Efficient porous carbon-supported MgO catalysts for the transesterification of dimethyl carbonate with diethyl carbonate

Article abstract of DOI:10.1016/j.molcata.2010.05.007

Well-dispersed carbon-supported MgO catalysts were prepared using a kind of porous carbon (NC-2) as support and magnesium nitrate solution as MgO precursor by a simple wet impregnation technique. Various characterization techniques, including XRD, N2 sorption, DRIFT, XPS and TPD, were carried out to investigate their physical-chemical properties, the states of MgO species and the interaction between MgO and NC-2 materials. The catalytic properties of MgO/NC-2 catalysts were investigated in the liquid-phase transesterification of dimethyl carbonate (DMC) with diethyl carbonate (DEC). Compared with other kinds of carbon-supported MgO catalysts, MgO/NC-2 shows remarkably higher activity for the formation of ethyl methyl carbonate (EMC). Moreover, the NC-2 supported catalyst possesses very high stability against leaching of active species under test reaction conditions, indicating the truly heterogeneous nature of this catalyst. The presence of relatively rich oxygen-containing surface groups on the NC-2 carbon support should be in favor of the high dispersion of MgO particles, thus being beneficial to the fabrication of active and stable heterogeneous catalysts for the transesterificaiton reaction.

Full text of DOI:10.1016/j.molcata.2010.05.007

Journal of Molecular Catalysis A: Chemical 327 (2010) 32–37
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Efficient porous carbon-supported MgO catalysts for the transesterification of
dimethyl carbonate with diethyl carbonate
Guoming Zhaoa,b, Jinghui Shia, Gang Liua,∗, Yan Liua, Zhenlu Wanga, Wenxiang Zhanga, Mingjun Jiaa,∗
a State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, Changchun 130023, China
b Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Well-dispersed carbon-supported MgO catalysts were prepared using a kind of porous carbon (NC-2)
as support and magnesium nitrate solution as MgO precursor by a simple wet impregnation technique.
Various characterization techniques, including XRD, N2 sorption, DRIFT, XPS and TPD, were carried out
to investigate their physical–chemical properties, the states of MgO species and the interaction between
MgO and NC-2 materials. The catalytic properties of MgO/NC-2 catalysts were investigated in the liquid-
phase transesterification of dimethyl carbonate (DMC) with diethyl carbonate (DEC). Compared with
other kinds of carbon-supported MgO catalysts, MgO/NC-2 shows remarkably higher activity for the for-
mation of ethyl methyl carbonate (EMC). Moreover, the NC-2 supported catalyst possesses very high
stability against leaching of active species under test reaction conditions, indicating the truly heteroge-
neous nature of this catalyst. The presence of relatively rich oxygen-containing surface groups on the
NC-2 carbon support should be in favor of the high dispersion of MgO particles, thus being beneficial to
the fabrication of active and stable heterogeneous catalysts for the transesterificaiton reaction.
© 2010 Elsevier B.V. All rights reserved.
Received 11 March 2010
Received in revised form 12 May 2010
Accepted 14 May 2010
Available online 11 June 2010
Keywords:
Magnesium oxide
Porous carbon
Transesterification
Ethyl methyl carbonate
1. Introduction
and shaping these materials to strong catalyst particles is cumber-
some. Taking these aspects into account, it is still an interesting
As a typical solid base, magnesium oxide (MgO) has been widely
used as active catalyst or catalyst support in a variety of organic
reactions, such as transesterification [1], dehydrogenation of alco-
hol [2], aldol condensation [3–6], isomerization of alkenes [7,8], and
cycloaddition of CO2 to epoxides [9].
subject to develop simple and efficient method for synthesizing
MgO-based materials with advantage features.
