Imidazolium-Salt-Functionalized Covalent Organic Frameworks for Highly Efficient Catalysis of CO2 Conversion

Article abstract of DOI:10.1002/cssc.201900570

The conversion of CO₂ into valuable chemicals is an ideal pathway for CO₂ utilization in industry, although the development of highly efficient catalysts remains a challenge. Herein, the design and synthesis of two covalent organic frameworks (COFs) functionalized with imidazolium salts were reported as catalysts for CO₂ conversion. The resultant COFs possessed highly crystalline structures, showed high stability and surface area, and contained dense catalytic active sites on the pore walls. They exhibited outstanding catalytic performances for the reaction of CO₂ with epoxides without any solvent or cocatalyst under mild conditions and afforded a record turnover number of 495 000. In addition, the COFs could serve as effective catalysts in the reductive reaction of CO₂ with amines. The results presented here thus demonstrate the exceptional potential of the functionalized COFs for various challenging CO₂ transformations.

Full text of DOI:10.1002/cssc.201900570

Accepted Article
Title: Imidazolium Salts Functionalized Covalent Organic Frameworks
for Highly Efficient Catalysis of CO2 Conversion
Authors: Jikuan Qiu, Yuling Zhao, Zhiyong Li, Huiyong Wang, Yunlei
Shi, and Jian Ji Wang
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To be cited as: ChemSusChem 10.1002/cssc.201900570
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Imidazolium Salts Functionalized Covalent Organic Frameworks
for Highly Efficient Catalysis of CO2 Conversion
Jikuan Qiu, [a]ƚ Yuling Zhao, [a]ƚ Zhiyong Li, [a] Huiyong Wang, [a]* Yunlei Shi[a,b] and Jianji Wang[a]*
Abstract: The conversion of CO2 into valuable chemicals is one of
class of crystalline porous materials with wide applications in
molecule storage and separation,[18-20] catalysis,[21-26] energy
the most ideal pathways for CO2 utilization in industry, while the
development of highly efficient catalysts remains a challenge. Herein, storage, and others.[27-29] These materials are constructed from
we report the design and synthesis of two novel imidazolium salts
functionalized covalent organic frameworks (COFs) for the catalysis
of CO2 conversion. The resultant COFs possess high crystalline
structure, show high stability and surface area, and contain dense
catalytic active sites on the pore walls. They exhibit outstanding
catalytic performance for the reaction of CO2 with epoxides without
any solvent and co-catalyst under mild conditions, and afford a
record turnover number of 495000. In addition, the COFs can be
served as effective catalysts in the reductive reaction of CO2 with
amines. The results presented here thus give the exceptional
potential of the functionalized COFs for challenging various CO2
transformations.
organic building blocks through reversible covalent bonds.[30-32]
A
significant feature is that they possess excellent properties such
as inherent porosity, high stability, ordered pore walls, and
extremely low density.[33-36] In recent years, COFs have been
employed as heterogeneous catalysts for the cycloaddition of
[37, 38]
epoxides with CO2. For example, Roeser and Yu groups
reported that covalent triazine frameworks composed of high
number of basic nitrogen sites efficiently catalyzed the
cycloaddition of CO2 with different starting epoxides. Bhanage
[39, 40]
and Liu groups
demonstrated that hydrogen bond donor
(HBD) such as -OH decorated COF materials could be used as
excellent catalysts for the chemical fixation of CO2 to cyclic
[41]
carbonate. Ma and co-workers
developed a novel porous
heterogeneous catalyst by encapsulating linear ionic polymers
and metal Lewis acid catalytic sites on the opened channels of
COFs, and then used as catalyst for the reaction of CO2 with
various epoxides. However, it is noted that most of these
catalysts exhibit low catalytic efficiency and/or work under
assistance of co-catalysts. Therefore, development of novel
COF catalysts with highly catalytic capacity remains a challenge
in CO2 transformation.
Introduction
With the large consumption of fossil energy, the emission of
greenhouse gas carbon dioxide (CO2) has caused serious
environmental problems such as global warming.[1] The
conversion of CO2 into valuable chemicals is one of the most
ideal pathways to reduce CO2 emission and fully utilize this
abundant, cheap, and nontoxic C1 source.[2,3] As a result,
considerable efforts have been devoted to the development of
catalytic methodologies for chemical fixation of CO2 to produce
valuable chemicals.[4-6] In particular, the cycloaddition of
epoxides with CO2 to form cyclic carbonates is an important and
atom-economic reaction, and the resultant products are
important heterocyclic compounds widely used in organic
synthesis.[7-9] Various catalysts have been investigated for the
cycloaddition reaction. Recently, some crystalline porous
materials have shown promising applications in gas adsorption
and catalysis because of their predictable control over structure.
