Biomass-derived metal-organic hybrids for CO2 transformation under ambient conditions

Article abstract of DOI:10.1039/d0gc00212g

The fabrication of catalysts that can activate CO₂ under ambient conditions is very interesting but challenging. Metal-organic hybrids (MOHs) have promising applications in catalysis, and their fabrication from renewable resources is very attractive. Herein, we report a simple protocol to fabricate metal-organic hybrids (MOHs) from chitosan, phytic acid and ZnCl₂, obtaining mesoporous MOH-Zn possessing-OH,-NH₂, and-PO₄ groups. The resulting MOH-Zn shows excellent activity for CO₂ activation and enables the cyclization of epoxides with CO₂ to proceed under ambient conditions, affording a high turnover frequency of 7.8 h^-1. The high performance of MOH-Zn originates from the synergistic effects among multi-functional sites in the catalysts.

Full text of DOI:10.1039/d0gc00212g

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View Article Online
DOI: 10.1039/D0GC00212G
ARTICLE
Biomass-derived metal-organic hybrids for CO transformation
2
under ambient conditions
ab
bd
ac
ab
a
ab
Yunyan Wu , Shouwei Zuo , Yanfei Zhao *, Huan Wang , Dongyang Li , Shien Guo , Zhijuan
Received 00th January 20xx,
Accepted 00th January 20xx
a
d
abc
abc
Zhao , Jing Zhang , Buxing Han and Zhimin Liu *
DOI: 10.1039/x0xx00000x
Fabrication of catalysts that can activate CO
hybrids (MOHs) have promising applications in catalysis, and their fabrication from renewable resources is very attractive.
Herein, we report a simple protocol to fabricate metal-organic hybrids (MOHs) from chitosan, phytic acid and ZnCl achieving
mesoporous MOH-Zn possessing -OH, -NH , -PO groups. The resultant MOH-Zn displays excellent activity for CO activation,
which can make cyclization of epoxides with CO proceed under ambient conditions, affording a high turnover frequency of
.8 h . The high performance of MOH-Zn is originated from the synergistic effects among multi-functional sites in the
catalysts.
2
under ambient conditions is very interesting but challenging. Metal-organic
2
2
4
2
2
-1
7
Nature provides us abundant renewable feedstocks with
functional groups including hydroxyl, amino, carboxyl groups,
which can be applied in designing functional materials.
Introduction
4
Catalysts play important roles in chemical industry. During
the past decades, many efforts have been devoted to creating
new catalysts with high efficiency via combining the merits of
heterogeneous and homogeneous catalysts, and various kinds
of hybrid catalysts including single atom catalysts, immobilized
metal complexes, single-active site heterogeneous catalysts and
Chitosan is a biopolymer composed of randomly distributed β-
(1-4)-linked d-glucosamine, which can be easily obtained from
chitin and is the second most plentiful biopolymer. The
presence of rich hydroxyl and amino groups in the backbone of
chitosan makes it be applied in many areas. For instance, it can
chelate with metal ions and provide Lewis base site to capture
1
so on, have been reported. Metal organic hybrids (MOHs)
5
CO
2
. Phytic acid is an organic phosphate compound that can be
derived from organic compounds and metal salts via
coordination can make the metal sites be well dispersed in the
form of single active sites, providing molecular interaction sites
for catalysis, meanwhile they can integrate the features of
organic compounds and metal together to generate new or
enhanced properties. Moreover, the morphology and
structure can be engineered specifically via careful design and
selection of novel components in the fabrication of MOHs. In
this context, MOHs provide possibility to bridge the gap
between heterogeneous and homogenous catalytic systems.
However, the synthesis of MOHs generally requires organic
compounds with unique structures, and the reaction process is
complicated, which induces high cost. Therefore, exploring
simple method and cheap precursors for the synthesis of MOHs
is attractive.
easily available from seeds and grains of plants, which has
strong ability to chelate with metal ions via six phosphate
groups and can be applied in collecting metal ions or in
6
catalysis. For example, mesoporous zirconium phosphonate
derived from phytic acid and ZrCl
4
showed high catalytic
2
7
efficiency for Meerwein-Ponndorf-Verley reaction. In this
context, chitosan and phytic acid are good natural organic
feedstocks, which may be applied in preparation of MOHs and
provide green and promising routes, but it is seldom reported.
