A Bifunctional Cationic Covalent Organic Polymer for Cooperative Conversion of CO2 to Cyclic Carbonate without Co-catalyst

Article abstract of DOI:10.1007/s10562-021-03534-7

Abstract: A cationic covalent organic polymer with bifunctional active site was synthesized, which was treated by N, N'-bis(5-bromomethylsalicylaldehyde)ethylenediamine (salen ligand) and tris(1H-imidazol-1-yl) triazine (TIT) in the presence of aluminum e

Full text of DOI:10.1007/s10562-021-03534-7

Catalysis Letters
https://doi.org/10.1007/s10562-021-03534-7
A Bifunctional Cationic Covalent Organic Polymer for Cooperative
Conversion of CO to Cyclic Carbonate without Co‑catalyst
2
Rui‑Ying Zhang · Yue Zhang · Jian Tong · Lin Liu · Zheng‑Bo Han1
1
1
1
1
Received: 11 November 2020 / Accepted: 8 January 2021
©
The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
A cationic covalent organic polymer with bifunctional active site was synthesized, which was treated by N, N’-bis(5-bromo-
methylsalicylaldehyde)ethylenediamine (salen ligand) and tris(1H-imidazol-1-yl) triazine (TIT) in the presence of aluminum
ethoxide. The bifunctional cationic covalent organic polymer was investigated by various characterization technologies
including PXRD, FT-IR, XPS, TG, SEM, EDS, N -adsorption and CO -adsorption. In this polymer, aluminum acts as lewis
2
2
acid site and bromine ion acts as nucleophile, cooperatively catalyzing the cycloaddition reaction of CO and epoxides.
2
Due to its cooperative eꢀect, a higher catalytic activity was found to exhibit 98.1% conversion of epichlorohydrin under
optimized conditions (Initial pressure 1.0 MPa, 0.57 mol% catalyst of COP-Al, 90 °C, reaction time 18 h, in the absence of
a co-catalyst). Notably, the heterogeneous catalyst still showed good activity and stability after ꢁve cycles.
Graphic Abstract
A salen-based cationic covalent organic polymers (COP-Al) was used as a bifunctional catalyst for the cycloaddition reaction
of CO and epoxides with high activity under solvent-free and co-catalyst-free conditions.
2
Keywords Cationic covalent organic polymer · Heterogeneous catalyst · CO · Cyclic carbonates · Cooperative eꢀect
2
Supplementary Information The online version of this article
(
https://doi.org/10.1007/s10562-021-03534-7) contains
1 Introduction
supplementary material, which is available to authorized users.
With the development of social industrialization, the con-
*
*
Lin Liu
centration of CO in the atmosphere continues to rise,
2
liulin@lnu.edu.cn
causing the greenhouse eꢀect to become more and more
serious [1–3]. The animals and plants are facing huge
survival challenges [4], therefore, exploring attractive
Zheng-Bo Han
ceshzb@lnu.edu.cn
1
College of Chemistry, Liaoning University,
Shenyang 110036, People’s Republic of China
materials to reduce CO is necessary. At the same time,
2
Vol.:(0
1
123456789)
3

R.-Y. Zhang et al.
as a rich, cheap, non-toxic and renewable substance, CO2
is also the most environmentally friendly C1 ingredient
and can convert into high value-added chemicals [5–7].
One of the products is the cyclic carbonate formed by the
based on salen-(Al) metalloligand, which can not only
capture CO but also transform it under mild pressure [32].
