Synthesis of glycerol carbonate from glycerol and diethyl carbonate over Ce-NiO catalyst: The role of multiphase Ni

Article abstract of DOI:10.1016/j.jallcom.2017.05.292

A series of Ce-NiO catalysts prepared by co-precipitation method were tested for glycerol transesterification with diethyl carbonate (DEC) to produce glycerol carbonate (GC). The microstructural and physicochemical properties of the catalysts were determined by XRD, XPS, SEM, EDX, CO₂-TPD, N₂-adsorption, FT-IR, and TG-DTG. The results showed that the particle size (100–350 nm) of the Ce-NiO was smaller than that of pure NiO (400–900 nm), suggesting addition of Ce in the catalyst synthesis could lessen the aggregation or facilitate the dispersion of NiO particles. The highest catalyst activity was observed over the Ce-NiO catalyst with Ce/Ni atomic ratio of 0.2 and calcined at 400 °C. 94.14% of glycerol conversion and 90.95% selectivity to GC were obtained over this catalyst under the optimum conditions (5 wt.% catalyst of glycerol, 85 °C, 8 h, glycerol/DEC ratio of 1:3). This catalyst can be reused up to three cycles with a slight decrease in its catalytic activity. It was found the well dispersed NiO particles and the strong basic sites derived from the substitution of Ce⁴⁺ by Ni²⁺ in the CeO₂ lattices synergistically promoted the glycerol conversion.

Full text of DOI:10.1016/j.jallcom.2017.05.292

Journal of Alloys and Compounds 720 (2017) 360e368
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Synthesis of glycerol carbonate from glycerol and diethyl carbonate
over Ce-NiO catalyst: The role of multiphase Ni
Yuanfeng Wu, Xianghai Song, Fufeng Cai, Guomin Xiao*
School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Ce-NiO catalysts prepared by co-precipitation method were tested for glycerol trans-
esterification with diethyl carbonate (DEC) to produce glycerol carbonate (GC). The microstructural and
physicochemical properties of the catalysts were determined by XRD, XPS, SEM, EDX, CO2-TPD, N2-
adsorption, FT-IR, and TG-DTG. The results showed that the particle size (100e350 nm) of the Ce-NiO
was smaller than that of pure NiO (400e900 nm), suggesting addition of Ce in the catalyst synthesis
could lessen the aggregation or facilitate the dispersion of NiO particles. The highest catalyst activity was
observed over the Ce-NiO catalyst with Ce/Ni atomic ratio of 0.2 and calcined at 400 ꢀC. 94.14% of glycerol
conversion and 90.95% selectivity to GC were obtained over this catalyst under the optimum conditions
(5 wt.% catalyst of glycerol, 85 ꢀC, 8 h, glycerol/DEC ratio of 1:3). This catalyst can be reused up to three
cycles with a slight decrease in its catalytic activity. It was found the well dispersed NiO particles and the
strong basic sites derived from the substitution of Ce4þ by Ni2þ in the CeO2 lattices synergistically
promoted the glycerol conversion.
Received 14 December 2016
Received in revised form
14 April 2017
Accepted 27 May 2017
Available online 27 May 2017
Keywords:
Glycerol
Diethyl carbonate
Glycerol carbonate
Transesterification
Ce-NiO
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
source is limited because of the toxicity and processing difficulty in
industries [10,11]. Glycerolysis of urea needs the intermittent
Biodiesel, as a renewable clean energy, plays a key role in sus-
tainable energy development. In recent years, this expansion in
biodiesel production is generating large amounts of glycerol (GL),
as a side product, jeopardizing the price of GL in the market [1,2].
Hence, the transformation of GL into high valued-added chemicals
is greatly significant to suppress its accumulation as a waste and
lessen the expense of biodiesel industry. Numerous pathways for
GL conversion have been reported for the synthesis of useful
glycerol derivatives [3e5]. Among these, glycerol carbonate is one
of the most promising chemical with high boiling point, low
toxicity and biodegradability, which can be used as novel solvent,
surfactant, chemical intermediates for glycidol, carries in batteries
and monomer for polymers [5e8].
removal of ammonia from the reactor and the purification process
is also complicated [12]. The use of CO2 as carbonyl source is
attractive with high atom utilization efficiency. The main drawback
of this reaction is thermodynamically limited in GL conversion
[13,14]. Carbonylation of GL with alkyl carbonates like ethylene
carbonate is also a useful approach. Nevertheless, GC is achieved
together with ethylene glycerol. The separation of the side product
is difficulty to carry out [15]. The desired route for synthesis of GC is
through carbonylation of GL with dialkyl carbonates because the
reaction starts with non-toxic materials under the mild conditions
[16]. Among them, GL transesterification with DEC for GC synthesis
is a green and promising route with only ethanol as the byproduct
and high GC yield.
Several routes have been described in literature for the synthesis
of GC from GL using different carbonyl agents [9]. These include
phosgenation, urea, gaseous mixture of carbon monoxide and ox-
ygen, carbon dioxide, cyclic carbonates and diethyl/dimethyl car-
bonates. The use of phosgenation and carbon monoxide as carbonyl
Most literature available has been reported on homogeneous
reaction [17,18], though others on heterogeneous reactions. How-
ever, the separation of homogeneous catalysts was difficult to
conduct, which is not beneficial for subsequent purification of re-
action products. Turney et al. [19] also reported that other catalysts
such as alkaline catalysts, Lipases, KF modified hydroxyapatite, Mg/
Al/Zr mixed oxides, triethylamine have been adopted for trans-
esterification. Nevertheless, most of these catalysts have their
drawbacks such as rapid deactivation, requirement of long reaction
* Corresponding author.
E-mail address: xiaogm426@gmail.com (G. Xiao).
http://dx.doi.org/10.1016/j.jallcom.2017.05.292
0925-8388/© 2017 Elsevier B.V. All rights reserved.

Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
361
time, additional solvent and a high reactant mole ratio. Therefore, it
was urgent to develop a highly efficient catalyst for this reaction.