3
a. Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid,
Interface and Thermodynamics, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, China. E-mail: liuzm@iccas.ac.cn,
lianyi302@iccas.ac.cn
Scheme 1. Photographs of the as-synthesized hydrogel, MOH-Zn and plausible
coordination network in MOH-Zn.
b.
University of Chinese Academy of Sciences, Beijing 100049, China.
Physical Science Laboratory, Huairou National Comprehensive Science Center,
Herein, we present a simple strategy to fabricate MOHs with
OH, -NH and -PO groups from chitosan, phytic acid and ZnCl ,
2 4 2
as illustrated in Scheme 1. In this approach, the MOH hydrogel
is first formed through complexation of metal ions with chitosan
and phytic acid in aqueous solution. Removing the excess metal
c.
-
Beijing 101407, China.
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese
d.
Academy of Sciences, 100049 Beijing, China.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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ARTICLE
Journal Name
salt and water from the hydrogel and followed by freeze-drying,
MOH-Zn with mesoporous structures can be obtained.
Interestingly, the resultant MOH-Zn shows excellent activity for
View Article Online
DOI: 10.1039/D0GC00212G
activating CO
sites and metal ions, and make the cycloaddition reaction of
epoxides with CO be capable of occurring under ambient
2
due to the cooperative effects among functional
2
-1
conditions, affording a high TOF value of 7.8 h . The high
performance of MOH-Zn is originated from the synergistic
effects among multi-functional sites in the catalysts.
Results and discussion
Preparation and structure characterization of MOH-Zn.
The MOH-Zn hydrogel was first prepared from chitosan,
2
ZnCl , phytic acid and water. Phytic acid is necessary for the
dissolution of chitosan in water, which can disrupt the
complicated H-bonding network of solid chitosan. The
subsequent addition of ZnCl
chitosan and phytic acid renders Zn ions to chelate with
2
into the aqueous solution of
2
+
abundant hydroxyl (-OH) and amino (-NH
2
) groups in chitosan
-
and with -PO
4
in phytic acid, finally resulting in the formation of
hydrogel. Removing water and superfluous metal salt via being
washed with ethanol, the as-formed hydrogel became white
powders after being freeze-dried, denoted as MOH-Zn.
Figure 2. Characterization for MOH-Zn. a. FT-IR spectra for MOH-Zn, phytic acid and
chitosan; b. XPS spectra of N 1s in chitosan and MOH-Zn; c. XPS spectra of Zn 2p in
MOH-Zn, zinc phytate and ZnCl
transformed k -weighted EXAFS spectra; f. EXAFS fitting curves at R space of MOH-
Zn (Inset: shows a model of the Zn environment).
2
; d. Zn K-edge XANES spectra; e. Fourier
3
groups are present in MOH-Zn. X-ray diffraction (XRD) pattern
of MOH-Zn exhibits a broad diffraction peak without obvious
peaks assigning to Zn species (Fig. S1a), indicating the
amorphous structure of the resultant material. N
2
-sorption
analysis indicates that MOH-Zn shows type IV isotherm of N
2
sorption with an obvious loop (Fig. S1b), inductive of
mesoporous structure. However, its specific surface area is only
Figure 1. Characterization for MOH-Zn. a. SEM image; b. HRTEM image; c-g. EDS
mapping images for C, N, O, P and Zn.
2
-1
3
-1
9
0 m ·g with a pore volume of 0.40 cm ·g . Thermogravimetry
(
2
TG) analysis indicates that the weight loss of MOH-Zn starts at
Scanning electron microscopy (SEM) and transmission
electron microscopy (TEM) observations (Figs. 1a-1b) indicate
that MOH-Zn displays crosslinked network structure composing
of nanowires with diameter around 40 nm, throughout which
elements C, N, O, P and Zn are uniformly distributed as indicated
by EDS mapping images (Figs. 1c-2g). The crosslinked network
structure could not form using hydrochloric acid or acetic acid
instead of phytic acid to promote chitosan dissolution, which
suggests that phytic acid plays a vital role in the formation of
cross-linked structure of MOH-Zn. It can be proposed that
o
o
33 C, and dramatically increases up to 40% at 300 C. This
o
indicates that MOH-Zn is thermostable below 233 C and most
of functional groups can be removed from MOH-Zn at
temperature higher than 300 C (Fig. S1c).
Coordination environment of MOH-Zn.
