Cycloaddition of CO2 with epoxides and esterification reactions using the porous redox catalyst Co-POM@MIL-101(Cr)

Article abstract of DOI:10.1039/c9nj02607j

The catalytic activity of the recently reported Co-POM@MIL-101(Cr) composite, synthesized from K₅[CoW₁₂O₄₀] (Co-POM) and chromium(iii) terephthalate (MIL-101), was studied in the solvent-free cycloaddition of CO₂ with epoxides and esterification of acetic acid with various alcohols. The materials containing varying amounts of Co-POM were synthesized using a one-pot HF-free method in a "bottle around ship" strategy. The material was thoroughly characterized using several methods such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance spectroscopy (EPR). Temperature programmed desorption (TPD) of NH₃ and CO₂, and the CO₂ adsorption capacity (adsorption isotherms) were used to study the acid-base properties of the materials. The combination of the electron-transfer character of Co(iii)-POM and ordered mesopores in MIL-101(Cr) creates an efficient catalytic system with mild conditions (90 °C and 20 bar CO₂ pressure) for solvent-free cycloaddition of CO₂ to various epoxides. Esterification of acetic acid with alcohols was also carried out using the Co-POM@MIL-101 catalysts and high yields were achieved for different alcohols. The catalysis experiments also clearly show that the active site in this heterogeneous catalyst is the Co(iii) center in the Keggin anion structure. It presumably conducts both the cycloaddition of CO₂ to epoxides and the esterification reaction via an outer-sphere electron transfer mechanism using the Co(iii)/Co(ii) redox pair. The heterogeneous Co-POM@MIL-101 catalysts were separated by simple filtration and reused five times in the cycloaddition of CO₂ with styrene epoxide and seven times for the esterification of acetic acid with benzyl alcohol with negligible leaching of Co-POM and no considerable loss of activity.

Full text of DOI:10.1039/c9nj02607j

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Mathur, A. Sandleben and A. Klein, New J. Chem., 2019, DOI: 10.1039/C9NJ02607J.
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Cycloaddition of CO2 with epoxides and esterification reactions
using the porous redox catalyst Co-POM@MIL-101(Cr)
Afsaneh Marandi,a Mehrnaz Bahadori,a Shahram Tangestaninejad,*a Majid Moghadam,*a Valiollah
Mirkhani,*a Iraj Mohammadpoor-Baltork,a Robert Frohnhoven,b Sanjay Mathur,b Aaron
Sandleben,b Axel Klein.b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
The catalytic activity of the recently reported Co-POM@MIL-101(Cr) composite, synthesized from K5[CoW12O40] (Co-POM)
and chromium(III) terephthalate (MIL-101), was studied in the solvent-free cycloaddition of CO2 with epoxides and
esterification of acetic acid with various alcohols. The Co-POM@MIL-101(Cr) composite was synthesized using a one-pot
HF-free method in a “bottle around ship” strategy. The material was thoroughly characterized using several methods such
as (powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray
photoelectron spectroscopy (XPS), and electron paramagnetic resonance spectroscopy (EPR). Temperature programmed
desorption (TPD) of NH3 and CO2, and the CO2 adsorption capacity (adsorption isotherms) were used to study the acid-
base properties of the materials. The combination of the electron-transfer character of Co(III)-POM and ordered
mesopores in MIL-101(Cr) creates an efficient catalytic system with mild conditions (90 °C and 20 bar CO2 pressure) for
solvent-free cycloaddition of CO2 to various epoxides. Esterification of acetic acid with alcohols was also carried out using
the Co-POM@MIL-101 catalysts and high yields were achieved for different alcohols. The catalysis experiments also clearly
show that the active site in this heterogeneous catalyst is the Co(III) center in the Keggin anion structure. It presumably
conducts both the cycloaddition of CO2 to epoxides and the esterification reaction via an outer-sphere electron transfer
mechanism using the Co(III)/Co(II) redox pair. The heterogeneous Co-POM@MIL-101 catalysts were separated by simple
filtration and reused five times in the cycloaddition of CO2 with styrene epoxide and seven times for the esterification of
acetic acid with benzyl alcohol with negligible leaching of Co-POM and no considerable loss of activity.
oxidations/epoxidations,11,14 hydrolysis of esters10, hydrolysis of
epoxides,14 (trans)esterifications,10,16,17 or in the water splitting
reaction.12 The combination of POMs and MOFs should allow
increasing stability, enhanced distribution of catalyst centers
through large surface area, and easy separation from the
reaction media.12,13
The idea that reduction of POM acidity can be achieved
through the interaction between the pores inner surface and
POM through encapsulation18 inspired us to design
POM@MOF composite in which the POM acts as an electron
transfer catalyst. For this reason, the Keggin anion
[Co(III)W12O40]5ˉ polyoxometalate (Co-POM) with the ability of
facile electron transfer through the redox couple
Co(II)/Co(III)14,19-22 was chosen and its performance in
heterogeneous catalytic reactions was investigated.
