Metal-free catalytic conversion of CO2 and glycerol to glycerol carbonate

Article abstract of DOI:10.1039/c7gc00260b

Using CO₂ as a carbonyl building block to synthesize valuable chemicals is an important issue in the field of green and sustainable chemistry. Herein, the conversion of CO₂ with glycerol to glycerol carbonate was investigated in the presence of 2-cyanopyridine. It was found that 2-cyanopyridine not only acts as the dehydrating agent to break the thermodynamic limit of the reaction, but also activates the carbonyl bond of CO₂ to catalyze the present carbonylation as confirmed by FTIR experimental spectra. Moreover, the activation closely depends on the stereo-structure of cyanopyridine, in that 3-cyanopyridine and 4-cyanopyridine do not have such activating function. The theoretical calculation demonstrated that 2-cyanopyridine could bond CO₂ through the conjugating nitrogen to form a five-membered ring, thus CO₂ is activated and then reacts with glycerol to produce glycerol carbonate. The reaction parameters were examined and evaluated for the reaction catalyzed with 2-cyanopyridine in the absence of any metal catalysts and additives. With increasing CO₂ pressure, the yield of glycerol carbonate increases, and under the optimum conditions an 18.7% yield is obtained which is one of the best results reported up to now. The present work provides a new way for activation of CO₂.

Full text of DOI:10.1039/c7gc00260b

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Metal-free catalytic conversion of CO2 and glycerol to glycerol
carbonate
Xinluona Su,a,b,c Weiwei Lin,*a,b Haiyang Cheng,a,b Chao Zhang,a,b Ying Wang,*d Xiujuan Yu,c Zhijian
Wud and Fengyu Zhao*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
CO2 as a carbonyl building block to synthesize valuable chemicals is an important issue in the field of green and sustainable
chemistry. Herein, the conversion of CO2 with glycerol to glycerol carbonate was investigated in the presence of 2-
cyanopyridine. It was found that 2-cyanopyridine not only acts as the dehydrating agent to break the thermodynamic limit
of the reaction, but also activates the carbonyl bond of CO2 to catalyze the present carbonylation as confirmed by FTIR
experimental spectra. Moreover, it closely depends on the stereo-structure of cynaopyridine, that 3-cynaopyridine and 4-
cynaopyridine does not have such activating function. The theoretical calculation demonstrated that 2-cyanopyridine
could bond CO2 through the conjugating nitrogen to form a five-membered ring, thus CO2 is activated and then reacts with
glycerol to produce glycerol carbonate. The reaction parameters were examined and evaluated for the reaction catalyzed
with 2-cyanopyridine in the absence of any metal catalysts and additives. With increasing of CO2 pressure, the yield of
glycerol carbonate increases, and under the optimum conditions a 18.7% yield is obtained which is one of the best results
reported up to now. The present work provides a new way for activation of CO2.
www.rsc.org/
6
glycerol with urea 4e, 5, and direct carbonation of glycerol with CO2
Introduction
have been explored. Among them, using CO2 as carbonyl source is
considered as the most competitive process as the toxic and
expensive carbonyl reagent is replaced, and the atom utilization of
this route is as high as 87%, in which water as a sole byproduct is
produced 7. However, the carbonylation of glycerol with CO2
directly is quite difficult due to the indolent of two substrates and
The utilization and conversion of CO2 and biomass as renewable
resources have been the important issues and paid more attention
in the fields of green and sustainable chemistry. The conversion of
CO2 to chemicals and fuels has attracted much interest as CO2 is
nontoxic, non-flammable, and cheap carbon-oxygen source 1. The
transformation of CO2 with glycerol directly to glycerol carbonate is
one of the most attractive reactions, as two renewable and cheap
resources are converted to the high valuable product 2. The glycerol
is a residual produced in the conversion of biomass to biodiesel and
the glycerol carbonate is a novel reagent that can be used in the gas
separation membrane, polyurethane foam, and polymeric materials,
as well as a kind of good and environmental benign solvent and
surfactant in the fields of coating, paint and detergent 3.
