Magnesium aluminum spinel as an acid-base catalyst for transesterification of diethyl carbonate with dimethyl carbonate

Article abstract of DOI:10.1007/s10562-014-1293-6

Mesoporous MgAl₂O₄ spinel (MAO), prepared via one-pot evaporation induced self-assembly strategy, was reported here as an acid-base bifunctionalization catalyst for the reaction for ethyl methyl carbonate from dimethyl carbonate and

Full text of DOI:10.1007/s10562-014-1293-6

Catal Lett
DOI 10.1007/s10562-014-1293-6
Magnesium Aluminum Spinel as an Acid–Base Catalyst
for Transesterification of Diethyl Carbonate with Dimethyl
Carbonate
Jun Wang
Jingcai Zhang
•
Lu Han
•
•
Shuping Wang
•
Yanzhao Yang
Received: 19 March 2014 / Accepted: 4 June 2014
Ó Springer Science+Business Media New York 2014
Abstract Mesoporous MgAl O spinel (MAO), prepared
2
of the effective processes is the esterification of chloro-
formate with ethanol in the presence of base catalyst [6].
However, this method is regarded not environmental
friendly because of the use of highly toxic regents. Another
route is the transesterification of dimethyl carbonate
(DMC) with EtOH [7–9]. The disadvantage of this method
is that three binary azeotropes (methanol-DMC, ethanol-
DMC and ethanol-EMC) are generated during the reaction
process, increasing the difficulty of separation.
4
via one-pot evaporation induced self-assembly strategy,
was reported here as an acid–base bifunctionalization cat-
alyst for the reaction for ethyl methyl carbonate from
dimethyl carbonate and diethyl carbonate. The physical/
chemical properties of MgAl O were characterized by
2
4
X-ray powder diffraction, N adsorption–desorption, tem-
2
perature programmed desorption and Fourier transform
infrared. The effects to the reaction by adjusting the cata-
lyst amount and reaction time were tested. The transeste-
rification induced by MAO is much faster, and meantime,
the thermal stability of MAO is much higher. Moreover,
the catalyst can be used directly after filtration without
drying and reused for at least five times with only 1.2 %
loss in catalytic activity.
In addition, EMC can also be synthesized by the
transesterification of DMC with diethyl carbonate (DEC)
[6, 10–17]. Zhen et al. [11] reported that Ti(OBu) and
4
Bu SnO are active homogeneous catalysts, but it is difficult
2
to separate the catalyst from the reaction mixtures. Lithium
diethyl amide and lithiated carbon were found to be able to
perform high activity for the reaction [6], however, the
high price greatly limits its wide application. MgO, known
as a typical solid base, was proved to be the most active
one among various metal oxide catalysts examined by Ji-
ang’s group [10] and performed well in the transformation
of the reactants either in a liquid phase or a vapor phase.
The highest yield of 44.2 % was obtained under the mod-
erate conditions. In a work reported by Y. Zhao and
coworkers [14], MOF-5, [Zn O(BDC) ] (BDC = benzene-
Keywords Heterogeneous Á Acid catalysis Á Base
catalysis Á Ethyl methyl carbonate Á Magnesium aluminum
spinel
1
Introduction
As the simplest asymmetrical carbonate, ethyl methyl
carbonate (EMC) is widely used as a co-solvent in a non-
aqueous electrolyte to promote the discharge capacity and
energy density of the lithium ion cells [1–5]. Various
methods have been reported for the synthesis of EMC. One
4
3
1,4-dicarboxylate), was found to show higher activity for
the reaction of DMC and DEC synthesizing EMC, and the
yield of 50.1 % was obtained under moderate conditions:
DMC, 1.802 g; DEC, 2.362 g; catalyst, 2 wt%; 100 °C;
3
h. Jia et al. [16] reported that DEC conversion of 47.7 %
was achieved with amorphous mesoporous aluminophos-
phate catalyst. In another work of his group [15], porous
carbon-supported MgO (MgO/NC-2) catalyst also shows
good activity for the reaction. Recently, Wang et al. [17]
discovered that a zeolitic imidazolate framework (ZIF-8)
[Zn(Melm)2] (Melm = 2-methylimidazole) shows an
J. Wang Á L. Han Á S. Wang Á J. Zhang Á Y. Yang (&)
Key Laboratory for Special Functional Aggregate Materials of
Education Ministry, School of Chemistry and Chemical
Engineering, Shandong University, Jinan 250100,
People’s Republic of China
e-mail: yzhyang@sdu.edu.cn
123