Numerous studies have confirmed that imidazolium salts are a
unique species for activating and subsequently transforming
[42-44]
CO2 into valuable chemicals.
Nevertheless, the catalytic
activity of these homogenous catalysts is usually not high, and
the separation of them from raw materials and products is often
difficult. Herein, we report a novel class of imidazolium salts
functionalized COFs synthesized by post-modification strategy.
The as-synthesized COFs show high crystalline structure and
porosities with the pore size of 2.6 nm and the surface area of
up to 2027 m2g-1, which provides the required accessibility to
guest molecules for quick diffusion. The materials possess
highly dispersed active sites in the pore channels, and exhibit
remarkable catalytic performance for the cycloaddition of CO2
with epoxides with a record turnover number under mild
conditions. Moreover, the COFs can also be served as highly
active catalysts for the formylation of amines with CO2.
[10, 11]
For example, metal–organic frameworks (MOFs) have
been served as excellent heterogeneous catalysts for this
reaction. [12-14]
Covalent organic frameworks (COFs)[15-17] are another novel
[a]
J. Qiu, Dr. Y. Zhao, Z. Li, Dr. H. Wang, Y. Shi, Prof. J. Wang
Collaborative Innovation Center of Henan Province for Green
Manufacturing of Fine Chemicals, School of Chemistry and
Chemical Engineering, Key Laboratory of Green Chemical Media
and Reactions, Ministry of Education
Results and Discussion
In order to chemically bind imidazolium salts on the pore walls
of COFs, we first synthesized the imine-linked COF material
containing hydroxyl groups via condensation reaction between
2-hydroxybenzene-1,4-dialdehyde 1 and amine 2 (Figure 1). The
hydroxyl groups could remain intact during the COF synthesis,
thus facilitating further chemical modifications. The reaction was
carried out in a mixture of o-dicholorobenzene and n-butanol
under solvothermal conditions at 120 oC for 3 days by using
Henan Normal University
Xinxiang, Henan, P. R. China.
E-mail: jwang@htu.cn; hywang@htu.cn
Y. Shi
College of Chemistry and Chemical Engineering, Lanzhou
University, Lanzhou, Gansu 730000, China
ƚ J. Qiu and Y. Zhao contributed equally.
Supporting information for this article is given via a link at the end
of the document.
[b]
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Figure 1. Schematic representation for the direct construction of imidazolium salts functionalized COF materials, COF-HNU3 and COF-HNU4, through channel-
walls engineering of COF-HNU2.
acetic acid as catalyst (see Experimental section for details).
The as-synthesized COF was designated as COF-HNU2, and its
hexagonal unit cell (P6) with the parameters of a =37.642298, b=
37.642298, c=3.468514, α=β=90° and γ=120° (Table S1). In this
FT-IR spectrum was compared with the building blocks (1 and 2), model, the Pawley refined pattern (red curve) matched well with
It was found from Figure S1 (see Supporting Information) that the experimental profile (blue curve), and their difference (green
the characteristic peak for C=N at 1612 and 1212 cm−1 appeared, curve) was very small. Figure 3 also showed the extended
while the peaks for aldehydic C−H stretching (at 2889 cm−1) and
C=O (at 1663 cm−1) of 1 and the N−H stretching (at 3209, 3354,
and 3434 cm−1) of 2 disappeared, which indicate that the
condensation was successful. The 13C solid state NMR spectrum
of COF-HNU2 showed a characteristic signal at 167 ppm
originated from the imine linkage carbon atoms (Figure S2).
Moreover, thermo gravimetric analysis (TGA) indicates that this
COF material was stable up to 430 °C (Figure S3).
structure of the framework. In contrast, the staggered orientation
(AB stacking mode) showed significant deviation from the
experimentally observed PXRD profile (Figures S7-S8, Table
S2).