For the encapsulation of the Co-POM, the MOF should have
large pores with small windows, capable of surrounding POMs
and to prevent their leaching. Furthermore, the synthetic
procedure for the MOF should not affect the properties of POM
or lead to destruction of the structure. The large pores with pore
windows smaller than Co-POM6,23 and the HF-free procedure for
the synthesis of MOF24 make MIL-101(Cr) suitable for this
purpose. MIL-101(Cr) provides 29 and 34 Å mesoporous cages
Introduction
Polyoxometalates (POMs) have attracted extensive attention in
catalysis during recent years because of some unique
characteristics such as fast reversible redox transformations
under mild conditions and adjustable acid-base and redox
properties in
a wide range. To circumvent the POM’s
disadvantages such as low thermal stability, high solubility in
water and polar media, and low surface area (1–10 m2g−1), POM
species have been supported on or encapsulated into suitable
solid carriers with high surface area using strong dispersion
forces.1-9. Among the various supports such as silica2, titania3,
activated carbon4, and zeolites5, metal-organic frameworks
(MOFs) are very common, regarding their high capacity for
catalyst loading and retention6-9. The approach to encapsulate
POMs in MOF cavities to provide heterogeneous catalysts has
been reported before10-17 and their catalytic activity has been
studied in important organic reactions such as
a
a Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan
81746-73441, Iran
b Department of Chemistry, University of Cologne, Greinstrasse 6, 50939 Köln,
Germany
† E-mail addresses: stanges@sci.ui.ac.ir (S. Tangestaninejad),
moghadamm@sci.ui.ac.ir (M. Moghadam), mirkhani@sci.ui.ac.ir (V. Mirkhani).
ORCID: 0000-0001-5263-9795 (ST), 0000-0001-8984-1225 (MM), 0000-0003-
0093-9619 (AK)
Electronic Supplementary Information (ESI†) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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with free opening windows of 12 and 16 Å25 and we consider substrate and instead trigger an electron-transfer mechanism
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DOI: 10.1039/C9NJ02607J
encapsulation of Co-POM to be very efficient for this MOF.
In our previous report, a Co-POM@MIL-101(Cr) composite
for the esterification.
The effect of several parameters including the amount of
was synthesized and introduced as an electron transfer catalyst catalyst and temperature for both reactions, the pressure of
to carry out the ring opening reaction of epoxides with carbon dioxide and reaction time for the conversion of CO2 and
methanol.14 In this work, we focus on the encapsulation effect the ratio of acid to alcohol for the esterification have been
on the Co-POM activity and performance in the Co-POM@MIL- evaluated in this work alongside with
a
thorough
101(Cr) composite for the cycloaddition reaction of CO2 with characterization of the catalyst using powder X-ray diffraction
epoxides and for the esterification of acetic acid with various (PXRD), scanning electron microscopy (SEM), transmission
alcohols. The two different reactions were chosen to study a electron microscopy (TEM), X-ray photoelectron spectroscopy
potential dual functionality of the MOF. In the esterification (XPS), and electron paramagnetic resonance spectroscopy (EPR).
reaction, MIL-101 just acts as support for the Co-POM catalyst
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while in the cycloaddition reaction, MIL-101 captures CO2
increasing its concentration around the catalytic species (Co-
Results and Discussion
POM).
Synthesis and characterization of the catalysts
Catalytic “CO2 fixation” into organic compounds for the
production of commercially significant chemicals is one of the
most promising approaches for CO2 emission management
Co-POM were prepared through the one-pot HF-free procedure
simultaneously supplying an intermittent and renewable C1-
Co-POM@MIL-101 composites containing varying amounts of
reported previously (Fig. 1).14
feedstock.26,27 Among all introduced CO2 transformation
strategies, cycloaddition of CO2 and epoxides to produce cyclic
carbonates (Scheme 1) is one of the most promising routes, and
significant progress has been made in recent years.28-30 Various
advanced catalysts, both homogeneous and heterogeneous,
have been developed in the past decade. Among currently
available options, porous materials including porous carbon,
porous silica and zeolites, porous organic polymers, and metal-
organic frameworks (MOFs) are particularly attractive owing to
their unique features such as large surface areas, high thermal
stabilities, diverse building blocks, and ability to capture and
storage of CO2.31-36 The high capacity of CO2 adsorption and the
presence of acidic or basic centers in this class of porous
materials make them interesting materials for CO2 capture and
its catalytic conversion. At the same time, numerous examples
of POM-based compounds have been reported as catalysts or
promoters for CO2 fixation processes.37,38
name
MIL-101(Cr)
initial amount of Co-POM
-
Co-POM@MIL-101(1)
Co-POM@MIL-101(2)
Co-POM@MIL-101(3)
Co-POM@MIL-101(4)
Co-POM@MIL-101(5)
0.4 g (0.129 mmol
0.8 g (0.258 mmol)
1.0 g (0.323 mmol)
2.0 g (0.645 mmol)
2.5 g (0.806 mmol)
The synergetic effect of POM and MOF as catalysts in the
formation of cyclic carbonates from olefins was recently
Fig. 1. One-pot HF-free synthesis of Co-POM@MIL-101 composites.