In a work reported by Zhu and co-workers, they found that
MgO-coated mesoporous SBA-15 material with relatively strong
basicity could be synthesized by direct adding magnesium acetate
into the initial mixture for the synthesis of mesoporous SBA-15
[17]. This result suggested that MgO supported materials with
desirable characteristics may be obtained by selecting suitable sup-
port and synthesis strategy. Compared with conventional supports
of silica and alumina, carbon is another kind of important sup-
port for the preparation of supported catalysts. In general, carbon
structure is resistant to acidic or basic media, and the interac-
tion between carbon and active phase is weak and the behavior of
the catalyst will basically governed by the chemical nature of the
active phase [18]. Recently, the rapid development in the synthe-
sis of nanostructured carbon materials (e.g., mesoporous carbon,
carbon nanofibers, carbon nanotubes) provides numerous oppor-
tunities for the preparation of novel supported metal and metal
oxide catalysts [19–21]. For example, bimetallic Pt–Ru nanoparti-
cles supported mesoporous carbon, in which the carbon support
were synthesized using mesoporous SBA-15 as the hard template,
exhibited excellent electrocatalytic performance and long-term
durability for the application in direct methanol fuel cell [22].
Mg–Al hydrotalcites were precipitated in the porous carbon bodies
Conventionally, MgO catalysts could be easily obtained by the
thermal decomposition of magnesium hydroxide or carbonate [10].
However, the resultant MgO catalysts usually exhibit some dis-
advantageous, like small specific surface areas, inhomogeneous
morphologies, and varied grain size, which are considerably limited
their application [11]. Hence, much effort has been devoted to syn-
thesize novel MgO-based materials with desirable characteristics
(e.g., high specific surface area, nanostructure and/or mesoporous
porosity). For instance, nanoscale MgO materials with high specific
surface area have been synthesized by sol–gel methods combin-
ing a hypercritical drying procedure [12–15]. MgO cubes with
controllable particle size could be obtained by chemical vapor
deposition method [16]. However, these approaches appear to be
rather expensive and complex for conventional catalytic applica-
tions. Furthermore, mechanical strength of MgO itself is rather low,
∗
Corresponding authors. Tel.: +86 431 85155390; fax: +86 431 8499140.
E-mail addresses: lgang@jlu.edu.cn (G. Liu), jiamj@jlu.edu.cn (M. Jia).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.05.007

G. Zhao et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 32–37
33
by consecutive impregnation of the reactants and an aging step, and
exhibited very high catalytic activity for the condensation reaction
[23,24].
at 1073 K for 6 h under an argon flow. The loading of MgO was in
the range of 1.6–20.0 wt.%.
For comparison, SBA-15 supported MgO catalyst (with 4.0 wt.%
MgO loading) was prepared using the above procedure. To have
basic sites exposed on the surface, pretreatment at relatively high
temperature was required under inert atmosphere [31]. The cata-
lyst was calcined at 1073 K for 2 h in argon before it was used in the
transesterification reaction.
Very recently, our groups reported a simple and efficient route
for the synthesis of porous carbon (denoted as NC-2) with meso-
porous and/or microporous characteristics by carbonizing a kind
of composite (CA-SU/AlPO) containing citric acid (CA), sucrose (SU)
and aluminum phosphate [25]. We found this material possesses
abundant surface oxygen-functional groups and could be directly
used as active and recyclable catalysts for the aerobic oxidation of
benzyl alcohol [26].
2.2. Catalytic performance
The typical liquid-phase transesterification of DMC with DEC
was carried out as follows: 4.5 g (0.05 mol) of dimethyl carbonate,
5.9 g (0.05 mol) of diethyl carbonate and 0.5 g of the catalyst were
charged to a 50-mL one-neck flask. Then the mixture was heated up
to 376 K with stirring under N2 atmosphere to start the reaction. The
reaction products were analyzed by a gas chromatography (GC-8A)
equipped with an HP-5 capillary column and FID.