Ceria is a basic catalyst. Although it is not very reactive in
transesterification reactions, it is a good candidate to improve the
basicity of solid basic catalyst, therefore enchaining the catalytic
activity in base-catalyzed reaction [20,21]. The utilization of Ce-
MgO in the synthesis of dimethyl carbonate (DMC) from ethylene
carbonate and methanol resulted in 95% DMC selectivity and 64%
DMC yield, which were far superior to the MgO (DMC yield was
only 49%) [22], Magnesium incorporation into cerium generated
the strongest basic sites, compared with other alkali or alkaline
earth metal ion, because of the higher oxygen vacancy concentra-
tion created simultaneously [23,24].
Ce-NiO catalysts have been applied in many fields such as CH4
oxidation [25], dry reforming of methane [26], H2 production [27]
and CO oxidation [28]. But it has not been reported as a catalyst
in many reactions. Besides, to the best of our knowledge, the per-
formance of Ce-NiO catalysts was not investigated in the synthesis
of GC from GL and DEC. Thus, in this paper, Ce-promoted NiO as
solid base catalyst was simply prepared by a co-precipitation
method and characterized by various techniques. The effects of
reaction parameter on the catalytic performance including calci-
nation temperature, Ce/Ni atomic ratio, reaction temperature,
catalyst amount, GL/DEC mole ratio, reaction time as well as the
catalyst recyclability was studied in details.
min. The mean crystal size of NiO and CeO2 was estimated ac-
cording to main plans (0 1 2) of NiO and (111) of CeO2, by Scherrer
equation [29].
Microscopic morphology of the catalysts was characterized by
field emission scanning election microscopy (FESEM). The metal
elements distribution was recorded by energy dispersive X-ray
spectrum (EDX).
X-ray photoelectron spectroscopy (XPS) measurements were
conducted on an ESCALAB-250 (Thermo-VG Scientific, USA) spec-
trometer equipped with Al Ka (1486.6 eV) irradiation. The binding
energies value were calibrated internally based on the adventitious
carbon deposit C (1s) peak at 284.6 eV.
Specific surface area (BET) and pore characteristics of the cata-
lyst were detected by N2 physisorption at liquid nitrogen temper-
ature (-196 ꢀC) using a Beishide 3H-2000 analyzer after the catalyst
was degassed at 200 ꢀC for 12 h.
Basic sites of the catalyst were measured by temperature-
programmed desorption of CO2 (CO2-TPD) performed using the
TP-5056 equipment connected to a TCD detector. The catalysts
(0.10 g) were first pretreated in Helium atmosphere at 200 ꢀC for
1 h, then cooled down to 30 ꢀC maintained in the CO2 flowing gas
for 30 min and purged with He for 50 min in order eliminate the
physically adsorbed CO2. Subsequently, the sample was heated at a
linear rater of 10 ꢀC/min to 800 ꢀC in order to acquire the CO2
desorption curve.
Fourier transform infrared (FT-IR) spectra of the catalysts were
detected on a Nicolet 5700 spectrometer using the KBr disc method
and the wavenumber range of the spectra was obtained from 400 to
4000 cmꢁ1 with a 2 cmꢁ1 resolution.
2. Experimental
2.1. Chemicals
Thermogravimetric (TG) analysis of the catalyst was conducted
in the range of 30e800 ꢀC under dry air atmosphere on a thermal
analyzer SDT Q600 by using 10 mg catalysts with a heating rate of
20ꢀ/min.
Ce(NO3)3$6H2O, Ni(NO3)2$6H2O, Na2CO3 and ethylene glycol
monobutyl ether were purchased from Aladdin Industrial Corpo-
ration, shanghai, China, GL, DEC and ethanol were purchased from
Sinopharm Chemical Reagent Co. Shanghai, China. All the reagents
were of analytical grade without further purification.
2.4. Catalytic reaction
2.2. Catalyst preparation
Transesterification of DEC with GL to produce GC, depicted in
Scheme 1a, was performed in a round bottom flask equipped with a
magnetic stirrer and a thermocouple.
The Ce-NiO with different Ce/Ni ratio was prepared by co-
precipitation method. In a typical process, a mixed aqueous so-
lution (Ce(NO3)3$6H2O, Ni(NO3)2$6H2O) and 3 mol/L Na2CO3 were
simultaneously added dropwise to 10 mL deionized water under
vigorous stirring to achieve pH value of 9.0. After 12 h reaction, the
precipitate was separated via filtration, washed with deionized
water to remove sodium ion until the precipitate was nearly
neutral. Afterwards, the precipitate was dried at 80 ꢀC for 10 h, and
then treated in static ambient air at 400 ꢀC for 5 h. Finally, the as-
prepared Ce-NiO catalyst was grind into the designated size and
used for GL transesterification. The Ce-NiO catalysts with different
composition were denoted as xCeNiO-400, where, x represents the
Ce/Ni atomic ratio (x ¼ 0.2, 0.4, 0.6, 0.8, and 1.0, respectively). To
study the influence of the calcination temperature, the 0.2CeNiO
catalysts were calcined at different temperature (from 300 to
600 ꢀC) and the catalysts were denoted as xCeNiO-T (x ¼ 0.2,
T ¼ 300, 400, 500, 600, respectively), where T represents the
pretreatment temperature. For comparison, the pure NiO and
CeO2 were synthesized under the same conditions without addi-
tion of Ce(NO3)3$6H2O or Ni(NO3)2$6H2O, and calcined at 400 ꢀC
for 5 h.
Typically, GL, DEC and catalyst were charged into the glass
reactor heated by oil bath with a set point. During the reaction, the
system was stirred variously. After 6 h reaction, the system was
cooled down to room temperature. The recovered catalyst from
mixture was separated via centrifugation, washed with ethanol to
remove organic components, and dried at 40 ꢀC in an oven over-
night for further research. The catalyst-free liquid (ethylene glycol
monobutyl ether as the internal standard) was collected and
detected by flame ionization detector Gas chromatograph (Teng
Hai, Shandong, China, GC-6890) equipped with a SE-54 capillary
column (30 m ꢂ 0.32 mm ꢂ 1
mm).
GL conversion was defined as the ratio of C-based mole of all the
products to C-based mole of initially added GL. GC selectivity can be
2.3. Catalyst characterization
X-ray diffraction (XRD) patterns of the Ce-NiO were recorded in
2q a
range of 5-85ꢀ on the Rigaku D/max-A instrument using Cu k
radiation performed at 40 kV and 20 mA with a scan step of 20ꢀ/
Scheme 1. (a) one-pot synthesis of GC from GL, (b) GC decarbonylation to glycidol.