The morphology of the COF-HNU2 was characterized using
scanning electron microscopy (SEM). The complex aggregates
were formed in the material with the size between 0.2 and 1.0
μm (Figure 2a and Figure S4). The structure of COF-HNU2 was
measured by transmission electron microscopy (TEM), and clear
lattice fringes with a spacing of 3.5 nm were commonly observed
(Figure 2b-c), confirming the formation of long-ordered channels
in the structure. In addition, the parallel crystal planes with the
interlayer distance of 0.34 nm (Figure 2d) was also observed for
COF-HNU2. This was very close to the (100) reflection as seen
in the profile, indicating highly ordered alignment for the COF.
The exact crystal structure of COF-HNU2 was determined by
powder X-ray diffraction (PXRD) analyses in conjunction with
structural simulations. As shown in Figure 3, the as-synthesized
COF-HNU2 exhibited strong diffraction peaks at 2θ = 2.8, 4.9,
5.7, 7.5, and 9.98° (blue curve), corresponding to the (100),
(110), (200), (210), and (220) planes, respectively. The broad
peak at 2θ ~ 25.3° corresponded to the (001) facet, indicating an
interlayer distance of 0.35 nm. Using the optimal monolayer
structure, the ecliped orientaion (AA stacking mode) could
generate the PXRD pattern (Figure 3, black curve, and Figures
S5-6). The simulated PXRD pattern is in good agreement with
the experimental data. The refinement results gave the
Figure 2. SEM image (a) and TEM images (b-d) of COF-HNU2. The red
arrows in (c) highlight the straight channels with a diameter of ~3.5 nm; The
white arrows in (d) highlight the parallel crystal planes with the interlayer
distance of 0.34 nm. Scale bars, 500 nm, 100 nm, 50nm, and 5 nm for (a–d),
respectively.
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3-ium bromide in the presence of a base (Figure 1). The detailed
synthetic procedures were described in Experimental section. It
was found that the PXRD profile of the COF-HNU3 (Figure 3a,
orange curve) exhibited a similar XRD pattern shown by COF-
HNU2, and no noticeable morphological change was observed
as compared with that of COF-HNU2 (Figure S4 and Figure
S11). The BET surface area was calculated to be as high as
2027 m2 g−1 (Figure 4a, blue curve), the highest reported for an
imine-linked COF derived from post-modification strategy. The
pore size for the sample decreased from 3.6 nm to 2.6 nm
(Figure S12). These findings indicated that the lattice structure
maintained intact and the pore was accessible after modification.
In addition, COF-HNU3 was also stable in air and common
solvents, such as DMF, THF, MeOH, and hot water, and the
high crystallinity was retained under these conditions (Figure
S13).
Figure 3. The Experimental (orange) patterns of COF-HNU3 as well as the
experimental (blue), Pawley refined (red), simulated (black) patterns
calculated by using the eclipsed AA-stacking PXRD profile of COF-HNU2, and
the difference between experimental and Pawley refined patterns (green)
Insets, the extended structures of COF-HNU2 based on the eclipsed
arrangements: C, gray; O, red; N, blue; and H, white.
The permanent porosities were investigated by nitrogen
absorption-desorption isotherm. It was found that the COF-
HNU2 displayed a typical IV type absorption curve at 77 K
(Figure 4a, red curve), indicating the characteristic of
mesoporous materials. The Brunauer-Emmett-Teller (BET)
surface area was calculated to be 4313 m2 g−1, which is the
highest value among the reported 2D COFs up to date. The
large BET surface area could be attributed to the high
crystallinity. The total pore volume was also estimated (at P/P0 =
0.99) to be Vp = 2.9 cm3g-1 for COF-HNU2. Calculated by
nonlocal density functional theory (NLDFT), COF-HNU2 showed
a large pore size of 3.6 nm (Figure S9), which agrees well with
the predicted value from the eclipsed structure. In addition, the
framework of COF-HNU2 was very stable and retained its
crystallinity after soaking for 72 hours in a variety of solvents
such as DMF, THF, n-hexane, water, and aqueous acid (0.1 M
HCl) and base (3 M NaOH) solutions (Figure S10). The high
stability was ascribed to its structural characteristics including
intramolecular hydrogen bonding (-O-H…O=C-NH) and high
crystallinity. [45, 46]
Figure 4. Nitrogen absorption curves of COF-HNU2 and COF-HNU3 (a)
performed at 77 K; 13C CP/MAS solid state NMR spectrum of COF-HNU3 (b).