Herein, we attempted to fabricate carbon-supported MgO
nanocomposites using NC-2 carbon material as support and mag-
nesium nitrate as MgO precursor through a wet impregnation
method. The catalytic properties of these materials were investi-
gated in the liquid-phase transesterification of dimethyl carbonate
(DMC) with diethyl carbonate (DEC), which is an important base-
catalytic reaction for the synthesis of ethyl methyl carbonate (EMC,
an important cosolvent in a nonaqueous electrolyte) [27–29]. Pre-
viously, it was reported that solid base of MgO is one of the most
active catalysts for this reaction [30]. In the present work, we found
that the resultant MgO/NC-2 catalysts exhibit remarkably higher
transesterification activity than other carbon-supported MgO cat-
alysts. Combining a variety of characterization results, the catalytic
property of MgO/NC-2 was correlated with the surface chemistry
of the carbon materials.
2.3. Characterization
N2 adsorption/desorption isotherms were measured at 77 K,
using
a Micromeritics ASAP 2010N analyzer. Samples were
degassed at 523 K for 8 h before measurements. Specific surface
areas were calculated using the BET model. Pore volumes were esti-
mated at a relative pressure of 0.94 (P/P0), assuming full surface
saturation with nitrogen. Pore size distributions were evaluated
from desorption branches of nitrogen isotherms using the BJH
model.
2. Experimental
Powder XRD diffraction patterns were recorded on Shimadzu
XRD-6000 diffractometer (40 kV, 30 mA) using Ni-filtered Cu K␣
radiation.
2.1. Catalysts preparation
DRIFT spectra were recorded on a Nicolet AVATAR 370 DTGS
spectrometer. After drying in air at 393 K, the carbon samples were
mounted on the sample holder of the DRIFT attachment. The DRIFT
spectrum of each sample was recorded from 256 scans at a resolu-
Porous carbon (NC-2) support was prepared by direct car-
bonizing a composite (CA-SU/AlPO) containing citric acid (CA)
and aluminum phosphate as reported previously [25]. Typically,
H3PO4 (85 wt.%) was dropped into a mixed aqueous solution of
Al(NO3)3·9H2O, sucrose (SU) and CA under vigorous stirring at
ambient temperature, leading to a composition in molar ratio of
SU/CA/P/Al = 1.0/0.5/1.0/1.0. Then an aqueous ammonia solution
(10 wt.%) was used to adjust the pH value of the solution to 5.0.
The solid CA-SU/AlPO composite was formed after removing water
and all other volatiles by heating the mixed solution at 363 K for
10 h. After that, the CA-SU/AlPO composite was pretreated at 573 K
in open air for a few minutes, then carbonization of the compos-
ite was carried out at 1073 K for 6 h under an argon flow. The black
carbonized composite was treated with 4 M HNO3 solution at 323 K
to remove AlPO component, and is filtered and dried at 383 K to
obtain the resulting NC-2 carbon materials. Moreover, an additional
method was used to modify the surface chemistry of the NC-2 car-
bon material: heat-treatment at 1073 K in the flow of H2 for 6 h to
obtain a modified NC-2 material (denoted as NC-2 (H2)). Except for
special mention, the carbon material is referred to the one that is
not modified.
tion of 2 cm−1
.
The temperature-programmed desorption of carbon dioxide
(CO2-TPD) was carried out on Autochem II 2920 (Micromeritics,
USA). The sample (100 mg) was first placed in the reactor and
treated at 1073 K for 2 h in air. After cooling to 323 K, the sample
was exposed to 10% CO2/Ar mixture flow (20 ml/min) for 1 h. Then
the sample was flushed in Ar flow at 323 K for removal of physi-
cally adsorbed CO2. An CO2-TPD profile of the sample was recorded
by increasing the temperature from 323 to 1073 K at a heating
rate of 10 K/min under 20 mL/min of Ar flow. The desorbed prod-
ucts were analyzed by a quadrupole mass spectrometer (FISONS
Instruments). The concentrations of CO2 were determined by the
intensities of m/z at 44.