362
Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
calculated based on the ratio of C-based mole of GC to C-based mole
of all products.
CeO2 was observed (Fig. 1d). This was ascribed to the asymmetry in
the crystal structure which was caused by the substitution of Ce4þ
by Ni2þ inside the CeO2 lattices [31]. As mentioned above, we
speculated the catalyst as prepared with high Ni content was
consist of NiO in aggregates as well as in well dispersed particles
with some Ni2þ possibly incorporated into CeO2 lattices, which can
be further validated by the result of H2-TPR (Fig. S1). A tentatively
proposed model of Ce-NiO was presented in Scheme 2. Ce-O-Ni
superbonds were formed through chemical adsorption interac-
tion between the oxygen, Ce and Ni ions. Besides, the equivalent
number of oxygen vacancies was generated when the Ni2þ
substituted for a Ce4þ in a C2v surface site.
To study the effect of calcination temperature on the Ce-NiO
catalyst, the 0.2CeNiO-T catalysts were investigated (Fig. 1b). For
0.2CeNiO-300 catalyst, no apparent phases of NiO or CeO2 were
observed, elucidating the CeO2 and NiO were amorphous or that
both crystallite sizes were below the detection limitation. While
with increase in calcination temperature, the intensities of the two
crystallite diffraction peaks are gradually enhanced, indicating the
elevated pretreatment temperature could facilitate grain growth of
the 0.2CeNiO-T catalysts (Table 1).
3. Results and discussion
3.1. Characterization of catalysts
XRD patterns of NiO, CeO2 and Ce-NiO catalysts with different
composition and calcined at 400 ꢀC for 5 h are shown in Fig. 1a. For
each catalyst, the obvious crystallites of CeO2 (JCPDS 65-2975) [30]
and NiO (JCPDS 22-1189) were observed, respectively and no any
other mixed crystallite peaks of CeO2-NiO were detected, which
suggested the xCeNiO-400 catalysts were successfully prepared.
The mean crystal sizes of NiO and CeO2 particles are presented in
Table 1. When the Ce/Ni ratio varies from 0.2 to 1.0, the mean crystal
size of NiO first increases from 6.4 to 10.3 nm and then decreases to
6.2 nm, while the mean crystal sizes of CeO2 in the bimetal samples
were found smaller than that of the pure CeO2, indicating the
different interactions between the nickel and cerium species inside
the solid [27].
To further study the interaction between nickel and cerium, low
To observe the morphology of CeO2, NiO and the Ce-NiO cata-
lysts, the FESEM images are presented in Fig. 2. It can be seen from
Fig. 2a the micrographs of pure CeO2 possessed lamellae structure
[32], while that of Ce-NiO catalysts was foam-like in shape
(Fig. 2cef) [33]. Padmanathan et al. [34] obtained the analogous
structure of Ce-NiO prepared via sol-gel technique. It was found
scan XRD patterns of Ce-NiO and NiO, CeO2 catalysts in 2q range
from 25 to 35ꢀ and 35 to 45ꢀ were detected, respectively, and the
result is presented in Fig. 1ced. The (1 1 1) plain of CeO2 shifts to
higher diffraction angle compared with that of pure ceria (Fig. 1c),
While no shift in the position of the diffraction peaks of NiO in the
bimetal samples with respect to the diffraction pattern of the pure
Fig. 1. XRD patterns of (a) NiO, CeO2, xCeNiO-400 catalysts and (b) 0.2CeNiO-T catalysts. Low scan XRD patterns in 2q
range of (c) 25-35ꢀ. (d) 35 to 45ꢀ, respectively.

Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
363
Table 1
Surface area (BET) and crystallite size (calculated from the Scherrer equation).
Catalyst
NiO (nm)
CeO2 (nm)
BET surface area (m2gꢁ1
)
Total pore volume (m3gꢁ1
)
NiO-400
CeO2-400
10.4
e
e
56.07
72.08
30.49
39.59
41.10
52.94
71.80
143.54
25.62
25.24
0.20
0.13
0.18
0.20
0.21
0.27
0.32
0.46
0.15
0.13
8.5
3.8
4.6
4.8
5.0
5.2
e
0.2CeNiO-400
0.4CeNiO-400
0.6CeNiO-400
0.8CeNiO-400
1.0CeNiO-400
0.2CeNiO-300
0.2CeNiO-500
0.2CeNiO-600
6.4
6.9
10.3
7.8
6.2
e
9.8
13.3
6.9
13.9
from Fig. 2bef that the particle size (100e350 nm, Fig. S2b) of the
Ce-NiO was smaller than that of pure NiO (400e900 nm, Fig. S2a),
suggesting addition of Ce in the catalyst synthesis could lessen the
aggregation or facilitate the dispersion of NiO particles. EDX anal-
ysis was used to investigate the chemical composition of these
samples as shown in Fig. S3. From the EDX spectrum, there were
four kinds of element (C, O, Ce, Ni) observed. Among these catalysts,
the maximum error between the experimentally determined metal
composition and the expected values is less than 6% (Table S1).