2
Inspired by them, we demonstrate a cationic COP by post-
synthetic metalation strategy [33]. It is synthesized with
N,N’-bis(5-bromomethylsalicylicaldehyde)ethylenediamine
(salen ligand), tris(1H-imidazol-1-yl)triazine (TIT) and alu-
minum ethoxide (Scheme 1). The salen-Al complex has been
coupling of CO and epoxides, which is widely used in
2
medicine, ꢁne chemical and other industries [8]. Although
the industrialization of homogeneous catalysts to regener-
ate carbonate have been achieved, the separation of the
products is diꢂcult [9, 10]. Therefore, constructing high
eꢂciency heterogeneous catalysts to facilitate the cycload-
dition reaction still remains a challenge.
reported as a homogenous catalyst in the conversion of CO
2
to cyclic carbonate at mild conditions [34, 35]. Combining
its advantages with COP, we have produced a heterogeneous
catalyst which can capture and transform CO eꢀectively
2
Various of heterogeneous catalysts are reported to solve
the above problem, such as metal–organic frameworks
under co-catalyst-free condition.
(
MOFs) [11–14], composite materials [15–17], covalent
organic polymers (COPs) [18, 19], zeolite [20, 21], and
so on. Among, COPs have wide ꢃexibility in monomer
selection and design [22–24], which makes the material
have broad application in the ꢁelds of adsorption [25],
waste scavenger [26], catalysis [27–30], and so on. More
recently, Wang and Ding et al. summarized two major
modes of immobilization involving metals in heterogene-
ous metal-catalysts synthesis, which brought a promising
2 Experimental Section
2.1 Materials and Instrumentation
All reagents and Chemicals were purchased from commer-
cial vendors and could be used directly without further puri-
ꢁcation. Speciꢁcally, imidazole, hydrobromic acid, ethylen-
ediamine, acetone, toluene, ethyl ether were purchased from
Sinopharm Chemical Reagent Co., Ltd (Ningbo, China) and
method for cooperative conversion of CO to cyclic car-
2
bonates [31]. The “classical anchoring method” refers to
the direct grafting of anchoring groups on various insolu-
ble substrates by forming covalent bonds. However, these
catalytic systems usually require lots of nucleophilic rea-
gent (such as tetrabutylammonium bromide) as co-cata-
lysts. Thus, the “two-in-one” strategy was developed to
solve it, in which two diꢀerent catalytic active sites (Lewis
acid and nucleophiles) are jointly integrated into single
material to produce a bifunctional solid catalyst. Cao et al.
reported a bifunctional cationic porous organic polymer
salicylaldehyde, formaldehyde, zinc chloride (ZnCl ), tri-
2
ethylamine (TEA) were purchased from Shanghai Aladdin
Bio-Chem Technology Co., LTD; while cyanogen chloride
were obtained from ShangHai D&B Biological Science and
Technology Co., Ltd.
Powder X-ray diꢀraction (PXRD) was carried out with
Bruker AXS D8 advanced automatic diꢀractometer. Cu-Kα
inverse radiation (1.54056 Å) was taken as the X-ray source
and tested in the in the 2θ range of 5°–80°, under the con-
ditions of 40 kV and 40 mA. Fourier-transform Infrared
(
FT-IR) spectrum characterization was performed on KBr
Scheme 1 Synthesis of COP-Al
1
3

A Bifunctional Cationic Covalent Organic Polymer for Cooperative Conversion of CO to Cyclic…
2
−
1
microspheres in the range of 4000–450 cm using a Nicolet
DX spectrometer. Thermogravimetric analysis (TGA) was
2.4 Synthesis of TIT
5