investigated by incorporating [ZnW12O40]6ˉ in
structure.39,40
a Zn-MOF
The morphology of the Co-POM@MIL-101(3) composite was
studied using TEM and SEM (Figures are shown in the Electronic
Supporting
Information
ESI†).
The
images
reveal
O
micrometre-sized crystallites (Fig. S1) with sizes and shapes
similar to those previously reported.14 Spherical interior
particles show the incorporation of Co-POM into the MOF pores.
The energy-dispersive X-ray spectroscopy (EDX) results obtained
from SEM analysis clearly show the presence of Co and W from
the Co-POM and Cr from the MIL-101(Cr) components (Fig. S2).
The total amount of Co in Co-POM@MIL-101(3) is 0.1-0.2(1)
wt%, the value for W of 27.9(2) wt% agrees roughly with a 7:1
ratio of MIL-101(Cr) and Co-POM. The elemental mapping
analysis indicates a good distribution of Co-POM into the pores
of MIL-101(Cr) (Fig. S2).
O
[CO2]
O
R
O
R
Scheme 1. Cycloaddition of CO2 and epoxide to a 1,3-dioxolan-2-one (cyclic carbonate).
The most common way to prepare an ester is the reaction of a
carboxylic acid and an alcohol with the removal of water. This
process is commonly carried out with base or acid catalysts.41-43
Drawbacks of the such as severe conditions, noxious organic
solvents, and exhaustive work-up can be circumvented by
employing environmentally benign conditions and using
heterogeneous acid catalysts.16,44,45 Assuming a lack of acidic
character of the catalyst through the encapsulation,18 we
wanted to test Co-POM@MIL-101 in the esterification of acetic
acid to gauge if the encapsulation of the Co-POM catalyst can
effectively prevent its Lewis acid-base interaction with the
The X-band EPR spectrum of Co-POM@MIL-101(3) (Fig. 2, black
trace) represents the typical isotropic, broad signal of MIL-101
containing Cr(III) (d3).46 The spectrum of the Co-POM-rich Co-
POM@MIL-101(5) (Fig. 2, red trace) seems to be composed of
2 | New. J. Chem., 2019, 00, 00-00
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the signal for MIL-101 with 8% of the original intensity and a anion [CoW12O40]5‒. Signals for Cu 2p, 3s, and V3iepw AirnticltehOenlinCeo-
further broad signal (see inset). We ascribe the loss of signal POM@MIL-101(3) survey spectrum are caused by the Cu metal
intensity for the second sample to oxidation of Cr(III) foil, which was used for sample preparation to avoid sample
presumably to diamagnetic Cr(IV), while the broad featureless charging effects during measurement.
residual signal is probably due to Co(II) ions.47-49
DOI: 10.1039/C9NJ02607J
High-resolution Cr 2p spectra of both samples (Fig. 3,
bottom) are in line with the results of EPR measurements. While
in Co-POM@MIL-101(3) only one doublet is observed at 577.3
eV and 587.1 eV in good agreement with binding energies (BEs)
for Cr(III) in Cr(OH)3.51 The spectrum for Co-POM@MIL-101(5)
exhibits next to the Cr(III) signal another doublet at 580.1 eV and
589.7 eV matching well with binding energies for Cr(IV) found in
CrO3,51 with a 62:38 ratio of Cr(IV) to Cr(III). Similar observations
can be made in the high-resolution spectra of the W 4f / W 5p
region (Fig. S3): Co-POM@MIL-101(3) shows only one doublet
each, with binding energies of 35.6 eV and 37.8 eV for the W 4f
doublet similar to W(IV) in WO3,52 whereas Co-POM@MIL-
101(5) features an additional doublet each, shifted to higher
binding energies (38.6 eV and 40.8 eV). The intensity ratio here
exhibits the same 62:38 ratio for the high binding energy
doublet in comparison to the original W(IV) doublet as found for
Cr(IV) to Cr(III). This goes along with the observation in the O 1s
high-resolution spectra (Fig. S4) that the “lattice oxide” peak
located at 530.7 eV, obviously attributed to the W-O bond in the
Co-POM, decreases from Co-POM@MIL-101(3) to Co-
POM@MIL-101(5), while the “defect oxide” component
increases. Therefore, we suggest the high-BE species of W(IV) to
be located at the oxidized Cr host matrix, which is promoted by
oxidation of Cr(III) to Cr(IV) by the Co(III)/Co(II) redox pair.