J. Wang et al.
efficient activity on the transesterification of DMC with
DEC under the optimum reaction conditions: DMC,
approximately 1.0 g (EO)20(PO)70(EO)20 triblock
copolymer (Pluronic P123) was dissolved in 20 mL abso-
lute ethanol under stirring. Then, 1.6 mL of 67 wt% nitric
acid, accompanied by 1.02 g aluminum isopropoxide
(C H AlO ) and 1.28 g magnesium nitrate hexahydrate
0
.1 mol, DEC, 0.1 mol, catalyst, 0.208 g, 100 °C and 3 h.
A relatively high EMC yield of 50.7 % was achieved after
reacting for 3 h. After filtering, washing with ethanol and
drying in oven, ZIF-8 could be reused for at least three
times without evident activity loss. However, exploring
much more active heterogeneous catalysts is still attractive
for the reaction under mild conditions.
9
21
3
were added (total amount of Mg and Al is 10 mmol) into
the above mixtures. After stirring for at least 5 h at room
temperature, the homogeneous sol was incubated in a
drying oven under 60 °C for 48 h to allow the solvent
evaporation. A white solid material (denoted as MAO-x,
where x is the mole ratio of Mg to Al according to the
mixture added in catalyst preparation process) was
obtained after calcination at 700 °C for 6 h in air. In order
to investigate the synergistic effect of Mg and Al, the
mesoporous alumina without Mg was facilely fabricated by
the same method as that of MgAl O .
MgO–Al O –SBA-15 catalyst, known as a kind of acid–
2
3
base bifunctional mesoporous material, was proved to
perform with a high yield (46 %) of EMC by Chen et al.
[
13]. Acid–base bifunctional mesoporous materials, which
combine specific chemical reactivity of the acid–base
materials and the long-term stability of the mesoporous
structure, have drawn great interests in their applications.
Acid–base bifunctionalization is a concept that explains the
roles of acid and base sites in the process of catalytic
reaction. As a solid catalyst, acid–base catalysts have
shown favorable advantages in many cases, such as
enhancing of the reaction velocity, prolonging of the cat-
alyst life and causing fewer disposal problems [13, 18, 19].
Recently in our work, we found that MgAl O spinel
2
4
For comparison, pure commercial MgO powder was
used after further treatment at 500 °C for 5 h in air.
2.3 Catalyst Characterization
The phase purity of the samples was determined by XRD
with a Bruker D8 advance X-ray diffractometer with Cu-
2
4
prepared by one-pot evaporation induced self-assembly
strategy performed an excellent catalytic activity for the
reaction of DMC with DEC. The reaction with this catalyst
could almost reach equilibrium after 30 min. In addition, as
a solid acid–base bifunctional catalyst, MgAl O spinel
K radiation (k = 0.15418 nm) in the 2h range from 10 to
a
70°. N adsorption–desorption isotherms were measured
2
with a Quadrasorb-SI apparatus at -196 °C. The specific
surface areas were calculated by the Brunauer–Emmett–
Teller (BET) method, and the pore size distribution was
calculated from the desorption branch using the Barett–
Joyner–Halenda theory. Temperature programmed
2
4
could be easily regenerated by drying in oven or reused
directly after filtration. Although the yield is 1 % lower in
our work compared with previous work (ZIF-8), the reac-
tion time of equilibrium is greatly shortened and the cat-
alyst can be reused continuously. The finding may promote
its industrial application in the synthesis of EMC.
desorption (TPD) was carried out using CO or ammonia
2
gas as probe molecules [16]. Typically, 50 mg portion of
each sample was calcined at 800 °C for 1 h, and then
-
1
cooled to 50 °C. Carbon dioxide (99.9 %, 20 mL min
)
-
1
or ammonia gas (99.9 %, 20 mL min ) was injected into
the stream, and the system was maintained at 50 °C for
30 min. After reaching saturation, the system was purged
with flowing Ar for 1 h at 50 °C, the sample was heated at
a rate of 10 °C min in Ar (40 mL min ), and the con-
centration change of the desorbed CO2 was monitored
using an online thermal conductivity detector.