performed using a Perkin-Elmer Pyrisl thermogravimetric
The ligand was synthesized according to a reported pro-
cedure (Scheme S1) [36]. Imidazole (30 mmol, 2.04 g)
and TEA (30 mmol, 3.03 g) were dissolved into 100 mL
tetrahydrofuran solution. The mixture was heated to 50 °C
−
1
analyzer under conditions of 5 °C min and ꢃowing N gas
2
at 25 to 800 °C. X-ray photoelectron spectroscopy (XPS)
was carried out by Thermo ESCALAB 250 with monochro-
matic Al Ka (HV=1486.6 eV) and calibrated with an energy
of 20 eV and C1s (284.6 eV). Catalytic reaction product
conversion was measured by SP-2100 A gas chromatograph
in an atmosphere of N and stirred until dissolved. After
2
1 h, cyanogen chloride (10 mmol, 1.845 g) was dissolved
in 50 mL tetrahydrofuran solution, and the solution was
added to the ꢃask drop by drop with a needle. The mix-
ture was further heated to 75 °C and stirred for 2 h. After
the reactants were cooled, tetrahydrofuran was removed
by rotary evaporation. The crude product was rinsed with
deionized water for 3 times and then dried overnight to
(
GC) equipped with kromate-bond series capillary column
and ꢃame ionization detector. Scanning Electron Microscope
SEM) of the samples were imaged and collected by SU8010
(
ꢁ
eld transmitter. Energy Dispersive Spectrum (EDS) were
acquired on the SEM (AMETEK Instruments). Nitrogen
adsorption and desorption isotherms were determined by
1
obtain 1.9 g white solid product with a yield of 93%. H-
3
H-2000PS1 analyzer (Beishide Instrument Company). The
NMR (DMSO, 300 MHz): δ 7.20 (q, 1H), 7.86 (q, 1H),
1
−1
monomer was tested by H NMR Spectra Recorded on a
Varian 300 MHz NMR spectrometer.
8.64 (q, 1H) (Fig. S3). FT-IR (KBr pellets, cm ): 3113
(C=C), 1587 (C=N), 1455, 1099 (C–N) (Fig. S6).
2
.2 Synthesis
2.5 Synthesis of COP
of 5‑(bromomethyl)‑2‑hydroxybenzaldehyde
Salen ligand (4.99 mmol, 2.255 g) and TIT (5.99 mmol,
1.639 g) were dissolved into tetrahydrofuran (100 mL),
and refluxed for 3 days. Then it was centrifuged and
washed three times with N,N’-dimethyl formamide (DMF)
and methanol under ultrasound condition. After that, it
was dried in a vacuum oven at 60 °C for 24 h and the yel-
low solid was obtained with a yield of 1.06 g.
Salicylaldehyde (80 mmol, 8.35 mL), 38% formaldehyde
(
12 mL) and ZnCl (4 mmol, 0.6 g) were introduced into
2
a three-necked ꢃask, then hydrobromic acid (50 mL) was
added. The mixture was stirred for 24 h under the protec-
tion of N . Then the resulting pink solid was ꢁltered and
2
dissolved in ether. The organic phase was steamed to dry
and recrystallized with petroleum ether. The white pow-
der 5-(bromomethyl)-2-hydroxybenzaldehyde (8.34 g) was
1
obtained with a yield of 48.5%. HNMR (CDCl , TMS,
2.6 Synthesis of COP‑Al
3
ppm): 11.07(1H, s, OH), 9.90 (1H, s, CHO), 7.44 (1H, s,
Ar–H), 7.17 (1H, d, Ar–H), 6.80 (1H, d, Ar–H), 4.50 (1H,
COP (150 mg), toluene (50 mL), was added to a 100 mL
round-bottom ꢃask, ultrasonic for 30 min and then alu-
minum ethoxide (300 mg) was added. The the mixture
was heated to 110 °C for 24 h. After centrifugal, it was
washed by DMF and methanol and extracted by Soxhlet
with methanol, acetone and dichloromethane for 3 days.
Dried in a vacuum oven at 60 °C for 12 h, and the yellow
solid was obtained with a yield of 207 mg.
−
1
s, CH Br) (Fig. S1). FT-IR (KBr pellets, cm ): 3240 (OH),
2
2
852, 2750 (Aliph-H), 1655 (C=O), 1208 (CH Br), 737
2
(
C–Br) (Fig. S4).