8
the limitation of the reaction equilibrium . In order to promote the
reaction rate, a certain co-reactant or coupling reagent such as
ethylene carbonate 9, propylene oxide 10 was added to the reaction,
but the results were still far from the expected as large amounts of
the additional coupling reagent should be used. It was found that
when the reaction of glycerol and carbon dioxide was catalyzed
n
with Bu2SnO homogeneous catalyst, only 1.9% yield of glycerol
o
carbonate was obtained under the reaction conditions of 180 C, 5
MPa, 6 h 11, while the yield of glycerol carbonate could reach 30%
Traditionally, glycerol carbonate is synthesized from the
reaction of glycerol with phosgene. As the high toxicity and
corrosive nature of phosgene, alternative routes such as
transesterification of glycerol with carbonates 4, carbonation of
o
with addition of methanol solvent at the conditions of 120 C, 13.8
MPa, 4 h 7, and it reached 35% in the presence of dehydrating
reagent of 13X (soda) zeolite at the same conditions. Sun et al.
reported the synthesis of propylene carbonate from propylene
glycol and CO2 could be effectively performed in a solvent of
acetonitrile 12. Moreover, it was recently reported the yield of
glycerol carbonate could be enhanced when acetonitrile was used
as a solvent and dehydration reagent in the carbonylation of
glycerol and CO2. For example, a 14.3% yield of glycerol carbonate
was obtained with heterogeneous catalyst of La2O2CO3–ZnO metal
a.State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 P.R. China,
E-mail: zhaofy@ciac.ac.cn; linwei@ciac.ac.cn; Fax&Tel.: +86-431-8526-2410;
b.Laboratory of Green Chemistry and Process, Changchun Institute of Applied
chemistry, Chinese Academy of Sciences, Changchun 130022 P.R. China
c. Department of Environmental Science and Engineering, Heilongjiang University,
Harbin, 150080, P.R. China
d.State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P.R. China
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
o
o
oxides at 170 C, initial pressure 4 MPa at 20 C 6a, and 15.2% yield
was achieved with Cu/La2O3 catalyst at 150 oC, 7 MPa, 12 h
Moreover, Zn/Al/La/M (M = Li, Mg and Zr) 6d and Zn/Al/La/X(X=F, Cl,
.
6b
6c
Br)
hydrotalcites respectively gave 15.1% and 16% yield of
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glycerol carbonate at 170 oC, 4 MPa (initial pressure at 20 oC). nanopolyhedra CeO2 gave
Journal Name
a
higher yield. However,
Although the improved yield was obtained with using acetonitrile as nanopolyhedra CeO2 was not so effective in the absence of 2-
the dehydration agent, however, acetonitrile is easily hydrolysis to cyanopyridine, in which glycerol was only converted 1.6%. It
acetic acid which could etherify with glycerol to decrease the yield was unexpected, glycerol could be converted 31.1% in the
of glycerol carbonate. The dehydration agent is important to the presence of 2-cyanopyridine without addition of any metal
carbonylation of alcohols with CO2, 2-cyanopyridine was reported oxide catalysts, and the glycerol carbonate yield reached
to be effective dehydration agent in the synthesis of dimethyl 11.4%, which was similar to the cases of the most metal oxide
13
carbonate from methanol and CO2 and it was also found to be catalysts used (Table 1).
effective for the carbonylation of glycerol with CO2 directly
catalyzed by CeO2 catalyst 14
.
Table 2 The results for carbonylation of glycerol with CO2 over
Although some progresses have been achieved, however, the CeO2 catalysts.
carbonylation of CO2 with glycerol directly has been less studied up
to now because of the inert CO2 and the limitation of
thermodynamics and chemical equilibrium of the reaction;
therefore it leaves a great challenge to the researchers. In this work,
we firstly screened several metal oxide catalysts for the
carbonylation of glycerol and CO2 directly in the presence of 2-
cyanopyridine. Surprisingly, we found that the reaction can be
performed effectively with 2-cyanopyridine in the absence of any
metal catalysts and additives. This result stimulated us to discuss
the function of 2-cyanopyridine played in the present carbonylation
with the in-situ high-pressure FTIR and theoretical calculations. The
findings of this work will attract attention of researchers in the
fields of environmental catalysis, green synthesis, conversion of
biomass as well as the activation and transformation of CO2.