3. Results and discussion
3.1. Catalyst characterization
Reference samples of SBA-15 and CMK-3 were prepared
according to a literature procedure [19]. Commercially available
coal-based activated carbon (denoted as CC, from Ningxia Henghui
Actived Carbon Co. Ltd.) and almond nutshells-based activated car-
bon (denoted as AC, from Limin Active Carbon Co. Ltd.) were also
used in this study.
The carbon-supported MgO catalysts were synthesized by wet
impregnation method. Typically, a fully dried carbon support was
added into a water solution of Mg(NO3)2, and the resultant mixture
was stirred for about 3 h to impregnate the activated carbon with
Mg-containing solution at room temperature. After that, water was
evaporated away from the mixture at a temperature of 353 K under
atmosphere pressure. The resultant solid composite was calcined
Fig. 1 shows the XRD patterns of different carbon supports and
the supported MgO catalysts (with 4.0 wt.% MgO loading). All car-
bon supports exhibit two broad diffraction peaks centered at 26◦
and 44◦, which can be generally indexed to (0 0 2), (1 0 1) diffrac-
tion for glass-like carbon bearing graphitic characteristics [25,32].
Besides, the 4.0 wt.% MgO/CMK-3 sample shows two weak diffrac-
tion peaks centered at 43◦ and 63◦, which can be generally indexed
to (2 0 0), (2 2 0) diffraction for the presence of a certain amount of
MgO crystalline phase [33]. While the peaks due to MgO phase are
not found in the patterns of 4.0 wt.% MgO/NC-2, 4.0 wt.% MgO/CC
and 4.0 wt.% MgO/AC, indicating that MgO species should be highly
dispersed on the surface of these carbon supports.

34
G. Zhao et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 32–37
Fig. 1. (A) XRD patterns of different supports: (a) NC-2; (b) CMK-3; (c) AC; (d) CC (ꢀ: diffraction for glass-like carbon bearing graphitic characteristics). (B) XRD patterns of
the carbon-supported 4.0 wt.% MgO catalysts (ꢁ: diffraction for the presence of a certain amount of MgO crystalline phase).
Fig. 3. CO2-TPD profiles of the pure MgO and carbon-supported MgO catalysts: (a)
Fig. 2. XRD patterns of MgO/NC-2 catalysts with different MgO contents: (a) NC-2;
4.0 wt.% MgO/AC; (b) 4.0 wt.% MgO/CC; (c) 4.0 wt.% MgO/NC-2; (d) MgO; (e) 4.0 wt.%
MgO/CMK-3.
(b) 1.6 wt.% MgO/NC-2; (c) 4.0 wt.% MgO/NC-2; (d) 7.7 wt.% MgO/NC-2; (e) 14.3 wt.%
MgO/NC-2; (f) 20.0 wt.% MgO/NC-2 (ꢁ: diffraction for the presence of a certain
amount of MgO crystalline phase).
assigned to the existence of weak and medium basic sites, asso-
Fig. 2 shows the XRD patterns of a few representative samples of
the MgO/NC-2 composites with different Mg loading. It can be seen
that MgO species could be highly dispersed on the NC-2 support
even the loading of MgO reaches 7.7 wt.%. With further increasing
the MgO loading (equal or above 14.3 wt.% MgO), significant MgO
crystalline phase can be observed.
The relevant structure parameters of the carbon-supported MgO
samples and their parent carbon supports are given in Table 1.
Compared with the carbon supports, the corresponding carbon-
supported MgO samples show lower specific surface area, smaller
pore volume and mean pore size, which can be assigned to the
deposit of magnesium oxides on the walls and/or in the mouth of
the smaller pores of the carbon materials.