The assignments of 13C chemical shifts of alkyl chain in COF-HNU3 are
indicated in the chemical structure. Asterisks indicate spinning side bands.
Encouraged by the high crystallinity, large BET surface area,
and excellent stability of COF-HNU2, we developed two novel
COF materials (COF-HNU3 and COF-HNU4) by anchoring the
imidazolium salts onto the channel walls through nucleophilic
substitution reaction between the phenolic hydroxyl groups in
COF-HNU2 and 1-(3-bromopropyl)-3-methyl-1H-imid-azol-3-ium
bromide or 1-(3-bromopropyl)-4-chlorine-3-methyl-1H-imidazol-
The atomic-level structure of COF-HNU3 was assessed by X-
ray photoelectron spectroscopy (XPS) and solid-state NMR
spectroscopy. The XPS spectrum revealed a bromine signal at
binding energy of 70.2 and 69.2 eV (Figure S14), verifying the
successful post modification. The 13C NMR spectra showed the
signals at 56, 46, 36, and 31 ppm (Figure 4b), respectively,
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which could be assigned to the alkyl-C species of the
imidazolium salt moieties. Furthermore, the content of
imidazolium salt sites was analyzed by elemental analysis, and
the bromine content up to 17.9 wt% was found, which
corresponds to 2.2 mmol per gram of the imidazolium salt
moieties. This result reveals that more than 90% of the OH
groups (2.35 mmol per gram of the COF-HNU2) reacted with the
imidazolium bromide salt. The COF-HNU4 was prepared under
the similar conditions and detailed characterization of COF-
HNU4 was given in Supporting Information (Figures S15-S19).
hydrogen bonding with the epoxide, thus promoting the reaction
of epoxides with CO2. Moreover, it was worth noting that the
catalytic system developed here was applicable to the synthesis
of cyclic carbonates with excellent yields (94-96%) for the
cycloaddition of various epoxides with CO2 (Table 2). As far as
we know, COF-HNU3 exhibited the highest TON value under
similar conditions among the very few COF-based
heterogeneous catalysts that could catalyze the cycloaddition of
[37-41, 49]
epoxides with CO2.
Especially, the amount of catalyst
used was very low, which was usually not the case for metal-
free catalysts.
Table 1. The cycloaddition reactions of (1a) with CO2 catalyzed by
kinds of catalysts[a]
Table 2. Cycloaddition reactions of epoxides with CO2 to cyclic
carbonates catalyzed by COF-HNU3 [a]
O
O
Catal.
O
O
O
+
CO2
Catal.
O
O
O
+
CO2
R
R
2a
1a
Entry
Cat.
Yield/%[b]
TON
Entry
1
Epoxide
Product
Time/h Yield/%[b]
O
O
1
COF-HNU3
COF-HNU4
COF-JLU7
99
95
98
495000
475000
9000
O
O
O
O
48
36
36
95
96
96
2
3[c]
2
3
4
O
O
Cl
Br
N
N
4
32
--
Cl
Cl
O
O
O
Br
5
29
--
--
N
N
Br
O
O
O
O
Br
O
7[d]
COF-HNU2
trace
[a]Reaction conditions: 1a (10 mmol), 100 oC, 48 h, CO2 = 2 MPa, catalyst
O
O
[b]
(0.002 mol%, based on the imidazolium salt catalytic site).
yield. [c]Data were obtained from Ref.[40] [d] COF-HNU2 (5 mg).
Isolated
36
72
95
94
.
Owing to the excellent porosity and high density of the active
sites of imidazolium salts within the nanoscopic channels, the
materials were examined for catalyzing the cycloaddition
reaction of epoxides with CO2. It was found that all the
imidazolium salts functionalized COFs showed excellent
catalytic performance for the cyclization reactions under solvent-
free and co-catalyst-free conditions. In these functionalized
COFs, turnover number (TON) of COF-HNU3 was as high as
495000 (Table 1, Entry 1), probably ascribing to its high surface
area. In comparison with the COF-JLU7 catalyst that is the best
5
O
O
O
O
[a]Reaction conditions: epoxide (5 mmol), CO2 (2 MPa), 100 oC, and COF-
HNU3 (0.002 mol%, based on the imidazolium salt catalytic site). [b] Yields
were determined by 1H NMR spectroscopy.
[40]
transition-metal-free COF catalyst reported for this reaction,
COF-HNU3 and COF-HNU4 displayed about 50-fold higher TON
value under similar conditions (Table 1, Entries 1-3).