Entry
Catalyst
Conversion
(%)
Yield
(%)
1
2
3
4
5
CeO2 Mesoporous
CeO2 nanocube
29.3
10.3
34.4
28.1
38.2
35.5
10.4
12.9
13.5
14.2
CeO2 nanorods
CeO2 nanowires
CeO2 nanopolyhedra
aCeO2 nanopolyhedra 1.6
-- 31.1
0.8
6
11.4
Reaction conditions: Catalyst 0.085 g, glycerol 1.15 g, 2-
cyanopyridine/glycerol(mole ratio) 2:1, CO2 10 MPa, 170 oC,
12 h. a Without 2-cyanopyridine.
The function of 2-cyanopyridine
Results and discussion
In order to investigate the function of 2-cynopyridine in the
carbonylation of CO2 and glycerol, several kinds of dehydrating
reagents containing nitrogen in their molecules were examined in
the absence of any metal oxide catalysts, and the results are shown
in Table 3. The yield of glycerol carbonate was only 0.8% in the
absence of dehydrating reagent as the limitation of reaction
Screen of metal oxide catalysts
Several metal oxides as catalyst were screened for the
carbonylation of glycerol and CO2 with 2- cyanopyridine as
dehydrating agent, and the results are listed in Table 1. It was
found that all the examined catalysts of ZnO, ZrO2, Al2O3, TiO2
and CeO2 were active, with them, the conversion of glycerol
reached 41.3%, 30.9%, 37.2% , 34.5% and 35.5%, respectively.
By comparison, the higher yield (14.2 %) of glycerol carbonate
was obtained over the CeO2, which was more effective and
selective for carbonlytion of glycerol and CO2 directly under
the reaction conditions.
Table 3 The results for carbonylation of CO2 and glycerol with
different dehydration reagents.
Entry
Dehydrating agent
--
Conversion (%)
Yield (%)
0.7
1
2
3
1.4
Table 1 The results of carbonylation of glycerol with CO2 to
glycerol carbonate over different metal oxides.
Acetonitrile
3-Cyanopyridine
11.1
37.7
1.5
5.3
Entry
Catalyst
Conversion (%)
Yield (%)
1
2
3
4
5
ZnO
41.3
30.9
37.2
34.5
35.5
11.9
10.9
10.4
10.5
14.2
4
5
4-Cyanopyridine
2-Cyanopyridine
46.7
31.1
3.8
TiO2
ZrO2
Al2O3
CeO2
11.4
Reaction conditions: glycerol 1.15 g, dehydrating agent/glycerol
(mole ratio) 2:1, CO2 10 MPa, 170 oC, 12 h.
Reaction conditions: catalyst 0.085 g, glycerol 1.15 g, 2-
cyanopyridine/glycerol(mole ratio) 2:1, CO2 10 MPa, 170
oC, 12 h.
equilibrium (entry 1), and acetonitrile also gave a lower glycerol
carbonate yield (1.5%) under the reaction conditions (entry 2). For
the cases of 3-cyanopyridine and 4-cyanopyridine, the yield of
glycerol carbonate was increased to 5.3% and 3.8%, respectively
(entries 3, 4), but they were still lower than the yield of 11.4%
obtained with 2-cyanopyridine (entry 5), which suggested that the
structure of dehydrating reagent, namely the stereo-position of the
Next, we checked the catalytic properties of CeO2 with
different crystal structure. The results are presented in Table 2,
it is clearly that the conversion of glycerol and yield of glycerol
carbonate depended on the microstructure of CeO2, the
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cyano group, had significant effect on the present carbonylation there are two ways for CO2 to connect or interact with the
reaction. The high-efficiency of 2-cyanopyridine superior to the cyanopyridine, one is on the site-a (N in pyridine) and the
other nitriles was also found and reported in the reaction of CO2
Table 4 Theoretical calculations of the structures and binding
with methanol, which was ascribed to the relatively strong alkalinity
energies of CO2 connecting with different cyanopyridines.
and the intermolecular hydrogen bonding formed between H atom
in amide group and N atom in pyridine ring 13b. In addition, it was
Possible connection structure
also reported that the effective dehydrating reagent of
cynaopyridine with a CN group at the 2-position of 6-membered
ring heteroaromatics for the organic carbonate synthesis from CO2
a-T
b-T
c-T
and alcohol over CeO2 catalyst 13a
.