2
.3 Synthesis of N, N’‑bis(5‑bromomethyl
salicylaldehyde) Ethylenediamine (Salen
Ligand)
5
-bromomethyl-2-hydroxybenzaldehyde (20 mmol, 430 mg)
2.7 The Cycloaddition of CO with Epoxides
2
was dissolved in 25 mL methanol, and then ethylenediamine
(
10 mmol, 0.68 mL) was added. The mixture was reꢃuxed
Firstly, the COP-Al was vacuumed at 110 °C for 12 h to
remove the remaining guest molecules on the surface. In a
20 mL high-pressure reactor, 30 mg catalyst and 10 mmol
substrate (propylene oxide, epichlorohydrin and styrene
oxide) were added. The mixture was then reacted at 90 °C
for 6 h. After that, the mixture was put in the refrigerator
overnight and ꢁltered to obtain yellow solid (1.9 g) with
1
a yield of 83.7%. HNMR (DMSO, TMS, δ ppm): 13.36
(
2H, s, OH), 7.25–6.64 (6H, m, Ar–H), 8.60 (2H, s, CH=N),
4
.35 (4H, s, CH Br), 3.92 (4H, t, N–CH –CH –N) (Fig. S2).
and 1 MPa CO for 18 h. The stirring speed of the reactor
2
2
2
2
−
1
FT-IR (KBr pellets, cm ): 3427 (OH), 2972, 2926 (Aliph-
was set at 350 rpm. At the end of the reaction, the reactor
H), 1638 (C=N), 1090 (CH Br), 832 (C–Br) (Fig. S5).
2
1
3

R.-Y. Zhang et al.
was cooled to room temperature rapidly, and the conver-
sion was determined and calculated by GC.
and C–C (284.5 eV) groups (Fig. 2a). The N 1 s peak could
be divided into three peaks at 398.6, 399.6, and 400.9 eV
(
Fig. 2b). The peaks at 398.6, 399.6 and 400.9 eV could
2.8 The Recyclability Test Procedure
be ascribed to pyridinic (− C=N −) of the salen lgand,
pyrrolic nitrogen (C−N−C) of TIT and imidazolium unit
+
The recovered COP-Al was separated by centrifuged and
washed by methanol and DMF for 3 times under ultrasound
condition. After soaking in methanol for 12 h and dried in a
vacuum oven at 60 °C for 12 h, cyclic catalytic experiments
were carried out.
(− C=N −). The binding energy peak of bromide ion
appeared at 67.2 and 67.8 eV could be related to the Br
3d and Br 3d levels (Fig. 2c), which conꢁrmed that the
3
/2
5/2
–
bromine is in the state of Br for COP-Al. The peak of Al
2P in the appeared red shift at 74.15 eV could be related
to the change of the electronic environment of aluminum
after the formation of COP-Al (Fig. 2d). Two of the oxygen
atoms that coordinate with Al come from −OH in the salen
ligand, and the remaining one comes from the oxygen in
the aluminum ethoxide, which could further substantiate the
successful synthesis of COP-Al [24, 37].
3
Results and Discussion
3.1 Structure Characterizations
To determine the structure of COP-Al, FT-IR spectras
of salen ligand, TIT, COP and COP-Al were performed
Subsequently, PXRD showed a wide peak at 25°, which
proved that the morphology of COP-Al is amorphous (Fig.
S8). The amorphous structure was also characterized by
SEM, showing coral-like porous structure of COP-Al
(Fig. 3a). In addition, EDS spectras using SEM further con-
ꢁrmed the uniform distribution of C, N, O, Br and Al in the
polymer COP-Al (Fig. 3b). TGA diagram showed that COP-
Al could be stabilized at 192 °C (Fig. S9).
