, stability and recoverability for the reaction. We proposed that the presence of
suitable weak acid–base pairs on the surface of the mesoporous AlPO material should play a critical role in the
activation of reactants to produce EMC.
Keywords:
©
2011 Elsevier B.V. All rights reserved.
Amorphous mesoporous aluminophosphate
Transesterification
Ethyl methyl carbonate
1
. Introduction
catalysts are quite expensive, thus limiting their application. Shen et
al. [9] investigated the catalytic properties of several kinds of solid
basic catalysts, and found that MgO is the most active catalyst. Chen
et al. [11] reported that a kind of acid–base bifunctional mesoporous
Recently, interest on developing novel and efficient ways to
synthesize ethyl methyl carbonate (EMC) is growing since EMC can be
utilized as a cosolvent in a nonaqueous electrolyte to improve the
performance of the alkali metal ion cells [1–3]. Traditionally, EMC is
synthesized by the esterification of methyl chloroformate with
alcohol over base catalyst [4]. However, this route is not environ-
mentally benign since methyl chloroformate is highly toxic. Another
route to synthesize EMC is the transesterification of dimethyl
carbonate (DMC) with ethanol [5–7]. However, the formation of
three binary azeotropes during the reaction course brings a serious
difficulty in the separation.
Alternatively, EMC can also be obtained by the transesterification
of diethyl carbonate (DEC) with DMC. The main advantage of this
approach is that the separation step after the reaction (to purify
product) could be avoided since all the reaction mixtures (including
DEC and DMC) can be used directly as solvent in a nonaqueous
2 3
material, i.e., MgO–Al O –SBA-15, exhibits a moderate activity for
the synthesis of EMC. In another work reported by Palani et al. [10],
they found that Al–MCM-41 and Al–Zn–MCM-41 are active catalysts
in the vapour-phase transesterification reaction of DEC with DMC.
However, rapid deactivation could be observed due to the coke
formation. In addition, metal–organic frameworks (MOFs) (Zn
4
O
(BDC) ) [12] could also be used as an active solid acid catalyst for the
3
transesterification of DEC with DMC. Relatively high yield of EMC
was achieved. MOFs could be recovered by drying under vacuum and
were reused three times with a slight decrease in its catalytic
activity. Currently, it is still an attractive subject to search and to
develop highly active, stable and easily recycled heterogeneous
catalysts under mild conditions for the transesterification of DEC
with DMC.
electrolyte [8–10]. For this process, compounds such as Ti(OBu)
4
and
Very recently, our group reported that carbon-supported MgO
materials (MgO/NC-2) [13] prepared by a wet impregnation tech-
nique, exhibit high activity in the transesterification reaction and the
used catalyst can be recycled after heating activation at high
temperature. Herein, the catalytic performance of a kind of mesopor-
ous aluminophosphate (AlPO), prepared by using the so-called citric
acid route [14–16], was investigated for the transesterification of DEC
with DMC in comparison with other solid acid and/or base catalysts. It
was found that mesoporous AlPO shows very high activity and
stability, and can be easily recycled without any special treatment
(e.g., heat-activation) on the used catalyst.
Bu SnO were found to be active homogeneous catalysts. However,
2
the separation of the homogeneous catalysts from the reaction
system is quite difficult [8]. Besides, several heterogeneous catalyst
systems have also been investigated [4,9,10]. For example, Gan et al.
[
4] reported that lithium diethylamide and lithiated carbon are
active heterogeneous catalysts for the reaction. However, these
⁎
Corresponding author. Tel.: +86 431 85155390; fax: +86 431 8499140.
E-mail address: jiamj@jlu.edu.cn (M. Jia).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.01.002

722
J. Shi et al. / Catalysis Communications 12 (2011) 721–725
2
. Experimental
5
4
3
2
1
0
0
0
0
0
2
.1. Catalyst preparation
The amorphous mesoporous AlPO was prepared as described
previously [14–16]. Typically, H
aqueous solution of Al(NO ·9H
temperature, leading to composition in molar ratio of
.0:1.0:1.0:0.86=Al(NO /CA/H PO /H O. After that, an aqueous
3
PO
4
(85%) is dropped into a mixed
3
)
3
2
O and citric acid (CA) at ambient
a
1
3
)
3
3
4
2
ammonia (10 wt.%) solution was added dropwise until pH=5.0. The
mixture was heated at 363 K in air and then the resulting white solid
was calcined at 873 K.