2-cyanopyridine Eb = 74.69
3-cyanopyridine Eb = 72.83
4-cyanopyridine Eb = 67.39
Eb = 92.26
Eb = 92.63
Eb = 92.57
Eb = 57.71
The unit of energy is kcal/mol. a-T indicates CO2 connect to N in pyridine;
b-T indicates CO2 connect to N in C≡N; and c-T indicates CO2 connect to
both N in pyridine and N in C≡N.
Fig.1. FTIR spectra of (a) 2-cyanopyridine, (b) 2-cyanopyridine
pretreated with CO2, (c) 3-cyanopyridine, (d) 3-cyanopyridine
pretreated with CO2, (e) 4-cyanopyridine, (f) 4-cyanopyridine
pretreated with CO2.
other is on the site-b (N in cyano group, -C≡N). For these two
kinds of interaction, the absorption energies are 74.69, 72.83
and 67.39 kcal/mol for CO2 connecting with the N in pyridine,
and 92.26, 92.65, 92.57 kcal/mol for CO2 connecting with a N
in cyano group, of 2-cynaopyridine, 3-cynaopyridine, and 4-
cynaopyridine, respectively. There is no large difference
among them. However, for the 2-cynaopyridine, besides the
above two kinds of connection, there is the third connecting
way, that is a CO2 molecule connecting with one nitrogen in
cyano group and the other nitrogen in pyridine ring
simultaneously to form a five-membered ring intermediate
In order to reveal the function of cyanopyridine, FTIR spectra
were measured for 2-cyanopyridine, 3-cyanopyridine or 4-
cyanopyridine after adsorbed CO2. The sample was added to the
high-pressure reactor, then 10 MPa CO2 was introduced and stirred
o
continuously at 170 C for 6 h. The final sample was collected after
the reactor was cooled to room temperature and vented CO2, then
it was measured and the infrared spectroscopy was recorded. As
shown in Fig. 1, it is clearly that several new bands presented at
1263, 1373, 1526, and 1689 cm-1 for the 2-cyanopyridine pretreated
with CO2 by comparing to the pure 2-cyanopyridin. The band at
1373 cm-1 is ascribed to C-N bond in the ring and 1263 cm-1 is (2c-T), and its adsorption energy is 57.71 kcal/mol, the lowest
one among the three kinds of interactions. Therefore,
compared with 3-cyanopyridine and 4-cyanopyridine, it is
assigned to the new C-N bonds formed from the interaction
between cyano group and CO2 15; the band at 1526 cm-1 is assigned
to C=N bond (N in C≡N)16 and the band at 1689 cm-1 assigned the
C=O bonds17. However, for the 3- cyanopyridine and 4-
cyanopyridine pretreated with CO2, no any new absorbing bonds
were found compared with their original spectra, suggesting the
interaction between them with CO2 was much weak. While, the
interaction between 2-cyanopyridine and CO2 was very strong that
some new bonds formed when CO2 connected with 2-cyanopyridine,
thus 2-cyanopyridine presented
a function to promote the
carbonylation of CO2 with glycerol significantly.
Fig.2 (a) The calculated IR spectrum of 2c-T (in black) and 2-
cyanopyridine (in red). (b) The optimized structures of 2-
cyanopyridine and CO2 which can form a five- member ring.
The interaction between CO2 and 2-cyanopyridine
To certify the interaction between CO2 and 2-cyanopyridine,
theoretical calculation was performed to simulate the
optimized structure and the Eb values. As shown in Table 4, CO2 molecule is activated and then to react with glycerol and
much easier for 2-cyanopyridine to interact with CO2, thus the
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produce glycerol carbonate with the higher yield compared to
the 3-cyanopyridine and 4-cyanopyridine. To further confirm calculation results,
On the basis of the experimental and theoretical
possible reaction route for the
a
the five-membered structure intermediate was formed carbonylation of CO2 with glycerol promoted by 2-
between CO2 and 2-cyanopyridine, the IR spectra for 2a-T, 2b- cyanopyridine was proposed and shown in scheme 1. First, 2-
T
and 2c-T were calculated and compared with their cyanopyridine activated CO2 to form a five-member ring
experimental spectra. For the case of 2a-T and 2b-T (Fig. S1, intermediate, then it reacted with glycerol to form glycerol
S2), there are two new characteristic peaks at 1287, 1345 cm-1 carbonate. During the reaction, 2-cyanopyridine was
and 1597, 1883 cm-1, respectively, which are not consistent transferred to 2-picolinamide, it acted as dehydrating reagent
with the experimental results. While, the IR spectrum and promoter in the present carbonylation reaction.