−
1
(
Fig. 1). It was worth noting that the peak value of 832 cm
corresponded to the disappearance of C–Br bond vibration,
indicating that all salen ligands were consumed in the reac-
tion. Three new absorption peaks appeared at 1037, 1716
−
1
and 1765 cm , which might be related to the stretchable
vibration of the TIT skeleton of COP (Fig. 1c). In addi-
−
1
tion, the peak of the salen ligand C=N bond at 1638 cm
In order to study the gas adsorption performance of COP-
Al, the adsorption isotherm of N and CO were tested. After
−
1
transferred to 1598 cm , which further demonstrated the
2
2
−
1
formation of COP. And a new peak at 609 cm related to
the Al–O bond was observed, which conꢁrmed the forma-
tion of the COP-Al (Fig. 1d).
was activated by vacuum at 383 K for 24 h, COP-Al exhib-
ited type IV isotherm, and its Brunauer–Emmett–Teller
2
−1
(BET) surface area was 34 m g (Fig. 4a). In addition, the
relatively low pore volume again indicates that the pores in
the polymer matrix may be ꢁlled with bromide ions [38].
Fig. S10 shows the pore size distribution of the COP-Al,
which proved to be a mesoporous material. In addition, the
In addition, the structure of COP-Al was further deter-
mined by the XPS analysis (Fig. S7). Figure 2 shows the C
1
s, N 1 s, Br 3d and Al 2p XPS data of COP-Al. The XPS
patterns COP-Al in C 1 s region exhibited three peaks, which
could be attributed to C–O (288.5 eV),−CH −(285.5 eV),
COP-Al has the ability to absorb CO . When the pressure
2
2
is close to 101 kPa, the adsorption capacity of CO reaches
2
−
1
−1
1
8.3 mL g at 273 K, and 11.6 mL g at 298 K (Fig. 4b).
Then, COP-Al was soaked in DMF, ethyl acetate, water,
methanol, chloroform, acetone and other solvents com-
monly used in the laboratory for 24 h, the structure was still
not destroyed, indicating that the structure of COP-Al was
highly stable (Fig. S11).
3.2 Catalytic Performances
On the basis of the coexistence of Lewis acid Al site and
−
nucleophile Br ion on the polymer skeleton of COP-Al,
we decided to evaluate COP-Al as a bifunctional catalyst
to catalyze cycloaddition of CO and epoxides. Firstly, the
2
cyclic addition of CO and propylene epoxide (PO) was
2
selected as the model reaction to study the inꢃuence of reac-
tion time. When the reaction time was 6 h, 12 h, 18 h and
2
4 h, the conversion of PO were 37.5%, 60.4%, 96.4% and
Fig. 1 FT-IR spectras. a TIT, b salen ligand, c COP, d COP-Al
97.2% (Table 1, entries 1–4). As shown in Fig. S12a, the
1
3

A Bifunctional Cationic Covalent Organic Polymer for Cooperative Conversion of CO to Cyclic…
2
Fig. 2 a C 1 s, b N 1 s, c Br 3d and d Al 2p XPS spectra of COP-Al
Fig. 3 a SEM image of COP-Al and b EDS elemental-mapping images of COP-Al. C: Blue; N: orange; O: cyan; Br: green; Al: yellow
conversion of PO gradually increased with the increase of
the catalytic reaction time. When the reaction time increased
from 18 to 24 h, the conversion of PO did not change much.
Therefore, 18 h was chosen as the best time for the reac-
tion, and the subsequent catalytic reaction was carried out
with this time. At the same time, we studied the eꢀect of
COP-Al dose on catalytic eꢂciency. The conversions of PO
were 71.4%, 96.4%, and 96.2%, when using 20 mg, 30 mg
and 40 mg catalysts (Table 1, entries 3, 5, and 6). There-
fore, it can be concluded that the amount of catalyst has an
important inꢃuence on the PO conversion. In other words,
the concentration of the catalytic site determines the cata-
lytic eꢂciency. The highest conversion was obtained with
30 mg catalyst, and this dose was used for subsequent cata-
lytic reactions. In addition, we also studied the eꢀect of the
pressure on the reaction. When the catalytic pressure was
1
3

R.-Y. Zhang et al.