ciated to the Mg2+–O2− pairs. The presence of a certain amount
of weak and medium basic sites could be also observed on the
samples of 4.0 wt.% MgO/CC and 4.0 wt.% MgO/AC. The area of
desorption peak of 4.0 wt.% MgO/CMK-3 is much less than other
three carbon-supported MgO catalysts, indicating that the num-
ber of basic sites is quite low in this sample. This might be mainly
due to the fact that MgO species exist in the form of large crys-
talline particles over the sample of MgO/CMK-3 as suggested by
the XRD characterization. Notably, the desorption peak of 4.0 wt.%
MgO/NC-2 turns to narrow, implying that MgO species should be
uniformly dispersed on the surface of NC-2. Compared with pure
MgO and other carbon-supported MgO catalysts, the basicity of
MgO/NC-2 decreases somewhat, which should be caused by the
presence of relatively strong interaction between MgO species and
NC-2 support. It should be mentioned here that there are nearly no
detectable basic sites on the surface of MgO/SBA-15 (not shown).
The basicity of the supported MgO/NC-2 catalysts was inves-
tigated by CO2-TPD (Fig. 3). Pure MgO shows a very broad CO2
desorption peak, extended from 353 to 823 K, which could be
Table 1
The structure parameters of carbon supports and carbon-supported MgO catalysts.
Samples
BET surface area (m2 g−1
)
Pore vol. (cm3 g−1
)
Pore sizea (nm)
NC-2
4.0 wt.% MgO/NC-2
CMK-3
4.0 wt.% MgO/CMK-3
4.0 wt.% MgO/AC
4.0 wt.% MgO/CC
1072
797
1564
1453
779
0.91
0.70
1.51
1.27
0.13
0.28
3.5
3.3
4.0
3.4
3.2
2.6
862
a
Calculated using the BJH model on the desorption branch of the N2 adsorption/desorption isotherms.

G. Zhao et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 32–37
35
Fig. 4. (A) DRIFT spectra of different carbon supports: (a) NC-2; (b) CMK-3; (c) AC; (d) CC. (B) DRIFT spectra of the carbon-supported 4.0 wt.% MgO catalysts: (a) MgO/NC-2;
(b) MgO/CMK-3; (c) MgO/AC; (d) MgO/CC.
This might be due to the fact that the abundant hydroxyl groups
(Si–OH) existed on the surface of SBA-15 could easily react with
MgO species to form inactive magnesium silicate species under the
preparation conditions.
Fig. 4 shows the DRIFT spectra of different carbon supports
and the supported 4.0 wt.% MgO catalysts. The broad bands cen-
tered at 1390 and 1000 cm−1 can be mainly assigned to the C–O
stretch vibrations in ether type structure [26]. The broad band
in 3100–3500 cm−1 region can be attributed to the O–H stretch
vibrations from hydroxyl, phenolic and carboxylic groups [26]. The
appearance of very broad bands in the range of 1600–2300 cm−1
can be attributed to the stretching vibrations of C O moieties in
(i) quinone or conjugated ketone structure (around 1640 cm−1);
(ii) carboxylic acid, lactone, acid anhydride (in the range of
1670–1900 cm−1) [26,34–36]. Among these carbon supports, it can
be seen that NC-2 possesses relatively abundant surface oxygen-
functional groups. After supporting MgO to the surface of carbon
Fig. 5. Dependence of the DEC conversion on the reaction time of the carbon-
supports, no obvious change could be observed in the DRIFT spec-
tra of 4.0 wt.%MgO/CMK-3, 4.0 wt.%MgO/AC and 4.0 wt.%MgO/CC
in comparison with the corresponding carbon supports. However,
supported MgO catalysts: (ꢂ) 4.0 wt.% MgO/CMK-3; (᭹) 4.0 wt.% MgO/AC; (ꢃ)
4.0 wt.% MgO/CC; (ꢀ) 4.0 wt.% MgO/NC-2; Reaction conditions: catalyst, 0.5 g; DMC,
0.05 mol; DEC, 0.05 mol; reaction temperature, 376 K.
the relative intensity of the DRIFT peaks of 4.0 wt.%MgO/NC-2 is
much lower than the support of NC-2, implying that quite amount
of surface oxygen-functional groups in NC-2 may interact with MgO
gest that carbon is an efficient support for the preparation of active
MgO supported catalyst.