calculated for the structure of 2c-T gave out four new peaks at
1270, 1368, 1579, 1842 cm-1 (Fig. 2 a), which coordinated
closely with the experimental results. It confirmed again the
stronger interaction exited between CO2 and 2-cyanopyridine
and the five-member ring structure intermediate was formed.
The peaks at 1270, 1368, 1579, 1842 cm-1 corresponds to the
C-N in pentagon, C-N in the ring, C=N in the ring, C=O out of
ring, respectively.
The Influence of reaction conditions
The reaction parameters have been discussed for the present
carbonylation of glycerol with CO2 directly promoted by 2-
cyanopyridine in the absence of any metal catalysts. The effect
of CO2 pressure was checked in a range of 4-20 MPa, and the
results are shown in Fig. 4a and Fig. S3. With enhancing CO2
pressure from 4.0 MPa to 20.0 MPa, both the yield of glycerol
carbonate and conversion increased, they increased from 6.8%
to 17.8% and 28.7% to 46.4%, respectively. Meanwhile, the
formation of 2-picolinamide increased either. The same trend
was also found for the effect of 2-cyanopyridine amount (Fig.
4b), the yield of glycerol carbonate and conversion increased
with the increase in the amount of 2-cyanopyridine, and the
highest yield was obtained at a mole ratio of 2-cyanopyridine
to glycerol of 3, with further increasing the amount of 2-
cyanopyridine, the yield declined slightly, even though the
conversion still increased. It was also found in Fig. 4c that the
yield of glycerol carbonate increased with prolonging reaction
time, and it increased from 4.6% to 16.8% when the reaction
time was extended from 1 h to 12 h. While the conversion of
glycerol increased within the initial 6 h, and then remained
almost invariable. As shown in Fig 4d, the conversion of
glycerol increased from 29.3% to 46.5% and the yield of
glycerol carbonate increased from 11% to 18.7% with rising
temperature from 150 oC to 180 oC.
Fig.3. In-situ FTIR spectra recorded at different time during the
reaction.
Moreover, the high-pressure in-stiu FTIR spectroscopy
was operated to monitor the reaction process. As shown in Fig.
3, some new peaks were found, but they were very weak due
to the low concentration of glycerol carbonate formed in the
mixture and the interfering of the stronger vibration of
carbonyl group of DMF solvent. Nevertheless, the peak at
1134cm-1 assigned to the band of secondary alcohol of glycerol,
it disappeared with the reaction conducting, and the peaks at
1521, 1416 and 773 cm-1 increased, which ascribed to glycerol
5b,
carbonate
18. These results illustrated that the glycerol
reacted with CO2 directly to produce glycerol carbonate
gradually in the presence of 2-cyanopyridine without addition
of any metal catalyst and additives.
N
N
N
N
O
O
O
O
N
N
N
N
OH
Fig. 4 Effect of (a) CO2 pressure, (b) amount of 2-cyanopyridine,
(c) reaction time, (d) reaction temperature on carbonylation of
glycerol with CO2. Reaction conditions: glycerol 1.15 g, CO2: 15
MPa (b, c, d), 2-cyanopyridine 3.9041 g (a, c, d), T:170 oC
(a,b,c), 12 h (a,b,d).
C
O
HO
+ H+
OH
O
O
O
- H+
NH
O
NH
O
O
N
O
N
- H+
+ H+
- H+
+ H+
N
NH2
O
O
O
+
O
O
OH
N
N
O
O
O
HO
O
OH
OH
OH
HO
For the transformation of CO2, solvent often has a significant
influence on the reaction 19. The effect of several solvents was
also checked for the present carbonylation, it was found the
glycerol carbonate yield in NMP and DMF was 11.5% and
HO
Scheme 1 Possible reaction route for carbonylation of CO2 with
glycerol in the presence of 2-cyanopyridine.