Fig. 4 a N adsorption isotherms patterns of COP-Al at 77 K. b CO adsorption isotherms patterns of COP-Al at 298 K and 273 K
2
2
Table 1 Cycloaddition of CO with epoxides catalyzed by COP-Al
2
a
Entry
R
Catalyst (mmol)
Temperature
°C)
Pressure (MPa)
Time (h)
Conversion (%)
(
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
0.057
0.057
0.057
0.057
0.036
0.075
0.057
0.057
0.057
0.057
0.057
_
0.075
0.075/0.72
0.075/0.72
0.057
0.057
0.057
0.057
0.057
90
90
90
90
90
90
50
70
90
90
90
90
25
25
25
90
90
90
90
90
1
1
1
1
1
1
1
1
0.1
0.5
1.5
1
0.1
0.1
0.1
1
1
1
1
1
6
37.5
60.4
96.4
97.2
71.4
96.2
52.5
73.8
31.8
67.0
97.9
Trace
1.2
60.4
85.0
27.2
98.1
91.5
95.4
87.7
12
18
24
18
18
18
18
18
18
18
18
48
48
72
18
18
18
18
18
0
1
2
3
4
5
6
7
8
9
0
b
c
c
d
CH Cl
2
Ph
C H
2
5
CH OC H
9
2
4
a
b
Reaction condition epoxides (10 mmol), catalyst (0.057 mmol, 0.57 mol%), without co-catalyst; Calculated by GC data; No catalyst was added;
c
d
COP-Al (0.075 mmol, 0.75 mol%), TBAB (0.72 mmol); COP (0.057 mmol, 0.57 mol%)
1
3

A Bifunctional Cationic Covalent Organic Polymer for Cooperative Conversion of CO to Cyclic…
2
0
.1 MPa, 0.5 MPa, 1 MPa and 1.5 MPa, the conversion of
PO were 31.8%, 67.0%, 96.4% and 98.1% (Table 1, entries
, 10, 3 and 11). Besides, we also studied the eꢀect of the
9
temperature on the catalytic eꢂciency. When the catalytic
temperature was 50 °C, 70 °C and 90 °C, the conversion of
PO were 52.5%, 73.8% and 96.4%, respectively (Table 1,
entries 3, 7 and 8). Therefore, it can be concluded that the
temperature of catalytic reaction has an important inꢃuence
on the conversion of PO. When the reaction temperature
was 90 °C, the catalyst obtained the highest PO conversion,
and subsequent catalytic reactions were carried out at this
temperature.
Through the previous optimization, we concluded that the
optimal conditions for the reaction were 1 MPa, 90 °C and
Fig. 5 Recycling test of COP-Al for the cycloaddition of CO with
2
epichlorohydrin
1
8 h without co-catalyst. Then ꢁve diꢀerent epoxides were
studied to determine the substrate scope of COP-Al. To our
delight, all substrates were eꢂciently converted to the cor-
responding cyclic carbonates (Table 1, entries 3 and 17–20).
Specially, when the substrate was epichlorohydrin, the con-
version was the highest, reaching 98.1% (Table 1, entry 17).
For comparison, we performed a controlled experiment, in
which almost no cyclic carbonates were produced when no
catalyst was added to the reaction system (Table 1, entry
1
2). In order to further prove the role of lewis acid site in
the whole catalytic reaction, we carried out an experiment
using COP as catalyst, and the result showed that when the
lewis acid site was not contained in the system, the eꢂciency
of the catalyst was greatly weakened (Table 1, entry 16).
This set of experiments fully proved that the COP-Al was an
eꢀective catalyst to promote the reaction. To further explore
the catalytic performance of the COP-Al, the experiment
under 25 °C and 0.1 MPa was investigated. To our delighted,
COP-Al/TBAB gave a conversion of 60.4% (Table 1, entry
1
4), 50 times that of COP-Al (Table 1, entry 13). Further-
more, COP-Al/TBAB exhibited 85.0% conversion of PO
when the time increased to 72 h, indicating that COP-Al
can be used in the cycloaddition reaction at ambient con-
Scheme 2 Proposed synergistic catalysis reaction mechanism of
−
COP-Al for the CO cycloaddition reaction
ditions with the augment of nucleophile Br concentration
2
(
Table 1, entry 15).