Fourier transform infrared (FT-IR) spectrum of MOH-Zn
−1
shows a broad band at 3400 cm as shown in Figure 2a,
assigning to the stretching vibration of O-H and N-H, giving the
direct evidence of the presence for free -OH and -NH
2
groups in
2
+
MOH-Zn. Comparing the FT-IR spectra of chitosan and MOH-Zn,
phytic acid acts as multidentate linker to bond with Zn ions
that complex with -OH or -NH in chitosan, thus linking chitosan
it was found that the absorption peak of -NH
2
shifted from 1597
2
in chitosan) to 1525 cm- (in MOH-Zn), suggesting the
1
(
chains to form crosslinked networks.
Inductively coupled plasma (ICP) analysis on MOH-Zn (Table
S1) showed that the contents of element Zn, P and N were 8.24,
2
complexation of Zn(II) with NH group in chitosan chains.
Notably, adsorption peak assigned to P-O (in P-O-Zn) vibration
appeared at 995 cm , which shifted to lower wavenumber
compared with P-O in phytic acid (1008 cm ), indicating that
phytic acid involved the formation of MOH-Zn by chelating with
Zn(II) as well. In the process to prepare MOH-Zn hydrogel,
chitosan, phytic acid and Zn(II) ions were randomly present in
the aqueous solution, so Zn(II) ions may be apt to complex with
-1
5
.05 and 4.79 wt%, respectively, corresponding to a Zn/P/N
atom ratio of 1/1.3/2.7. Considering the amounts of -OH and -
NH in the used chitosan and that of phytic acid, the Zn content
in MOH-Zn is obviously deficient if all -OH, NH and -PO groups
were complexed with Zn(II). That is, plenty of free -OH or -NH
-1
2
8
2
4
2
2
| J. Name., 2012, 00, 1-3
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the -NH
ARTICLE
2
, -OH and phosphate groups nearby, forming Zn- analysis indicate that the single active Zn atom sites are well-
View Article Online
DOI: 10.1039/D0GC00212G
coordinating moieties such as O-Zn-NH
the fact that phytic acid was necessary for the formation of
crosslinked networks, it can be deduced that it is possible for from chitosan, phytic acid and corresponding metal chlorides
Zn(II) to complex simultaneously with -NH and/or -OH in were also obtained, and information on these materials are
chitosan chain and with -P-O in phytic acid, forming P-O-Zn-NH provided in Figure S2-S5 and Table S2-S3, indicating the
moieties in MOH-Zn. In addition, due to the large steric universality of the fabrication method for various MOHs.
hindrance of chitosan chain, plenty of free -OH and -NH groups
2 2
, P-O-Zn-NH , etc. From spread throughout the hybrid.
Other MOHs including MOH-Mn, MOH-Cu, MOH-Al derived
2
2
2
remain in MOH-Zn, which can provide abundant active sites and
have specific applications in catalysis.
The oxidation states of N and Zn in MOH-Zn were evaluated
by X-ray photoelectron spectroscopy (XPS). In the N 1s XPS
spectrum of MOH-Zn (Fig. 2b), the peak with binding energy
(
BE) of 399.7 eV is assigned to N in free NH
new peak at 401.9 eV can be attributed to N in NH
coordinated with Zn (Zn-N), inductive of complexation of Zn(II)
with -NH in chitosan. Compared to that in ZnCl (1046.4 eV),
2
groups. Besides, a
2
groups
2
2
Figure 3. a. CO
2
-TPD spectrum of MOH-Zn; b. CO
2
uptake isotherms of MOH-Zn at
the BE of Zn 2p in zinc phytate shifts to lower value (1045.8 eV),
while that in MOH-Zn further shifts to the lowest value (1045.4
eV; Fig. 2c). This suggests the complexation of Zn(II) with both
phytic acid and chitosan, which affords electron transfer from -
OH, -NH and -PO groups to Zn(II).
2 4
To further unveil Zn bonding configurations in MOH-Zn,
synchrotron radiation-based X-ray absorption spectroscopy
2
73 K and 298 K.
2
CO activation and its reaction with epoxides over MOH-Zn.