2
Experiment
-
1
-1
2
.1 Chemical Reagents
Dimethyl carbonate (DMC [99 %) and diethyl carbonate
DEC [99 %) were purchased from Tianjin Guangfu Fine
(
Chemical Research Institute. (EO)20(PO)70(EO)20 triblock
copolymer (Pluronic P123) was purchased from Sigma-
Aldrich. All other chemicals were analytically pure and
purchased from Tianjin Kemiou Chemical Reagent Con-
ference. All reagents were used without further purification.
2.4 Catalytic Reaction
Transesterification of DEC with DMC was carried out as
follows: 4.5 g (0.05 mol) of DMC, 5.9 g (0.05 mol) of
DEC, and 5 wt% (based on the total mass of the reactants)
of catalyst were charged in a 100 ml one-neck flask,
equipped with a reflux condenser. Then the mixture was
heated up to 103 °C. The reaction products were analyzed
by a gas chromatography (GC-2014C) equipped with an
OV-17 capillary column and FID. In the experiment of
investigating the reusability of catalyst, catalyst was
2
.2 Preparation of the Catalyst
Mesoporous MgAl O composite metal oxides with dif-
2
4
ferent Mg/Al mole ratios were synthesized via a volatile
process as reported previously [20]. Typically,
1
23

Magnesium Aluminum Spinel as an Acid–Base Catalyst for Transesterification
Fig. 1 XRD patterns of different catalysts: a MgO, b MAO-1,
c MAO-1.5, d MAO-2, e MAO-3. 289 9 202 mm (300 9 300 DPI)
separated by filtration, dried in oven at 80 °C for 5 h, and
reused for the next time.
3
Results and Discussion
3
.1 Characterizations
The XRD patterns of different catalysts are shown in
Fig. 1. It is noticeable that sample MAO-2 exhibited typ-
ical diffraction lines ascribed to MgAl O spinel (JCPDS
Fig. 2 CO2-TPD (a) and NH3-TPD (b) patterns of catalysts calcined
at 700 °C. 282 9 376 mm (72 9 72 DPI)
2
4
2
1-1152) in the wide-angle XRD pattern [21, 22]. In order
to demonstrate the changes of the lattice after calcining the
mixture of C H AlO and Mg(NO ) wide-angle XRD
9
21
3
3 2
prepared materials. Figure 2 shows the TPD profiles of
different magnesium aluminum spinel catalysts. All the
MgAl O spinel catalysts only show a single desorption
pattern of pure MgO is also shown in Fig. 1. In addition,
the phaenomena that the intensities of diffraction peaks
gradually become weaker and the location of the main
diffraction peak moves towards lower two theta degree
with the increase of Mg was observed. The same results
were obtained in previous literatures [18, 23]. However,
when the mole ratio of Mg/Al is three, peaks of MgO and
MgAl O prove the coexistence of both phases in MAO-3,
2
4
peak, which means a single alkali type. As shown in
Fig. 2a, a desorption peak starts to appear lower than
200 °C and extends into a broad peak in the sample MAO-
0.5, which means it is weak alkaline on the surface. With
the increasing of Mg, position of peaks is apt to appear at
higher temperature, indicating the basicity of the catalysts
is enhanced. For example, a single peak starts to form from
around 220 °C in the MAO-2 sample, which suggests that
the medium base sites are located on the surface of the
catalyst. However, when the value of n(Mg)/n(Al) was
three, the catalyst tends to show weak basicity, which is
ascribed to the coexistence of MgO and MgAl O , which
2
4
indicating that Mg was over added. All these facts prove
that the new phase of MgAl O was fabricated in the
2
4
process of calcination at 700 °C for 5 h in air.