0
0
20
40
60
80 100 120
A reference sample of the MgO powder was prepared by a
precipitation method using Mg(NO
NH OH (30%, 100 mL) was added dropwise to a solution of Mg
NO ·6H O (50 g) in 80 mL of distilled water under stirring at
13 K. Magnesium hydroxide was precipitated and digested in the
mother liquor at 333 K for 4 h. The precipitate was washed with
distilled water, and then calcinated at 873 K for 2 h in argon.
AlPO-5 was synthesized by the standard gel route in which
aluminum isopropoxide, phosphoric acid, triethylamine (TEA) and
3
)
2
and NH
4
OH [9]. A solution of
Reaction time (min)
4
Fig. 1. Dependence of the DEC conversion on the reaction time with different catalysts:
■) blank; (●) P ; (▲) AlPO-5; (▼) Al ; (◆) MgO; and (◄) AlPO. Reaction conditions:
catalyst 0.5 g, DMC 0.05 mol, DMC/DEC=1, and reaction temperature 366 K.
(
3
3
)
2
2
(
O
2 5
2 3
O
2 3 2 5
activity decreases in the order: AlPONMgONAl O NAlPO-5NP O .
Previously, Shen et al. [9] have reported that MgO is one of the most
active catalysts for the transesterification of DEC with DMC. Our
results clearly show here that the mesoporous AlPO catalyst is even
more active than the MgO catalyst.
distilled water were mixed. The molar ratio was Al
O=1:1:1:1:40. P (Beijing Chemical Works) and Al
Chemical Works) were commercial samples.
2
O
3
/P
2
O
5
/TEA/
H
2
O
2 5
2 3
O (Beijing
The effect of the reaction temperature on the transesterification
activity of the mesoporous AlPO catalyst was also investigated (Fig. 2).
It was found that the conversion of DEC decreased with the decrease
of the reaction temperature. However, the AlPO catalyst is still very
active even at the reaction temperature of 336 K, a 43.8% conversion
of DEC could be obtained after 2 h reaction. These results suggest that
the mesoporous AlPO catalyst possesses very good activity under mild
reaction conditions.
A hot leaching test (typically half way through every reaction in
which the materials were tested) was performed to study whether the
reaction takes place homogeneously or heterogeneously (Fig. 3).
There is almost no detectable subsequent conversion in the filtrated
solution at the reaction temperature, suggesting that the mesoporous
AlPO catalyst behaves in a truly heterogeneous manner in the
transesterification reaction.
In addition, the mesoporous AlPO material can be reused after
being quantitatively recovered by simple centrifugation. The catalytic
activity decreases slightly with the increase of recycle time, which
might be attributed to the adsorption of a small amount of reactants
and/or products on the surface of the AlPO catalyst (Fig. 4). In a recent
work reported by our group [13], we found that carbon supported
MgO catalyst (MgO/NC-2) is also quite active and reusable for the
2
.2. Catalyst characterization
N
2
adsorption–desorption isotherms were measured at 77 K, using
a Micromeritics ASAP 2010N analyzer. Pore volumes were estimated
at a relative pressure of 0.94 (P/P ), assuming full surface saturation
with nitrogen. Pore size distributions were evaluated from desorption
branches of nitrogen isotherms using the BJH model.
0
Temperature-programmed desorption (TPD) was carried out
using CO
5
6
2
or NH
0 mg of fresh sample was first calcined at 873 K under Ar stream for
0 min and then cooled to 323 K. Carbon dioxide (99.99%) or
3
as probe molecules. In a standard procedure,
ammonia (99.99%) was injected into the stream until saturation was
reached, and the system was maintained at 323 K for 30 min. After the
system was purged with flowing Ar for 1 h at 323 K, the sample was
heated at a rate of 10 K min
concentration change of the desorbed CO
using an online thermal conductivity detector (TCD).
−
1
in He (30 mL/min), and the
2
or NH was monitored
3
2
.3. Catalyst tests
The liquid-phase transesterification of DEC with DMC was carried
out as follows: 5.9 g (0.05 mol) of DEC, 4.5 g (0.05 mol) of DMC and
.5 g of the catalyst were charged to a 50-mL two-neck flask. Then the
0
mixture was heated up to 366 K with stirring to start the reaction. The
reaction products were analyzed by gas chromatography (GC-8A)
equipped with an HP-5 capillary column and FID.