A further interesting feature on the intrinsic CO2 absorption
capability of MIL-10153,54 is revealed in the C 1s spectra (Fig. S5)
of both samples. The as prepared measured sample Co-
POM@MIL-101(3) shows a large signal at 291.7 eV in the C 1s
spectrum accompanied by a pronounced signal at 538.1 eV in
the O 1s spectrum (Fig. S4), both representing gaseous CO2
molecules absorbed in the pores of Co-POM@MIL-101.55,56 For
the later measured, and therefore longer in vacuum stored Co-
POM@MIL-101(5), these features are already strongly
decreased.
The Lewis acidity and basicity of Co-POM, MIL-101(Cr), and
Co-POM@MIL-101(3) were studied using temperature
programmed desorption (TPD) experiments with ammonia (NH3)
and carbon dioxide (CO2), respectively (Fig. 4). The acidity and
basicity were determined from the peak area of the desorbed
NH3 and CO2 (Table 1). Taking into account the thermal stability
of Co-POM and MIL-101(Cr), 800 °C and 350 °C were chosen as
the final temperatures for the data collection. The NH3-TPD
profile of Co-POM showed a desorption peak in the T range of
200 to 500 °C with a 280.4-339.2 µmol NH3/gcat ammonia
adsorption capacity, which was attributed to weak/moderate
acidic sites and a low intense desorption peak at higher T (500 to
800 °C) was referred to strong acidic sites (Fig. 4b). In view of
the NH3-TPD pattern for MIL-101(Cr), the acidity was classified
into two groups: weak to medium (50 to 320 °C) and strong (320
to 350 °C) which is in accordance with recent work.57 MIL-
101(Cr) showed small desorption peaks in the weak-medium
acid range with 1006 µmol/gcat desorption capacity in line with
low acidity. In the case of the strong acidity sites of MIL-101(Cr),
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Fig. 2. X-band EPR spectra of Co-POM@MIL-101(3) (black) and Co-POM@MIL-101(5) (red)
powder samples at 110 K, attenuation 25 dB, frequency. In inset shows that the signal of
Co-POM@MIL-101(5) (red) is composed of 8% residual absorption of MIL-101 and signals
presumably due to Co(II).
Survey Co-POM@MIL-101(3)
Survey Co-POM@MIL-101(5)
Co 2p
region
K 2p
region
Co 2p
region
K 2p
region
1000 900 800
700 600
500 400
300 200
100
0
1000 900 800
700 600
500 400
300 200
100
0
Binding Energy (eV)
Binding Energy (eV)
HR Cr 2p Co-POM@MIL-101(3)
Cr 2p1/2 Cr 2p3/2
HR Cr 2p Co-POM@MIL-101(5)
Cr 2p1/2 Cr 2p3/2
W 4s
W 4s
Cr6+
Cr3+
Cr3+
612 608 604 600 596 592 588 584 580 576 572 568
Binding Energy (eV)
612 608 604 600 596 592 588 584 580 576 572 568
Binding Energy (eV)
Fig. 3. XPS Survey Spectra for Co-POM@MIL-101(3) (top left) and (top right) Co-
POM@MIL-101(5). XPS high-resolution spectra of the Cr 2p region for Co-POM@MIL-
101(3) (bottom left) and Co-POM@MIL-101(5) (bottom right).
Co-POM@MIL-101(3) and Co-POM@MIL-101(5) were
further investigated by X-ray photoelectron spectroscopy (XPS)
regarding elemental composition and redox chemistry. XPS
survey spectra (Fig. 3, top) for both samples show typical signals
for C, O, N, Cr, and W, but neither for K nor for Co. Latter can be
explained by the low Co content (far below 1 at%) in both
samples in combination with the presence of large amounts of
the heavy element W.50 The absence of signals for K (in line with
the EDX results) reveals the complete stripping of K+ ions during
the synthesis of Co-POM@MIL-101 leaving back the Keggin
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it is difficult to determine the accurate amount of desorption curves were calculated using the Barrett, Joyner, and Halenda (BJH)
capacity due to decomposition of MIL-101(Cr). For the Co- equation. The pore size distribution curve oDfOCIo: -1P0O.10M3@9/CM9INLJ-1002160(37)J is
POM@MIL-101(3) composite, the origin of this peak can be in good agreement in comparison with pure MIL-101(Cr). However,
View Article Online
either MIL-101 or Co-POM.
the decrease of total pore volume in the composite catalyst
confirming that the Co-POM species were successfully encapsulated
to the inner pores of MIL-101(Cr) framework. Nevertheless, the free
pore space preserved after encapsulation was sufficient for the
efficient transfer of substrate molecules for catalysis as shown later.