species during the preparation process. Previously, it was reported
Fig. 6 presents the comparative results of catalytic activities of
that magnesium oxide/hydroxide could be uniformly deposited on
MgO/NC-2 catalysts with different Mg loading. It can be seen that
the surface of pre-oxidized pitch-based activated carbon fibers,
the conversion of DEC increases when the MgO loading increases
due to the interaction between Mg species and surface oxygen-
from 1.6 to 7.7 wt.%. With further increasing the MgO loading (up
functional groups (e.g., –COOH groups) of the carbon support
to 14.3 wt.%), the time that reaction reaches equilibrium turns to
[37,38]. In the present work, we suppose that the existence of abun-
dant surface oxygen-functional groups in NC-2 may be useful for
building a suitable interaction between NC-2 support and the Mg
species (i.e. magnesium nitrate) during the preparation process,
thus resulting in the uniform dispersion of MgO species on the
surface of NC-2 support.
3.2. Catalytic performances
Fig. 5 presents the catalytic performance of various carbon-
supported MgO catalysts (with 4.0 wt.% MgO loading) for the
transesterification of DMC and DEC. All the catalysts are active
for the transesterificaiton reaction with nearly 100% selectiv-
ity to EMC. Among them, 4.0 wt.% MgO/NC exhibits the highest
activity, a 49.3% yield of EMC could be achieved after 0.5 h
reaction. The catalytic activity decreases in the order: MgO/NC-
2 > MgO/CC > MgO/AC > MgO/CMK-3. For comparison, the catalytic
property of SBA-15 supported MgO (4.0 wt.% MgO/SBA-15) was also
investigated. Very low EMC yield (0.9%) was achieved after 2 h of
reaction on the MgO/SBA-15 catalyst, which is consistent to its
weak basic characteristic as mentioned above. These results sug-
Fig. 6. Dependence of the DEC conversion on the reaction time of the MgO/NC-2 cat-
alyst with different MgO contents: (ꢄ) 1.6 wt.% MgO/NC-2; (ꢀ) 4.0 wt.% MgO/NC-2;
(ꢁ) 7.7 wt.% MgO/NC-2; (ꢁ) 14.3 wt.% MgO/NC-2; (♦) 20.0 wt.% MgO/NC-2 calcined at
1073 K. Reaction conditions: catalyst, 0.5 g; DMC, 0.05 mol; DEC, 0.05 mol; reaction
temperature, 376 K.

36
G. Zhao et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 32–37
Fig. 9. Dependence of the DEC conversion on the reaction time of the 4.0 wt.%
MgO/NC-2 catalyst with different supports treated method: (ꢂ) NC-2 without any
disposal; (ꢀ) NC-2 calcined at 1073 K for 6 h in the flow of H2. Reaction conditions:
catalyst, 0.5 g; DMC, 0.05 mol; DEC, 0.05; reaction temperature, 376 K.
Fig. 7. Heterogeneous reaction check for 4.0 wt.% MgO/NC-2 calcined at 1073 K (ꢄ),
by continuing the reaction after removing the 4.0 wt.% MgO/NC-2 catalyst (×) by
filtration at reaction temperature. Reaction conditions: the suspension, which con-
tained 0.05 mol of DMC, 0.05 mol of DEC and 0.5 g of catalyst, was stirred and heated
to reflux temperature (376 K).
the form of small MgO nanoparticles, while serious agglomeration
of MgO particles on the surface of the CMK-3 occurs. This might be
the main reason for why MgO/NC-2 exhibits relatively high activity
compared with other carbon-supported MgO catalysts. We suppose
that the structure characteristics (e.g., high specific surface area,
porosity) and surface chemistry (e.g., polarity, electro-property) of
NC-2 support should be beneficial to the formation of such efficient
catalyst.
slight longer, indicating the decrease in catalytic activity of these
catalysts. According to the results of XRD characterizations, it was
known that MgO could be highly dispersed on the surface of NC-
2 support when the loading of MgO below 14.3 wt.%. Hence, the
relatively high activity of the sample with lower MgO loading
(≤7.7 wt.%) may suggest that the highly dispersed MgO particles
(nanoparticles) should be the main active centers for the transes-
terification reaction. The slight decrease in catalytic activity of the
samples with higher MgO loading (≥14.3 wt.%) should be mainly
assigned to the appearance of relative large crystalline MgO.