As is known, MgO is one of the most common solid
base catalysts, and Al O is a common-used solid acid
2
3
catalyst [24, 25]. A bifunctional material can be prepared
by grinding the precursors of them [13, 26]. In our work,
we found that the bifunctional materials can also be fab-
ricated by chemical mixing. CO -TPD and NH -TPD
2
4
was proved by CO -TPD test of pure MgO. A very broad
2
CO desorption peak extends from 150 to 400 °C, dem-
2
2
3
onstrating the coexistence of weak and medium basic sites
analyses were used to present the basicity and acidity of the
on the surface of MgO. In addition, Fig. 2b shows the
123

J. Wang et al.
Table 1 The structure parameters of mesoporous MAO-x (x = 0.5,
.5, 1, 2, 3)
Table 2 Transesterification of DMC with DEC in the presence of
different catalysts
1
a
a
Yield (%)
Samples
BET surface area
(
Mean pore size
(nm)
Pore vol.
-1
Entry
Catalyst
Time to reach
equilibrium (min)
2
m g
-1
3
(cm g
)
)
MgO
15
3.3
9.6
0.049
0.348
1.003
0.583
0.536
0.535
0.584
1
2
None
–
–
30
MAO-3
MAO-2
MAO-1.5
MAO-1
MAO-0.5
109
205
142
164
133
131
MAO-2
MOF-5
ZIF-8
49.0
50.1
50.7
44.6
48.9
48.7
b
3
12.5
12.3
12.2
12.4
12.5
180
180
120
30
c
4
5
6
7
MgO
MAO-1
MAO-1.5
Al O
2 3
30
a
Calculated by the BJH model on the desorption branch of the N
adsorption/desorption isotherms
2
Reaction conditions: DMC (0.05 mol), DEC (0.05 mol), catalyst
(0.5 g), 373 K and 30 min
a
Determined by GC, calculated in terms of DEC
b
Cited by literature [14], DMC (0.02 mol), DEC (0.02 mol),
MOF-5(1 wt%), 373 K and 3 h
NH -TPD patterns of different catalysts. The typical
3
c
Cited by literature [17], DMC (0.1 mol), DEC (0.1 mol), catalyst
0.208 g), 373 K and 3 h
streamed bread peaks are observed in all of the samples,
which suggest that the acid sites on the surface of the
magnesium aluminum spinel are not well-distributed [27].
The distribution temperature of desorption peaks indicates
(
Obviously, no catalytic activity could be observed in the
experiment without addition of catalyst, which is consistent
with previous articles [14, 16]. EMC yield of around
49.0 % (error bar \ 0.3 %) was obtained after adding
MAO-x (x = 1-2) catalyst and reacting for 30 min in our
work. Comparatively, both ZIF-8 and MOF-5 perform
higher activity in the total yield of products, but much more
reaction time will be needed. Jia et al. [15] also reported
that porous carbon-supported MgO catalyst (MgO/NC-2)
can obtain the EMC yield of 49.3 % after reaction for
30 min but a full recovery of the MgO/NC-2 catalyst
required a heat treatment under an argon atmosphere at
800 °C [16], while catalyst MAO-x (x = 1–2) can be
reused directly after a simple filtration. In addition, the
catalyst was fabricated by calcining at 700 °C, which also
indicates the higher thermal stability of the catalyst.
However, ZIF-8 was stable only under 400 °C according to
the DTA results given in Wang’s article [17]. Zhao et al.
[14] reported that the framework of MOF-5 was unstable
when exposed to air. It is noteworthy that the reaction
could take place without stirring because the catalyst has a
great number of big pores, which can contribute to the
formation of gasification center and prevent serious
bumping. Hence, catalyst MAO-x (x = 1–2) is a better
heterogeneous catalyst for the reaction.
the existence of weak acid sites on the catalyst. NH -TPD
3
of mesoporous alumina without Mg was also investigated.
The profile of Al O expresses coexistence of weak acidity
2
3
and strong acidity. Acid amount and base amount estimated
from the area of TPD profiles can be treated as a function
of catalytic activity. In this work, we concluded that the
basicity of all samples seems to be more important for
catalytic activity since acidity seems to be almost the same.