The as-synthesized MOH-Zn is expected to activate CO
to the presence of various basic sites such as -OH and -NH
temperature-programmed desorption of CO (CO
analysis was performed in the temperature range of 0-200 C to
avoid decomposition of MOH-Zn at higher temperatures. A
2
due
2
. The
2
2
-TPD)
(XAS) was conducted to explore the metal coordination
environment. X-ray absorption near-edge structure (XANES)
and extended X-ray absorption fine structure (EXAFS) at the Zn
K-edge of MOH-Zn were detected with standard Zn foil (for Zn-
Zn bond), zinc phthalocyanine (ZnPC, for N-Zn bond) and zinc
wide desorption peak appeared around 100 C in the CO
spectrum (Fig. 3a), which indicates that MOH-Zn can capture
CO efficiently at low temperature and possesses strong
2
-TPD
2
9
basicity. The CO uptake capacities of MOH-Zn were determined
to be 0.31 and 0.19 mmolg- at 273 and 298 K (1 bar),
respectively (Fig. 3b). Though the uptake capacities of CO are
2
not too high, the isosteric heats of adsorption was estimated to
be 22.9 kJmol- at low adsorption value, suggesting a stronger
phytate (for O-Zn bond) as references. As shown in Figure 2d,
2
1
the XANES spectrum for MOH-Zn shows an absorption
threshold and near-edge portion near to zinc phytate, indicating
that the valence state of the Zn ion was +2 and more Zn(II) ions
1
were complexed with O from -OH and -PO
phytic acid in MOH-Zn. This is reasonable because the amount
of –OH and –PO is much larger than that of NH in the hybrids.
4
in chitosan and
dipole–quadrupole interaction between MOH-Zn and CO
2
1
0
molecules. The Lewis basic sites including hydroxyl and amino
4
2
3
groups may provide MOH-Zn ability to activate CO under the
ambient conditions. Additionally, hydroxyl and amino groups
are good hydrogen-bond donors, which could active molecules
through forming H-bonding. All the active properties may
endow MOH-Zn with good catalytic abilities as a heterogenous
catalyst in the conversion of CO
The atom-economic reaction between epoxides and CO
attractive route to access cyclic carbonates that are important
chemicals with wide applications in organic synthesis or
polymer chemistry. Considering that MOH-Zn possesses rich
Lewis base sites and H-bond donor sites, which can activate CO
and epoxides, it was examined for catalysing cycloaddition of
epoxides with CO under ambient conditions. To our delight,
MOH-Zn could efficiently catalyse the cyclization of propylene
oxide (PO, 1a) with CO in the presence of tetrabutylammonium
bromide (TBAB) under ambient conditions, affording turnover
frequencies (TOFs) of 12.3 h- and 7.8 h at the PO conversion
of 37% and 95%, respectively (Table 1, entries 1-2). For
comparison, blank experiments were performed (Table 1,
entries 3-7). It was indicated that MOH-Zn hardly showed
activity for the reaction under ambient conditions (Table 1,
The corresponding Fourier transformed (FT) k -weighted
EXAFS spectrum of MOH-Zn reveals that MOH-Zn exhibits only
one peak around 1.50 Å (Fig. 2e), which can be assigned to Zn-
N and/or Zn-O bonding taking ZnPC and Zinc phytate as
references. The EXAFS analysis also verifies that the Zn atoms in
MOH-Zn completely coordinate with chitosan chain and phytic
acid rather than being absorbed on the surface of the hybrids in
2
2
.
2
is an
2
the form of ZnCl because no peak attributed to Zn-Cl is
detected. Zn-Zn (2.27 Å) peak is also absent, manifesting the
atomic uniform dispersion of Zn in MOH-Zn.
1
1
Quantitative EXAFS curve fitting analysis was used to extract
the dominant coordination condition for the first shell of Zn
atom in MOH-Zn. Combined with element analysis, FT-IR and
XPS results, the possible chemical structure of MOH-Zn
proposed in Scheme 1 was used as a model structure to fit the
2
2
2
3
corresponding Fourier transformed (FT) k -weighted EXAFS
1
-1
spectrum of MOH-Zn in R space, and the results are shown in
Figure 2f. The geometric structure is well-fitted with total
coordination number of Zn atom with N and O atoms of 4, and
the corresponding structural parameters extracted from the
EXAFS fitting are provided in Table S1. The XANES and EXAFS
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J. Name., 2013, 00, 1-3 | 3
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entry 3), while TBAB was effective (Table 1, entry 4), and filtrate by ICP-MS analysis. These results indicate that the as-
View Article Online
DOI: 10.1039/D0GC00212G
exhibited higher performance at 100 C and 3 MPa (Table 1, synthesized MOH-Zn was stable for the reaction.