To further illuminate the surface oxygen species as well as the
chemical state of the elements existing in Ce-NiO catalysts with
different shape, XPS was performed and the results are shown in
Fig. 3. Apart from Ce 3d, Ni 2p and O 1s signals (Fig. 3a), C1s signal
was also detected in the 0.2CeNiO-400 catalyst; maybe the car-
bonates (NiCO3, Ce2(CO3)3) were incompletely decomposed. Be-
sides, no N 1s signal was observed, indicating the nitrate was
removed in the prepared process. The spectra of Ni 2p of the Ce-NiO
catalysts are shown in Fig. 3b. The spectra of nickel species exhibit a
main peak around 853.8 eV belonging to the Ni 2p3/2 (þ2) line [35],
and a broad peak around 860.8 eV represents the shake-up satellite
peak of Ni2þ (NiO) and Ni3þ (Ni2O3), respectively [36]. Interestingly,
the Ni2þ binding energy of 0.2CeNiO-T samples gradually decreases
with the calcination temperature increase, indicating that electrons
increased around Ni in Ce-NiO catalysts, and further demonstrating
the existence of synergistic interaction between Ce and Ni through
the redox equilibrium of Ce3þþ Ni3þ 4 Ce4þþ Ni2þ. The Ni2þ
binding energy of 0.2CeNiO-300 is relatively higher compared with
other samples, therefore the Ce3þ and adsorbed oxygen species
increased simultaneously during electrons transfer from Ni2þ to
Ce4þ. The Ce 3d spectra of these catalysts were fitted to eight peaks
as displayed in Fig. 3c. The peaks labeled as v, v0, v00 and v000 corre-
spond to Ce 3d5/2 line, and the other four peaks labeled as u, u0, u00
and u000 are ascribed to Ce 3d3/2 line [37]. This result suggests that
the cerium existed on the Ce-NiO catalyst surface mainly as Ce4þ
[38]. In addition, these findings could confirm a similar oxidation
state of the atoms on surface and in the bulk and exclude the ex-
istence of metallic species in Ce-NiO catalyst [28]. The XPS spectra
of O 1s for the Ce-NiO catalysts were fitted with three components
as presented in Fig. 3d. The presence of the main peaks denoted as
O0 (529.2 eV) are lattice oxygen in ceria and nickel oxides, and the
shoulder peaks denoted as O00 in range between 531.0 and 531.6 eV
correspond to the adsorbed oxygen which was originated from the
replacement of Ce4þ by Ni2þ in the CeO2 lattices. Besides, a peak
(O000) at high binding energy around 532.9 eV represents carboxyl
oxygen of carbonates [39], which can be confirmed by the result of
EDX (Fig. S3). The ratio of these two kinds of oxygen species was
calculated based on the area of O0 and O00. The O00/O0 ratios of all
catalysts demonstrated that more active oxygen was adsorbed on
surface of 0.2CeNiO-400 catalyst, which could be related to the
formation of unique structure that provides sufficient space for
molecular activation [40].
Scheme 2. A tentatively proposed model of Ni dopant onto CeO2 lattice.
Fig. 2. FESEM images of (a) CeO2-400, (b) NiO-400, (c) 0.2CeNiO-400, (d) 0.6CeNiO-
400, (e) 0.2CeNiO-300, (f) 0.2CeNiO-600 catalysts.

364
Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
Fig. 3. XPS spectra of NiO, CeO2, 0.6CeNiO-400, 0.2CeNiO-300, 0.2CeNiO-400, 0.2CeNiO-600 catalysts. (a) full spectrum, (b) Ni 2p, (c) Ce 3d, and (d) O 1s.
The FT-IR spectra of NiO, CeO2 and Ce-NiO catalysts are pre-
group of H2O [41]. The band at 1388 cmꢁ1 is attributed to CO32ꢁ from
the incomplete decomposing carbonates [42], this can be evi-
denced by the results of XPS (Fig. 3a) and EDX (Fig. S3). The spectra
of ceria exhibit a band at 559 cmꢁ1 corresponding to Ce-O band
[43]. NiO shows a strong adsorption band at 426 cmꢁ1associated
with Ni-O bond vibration [44]. It was found that the characteristic
sented in Fig. 4. For all catalysts, the band at 3200-3500 cmꢁ1 and
around 1579 cmꢁ1 correspond to stretching and vibration of eOH
Ce-O band of Ce-NiO catalysts was shifted from 559 to 518 cmꢁ1
,
this may be related to the shrinkage of CeO2 crystal structure which
resulted from the doping of Ni2þ in the CeO2 lattices, in according
with the result of XRD (Fig. 1c).
Fig. S4 gives the N2 adsorption-desorption isotherms of NiO,
CeO2 and xCeNiO-T catalysts. For each catalyst, the N2 adsorption-
desorption curves are of type IV. Basically, N2 adsorption did not
occur on the low pressure side (P/P0 < 0.7), while a large number of
N2 adsorbed at high pressure side (P/P0 > 0.7), suggesting the weak
adsorption of N2 for NiO, CeO2 and Ce-NiO catalysts. N2 adsorption-
desorption isotherms overlapped on the low-pressure side, but an
obvious hysteresis loop emerged on the high-pressure side, eluci-
dating the existence of mesoporous structure that was due to the
aggregation of Ce-NiO particles, in good agreement with the result
of FESEM (Fig. 2). As Table 1 lists when Ce/Ni ratio of the xCeNiO-
400 catalysts varies from 0.2 to 1.0, the specific surface area in-
creases from 30.49 to 71.80 m2g-1. On the contrary, with calcination
temperature rise from 300 to 600 ꢀC, the specific surface area of the
0.2CeNiO-T catalysts drops from 143.54 to 25.24 m2g-1. It is
Fig. 4. FT-IR Spectra of NiO, CeO2, xCeNiO-400 and 0.2CeNiO-T catalysts.

Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
365
interesting to find the total pore volume of the Ce-NiO changes in
the same way of specific surface area. Therefore, the appropriate
Ce/Ni ratio and calcination temperature are significant parameters
for the synthesis of desired catalyst. The BJH pore-size distribution
curves of Ce-NiO catalysts are presented in FigS.5 showing a
bimodal pore sizes in range of 3e35 nm, which is similar to the
result reported by Tang et al. [40].
50e245 ꢀC, a broad peak within 245e480 ꢀC, and an intense peak at
540 ꢀC, which corresponds to the CO2 desorption from weak,
moderate and strong basic sites, respectively. The weak and mod-
erate basic sites amounts gradually decrease with calcination
temperature rise, which could be due to the elevated calcination
temperature leading to the decrease in specific surface area and
loss of basic sites (Table 1). While the strong basic sites amounts
gradually increase after the calcination at 400 ꢀC (Fig. S6b), this may
be attributed to the moderate basic sties converting to strong basic
sites through the substitution of Ce4þ by Ni2þ with temperature
rise.