Furthermore, the structure parameters of MAO samples
were investigated by N adsorption–desorption measure-
2
ment and summarized in Table 1. Relatively higher spe-
2
-1
cific surface area (205 m g ) was obtained from MAO-2
material. It is worthy noticing that as the increase of Al
species, the BET surface area decreases dramatically, and
2
-1
the specific surface area of pure Al O was 131 m g
2
.
3
However, sample MAO-1.5 and MAO-3 show lower spe-
cific surface area, which is possibly due to the existence of
MgO. In order to prove this, the BET of pure MgO powder
was investigated and shown in Table 1 obtaining
2
-1
1
4.7 m g . The average pore size of MAO-x (x = 0.5–2)
is around 12 nm, which is the specific characteristic of
mesoporous (2–50 nm) materials [28]. In addition, pore
size of MAO-3 is 9.6 nm since there is more MgO phase in
MAO-3 (observed in Fig. 1). Comparing with the pore size
reported earlier [15], we believe that the pore size here
does not bring serious constraint of the diffusion of
reactants.
3.3 Effect of the Reaction Time
Figure 3 presents the effect of reaction time on the product
yield in the presence of different catalysts for the transe-
sterification. All the samples are active for the reaction
with excellent selectivity ([97 %) towards EMC. Among
the catalysts, the new prepared MAO-2 obviously performs
3
.2 Catalytic Performance
The activities of different catalysts for the reaction of DMC
with DEC to synthesize EMC are summarized in Table 2.
1
23

Magnesium Aluminum Spinel as an Acid–Base Catalyst for Transesterification
Fig. 3 Dependence of the EMC yield on the reaction time with
different catalysts. 289 9 202 mm (300 9 300 DPI)
Fig. 4 Effect of time of different catalyst (MAO-2) amount on the
yield of EMC, Reaction conditions:. n(DMC)/n(DEC) = 1,103 °C,
2
89 9 202 mm (300 9 300 DPI)
higher activity, and the EMC yield of 48.6 % was achieved
after reacting for 20 min. In addition, different activities of
MgAl O catalysts were obtained. While sample MAO-2,
prove that the interaction between acid and base sites on
the surface of the MAO-x (x = 1–2) materials play a
crucial role in the reaction.
2
4
MAO-1.5 and MAO-1 performed a quite similar catalytical
activity in consideration of 0.3 % of error bars for the
reaction, the equilibrium of the reaction was nearly reached
in 30 min, because medium base are better than other bases
for the reaction and higher specific area provides more
opportunity for the active sites contacting with reactants
3.4 Effect of the Catalyst Amount on EMC Yield
The effect of mass ratio of catalyst MAO-2 to reactant was
tested and shown in Fig. 4. Catalyst amount is ranged from
1.0 to 10.0 wt% based on the total reactant mixture. As
shown in Fig. 4, the yield of EMC still increases after
reacting for 30 min with a small amount of catalyst
(\2 %), which means the reaction needs more time to
reach the equilibrium. When the catalyst amount is higher
than 3 %, EMC yield has no obvious distinction as time
passes by, meaning that the reaction has reached equilib-
rium within 30 min. The result is ascribed to the expla-
nation that more catalyst means more active acid–base sites
for the reaction, and more catalyst amount (\5 %) will
shorten the time of reaching equilibrium [17, 29]. In
addition, at the optimal time (30 min), EMC yield increa-
ses with catalyst amount when it is lower than 5 %, and
keeps constant as the addition of the catalyst’s amount to
9 %. It is arresting that the maximum yield of small
amount of catalyst (1 %) is similar to that of higher amount
within 2 h, which is due to that the reaction is almost
reaching equilibrium after reacting for 2 h. Thus, the cat-
alyst MAO-2 performs well in catalyzing the reaction and
the optimize amount for the reaction is 5 %.