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To demonstrate the potential of the Co-POM@MIL-101
composites for CO2 gas absorption (Fig. S7 in the ESI†), we
measured the adsorption isotherms of CO2 at 0 °C after
evacuation of the samples at 100 °C for 12 h. As expected, the
CO2-adsorption capacity of composite catalyst is lower than pure
MIL-101(Cr), because of the presence of Co-POM in the pore of
MIL-101.
Fig. 4. Temperature programmed NH3 and CO2 desorption (TPD) profiles of Co-POM, MIL-
101(Cr), Co-POM@MIL-101(3).
Fig. 4c and 4d shows the CO2-TPD profiles of the Co-POM@MIL-
101(3) composite, Co-POM, and MIL-101(Cr) and corresponding
numerical values of the integrated desorption peaks were
obtained 1109.5, 522, and 1485 µmol CO2/gcat, respectively
(Table 1). The observed basicity was attributed the
terephthalate O atoms in the MOF or to O atoms in the WO6
clusters in POM structure.57,58 However, the thermal stability of
MOFs should be taken into full account during examination. Due
to the existence of organic ligands, the degradation of MOFs can
also yield CO2 in most cases. It is unlikely to distinguish the CO2
desorbed from basic sites and the CO2 from MOFs59 degradation
that this phenomenon can be observed in the CO2-TPD profile of
MIL-101 and composite catalyst (Fig. 4).
The N2 adsorption in BET (Brunauer–Emmett–Teller) experiments
at 77 K (Fig. 5) showed two uptakes at P/P0= 0‒0.15 and P/P0=
0.15‒0.22 resulting from two kinds of nanoporous windows. For the
Co-PO@MIL-101(3) sample the uptake volume is markedly decreased
compared with MIL-101 in line with the encapsulation of the Co-
POM. Also, N2 adsorption-desorption for MIL-101(Cr) and Co-
POM@MIL-101 with different Co-POM loading revealed a decrease in
nitrogen adsorption (Fig. S6 in the ESI†). The pore size distribution
Fig. 5. N2 adsorption-desorption isotherms (top) and BJH plot (bottom) for MIL-101(Cr)
and Co-POM@MIL-101(3)
Table 1. Results from temperature programmed desorption (TPD) measurements for NH3 and CO2
sample
total NH3
µmol/g catalyst
NH3-TPD
medium
total CO2
µmol/g catalyst
CO2-TPD
medium
weak acid
strong
acid
weak
base
43.7
218
strong base
Co-POM
MIL-101(Cr)
Co-POM@MIL-
101(3)
1372a
1463.5b
1278b
222.1
1006
884.1
709.7
-
-
439.69
458.1
394.47
522
1485
1109.5
339.1
-
-
138.7
1269.4
965.6
144
a 96-800 °C. b 98-350 °C
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Table 2. Results of the ICP and BET analysis for Co-POM@MIL-101 with varying amounts of Co-POM.
amount of loaded POMa
(mmol/g)
BET surface area
(m2/g)
average pore diameter
total pore volume
(cm3/g)
sample
Co-POM (g)
(nm)
MIL-101
0
0.4
0.8
1
-
2564
1842
988
2.36
1.5
Co-POM@MIL-101(1)
Co-POM@MIL-101(2)
Co-POM@MIL-101(3)
Co-POM@MIL-101(4)
0.0050
0.0084
0.0100
0.0130
2.6
2.0
1.8
1.7
0.82
0.50
0.47
0.33
683
2
545
aDetermined by ICP.
Table 3. The effect of the initial POM amount in the catalytic activity of the Co-
POM@MIL-101 catalysts in the cycloaddition of CO2 with styrene epoxide a
Cycloaddition of CO2 with epoxides
sample
Co-POM
(g)
conversion
(%) b
selectivity (%) b
The Co-POM@MIL-101 catalysts were used for the
cycloaddition of styrene oxide as a model reaction at 110 °C
under 20 bar CO2 pressure and solvent-free conditions using
tetra-n-butylammonium bromide (TBABr) as co-catalyst for
this reaction (Table 3). TBABr is used in this reaction for
activation of the reactants opening the epoxide ring through
nucleophilic attack and form a bromo-alkoxide and also an
active CO2 molecule.60 As expected, the conversion increases
with increasing Co-POM loading from 0.4 to 1.0 g. However,
also MIL-101(Cr) catalyses the reaction, although with
somewhat poorer performance. A further increase of Co-POM
to 2.0 g resulted in a reduction in both conversion and
selectivity. This is in line with the ICP analysis (Table 2)
confirming a larger loading for Co-POM@MIL-101(4) with
0.0130 mmol/g encapsulated Co-POM reducing the specific
surface area and total pore volume.