To investigate thermal behaviors of Ce-NiO catalysts, the un-
calcined 0.2CeNiO sample was chosen to study the process of
weight loss (Fig. 6a). It is identified that the TG profile can be
generally divided into five stages according to DTG curve. The first
stage below 65 ꢀC is sufficient for removal of partial physisorbed
water [47]. Desorption of structural water requires a higher tem-
perature about 217 ꢀC [48]. The third from 217 to 340 ꢀC is consists
of the simultaneous loss of water molecules and CO2 from car-
bonate decomposition. A relatively higher temperature in rang of
340 and 415 ꢀC in weight loss is assigned to the structure collapse
and forms the foam-like shape, in good agreement with the result
of FESEM (Fig. 2). Therefore, the basic site concentration of
0.2CeNiO-300 catalyst was not the highest compared with the
other samples, which was primarily caused by the incomplete
decomposition carbonates rather than the adsorbed CO2. The last
stage from 415 to 800 ꢀC, only 1.21% of weight loss is due to the
moderate basic sties converting to strong basic sites, which can be
confirmed by the result of CO2-TPD in Fig. 5b. Weight loss of 4.87%
for the 0.2CeNiO-400 catalyst was recorded, while 17.41% for the
first cycle catalyst (Fig. 6bec). The excess weight loss may be due to
the combustion of residual ester, which implies the surface of this
catalyst was gradually covered by organic compound during the
liquid-phase reaction.
CO2-TPD profiles of the catalysts are exhibited in Fig. 5. Ac-
cording to CO2-TPD technology, it can be roughly divided into three
regions, the weak (50e200 ꢀC), moderate (200e400 ꢀC) and strong
(>400 ꢀC) basic sites [45]. The weak basic site of the catalyst is
mainly ascribed to OHꢁ groups. While the mediate and strong basic
site correspond to the metal-O groups and Oꢁ2 groups [46]. Only a
small CO2 desorption peak area was observed for pure NiO and
CeO2 (Fig. 5a). However, for the bimetal catalysts, desorption peak
area representing strong basic sites grows larger, which may be
related to generation of more Oꢁ2 groups through the substitution
of Ce4þ by Ni2þ in the CeO2 lattices. CO2-TPD profiles can be
deconvoluted and the peak area can be regard as the relative
concentration of basic sites (Table S2). It can be seen that the total
and strong basic sites simultaneously increase to the maximum
(x ¼ 0.8), and then decrease (x ¼ 1.0) with Ce/Ni ratio increase,
which implies that only a certain amount of Ni2þ can enter the CeO2
lattices, but beyond this amount, the Ni2þ stays on the CeO2
surfaces.
To study the effect of the calcination temperature on the basic
sites concentration, the 0.2CeNiO-T samples were detected
(Fig. 5b). The catalyst calcined at 300 ꢀC shows a weak peak within
3.2. Transesterification of GL with DEC
Various reaction conditions were considered in the carbonyla-
tion of GL to GC. The conversion of GL and the selectivity to GC were
adopted as the determining parameters. In the preliminary studies,
several reaction conditions were investigated.
Fig. 6. TG-DTG profiles of (a) uncalcined 0.2CeNiO, (b) first cycle 0.2CeNiO-400, (c)
Fig. 5. CO2-TPD Profiles of (a) NiO, CeO2, xCeNiO-400 and (b) 0.2CeNiO-T catalysts.
0.2CeNiO-400 catalysts.

366
Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
3.2.2. Effect of reaction conditions
Fig. 8a gives the effects of reaction temperature on GL trans-
esterification with DEC over 0.2CeNiO-400 catalyst. A remarkable
influence on GL conversion and GC selectivity was observed based
on the results. The GL conversion increases consistently as the re-
action temperature rise from 70 to 95 ꢀC. Nevertheless, the selec-
tivity to GC changes oppositely with a sudden decrease since 85 ꢀC,
which resulted from the formation of a large number of glycidol by
GC decarbonylation. Therefore, 85 ꢀC could be regard as the optimal
temperature for GL transesterification to produce GC.
In the transesterification of GL with DEC, the products distri-
bution is greatly affected by the mole ratio of reactants. The effect of
GL to DEC mole ratio was investigated as presented in Fig. 8b. The
results show at low reactant mole ratio (1:1), the GL conversion and
GC selectivity are rather low (64.68% and 41.03%, respectively),
which may arise from the high catalyst concentration at the low
reactant molar ratio. The GL conversion rises with increase in the
DEC to GL mole ratio. When the mole ratio of 1:3 was adopted, the
increasing rate in GL conversion of 2.07% is the highest compared
with other ratios in acquire of a satisfactory GL conversion. The GC
selectivity is enhanced as the DEC to GL mole ratio rise while the
selectivity to GD declines. This result indicates that the high DEC to
GL mole ratio favors the formation of GC.
The effects of catalyst amount on conversion of GL and selec-
tivity to GC are elucidated in Fig. 8c. The catalyst amount varies
from 1 wt.% to 9 wt.% of GL, while 100% selectivity to GC remain
unchanged. The conversion of GL consistently increases from
73.49% (1 wt.%) to 81.62% (5 wt.%), then drops to 78.27% (9 wt.%),
indicating the low concentration of catalyst cannot offer proper
concentration of basic sites to achieve a higher conversion of GL.
while, excessive concentration of catalyst could lessen the
desorption rate of GC from the catalyst surface, resulting in a low GL
conversion. This result agrees with the investigation on the effect of
reactant mole ratio.
Reaction time as a very significant parameter for GL trans-
esterification usually needs a long time to investigate. As shown in
Fig. 8d, the conversion of GL continuously increases as reaction
time prolonged to 10 h, and maximized to 97.35%, then decreases
slightly. While the GC selectivity changes obviously with a sudden
drop after 6 h and minimized to 52.25% (18 h), which suggested the
newly-formed GC gradually converted to glycidol as the reaction
proceeds. These results imply this catalyst could catalyze GL
transesterification and GC decarbonylation. Consequently, con-
cerning the yield of GC and energy consumption factor, 8 h was
considered as the optimal reaction time (94.14% of GL conversion
and 90.95% of GC selectivity).
Fig. 7. Effect of (a) Ce/Ni atomic ratio, and (b) calcination temperature on catalytic
activity of GL transesterification. GL 4.6 g (0.05 mol), DEC 11.8 g (0.1 mol), reaction
temperature 80 ꢀC, reaction time 6 h, and 5 wt.% catalyst of GL.
3.2.1. Effect of different catalysts
Fig. 7a shows the results of GL transesterification over xCeNiO-
400 catalysts. Only 17.3% of GL conversion was obtained over the
pure NiO catalyst. However, for the bimetal samples, there is an
obvious increase in GL conversion, indicating this reaction could be
enhanced by strong basic sites. But, as Ce/Ni ratio increased from
0.2 to 1.0, GL conversion gradually decreases from maximum
(76.95%, x ¼ 0.2) to 66.51%, which suggests strong basic sites is not
the only factor in determining GL conversion. However, at Ce/Ni
ratio of 0.2, the well dispersed NiO species is the main composition
of Ce-NiO catalyst, therefore the well dispersed NiO species also
could account for the high conversion of GL.