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10.1%, respectively, which are higher compared with the ethanol for several times to make sure that the residual
results in the solvents of acetone and hexane (Table S1). impurities were removed. The product was dried at 80 °C for
However, the yield of glycerol carbonate still could reach 11.4% overnight, and calcined at 500 °C for 4 h. For ZrO2, the
in the absence of any solvents.
preparation procedure was that ammonia solution was slowly
added to ZrOCl2·8H2O aqueous solution (6.445g in 100 mL of
distilled water) until the pH reached 9.0 and aging at 60 °C for
3 h. The solid was thoroughly washed with deionized water,
and then washed with ethanol for three times. After that, the
solid was dried at 80 °C for 24 h. Finally, the dried solids were
calcined at 400 °C for 4 h in N2 atmosphere. For Al2O3, the
preparation procedure was that NH3·H2O (3.85 M) was added
to Al(NO3)3 (0.5 M) solution until the pH was adjusted to 9.0
with vigorous stirring. The precipitate was filtered, washed
several times and then dried at 100 °C for 24 h. The obtained
product was calcined at 500 °C in air for 4 h. TiO2 (P25) were
purchased from ACROS.
Conclusions
The carbonylation of CO2 and glycerol to glycerol carbonate
was carried out by using 2-cyanopyridine as a dehydrating
agent in the present work. It was interesting to find that 2-
cyanopyridine could promote the reaction in the absence of
any metal catalysts and additives, and a high yield (18.7%) of
glycerol carbonate was obtained from the glycerol
carbonylation directly with CO2 at 180 oC, 15 MPa. By
comparson, however, 3- cyanopyridine and 4- cyanopyridine
were less effective, as the stereo-structure of cyanopyridine
was very important for the interaction between it with CO2. It
was certified that CO2 could connect with the conjugating
nitrogen atoms in the 2-cyanopyridine molecule to form a five-
member ring intermediate, and the activated CO2 then reacts
with glycerol to form the desired product of glycerol carbonate.
This work reveals a kind of pyridine compound could promote
the carbonylation of CO2 directly with glycerol in the absence
of any metal catalysts; and it opens a new way to activation of
CO2 via an organic reagent.
The carbonylation of CO2 with glycerol
The carbonlytion of CO2 with glycerol was carried out in 50 mL
stainless-steel autoclave equipped with a magnetic stirrer. In
typical experiment, glycerol, 2-cyanopyridine and/or catalysts
were charged into the reactor, the reactor was sealed and
flushed with CO2 more than five times to remove air, and then
placed into an oil bath preset to the reaction temperature for
15 min. Then CO2 was introduced into the reactor and the
reaction was started with continuously stirring. After the
reaction, the autoclave was cooled to room temperature and
the residue CO2 was vented slowly. The liquid products were
analyzed with a gas chromatograph (Shimadzu-14C, Restek
Stabilwax 30 m × 0.53 mm × 1 μm capillary column) and
identified by gas chromatograph/mass spectrometry (GC/MS,
Agilent 5890, FID, Capillary column, HP-5). For quantitative
analysis, diethylene glycol monomethyl ether (DEGME) was
used as the internal standard substance.