MIL-101(Cr)
0
0.4
0.8
1
66
68
73
88
69
83
84
88
88
85
Co-POM@MIL-101(1)
Co-POM@MIL-101(2)
Co-POM@MIL-101(3)
Co-POM@MIL-101(4)
2
a Reaction conditions: 15 mmol styrene epoxide, 200 mg catalyst, 1 mmol TBABr,
PCO2 = 20 bar, T =110 °C, 2 h.
On the other hand, the surface area is affected by both
initial and loaded Co-POM. Increasing the initial Co-POM
reduces the crystallinity of the structure of MOF and
subsequently the surface area. Considering all factors including
the specific surface area of the MIL-101 support, loading of Co-
POM, and the results from Table 3, Co-POM@MIL-101(3) with
0.0100 mmol/g encapsulated Co-POM was chosen as the
optimized catalyst loading for further reactions.
The cycloaddition of styrene epoxide with CO2 without the
catalyst performed as a control reaction at 110 °C under
solvent-free conditions and 20 bar CO2 pressure afforded no
product, proving that the catalyst is necessary (Table 4, entry
1). Also, the yield of the reaction was negligible when the
catalyst was used without co-catalyst (entry 3).
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epoxides with CO2 (Table 5). The results show excellent
View Article Online
conversion and selectivity for all sDuObsI:t1r0a.t1e0s3.9/CT9hNeJ02b60e7sJt
conversion was achieved for 1,2-epoxyhexane and
epichlorohydrin (Table 5, entries 1 and 4). The reactivity of 1,2-
epoxy-3-phenoxypropane was relatively lower than the other
substrates (Table 5 entry 6). Also, cyclohexane oxide as non-
terminal epoxide presented excellent conversion and good
selectivity (Table 5 entry 8) while poor reactivity has been
previously reported for this epoxide.64,65
Table 4: Cycloaddition of CO2 with styrene epoxide a
entry
catalyst
-
conversion (%)b
selectivity (%)b
1
2
3
4
5
6
7
0
negligible
18
0
negligible
55
Co-POMc
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
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28
29
30
31
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41
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45
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47
48
49
50
51
52
53
54
55
56
57
58
59
60
Co-POM@MIL-101(3)
TBABrd
49
82
Conversion
Selectivity
88
Co-POM/TBABre
MIL-101/TBABr
53
76
86
84
82
80
78
76
74
72
66
83
Co-POM@MIL-
101(3)/TBABr
88
88
a
Reaction conditions: 15 mmol styrene epoxide, 200 mg catalyst, 1 mmol
TBABr, PCO2 = 20 bar, T = 110 °C, 2 h. b Yields were determined by GC analysis. c
Reaction conditions: 15 mmol styrene epoxide, 10 mg Co-POM, PCO2 = 20 bar, T
= 110 °C, 2 h. d Reaction conditions: 15 mmol styrene epoxide, 1 mmol TBABr,
PCO2 = 20 bar, T = 110 °C, 2 h. e Reaction conditions: 15 mmol styrene epoxide,
10 mg Co-POM, 1 mmol TBABr, PCO2 = 20 bar, T = 110 °C, 2 h.
8
10
12
14
16
18
20
22
24
26
pressure of CO2 (bar)
Furthermore, the effects of reaction temperature, CO2
pressure, reaction time and amount of the catalyst were
investigated. The reactions of styrene oxide (15 mmol) in the
presence of TBABr (1 mmol) and catalyst (200 mg) under
pressure of CO2 (20 bar) and 110 °C at various reaction times
(1 to 5 h) were checked and 2 h was selected for the reaction
time based TOF (hˉ1) (Table S1 in the ESI†). Also, the effect of
reaction temperature was studied in detail (Table S2). The
results showed good conversion at 90 and 110 °C, while lower
conversion and selectivity was observed at 70 and 130 °C.
While at 70 °C the catalyst might not be active, at 130 °C the
decrease of the CO2 solubility in the liquid phase might play a
role. When exploring the effect of the catalyst amount on
conversion and selectivity under the optimized conditions, 90
°C, 20 bar CO2 pressure and 15 mmol styrene oxide under
solvent-free conditions (Table S3) the conversion and
selectivity was excellent at 200 mg catalyst load.
A detailed look at conversion and selectivity (Fig. 6)
reavealed that they both increased in the range of 10 to 20 bar
of CO2 pressure, but rising the pressure to 25 bar led to a slight
decrease in both conversion and selectivity. As expected,
increasing the solubility of CO2 in the liquid phase by
increasing the pressure results in the rise of both selectivity
and conversion. An alternative explanation is the formation of
an CO2-epoxide “complex” intermediate at higher pressure
overruling the catalyst-epoxide interaction.61-63 A combination
of the two opposite factors might be responsible for the
enhancement of selectivity and conversion up to 20 bar and
the reduction at a higher pressure of 22 and 25 bar (Fig. 6).