The effects of calcination temperature on GL transesterification
was investigated as displayed in Fig. 7b. When the calcination
temperature increases from 300 to 600 ꢀC, the conversion of GL
firstly increases from 75.83% (T ¼ 300 ꢀC) to the maximum (76.95%,
T ¼ 400 ꢀC), then reduces to 67.86% (T ¼ 600 ꢀC). However, the
catalyst calcined at 400 ꢀC possesses the minimum of strong basic
sites (Fig. S6b). Therefore, we can draw a conclusion that the
highest catalytic activity for GL transesterification is attributed not
only to the more strong basic sites but also to the well dispersed
NiO species. Hence, the 0.2CeNiO-400 catalyst can be considered as
the optimized catalyst in carbonylation of GL with DEC.
3.3. Catalyst recyclability and reaction mechanism
The recyclability of the catalyst is considered as an important
criterion to evaluate the catalytic activity, the 0.2CeNiO-400 fresh
sample was resused for GL transesterification. The results are listed
in Table 2. The conversion of GL decreases from 81.62% to 76.35%
after two cycles, and then significantly drops to 51.07% after the
fourth cycle. However, after treated at 400 ꢀC for 3 h, the catalyst
after four cycles shows an improvement in activity with a GL con-
version of 78.46%. It can be interpreted that the organic compound
adsorbed on the catalyst surface gradually increases, and resulted
in loss of catalytic activity. This validates the result of TG analysis
(Fig. 6 b and c). To identify the component of the organic compound
adsorbed on the catalyst surface, FT-IR spectra of the recovered
catalysts was detected (Fig. S7). Both peaks located at 1105 and
1053 cmꢁ1 emerged after the catalyst was reused, corresponding to
C-C and C-O stretching of 2-hydroxyethyl chain of GC [49]. There-
fore, GC depositing on the catalyst surface could cover the basic

Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
367
Fig. 8. (a) Effect of reaction temperature: GL 4.6 g, DEC 11.8 g, reaction time 6 h, 5 wt.% catalyst of GL. (b) Effect of reactant mole ratio: GL 4.6 g, DEC 5.90 g, 11.80 g, 14.75 g, 17.70 g,
20.65 g, 23.60 g, reaction time 6 h, 5 wt.% catalyst of GL at 85 ꢀC. (c) Effect of catalyst amount: GL 4.6 g, DEC 17.70 g, reaction time 6 h, n wt.% catalyst of GL at 85 ꢀC (n ¼ 1, 3, 4, 5, 6, 7,
9). (d) Effect of reaction time: GL 4.60 g, DEC 17.70 g, 5 wt.% catalyst of GL at 85 ꢀC.
Table 2
reusability of no less than three cycles with a slight decrease in
yield of GC. Besides, The Ce-NiO catalysts show a decrease in par-
The results of the resused 0.2CeNiO-400 catalysta.
ticles sizes compared with that of pure NiO, indicating addition of
Ce in the catalyst synthesis could lessen the aggregation or facilitate
the dispersion of NiO particles which plays a crucial role in pro-
moting GL conversion. It was found the highest catalytic activity for
GL transesterification on 0.2CeNiO-400 catalyst is attributed not
only to the strong basic sites but also to the well dispersed NiO
species. This work brings important improvements in the search of
green routes transform glycerol in high added value chemicals and
less environmental impact.
Entry
1
2
3
4
5
6
Selectivity (%)
Conversion (%)
100
81.62
100
79.84
100
78.35
100
76.52
100
51.07
100
78.46
a
Reaction conditions: GL 4.60 g, DEC 17.70 g, catalyst amount 0.23 g, reaction
temperature 85 ꢀC, reaction time 6 h.
sites, and then weaken the catalytic activity. Consequently, im-
provements and optimization in recyclability of catalyst are
required in future research.
4. Conclusions
Acknowledgments
A solid catalyst (0.2CeNiO-400) with very high activity towards
GL conversion was prepared and employed in the one-pot synthesis
of GC. A GL conversion of 94.14% and GC selectivity of 90.95% was
achieved over this catalyst at the optimum conditions (5 wt.%
catalyst of GL, 85 ꢀC reaction temperature, 8 h reaction time, GL/
DEC ratio of 1:3). The Ce-NiO catalyst is perfect in regeneration and
The financial supports from the National Natural Science
Foundation of china (Nos. 21276050, 21676054, 21406034), Natural
Science Foundation of Jiangsu (No. BK20161415), Fundamental
Research Funds for the Central Universities (No. 3207045414,
3207045101, 3207045426), Key Laboratory Open Fund of Jiangsu
Province (JSBEM201409) are gratefully acknowledged.

368
Y. Wu et al. / Journal of Alloys and Compounds 720 (2017) 360e368
[24] L. Jalowiecki-Duhamel, C. Pirez, M. Capron, F. Dumeignil, E. Payen, Hydrogen
Appendix A. Supplementary data
production from ethanol steam reforming over cerium and nickel based
oxyhydrides, Int. J. Hydrogen Energy 35 (2010) 12741e12750.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jallcom.2017.05.292.
[25] W. Shan, Reduction property and catalytic activity of Ce1ꢁXNiXO2 mixed
oxide catalysts for CH4 oxidation, Appl. Catal. A General 246 (2003) 1e9.
[26] Z. Wang, X. Shao, A. Larcher, K. Xie, D. Dong, C.-Z. Li, A study on carbon for-
mation over fibrous NiO/CeO2 nanocatalysts during dry reforming of
methane, Catal. Today 216 (2013) 44e49.
References
[27] W. Fang, C. Pirez, M. Capron, S. Paul, T. Raja, P.L. Dhepe, F. Dumeignil,
L. Jalowiecki-Duhamel, CeeNi mixed oxide as efficient catalyst for H2 pro-
duction and nanofibrous carbon material from ethanol in the presence of
water, RSC Adv. 2 (2012) 9626.
[28] C.A. Chagas, E.F. de Souza, R.L. Manfro, S.M. Landi, M.M.V.M. Souza, M. Schmal,
Copper as promoter of the NiOeCeO2 catalyst in the preferential CO oxida-
tion, Appl. Catal. B Environ. 182 (2016) 257e265.