50
4
3
2
1
0
0
0
0
3
. Results and discussion
3
.1. Catalytic performance
Fig. 1 shows the catalytic performance of the mesoporous AlPO and
other solid catalysts for the transesterification of DEC with DMC. It
should be mentioned first that a blank test (without addition of
catalyst) was also carried out, and no obvious activity could be
observed under the identical reaction condition.
0
0
20
40
60
80 100 120
In the presence of the above solid catalysts, the transesterification
reaction could occur with nearly 100% selectivity to EMC. Among
them, the mesoporous AlPO exhibited the highest activity, and a 47.7%
conversion of DEC was achieved after 0.5 h reaction, which is very
near from the equilibrium conversion of the reaction. The catalytic
Reaction time (min)
Fig. 2. Dependence of the DEC conversion on the reaction time of the AlPO catalysts
with different reaction temperatures: (■) 336 K; (●) 353 K; and (▲) 366 K. Reaction
conditions: catalyst 0.5 g, DMC 0.05 mol, and DMC/DEC=1.

J. Shi et al. / Catalysis Communications 12 (2011) 721–725
723
5
4
3
2
1
00
00
00
00
00
5
4
3
2
1
0
0
0
0
0
0
A
1
0
.4
.7
0.0
5
10
15
dP/nm
0
.0
0.2
0.4
0.6
0.8
1.0
0
60 120 180 240 300 360
P/P0
Reaction time (min)
Fig. 3. Heterogeneous reaction check for AlPO (□) and continuation of the reaction after
removing the catalysts by filtration (∇). Reaction conditions: catalyst 0.25 g, DMC
150
B
2
40
20
0
0.05 mol, DMC/DEC=1, and reaction temperature 366 K.
1
20
90
1
transesterification of DEC with DMC to EMC. However, a heat-
treatment (under an argon atmosphere at 1073 K) of the used catalyst
is required in order to fully recover the catalytic activity of the MgO/
NC-2 catalyst. Hence, it can be concluded that the mesoporous AlPO
catalyst possesses much better recoverability compared with the
carbon supported MgO catalyst.
0.6
1.2
1.8
dP/nm
6
3
0
0
3
.2. Catalyst characterization
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
N
2
adsorption–desorption isotherms of mesoporous AlPO and
microporous AlPO-5 materials are shown in Fig. 5. The AlPO and AlPO-
samples present type IV and type II isotherms (definition by IUPAC),
Fig. 5. N
2
adsorption–desorption isotherms and pore size distribution (inset) at 77 K of
(A) the mesoporous AlPO and (B) the microporous AlPO-5.
5
which are characteristic of mesoporous and microporous materials,
respectively.
p p
where, R is the semidiameter of the particles; ρ is the particle
In general, relatively narrow pore size (e.g., for microporous
materials) may bring serious constraint of the diffusion of reactants,
thus decreasing the reaction rate of the catalyst. Some addition
experiments and calculations were carried out in order to prove
whether the relatively low reactivity in the small pore AlPO-5 is
diffusion limited.
It was well known that the Weisz–Prater modulus [17] can be used
to demonstrate that the pore diffusion is not important when the
following inequality holds:
density; γA,app is the rate of reaction; and DA,eff is the effective
diffusivity.
The effective diffusion coefficient (DA,eff) is obtained from the
molecular diffusion coefficient (DAB), the catalyst particle porosity (ε
and tortuosity (τ ):
p
)
p
!
εp
DA;eff = DAB
:
ð2Þ
τp
In the present investigation in which the microporous AlPO-5 is
the catalyst and DEC is the representative reagent (A), the average
values for τ and ε can be assumed as 5 and 0.35, respectively on the
2
R ρ r
p
p
A;app
Cwp
=
b1
ð1Þ
DA;eff CA;s
p
p
basis of related literature [18–20]; and the diffusion coefficient DAB is
−
5
2 −1
estimated to be 3.8×10 cm s according to a reference method
−6
−1 −1
5
4
3
2
1
0
[21]; γA,app and CA,S are determined to be 9.2×10 mol s
g
cat
−1
and 5 mol L , respectively, from the initial reaction rate (calculated
from the reaction kinetic results); R is 15 μm according to SEM
is 1.1 g cm for the AlPO-5 catalyst. Substitu-
tion of the above quantities in equation, yielded the result of
Cwp=1.7×10 . This value is much lower than 1, indicating that
the pore diffusion limitation is not important (or can be neglected) for
the transesterification reaction of DEC with DMC on the microporous
AlPO-5 catalyst.