The stability of catalyst was an important index to evalu-
ate the performance of catalyst. Compared with homogene-
ous catalysts, catalyst COP-Al has signiꢁcant advantages.
damaged in the reaction system (Fig. S12b and Table S2).
All of above indicated the stability of the COP-Al.
According to experimental results, a proposed mechanism
We used the reaction of CO with epichlorohydrin to test
2
the stability of COP-Al. After the reaction of CO with
route of COP-Al for the cycloaddition of CO and epoxides
2
2
epichlorohydrin, COP-Al could be recovered and reused
after washing. Interestingly, after ꢁve consecutive reactions,
the product conversion remained at a high level (Fig. 5 and
Table S1), and the characteristic peaks of FT-IR spectrum
could be clearly observed (Fig. S13). To our delighted, The
COP-Al still maintained a good adsorption capacity, which
indicated that the framework of COP-Al did not collapse
signiꢁcantly after ꢁve cycles of experiments (Fig. S14). In
addition, the leaching test demonstrated that COP-Al was not
was illustrated in Scheme 2. During the catalytic process,
the aluminum ion participates in the unsaturated coordina-
tion of the COP as a Lewis acid site [39], producing a strong
electron-rich intermediate to absorb and activate the epox-
ides. At the same time, bromine ions acting as a nucleophile
attacked the less sterically hindered C–O bond in the epox-
ide, resulting in a ring-opening reaction and reacting with
a high concentration of CO to form a cyclic carbonate. In
2
addition, TIT was rich in nitrogen in organic ligands, which
1
3

R.-Y. Zhang et al.
can greatly increase the adsorption of CO and speed up the
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reaction [32].
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4
Conclusions
conversion of CO with propargylic alcohols. Angew Chem Int
2
In conclusion, a bifunctional cationic COP based on salen
ligand containing Lewis acid site and nucleophilic functional
group was synthesized by post-synthetic metalation strategy,
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which could promote the cycloaddition reaction of CO and
2
epoxides eꢂciently without co-catalyst. It is worth noting
that the COP-Al is reusable for ꢁve reaction circles without
signiꢁcantly drop. This study not only in line with the con-
cept of green chemistry, but also provides a new recyclable
1
4. Ding M, Flaig RW, Jiang HL et al (2019) Carbon capture and
conversion using metal–organic frameworks and MOF-based
materials. Chem Soc Rev 48(10):2783–2828
catalyst for CO capture and conversion. The future work is
2
to systematically prepare schiꢀ base COPs materials, which
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NiS/Au nanocomposites with eꢂcient charge separations for
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are expected to catalyze the cycloaddition reaction of CO
2
with epoxides under mild conditions.
1
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Acknowledgements We thank the National Natural Science Founda-
tion of China (21671090 and 21701076), LiaoNing Revitalization Tal-
ents Program (XLYC1802125), and Liaoning Province Doctor Startup
Fund (20180540056) for ꢁnancial support of this work.
cycloaddition of CO
with epoxides under ambient conditions.
2
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Author Contributions R-YZ: Writing-Original Draft, Software, Inves-
tigation. YZ: Investigation, Validation, Formal analysis. JT: Visualiza-
tion, Software. LL: Resources, Visualization. Z-BH: Conceptualiza-
tion, Methodology, Resources, Writing-Review & Editing, Supervision.
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polymer: the role of valence on cooperative conversion of CO2
to cyclic carbonate. ACS Appl Mater Int 12(1):609–618
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Nickel–zeolite composite catalysts with metal nanoparticles
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Compliance with Ethical Standards
2
Conflict of interest The authors declare no conꢃict of interest.
5
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1. Rimer JD (2018) Rational design of zeolite catalysts. Nat Catal
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