[1] P.A.L. Lopes, A.J.S. Mascarenhas, L.A. Silva, Sonochemical synthesis of
Cd1ꢁxZnxS solid solutions for application in photocatalytic reforming of
glycerol to produce hydrogen, J. Alloys Compd. 649 (2015) 332e336.
[2] D. Wang, X. Zhang, C. Liu, T. Cheng, Synthesis of glycerol carbonate from
glycerol and urea over lanthanum compounds, Reaction Kinetics, Mech. Catal.
115 (2015) 597e609.
[3] A. Dibenedetto, A. Angelini, M. Aresta, J. Ethiraj, C. Fragale, F. Nocito, Con-
verting wastes into added value products: from glycerol to glycerol carbonate,
glycidol and epichlorohydrin using environmentally friendly synthetic routes,
Tetrahedron 67 (2011) 1308e1313.
[4] Y. Nakagawa, K. Tomishige, Catalyst development for the hydrogenolysis of
biomass-derived chemicals to value-added ones, Catal. Surv. Asia 15 (2011)
111e116.
[29] N.M. Deraz, Effect of NiO content on structural, surface and catalytic charac-
teristics of nano-crystalline NiO/CeO2 system, Ceram. Int. 38 (2012) 747e753.
[30] W. Zou, C. Ge, M. Lu, S. Wu, Y. Wang, J. Sun, Y. Pu, C. Tang, F. Gao, L. Dong,
Engineering the NiO/CeO2interface to enhance the catalytic performance for
CO oxidation, RSC Adv. 5 (2015) 98335e98343.
[31] S. Xu, X. Yan, X. Wang, Catalytic performances of NiOeCeO2 for the reforming
of methane with CO2 and O2, Fuel 85 (2006) 2243e2247.
[5] C.H. Zhou, J.N. Beltramini, Y.X. Fan, G.Q. Lu, Chemoselective catalytic conver-
sion of glycerol as a biorenewable source to valuable commodity chemicals,
Chem. Soc. Rev. 37 (2008) 527e549.
[6] N. Lertlukkanasuk, S. Phiyanalinmat, W. Kiatkittipong, A. Arpornwichanop,
F. Aiouache, S. Assabumrungrat, Reactive distillation for synthesis of glycerol
carbonate via glycerolysis of urea, Chem. Eng. Process. Process Intensif. 70
(2013) 103e109.
[7] M.O. Sonnati, S. Amigoni, E.P. Taffin de Givenchy, T. Darmanin, O. Choulet,
F. Guittard, Glycerol carbonate as a versatile building block for tomorrow:
synthesis, reactivity, properties and applications, Green Chem. 15 (2013)
283e306.
[8] A.E. Diaz-Alvarez, J. Francos, B. Lastra-Barreira, P. Crochet, V. Cadierno, Glyc-
erol and derived solvents: new sustainable reaction media for organic syn-
thesis, Chem. Commun. 47 (2011) 6208e6227.
[32] A.F.F. Farias, K.F. Moura, J.K.D. Souza, R.O. Lima, J.D.S.S. Nascimento,
A.A. Cutrim, E. Longo, A.S. Araujo, J.R. Carvalho-Filho, A.G. Souza, I.M.G. Santos,
Biodiesel obtained by ethylic transesterification using CuO, ZnO and CeO2
supported on bentonite, Fuel 160 (2015) 357e365.
[33] Y. Li, Q. Zhang, R. Chai, G. Zhao, Y. Liu, Y. Lu, Structured Ni-CeO2-Al2O3/Ni-
Foam catalyst with enhanced heat transfer for substitute natural gas pro-
duction by syngas methanation, ChemCatChem 7 (2015) 1427e1431.
[34] N. Padmanathan, S. Selladurai, Electrochemical capacitance of porous
NiOeCeO2 binary oxide synthesized via solegel technique for supercapacitor,
Ionics 20 (2013) 409e420.
[35] A.C. Ferreira, A.M. Ferraria, A.M.B. do Rego, A.P. Gonçalves, M.R. Correia,
T.A. Gasche, J.B. Branco, Partial oxidation of methane over bimetallic nickel-
elanthanide oxides, J. Alloys Compd. 489 (2010) 316e323.
[36] S. Mahammadunnisa, P. Manoj Kumar Reddy, N. Lingaiah, C. Subrahmanyam,
[9] Y.T. Algoufi, U.G. Akpan, M. Asif, B.H. Hameed, One-pot synthesis of glycidol
from glycerol and dimethyl carbonate over KF/sepiolite catalyst, Appl. Catal. A
General 487 (2014) 181e188.
[10] J. Li, T. Wang, Chemical equilibrium of glycerol carbonate synthesis from
glycerol, J. Chem. Thermodyn. 43 (2011) 731e736.
[11] J. Hu, Y. Gu, Z. Guan, J. Li, W. Mo, T. Li, G. Li, An efficient palladium catalyst
system for the oxidative carbonylation of glycerol to glycerol carbonate,
ChemSusChem 4 (2011) 1767e1772.
[12] H. Li, D. Gao, P. Gao, F. Wang, N. Zhao, F. Xiao, W. Wei, Y. Sun, The synthesis of
glycerol carbonate from glycerol and CO2 over La2O2CO3eZnO catalysts,
Catal. Sci. Technol. 3 (2013) 2801.
NiO/Ce1ꢁxNixO2ꢁ
das an alternative to noble metal catalysts for CO oxida-
tion, Catal. Sci. Technol. 3 (2013) 730e736.
[37] T.B. Pascal Hartmann, Joachim Sann, Andriy Lotnyk, Jens-Peter Eufinger,
Lorenz Kienle, Jurgen Janek, Defect chemistry of oxide nonmaterial with high
surface area_ ordered espartos thin films of the oxygen storage catalyst
CeO2eZrO2, ACS Nano 7 (2013) 2999e3013.
[38] Y. Kobayashi, Y. Fujiwara, Chemical deposition of cerium oxide thin films on
nickel substrate from aqueous solution, J. Alloys Compd. 408e412 (2006)
1157e1160.