Finally, 20 bar CO2 pressure, 90 °C temperature, 2 h
reaction time, 15 mmol epoxide, 1 mmol TBABr and 200 mg
Co-POM@MIL-101(3) under solvent-free conditions were
selected as optimized conditions for the reaction of various
Fig. 6. Conversion and selectivity of styrene epoxide to cyclic carbonate as a function of
pressure (bar) at 90 °C using 15 mmol styrene epoxide, 200 mg Co-POM@MIL-101(3)
after 2 h.
The mechanism of the cycloaddition of CO2 with epoxides
using Co-POM@MIL-101(3) is proposed based on previous
reports.38,66,67 Various research suggested
a Lewis acid
mechanism for the Co(III)-catalyzed cycloaddition of CO2 with
epoxides,68 which cannot be considered for Co-POM@MIL-
101(3) because of the shielding of the cobalt center with 12
WO6 ligands. Alternatively, single-electron transfer from
epoxide to cobalt(III) can occur38 which produces oxygen
radicals and carbon cations as intermediates as well as Co(II)-
POM (Scheme 2). Nucleophilic attack of CO2 followed by
electron transfer from Co(II) to the intermediate forms the
cyclic carbonate and recovers Co(III)-POM. In order to confirm
the proposed mechanism, a model reaction (5 mmol acetic
acid, 55 mmol benzyl alcohol, Co-POM@MIL-101(3), T = 100
oC) was carried out in the presence of acrylonitrile and 2-6-di-
tert-butylphenol as radical scavengers. The yield of the
product was significantly reduced under these conditions.
This mechanism is also in line with the observed tendency of
Co-POM@MIL-101 to undergo electron transfer from Cr(III) to
Co(III) forming Co(II) (see EPR and XPS).
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Table 5: Cycloaddition of CO2 with various epoxides catalyzed by Co-POM@MIL-
View Article Online
DOI: 10.1039/C9NJ02607J
O
O
101(3)a
O
O
O
O
R
[CO2]
O
O
R
R
R
8
9
entry
1
epoxide
conversion (%) b
93
selectivity (%) b
91
10
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59
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Co(II)-POM
Co(III)-POM
O
O
2
3
4
5
90
89
94
92
95
74
92
95
O
C
O
O
O
R
CH2
O
R
O
O
C
O
O
Scheme 2. Proposed mechanism for cycloaddition of CO2 with epoxides catalyzed by
Co-POM@MIL-101(3).
Cl
As the esterification reaction is reversible; an excessive
amount of alcohol is beneficial for the yield of the ester
products. However, too much alcohol was unfavorable
because of dilution of the catalyst and acetic acid.69 Thus, a
molar ratio of 1:11 acid:alcohol was chosen for further studies.
O
O
O
O
6
81
90
Table 6. Effect of acid to alcohol molar ratio a
entry
acid to alcohol ratio
yield (%) b
O
1
2
3
4
1:5
1:8
68
75
84
84
7
8
88
87
88
65
1:11
1:14
O
a Reaction conditions: 200 mg catalyst, 15 mmol epoxide, PCO2 = 20 bar, T = 90 °C,
2 h. b Yields were determined by GC analysis.
a
Reaction conditions: 5 mmol acetic acid, benzyl alcohol, 100 mg Co-
POM@MIL-101(3), T = 100 °C, 25 min. b GC yield based on acid.
Esterification of acetic acid with alcohols
The esterification of acetic acid with various alcohols including
different derivatives of benzyl alcohol and aliphatic alcohols
such as 2-phenyl-1-propanol, 2-phenylethanol was studied in
the presence of the catalysts Co-POM@MIL-101(3). The molar
ratio of acid to alcohol was found to be the most significant
factor, hence this effect was investigated by changing the
molar ratio from 1:5 to 1:14 (Table 6). Other conditions
including the reaction temperature (100 °C) and amount of the
catalyst (100 mg) were held constant. The conversion
increased significantly with increasing acid to alcohol molar
ratio from 1:5 to 1:11.
For the selection of the best catalyst with respect to Co-POM
loading, esterification of acetic acid with benzyl alcohol with a
molar ratio of 1:11 was performed at 100 °C using 100 mg Co-
POM@MIL-101 with different amounts of Co-POM (Table S4).
The results show the best TOF for Co-POM@MIL-101(3) with
0.01 mmol/g of POM loading. Optimization of the amount of
Co-POM@MIL-101(3), based on the TOF (hˉ1), was carried out
using various amounts of the catalyst (50, 100 and 150 mg).