Nevertheless, COF-HNU2 without catalytic sites showed a very
low catalytic activity under the same reaction conditions (entry 7).
It has been reported that hydrogen bond can active the epoxide.
In general, homogeneous catalysts have superior activity
and/or selectivity compared to heterogeneous catalysts.[50]
However, as shown in Table 1, the catalytic activity of the
imidazolium salts functionalized COFs reported in this work was
remarkably higher than the homogeneous molecular catalysts of
the imidazolium salts (entries 1 and 2, entries 4 and 5). It is
[47, 48]
The as-prepared COF-HNU3 and COF-HNU4 have large
amount of imidazolium cations and Br- anions that can form
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known that the porosity and dispersion of active sites of the
catalytic materials are among the most important influential
factors for heterogeneous porous catalysis. COF-HNU3 and
COF-HNU4 have mesoporous framework, high BET surface
areas, and dense imidazolium and Br- active sites. Their
mesoporosity and ordered open channels contribute to the
exposure of active sites and favors the fast transportation of the
substrates. The combination of imidazolium salts endows a high
CO2 absorption capacity (Figure S20) and high enrichment of
CO2 near the active sites, thus promoting the rapid conversion of
the reactants. Therefore, the enhanced catalytic efficiency is
attributed to the highly dispersed active sites of the imidazolium
salts within framework of COFs.
various substitute groups could afford the target products in
excellent yields (up to 96%) and high selectivity (up to 99:1), and
the turnover frequency (TOF) of up to 192 h-1 (entry 1) was
achieved which is the highest number for metal-free catalysts
reported to date for N-formylation of amines with carbon dioxide
(Table S4). Interestingly, N−H bonds of p-chlorine PhNH2 were
proved to be reactive and mainly resulted in the mono-
formylaniline product with a high yield and selectivity (entry 6).
Furthermore, when catalyst dosage was reduced from 0.5 to 0.2
mol%, the reaction also worked well, but only with the TOF value
of 15 h-1 (entry 7). All these results clearly indicate that the
functionalized COFs possess remarkable catalytic activity for
this reaction. Compared with the reported homogeneous
[51]
carbene catalysts,
the TOF value in our functionalized COF
Table 3. Formylation of various amines with CO2 and phenylsilane
heterogeneous catalysis was 234 times that in homogeneous
carbene molecular catalysis (Table S4). Thus, the catalyst
loading and reaction time were significantly reduced by using
COF-HNU3 catalyst in the present work.
using COF-HNU3 as catalyst[a]
O
H
N
N
Cs2CO3 (0.5mol%), DMF
N
R2
R2
R2
+
+
CO2
+
PhSiH3
1equiv
Cat . (0.5mol%), 30 o
C
R1
R1
R1
1bar
2
1
3
Entry
R1
R2
Time/h
Yield/%[b]
Y2/Y3
TOF/h-1
1
2
3
4
5
H
H
CH3
i-Pr
1
1
1
1
5
96
94
95
96
91
99:1
98:2
96:4
97:3
97:3
192
188
190
192
91
CH3
H
CH3
CH3CH2
H
N
Figure 5. Recycle tests of the COF-HNU3. Reaction conditions: propylene
oxide (20 mmol), CO2 (2 MPa), COF-HNU3 catalyst (0.002 mol%, based on
the imidazolium salt catalytic site), 100 °C, and 48 h.
6
Cl
H
H
H
6
90
90
99
95:5
98:2
---
90
15
7[c]
CH3
CH3
12
24
The separation and recyclability of the catalyst is one of the
most important advantages for heterogeneous reactions in
8[d]
0.82
[52-54]
practical applications.
We investigated the recyclability of
[a]
COF-HNU3 in the cycloaddition reaction of propylene oxide with
CO2. After each cycle, the catalyst could be simply regenerated
by centrifugal separation. As shown in Figure 5, the catalyst
could be reused for at least ten times without significant loss of
catalytic activity. In addition, high crystallinity and porosity of
COF-HNU3 were almost remained after the recycling (Figures
S21-22).
Reaction conditions: aryl amine (1.0 mmol), COF-HNU3 (0.5 mol% based
on the imidazolium salt active site), Cs2CO3 (0.5 mmol), PhSiH3 (1.0 mmol), 2
ml of DMF, 30 oC. [b] Yields were determined by 1H NMR spectroscopy. [c] 0.2
[d]
[51]
mol% of COF-HNU3 was used.
used).