[39] X. Yao, Y. Xiong, W. Zou, L. Zhang, S. Wu, X. Dong, F. Gao, Y. Deng, C. Tang,
Z. Chen, L. Dong, Y. Chen, Correlation between the physicochemical properties
and catalytic performances of CexSn1exO2 mixed oxides for NO reduction by
CO, Appl. Catal. B Environ. 144 (2014) 152e165.
[40] C. Tang, J. Li, X. Yao, J. Sun, Y. Cao, L. Zhang, F. Gao, Y. Deng, L. Dong, Meso-
porous NiOeCeO2 catalysts for CO oxidation: nickel content effect and
mechanism aspect, Appl. Catal. A General 494 (2015) 77e86.
[41] T.M.C. Hoang, N.K. Rao, L. Lefferts, K. Seshan, Investigation of Ce-Zr oxide-
supported Ni catalysts in the steam reforming ofmeta-cresol as a model
component for bio-derived tar, ChemCatChem 7 (2015) 468e478.
[42] I. Ganesh, P.S.C. Sekhar, G. Padmanabham, G. Sundararajan, Influence of Li-
doping on structural characteristics and photocatalytic activity of ZnO nano-
powder formed in a novel solution pyro-hydrolysis route, Appl. Surf. Sci.
259 (2012) 524e537.
[43] M.L. Dos Santos, R.C. Lima, C.S. Riccardi, R.L. Tranquilin, P.R. Bueno, J.A. Varela,
E. Longo, Preparation and characterization of ceria nanospheres by
microwave-hydrothermal method, Mater. Lett. 62 (2008) 4509e4511.
[44] H. Jiang, T. Sun, C. Li, J. Ma, Peapod-like nickel@mesoporous carbon core-shell
nanowires: a novel electrode material for supercapacitors, RSC Adv. 1 (2011)
954.
[13] M. Aresta, A. Dibenedetto, F. Nocito, C. Pastore, A study on the carboxylation of
glycerol to glycerol carbonate with carbon dioxide: the role of the catalyst,
solvent and reaction conditions, J. Mol. Catal. A Chem. 257 (2006) 149e153.
[14] H. Li, X. Jiao, L. Li, N. Zhao, F. Xiao, W. Wei, Y. Sun, B. Zhang, Synthesis of
glycerol carbonate by direct carbonylation of glycerol with CO2over solid
catalysts derived from Zn/Al/La and Zn/Al/La/M (M ¼ Li, Mg and Zr) hydro-
talcites, Catal. Sci. Technol. 5 (2015) 989e1005.
ꢀ
[15] M.J. Climent, A. Corma, P. De Frutos, S. Iborra, M. Noy, A. Velty, P. Concepcion,
Chemicals from biomass: synthesis of glycerol carbonate by trans-
esterification and carbonylation with urea with hydrotalcite catalysts. The
role of acidebase pairs, J. Catal. 269 (2010) 140e149.
ꢁ
ꢁ
[16] J. Rousseau, C. Rousseau, B. Lynikaite_, A. Sackus, C. de Leon, P. Rollin,
€
A. Tatibouet, Tosylated glycerol carbonate, a versatile bis-electrophile to ac-
cess new functionalized glycidol derivatives, Tetrahedron 65 (2009)
8571e8581.
[17] Z.I. Ishak, N.A. Sairi, Y. Alias, M.K.T. Aroua, R. Yusoff, Production of glycerol
carbonate from glycerol with aid of ionic liquid as catalyst, Chem. Eng. J. 297
(2016) 128e138.
[18] F.S.H. Simanjuntak, S.R. Lim, B.S. Ahn, H.S. Kim, H. Lee, Surfactant-assisted
synthesis of MgO: characterization and catalytic activity on the trans-
esterification of dimethyl carbonate with glycerol, Appl. Catal. A General 484
(2014) 33e38.
[19] T.W. Turney, A. Patti, W. Gates, U. Shaheen, S. Kulasegaram, Formation of
glycerol carbonate from glycerol and urea catalysed by metal monoglycer-
olates, Green Chem. 15 (2013) 1925.
[20] Y.C. Wong, Y.P. Tan, Y.H. Taufiq-Yap, I. Ramli, H.S. Tee, Biodiesel production via
transesterification of palm oil by using CaOeCeO2 mixed oxide catalysts, Fuel
162 (2015) 288e293.
[21] S. Nasreen, H. Liu, L.A. Qureshi, Z. Sissou, I. Lukic, D. Skala, Ceriumemanganese
oxide as catalyst for transesterification of soybean oil with subcritical meth-
anol, Fuel Process. Technol. 148 (2016) 76e84.
[22] H. Abimanyu, C.S. Kim, B.S. Ahn, K.S. Yoo, Synthesis of dimethyl carbonate by
transesterification with various MgOeCeO2 mixed oxide catalysts, Catal. Lett.
118 (2007) 30e35.
[23] L. Jalowiecki-Duhamel, C. Pirez, M. Capron, F. Dumeignil, E. Payen, Hydrogen
production from ethanol in presence of water over cerium and nickel mixed
oxides, Catal. Today 157 (2010) 456e461.
[45] S.E. Kondawar, A.S. Potdar, C.V. Rode, Solvent-free carbonylation of glycerol
with urea using metal loaded MCM-41 catalysts, RSC Adv.
5 (2015)
16452e16460.
[46] L. Wang, Y. Ma, Y. Wang, S. Liu, Y. Deng, Efficient synthesis of glycerol car-
bonate from glycerol and urea with lanthanum oxide as a solid base catalyst,
Catal. Commun. 12 (2011) 1458e1462.
[47] B. Lu, K. Kawamoto, Preparation of mesoporous CeO2 and monodispersed NiO
particles in CeO2, and enhanced selectivity of NiO/CeO2 for reverse water gas
shift reaction, Mater. Res. Bull. 53 (2014) 70e78.
[48] E. Shangguan, Z. Chang, H. Tang, X.-Z. Yuan, H. Wang, Comparative structural
and electrochemical study of high density spherical and non-spherical Ni(OH)
2 as cathode materials for Niemetal hydride batteries, J. Power Sources 196
(2011) 7797e7805.
ꢀ
~
[49] V. Calvino-Casilda, G. Mul, J.F. Fernandez, F. Rubio-Marcos, M.A. Banares,
Monitoring the catalytic synthesis of glycerol carbonate by real-time atten-
uated total reflection FTIR spectroscopy, Appl. Catal. A General 409e410
(2011) 106e112.