Experimental
Catalyst preparation
CeO2 nanopolyhedra, nanorods, nanowires and nanocube
were prepared by a hydrothermal method. Ce(NO3)3·6H2O (4.5
mmol) was dissolved in 15 mL deionized water. This solution
was added to an aqueous NaOH solution of the appropriate
concentration (CNaOH; see below). The mixture was kept stirring
for 30 min at room temperature. Then, the slurry was
transferred into Teflon-lined stainless autoclave and heated at
different temperatures (T) for 24 h. After the hydrothermal
treatment, the precipitates were separated by filtration,
washed with deionized water and ethanol several times and
dried at 80 °C for 24 h. The values of CNaOH and T were varied
according to the target crystal shape (nanopolyhedra: CNaOH
=0.1 M, T=100 oC; nanorods: CNaOH =7 M, T=100 oC; nanowires:
CNaOH =5 M, T=100 oC; nanocube: CNaOH =7 M, T=180 oC). Meso-
CeO2, ZrO2, Al2O3 and ZnO were prepared by a precipitation
method. For Meso-CeO2, the preparation procedure was
Ce(NO3)3·6H2O (4.34 g) and CTAB (2.19 g) were dissolved in
200 mL distilled water. A NaOH solution (2 g in 300 mL of
distilled water) was added into solution system with stirring at
room temperature for 24 h. After thermal aging at 90 °C for 3 h,
the pale yellow precipitate was filtered and washed with hot
water (80 °C) to remove the residual CTAB. The resultant
powder was dried at 100 °C for 6 h and then calcined at 450 °C
Fourier-transform infrared (FTIR) spectroscopy
In situ high-pressure ATR-FTIR experiments were measured
using a Pike accessory equipped with a diamond ATR crystal
coupled to a 28 mL cell containing a quartz window on the
bottom plate. The experimental procedure was as follows:
1.15 g glycerol, 3.9 g 2-cyanopyridine and 2 mL N,N-dimethyl
formamide (DMF) were added to the kettle, then it was heated
to 170 °C and CO2 was introduced into the stainless steel kettle.
When the pressure reached a certain value, a background
spectrum was collected, and then the reaction was started
with continuously stirring. The FTIR spectra were registered
every 10 min for a period of 6 h on a Nicolet iS50 spectrometer
equipped with a MCT detector.
Fourier-transform infrared (FTIR) spectra of 2-, 3-, 4-
cyanopyridine and these reagents pretreated with CO2 for 6 h
at 170 oC were recorded at room temperature with a NICOLET
iS50 infrared spectrometer in the region of 400–4000 cm-1.
for 4 h. ZnO: NH3⋅H2O (4 M) solution was slowly dropped into
the 0.5 mol/L Zn(NO3)2 solution until the pH was adjusted to
8.0 with vigorous stirring at 60 °C. The mixture was aged for 5
h and the precipitate was filtered with deionized water and
Theoretical methods
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DOI: 10.1039/C7GC00260B
ARTICLE
Journal Name
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Theoretical calculation was used to explore the interaction
between CO2 and 2-cyanopyridine. All the electronic structure
and the energy calculations were carried out by the Gaussian
09 program 20. The equilibrium geometries and frequencies, as
well as IR spectrum, of all the structures were calculated at the
B3LYP/aug-cc-pVDZ level, i.e. Becke’s three-parameter
nonlocal-exchange functional with the nonlocal correlational
21
of Lee et al. (B3LYP) method with the aug-cc-pVDZ basis set
.
This method has been successfully used to estimate the
electrochemical reactivity of cyanopyridine in solution for CO2
reduction mechanism 22. To explore the interaction between 2-,
3-, 4-cyanopyridine and CO2, binding energies (Eb ) were
calculated based on the following equation,
Catal. Sci. Technol., 2015, 5, 989-1005.
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ꢀꢁ = ꢀꢂꢃꢂꢄꢅ − ꢀꢆ − ꢀꢇꢈꢉ
(1)
Where, ꢀꢂꢃꢂꢄꢅ is the total energy of 2-, 3-, 4-cyanopyridine and
CO2, ꢀꢆ is the energy of 2-, 3-, 4-cyanopyridine, and ꢀꢇꢈꢉ is the
energy of gas phase CO2, respectively. According to this
definition, a negative value indicates an exothermic process.
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Acknowledgements
The authors gratefully acknowledge the financial support from
the National Key Research and Development Program of China
(2016YFA0602900), the financial support from NSFC
(21603212, 21672204, 21673220) and Special Program for
Applied Research on Super Computation of the NSFC-
Guangdong Joint Fund (the second phase). Part of the
computational time is supported by the Performance
Computing Center of Jilin University and Changchun Normal
University.
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DOI: 10.1039/C7GC00260B
Graphical abstract
The synthesis of glycerol carbonate directly from CO2 and glycerol was promoted by
2-cyanopyridine in the absence of any metal catalyst.