O
entry 5). The combination of chitosan or zinc phytate with TBAB
MOH-Zn
showed the similar activities to that of TBAB (Table 1, entries 4,
, 7). From the above results, it can be deduced that the high
O
O
O
+
CO2
6
R1
R2
TBAB
R1
R2
performance of MOH-Zn/TBAB should be ascribed to the
synergistic effect between MOH-Zn and TBAB. Especially, the
presence of the Zn sites together with functional groups such as
O
O
O
O
O
O
O
O
O
O
O
O
Cl
Br
Cl
-
2 4
NH , -OH, -PO in MOH-Zn plays important role in catalysing the
2
a
2b
2c
2d
reaction. The functional groups are uniformly dispersed
throughout the whole MOH-Zn material, which can form H-
bond with PO, achieving the activation of PO to some extent,
and promoting its further transformation. Moreover, the
complexation of Zn(II) with -OH, -NH and -PO results in
a
b
a
b
a
b
c
d
9
9% /95%
99% /92%
99% /91%
99% /85%
1
2
O
O
O
O
O
O
O
O
O
O
O
2
4
O
O
C6H13
Ph
electrons transfer from the coordinating sites to Zn(II) as shown
in Figure 2c, which may facilitate to improve the activity of Zn(II)
2e
a
2f
c
2g
2h
97%e
d
d
c
d
9
9% /88%
99% /87%
93% /80%
to activate PO. Higher temperature and pressure promoted the Scheme 2. Reaction of CO2 with epoxides to cyclic carbonates catalysed by MOF-Zn.
catalytic activity conspicuously, and the cyclization of PO with Reaction conditions: a substrate (10 mmol), TBAB (7.2 mol%), MOH-Zn (5 mg, content of
o
b
-
1
o
Zn: 0.063 mol%), 100 C, CO
2
(3 MPa), 1 h. substrate (10 mmol), TBAB (7.2 mol%), MOH-
CO
3
2
over MOH-Zn afforded a high TOF of 2555 h at 100 C and
o
c
Zn (40 mg, content of Zn: 0.5 mol%), 30 C, CO
7.2 mol%), MOH-Zn (5 mg, content of Zn: 0.063 mol%), 100 oC, CO
substrate (10 mmol), TBAB (7.2 mol%), MOH-Zn (40 mg, content of Zn: 0.5 mol%), 30 C,
2
(1 atm), 24 h. substrate (10 mmol), TBAB
MPa (Table 1, entry 8), which is comparable to that obtained
over the Zn-complexed porous polymer Zn/HAzo-POP-2.
d
(
2
(3 MPa), 3 h.
1
3
o
e
Notably, MOH-Zn is much cheaper, more eco-friendly and CO (1 atm), 48 h. substrate (5 mmol), TBAB (7.2 mol%), MOH-Zn (20 mg, content of Zn
2
o
easier to access compared to Zn/HAzo-POP-2. In contrast, the 0.5 mol%), 100 C, CO
2
(3 MPa), 6 h.
resultant MOH-Zn exhibited much better performances than
To explore the universality of MOH-Zn, it was applied in the
reactions of CO with terminal epoxides possessing different
the reported chitosan-based catalysts such as chitosan-
1
4
15
2
supported zinc complex, quaternized chitosan and chitosan
1
2b
substituting groups as shown in Scheme 2. MOH-Zn allowed all
reactions to proceed smoothly under ambient conditions,
affording products in good to excellent yields. The reactions
were accelerated remarkably at 100 C and 3 MPa even with a
low catalyst amount of 0.063 mol%. Internal epoxide
functionalized ionic liquid (CS-EMImBr).
Table 1. Catalytic cyclization of propylene oxide (1a) with CO
2
.[a]
O
O
O
O
+
CO2
cyclohexene oxide could also react with CO
system, affording a product yield of 97% at 100 C and 3 MPa.
These results indicate that MOH-Zn is an efficient catalyst for
2
over the catalytic
1a
2a
o
[c]
Time
Yields[b] TOF
Entry
Cat.
Co-Cat.
-
1
/h
/%
/h
the cyclization of terminal epoxides with CO
carbonates under mild conditions.