0
0
0
0
0
p
−3
measurement, and ρ
p
−3
Moreover, the acidity and basicity of various materials are
determined by means of CO
patterns of various samples are presented in Fig. 6A. Pure MgO
shows a very broad CO desorption peak, extended from 353 to 823 K,
which could be assigned to the existence of weak and medium basic
sites. Al , AlPO-5 and mesoporous AlPO materials show a broad
2 3 2
-TPD and NH -TPD. The CO -TPD
0
20
40
60
80 100 120
2
Reaction time (min)
2 3
O
Fig. 4. Transesterification activities of AlPO during three reaction cycles: (■) 1st;
●) 2nd; and (▲) 3rd. Reaction conditions: catalyst 0.5 g, DMC 0.05 mol, DMC/DEC=1,
and reaction temperature 366 K.
desorption peak at relatively low temperature, implying the existence
of a certain amount of weak basic sites.
(

724
J. Shi et al. / Catalysis Communications 12 (2011) 721–725
relatively large numbers of weak acid sites on the surface of the
material [15].
A
d
Previously, Shen et al. [9] have proposed a mechanism about the
dissociative adsorption of DMC on the surface of the MgO catalyst to
yield the methoxide ion species firstly, which could attack the
carbon atom of the carbonyl group of DEC subsequently. The main
product EMC could be formed after the removal of the ethoxide ion
species from the intermediate. In another work reported by Zhou
et al. [12], they proposed a similar mechanism concerning the
c
b
a
4 3
transesterification reaction over the MOF (Zn O(BDC) ) catalyst, in
which the reagents (DEC and/or DMC) could be chemisorbed on the
Lewis acid site of MOFs. In our case, it was known that the
mesoporous AlPO catalyst contains a relatively large amount of
weak acid and base sites, which may exist in the form of neighboring
acid–base pairs on the surface of the mesoporous AlPO. Hence, it
should be reasonable to assume that there might be a relationship
between these acid–base pairs and the high catalytic activity of the
mesoporous AlPO catalysts. Thus a mechanism for the transester-
ification of DMC with DEC catalyzed by AlPO materials may be
proposed as shown in Scheme 1. First, chemisorption of DEC and
DMC could occur on the neighboring acid–base pairs simultaneously
4
00
500
600
700
800
Temperature (K)
B
c
(
step 1). Then the two adjacent chemisorbed species (e.g.,
b
a
+
−
COOC
2 5 3
H and CH O ) react directly to form EMC that desorbs
easily (step 2).
4
00
500
600
700
800
4
. Conclusions
The mesoporous AlPO material, prepared using the citrate acid
Temperature (K)
Fig. 6. CO
2
3 2 3
-TPD (A) and NH -TPD (B) patterns of catalysts calcined at 873 K. (a) Al O ,
route, is an efficient heterogeneous catalyst for EMC production by the
transesterification of DEC with DMC. The presence of abundant weak
acid–base pairs on the surface of the mesoporous AlPO material
should play a critical role on the activation of the reactants in the
transesterification reaction. Further detailed investigations are in
progress in order to clarify the correlation of the physicochemical
properties with the catalytic performance of the mesoporous AlPO
materials.
(b) AlPO-5, (c) AlPO, and (d) MgO.
NH
are shown in Fig. 6B. The desorption patterns of all the samples show
similar shapes, with a broad NH desorption peak centered at about
25–450 K, which indicates the presence of weak acid sites. Compared
with Al and AlPO-5 samples, the mesoporous AlPO material
3 2 3
-TPD profiles of Al O , AlPO-5 and mesoporous AlPO materials
3
4
2 3
O
contains a larger amount of acid sites. According to the related
literatures [22–24], it was known that the acidity of the AlPO-5
originates from either Lewis acid sites or terminal P–OH groups, and
the amount of acid sites in this microporous material is rather low due
to its relatively high crystallinity. On the other hand, the mesoporous
AlPO used in this work is amorphous essentially, and there are many
structural defects in the material, thus resulting in the formation of
Acknowledgements
This work is supported by the Development Project of Science and
Technology of Jilin Province (20070115), and the National Natural
Science Foundation of China (20773050 and 21003059).
Scheme 1. Possible mechanism of transesterification of DMC with DEC on the AlPO catalyst.

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