Result from literature
(5 mol% IPr was
To examine the universality of the imidazolium salts function-
alized COFs as useful catalysts for CO2 transformation, COF-
HNU3 which can generate carbene active sites in the presence
of base, was used as an effective catalyst in the reductive
functionalization of amines with CO2. Firstly, the reaction
conditions were optimized and the results were given in Table
S3, where Cs2CO3 was chosen as the base, DMF was used as
the solvent, and the reaction time was set at 1h. Then, we
explored the substrate scope for the reaction under the optimum
conditions, and the results were summarized in Table 3. It is
clearly indicated that the substituted aryl secondary amines with
Conclusions
In conclusion, we designed and synthesized a novel class of
imidazolium salts functionalized COFs, which have high
crystalline networks and BET surface area. The dense
imidazolium cation and Br- anion in the nanoscopic channels
could be served as efficient active catalytic centers toward
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General procedures for the reductive functionalization of CO2 with
amines
cycloaddition of epoxides with CO2. It was shown that COF-
HNU3 and COF-HNU4 could effectively catalyze the reactions
for CO2 fixation with excellent yields, and the TON value could
reach up to 495000, which is about 50 times that of the best
transition-metal-free COF catalyst reported for this reaction. The
remarkably high catalytic activity could be contributed to the
highly dispersed active catalytic sites within the pore of COFs. In
addition, COF-HNU3 also showed remarkable selectivity and
catalytic performance in the reductive N-formylation of amines
with CO2. This work reveals the great potential of the
imidazolium salts functionalized COFs as a novel class of
efficient catalysts in CO2 conversion.
Briefly, COF-HNU3 (0.5% mol based on imidazolium salt), Cs2CO3 (0.5%
mol) and dry DMF (2 mL) were loaded in a Schlenk tube (25 mL), then
the mixture was stirred for 4 h under N2 condition, then connected to a
CO2 balloon with three CO2 purge cycles. Amine (1.0 mmol) and PhSiH3
(1.0 mmol) were introduced into the tube, and stirred for 1 h at 30 oC. The
product yield was determined by 1H NMR (CDCl3, 600 MHz)
spectroscopy.
Acknowledgements
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China
(No.U1704251, 21733011, 21773058), the National Key
Research and Development Program of China (2017YFA0403
101), and the 111 project (No.D17007).
Experimental Section
Instrumentation
FT-IR spectra were collected on a Spectrum 400 spectrometer (Perkin-
Elmer). PXRD data were recorded from 2θ = 2° to 40° in 0.1° increment
on a Bruker D8 Advance diffractometer. The thermal properties of the
materials were evaluated using a thermogravimetric analysis (TGA)
instrument (STA449C) over the temperature range from 25 to 800 oC
under N2 atmosphere. The Brunauer-Emmett-Teller (BET) surface areas
were performed on a Quantachrome Instruments ASIQM 00002200-7
Keywords: Covalent organic frameworks • carbon dioxide •
imidazolium salts • heterogeneous catalysis • carbonates
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Thermo Scientific electron spectrometer.
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Synthesis of COF-HNU2
A solution of o-dicholorobenzene / n-butanol / 6 M acetic acid (1 mL/1
mL/0.2 mL) was put into a 10 mL Pyrex tube, then 2-hydroxybenzene-
1,4-dialdehyde (0.12 mmol, 18.0 mg) and 1,3,5-tris(4-aminophenyl)
benzene (0.08 mmol, 28.1 mg) were added. The mixture was degassed
and stirred at 120°C for 3 days in a sealed tube. The obtained solid was
collected and washed with ethanol and tetrahydrofuran for three times,
respectively. The product was dried at 120 °C for 12 h to get the
corresponding COF-HNU2 in 90% isolated yield.
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A novel class of imidazolium Salts
functionalized covalent organic
frameworks with highly crystalline
and surface area was designed
and synthesized, and found to
have a remarkable catalytic
Jikuan Qiuƚ, Yuling Zhaoƚ, Zhiyong
Li, Huiyong Wang*, Yunlei Shi and
Jianji Wang*
Page No. – Page No.
Imidazolium Salts Functionalized
Covalent Organic Frameworks for
Highly Efficient Catalysis of CO2
Conversion
activity in CO2 conversion with a
record turnover number.
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