The most interesting result is the high stability of the MgO/NC-
2 catalysts against leaching of the active species into the liquid
phase under the given reaction conditions. In a duplicate reaction
over 4.0 wt.% MgO/NC-2 (calcined at 1073 K), it was found that no
detectable subsequent conversion in the solution after removing
the catalyst by hot filtration at the reaction temperature (Fig. 7).
This is a very strong evidence for a real heterogeneous catalysis.
Moreover, it was found that MgO/NC-2 catalyst can be easily recy-
cled (with nearly consistent activity as the fresh one) by simple
heat activation of the used catalyst under an argon atmosphere at
1073 K for some while (Fig. 8).
According to the results of DRIFT and TPD, it has been proposed
that the presence of abundant surface oxygen-functional groups
in NC-2 may be useful for building a suitable interaction between
NC-2 support and the Mg species (i.e. magnesium nitrate) during
the preparation process, thus resulting in the uniform dispersion of
MgO species on the surface of NC-2 support. For the sake of a bet-
ter understanding of the role of surface oxygen-functional groups,
a reductive modification of the carbon materials was employed
before the impregnation. In short, an additional NC-2 supported
MgO catalyst (denoted as 4.0 wt.% MgO/NC-2 (H2)) was obtained
using a hydrogen-treated NC-2 as support (1073 K for 6 h in the
flow of H2). It was found from Fig. 9 that the 4.0 wt.% MgO/NC-
2 (H2) catalyst shows much lower activity than the one without
additional treatment. Previously, it has been reported that most
of the surface oxygen groups in carbon material could be elimi-
nated by such hydrogen treatment [36]. Hence, the experimental
results presented here confirmed further that the presence of
abundant surface oxygen groups is indeed a crucial factor for the
formation of highly active carbon-supported MgO catalyst. Besides,
other factors, including the structure characteristics and the surface
chemistry of carbon support, may also make considerable contribu-
tion to the high catalytic activity of the carbon-supported catalyst
by influencing the chemisorption intensity and/or the diffusion
velocity of reactants and products [39].
On the basis of the characterization results of XRD, it was known
that MgO species could be highly dispersed on the surface of NC-2 in
4. Conclusions
Well-dispersed carbon-supported MgO materials (MgO/NC-2)
could be obtained using porous carbon (NC-2) as support and mag-
nesium nitrate solution as MgO precursor through a simple wet
impregnation technique. These materials are efficient heteroge-
neous catalysts for the liquid-phase transesterification of DMC with
DEC to EMC. The presence of relatively rich oxygen-containing
surface groups on the NC-2 carbon support should be in favor of
the high dispersion of MgO particles, thus being beneficial to the
formation of active and stable catalysts for the transesterificaiton
reaction.
Fig. 8. Transesterification activities of 4.0 wt.% MgO/NC-2 calcined at 1073 K during
five reaction cycles. Reaction conditions: catalyst, 0.25 g; DMC, 0.05 mol; DEC, 0.05;
reaction temperature, 376 K; reaction time, 0.5 h.

G. Zhao et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 32–37
37
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This work is supported by the Specialized Research Fund for the
Doctoral Program of Higher Education (20040183003), Program for
New Century Excellent Talents in University, State Basic Research
Project (2005CB221405), Graduate Innovation Fund of Jilin Univer-
sity (20091013), and National Natural Science Foundation of China
(20403006 and 20773050).
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