[
10]. The reason why MAO-x (x = 1–2) show similar
activity is that they are all medium base, and the base
2
-1
amount seems to be at the same level and 140 m g of
specific surface area is enough for active sites contacting
with reactants in a short time. However, the solid MAO-0.5
and MAO-3 materials did not show any effective activity
for the reaction in a short time, which could be mainly
ascribed to the lower basicity (Fig. 2). But after 2 h, the
yield of nearly 47 % was obtained, which is maybe due to
the reaction almost reaches the equilibrium within 2 h in
the presence of the catalyst.
However, commercial MgO powder displays much
lower activity in a short reaction time, which maybe due to
the much lower surface area of MgO than MAO-x,
affecting the interaction between active sites and reactants.
The highest yield (44.6 %) of ethyl methyl carbonate was
obtained at 103 °C over commercial MgO powder catalyst
after 2 h. The yield is close to that (44.2 %) reported earlier
[
16]. Obviously, new prepared MAO-x (x = 1–2) solid
catalyst is much more active than sample MgO powder.
The activity of mesoporous Al O without Mg was also
2
3
tested to prove the coaction effect. Yield of 36.7 % (not
present in Fig. 3) was obtained after 2 h, which demon-
strates that acid sites are also active for the reaction and
shows lower activity than pure MgO. All these facts above
3.5 Catalyst Recycling
The reusability of the catalyst is considered as another
important property of catalyst. In this work, regeneration
123

J. Wang et al.
Fig. 5 FT-IR spectra of fresh MAO-2 and reused. 289 9 202 mm
300 9 300 DPI)
(
of sample MAO-2 was also examined. After 30 min of
reaction at 103 °C, the solid catalyst was filtered. After
drying in oven at 80 °C for 5 h, the catalyst was reused
for the next time. The recycle was repeated five times and
only 1.2 % yield decrease was found. Favourably, after
literaton, the catalyst can be used directly without drying
and the activity had no significant change compared with
the dried one, which is preferable for the future industrial
applications. We also examined the fresh and reused
catalyst by FT-IR (Fig. 5). According to previous work
-
1
[
30] the absorption band at 1,639 cm is attributed to
free water. The lower peak of reused catalyst is ascribed
to the loss of free water due to the side reaction of
Fig. 6 CO -TPD and NH -TPD profiles of fresh sample MAO-2 and
2
reused. 259 9 400 mm (72 9 72 DPI)
3
-
1
reactants with water. Peak at around 1,100 cm is rela-
ted to C–O bonds [31]. This is due to the chemical
absorption of diethyl carbonate and dimethyl carbonate
during the reaction. Whilst the observed peaks at around
4
Conclusion
-
1
6
98 and 520 cm are corresponded to [AlO ] groups and
6
Mg–O stretching. This indicates the formation of
MgAL O and no structure changes in the used catalyst.
MAO-x (x = 1–2), a highly effective acid–base bifunc-
tionalization mesoporous catalyst was prepared for the
transesterification of DMC with DEC to synthesize EMC.
High ethyl methyl carbonate yield (49.0 %) with the
reaction time of 30 min and excellent selectivity was
achieved under optimal conditions. As a heterogeneous
catalyst, MAO-x (x = 1–2) can be regenerated easily by
simply drying in oven and reused for at least five times
with 1.2 % decrease in catalytic activity. In addition, cat-
alyst can be used continuously after filtration, which
greatly promotes the industrial applications.
2
4
In addition, TPD analyses of fresh and used catalyst was
used to demonstrate the stability of acid–base sites. As
shown in Fig. 6 CO -TPD, the used catalyst still dem-
2
onstrates a medium base, and base amount decreases
slightly for reused catalyst, which may be the reason of
the slight activity loss. From NH -TPD profiles, we can
3
conclude that the acid amount of the two catalyst seem to
be same. Hence, the TPD analyses prove that the regen-
eration of used catalyst after filtration and drying in oven
at 80 °C for 5 h. All the results demonstrate that the
catalyst performs excellent reusability for the transesteri-
fication under the above-mentioned conditions.
Acknowledgments This work was supported by the Natural Sci-
ence Foundation of China (Grant No. 21276142).
1
23

Magnesium Aluminum Spinel as an Acid–Base Catalyst for Transesterification
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