2
to access cyclic
1
2
3
MOH-Zn
MOH-Zn
MOH-Zn
---
TBAB
TBAB
---
6
37
12.3
7.8
24
24
24
1
95
trace
10
Conclusions
4
5[d]
TBAB
TBAB
TBAB
TBAB
TBAB
In conclusion, mesoporous MOH-Zn with functional groups
has been prepared from chitosan, phytic acid and ZnCl , which
shows good catalytic activity for the cyclization of epoxides with
CO to cyclic carbonates under ambient conditions due to
---
18
2
6
7
8[d]
Chitosan
Zinc phytate
MOH-Zn
24
24
0.5
11
15
-
2
81
2555
cooperation among the functional groups and metal ions. The
molecularly dispersed functional groups including Zn, OH and
a
Reaction conditions: 1a (10 mmol), TBAB (7.2 mol%), MOH-Zn (40 mg, content of Zn:
.5 mol%), 30 oC, CO (1 atm). b Determined by 1H NMR (DMSO-d6, 400 MHz) using
NH
provides
2
improve the catalytic performance apparently. This work
general approach to fabricate heterogenous
0
1
2
,1,2,2-tetrachloroethane as an internal standard. c TOF = [moles of product]/[(total
a
d
moles of metal)*(reaction time)] in the presence of TBAB. MOH-Zn (5 mg, Content of catalysts with well-dispersed catalytic active sites employing
Zn: 0.063 mol%), 100 C, CO
o
2
, 3 MPa.
biopolymers as feedstocks. The resultant MOHs possess
multiple functional groups such as -NH , -OH, -PO and metal
2
4
In addition, MOH-Zn can be easily separated from the
reaction system and reused for the next run with adding fresh
TBAB. It could be recycled for 5 runs without obvious decrease
in activity (Fig. S6), and its morphology was kept unchanged
after the reaction (Fig. S7). Moreover, after separating MOH-Zn
from the reaction solution no Zn ion was detectable in the
sites, which can activate different substrates via interaction like
H-bonding, Lewis acid and base interaction and so on. They may
have great potentials as catalysts for the CO conversion, and
2
the related work is being performed in our laboratory.
Experimental section
4
| J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
Preparation of MOH-Zn.
For preparation of MOH-Zn, typically, chitosan (1 g) and
Samanta, S. Roy, R. Sasmal, N. Das Saha, K. RV.iePwrAardticeleeOpn, linRe.
Viswanatha, S. S. Agasti and T. K. Maji,DAOnI:g1e0w.10. 3C9h/Dem0G.CIn0t0.2E12dG.,
2
019, 58, 5008-5012; (d) Q. Zhao, Z. Tu, S. Wei, K. Zhang, S.
Choudhury, X. Liu and L. A. Archer, Angew. Chem. Int. Ed., 2018,
7, 992-996; (e) A. H. Chughtai, N. Ahmad, H. A. Younus, A.
phytic acid (2 g, 45 wt% in water) were mixed up and stirred for
o
2
h in a flask at 60 C. Then, ZnCl
2
(8 g), was added into the
5
o
system and stirred at 60 C for 10 h. Subsequently, the mixture
was cooled down to room temperature, and hydrogel was
obtained. After that, ethanol (50 mL) was added to the
hydrogel, and massive white powder immediately appeared.
The white powder was separated from the system through
Laypkov and F. Verpoort, Chem. Soc. Rev., 2015, 44, 6804-6849.
. J. Wei, G. Wang, F. Chen, M. Bai, Y. Liang, H. Wang, D. Zhao and
Y. Zhao, Angew. Chem. Int. Ed. , 2018, 57, 9838-9843.
3
4
. (a) C. Chen, X. Li, J. Deng, Z. Wang and Y. Wang, Chemsuschem,
2
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powder was dried by freeze drying for use, denoted as MOH-Zn.
Cycloaddition of epoxide with CO over MOH-Zn
Typically, certain amounts of MOH-Zn, epoxide and TBAB
were loaded into a flask (10 mL) that was equipped with a
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magnetic stirrer bar. The air in the flask was replaced with CO
and a CO balloon was then connected to the flask. The reaction
2
2
system was heated at 30 C and stirred for 24 h. For the
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reactions at high temperature and pressure (100 C, 3 MPa),
6
MOH-Zn, epoxide and TBAB were loaded into a stainless steel
autoclave with a Telflon tube (25 mL inner volume), and the
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2 2
to remove the air inside. Then, CO
was charged into the reactor up to 3 MPa, and the mixture was
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2
was vented.
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The product yield was determined by H NMR (DMSO-d6, 400
MHz) using1,1,2,2-tetrachloroethane as an internal standard.
To test the recyclability of MOH-Zn, the catalyst was recovered
by filtration, washed with ethanol for 4 times, and then dried
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Conflicts of interest
There are no conflicts to declare.
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