The most efficient conversion was obtained in the presence of
100 mg catalyst (containing 0.0010 mmol Co, Table S5). For the
exploration of the effect of reaction temperature on the yield,
four experiments were performed at room temperature, 50,
70 and 100°C (Table S6), and 70 °C was chosen as the optimum
reaction temperature.
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The progress of the reaction was monitored by GC and the
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DOI: 10.1039/C9NJ02607J
results are shown in Table 7. As can be seen, benzyl alcohols
with electron donating groups are more reactive than those
with electron withdrawing groups (entries 2-5). It is also
noteworthy that aliphatic alcohols such as 2-phenyl-1-
propanol and 2-phenylethanol (entries 6 and 7) were also
converted to their corresponding esters in high yields. The
turnover frequencies (TOF), mole of produced acetate ester
per mole of Co-POM per hour range from about 7000 to
13000.
From the TPD experiments (Table 1) we have learned that
MIL-101(Cr) has higher acidity compared with Co-POM while
the results in Table S4 (in the ESI) show no activity of MIL-
101(Cr) in the esterification reaction, while Co-POM@MIL-101
is a good catalyst. It is thus reasonable to assume that the
catalytic activity of Co-POM@MIL-101 is not related to its acid-
base properties. As said before the Co center is embedded
within the lacunar Keggin anion and thus hampered from acid-
base interaction with the substrate.70,71 Therefore, an
outer-sphere electron transfer is possibly triggering the
esterification mechanism as has been show before for
[CoW12O40]5− in other reactions.19-22
9
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Fig. 7. Subsequent reaction cycles of Co-POM@MIL-101(3) in the cycloaddition of CO2
with styrene epoxide, reaction conditions: 200 mg Co-POM@MIL-101(3), 15 mmol
styrene epoxide, PCO2 = 20 bar, T = 90 °C, 2 h for each run.
After each run, the filtrated catalyst was washed with water
and chloroform and activated under vacuum at 100 °C
overnight. The Co-POM leaching for both reactions was
determined by analyzing the collected filtrates using ICP. The
results showed that only negligible amounts of Co-POM
catalyst leached in both reactions (less than 1% after the last
run). The nature of the reused catalyst after the last run was
monitored by XRD (Fig. S8 in the ESI†) which illustrated no
significant difference between the fresh and re-used catalyst.
Using acrylonitrile and 2,6-di-tert-butylphenol as a radical
scavenger in a model reaction ((5 mmol acetic acid, 55 mmol
o
benzyl alcohol, Co-POM@MIL-101(3), T = 100 C) resulted in
the reduction of the conversion from 84% to less than 20%
confirming the presence of radical intermediates in the
esterification reaction.
When compared to related MOF/POM based
heterogeneous catalysts (Table 8), the Co-POM@MIL-101
system combines very low reaction times, solvent-less
reactions, high reusability and low reaction temperature with
high selectivity and TOF in this esterification reaction.
Reusability of the catalysts
In order to investigate the reusability of the catalyst Co-
POM@MIL-101(3) and exclude that leached homogeneous
catalytic species play a role in the esterification reaction,
activated catalyst and benzyl alcohol were reacted for 1 h
(conditions as in Table 6), then the catalyst was separated by
filtration. In the next step, acetic acid was added to the
reaction vessel and the reaction mixture was stirred again. The
reaction progress was followed by GC and no noticeable
conversion was observed. To study the stability and reusability
of Co-POM@MIL-101 catalyst in the cycloaddition of epoxide
with CO2, five reaction cycles were carried out using styrene
epoxide in a model reaction (Fig. 7). After each run, the
catalyst was filtered off, washed with ethyl acetate and
activated in a vacuum oven at 100 °C for 24 h to remove
trapped reactants. Also, seven cycles of esterification reaction
were carried out using acetic acid and benzyl alcohol in a
model reaction (Fig. 8).
Fig. 8. Subsequent reaction cycles of Co-POM@MIL-101(3) in the esterification of acetic
acid with benzyl alcohol, reaction conditions: 5 mmol acetic acid, 55 mmol alcohol, 100
mg catalyst, T = 70 °C, 25 min for each run.
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Table 7: Esterification of acetic acid with various alcohols catalyzed by Co-POM@MIL-101(3)a
entry
1
alcohol
Ester
OCOCH3
time (min)
25
yield (%)b
84
TOFc (h-1)
10500
OH
HO
H3COCO
2
25
100
12500
OCH3
OCH3
HO
OCOCH3
3
4
25
40
92
11500
7500
OCH3
OCH3
HO
HO
OCOCH3
OCH3
H3CO
100
OCOCH3
5
45
25
100
100
6700
NO2
OH
NO2
OCOCH3
6
12500
OH
OCOCH3
7
25
97
12100
a Reaction conditions: 5 mmol acetic acid, 55 mmol alcohol, 100 mg catalyst, T = 70 °C. b GC yield based on acid. c (mol product/mol cobalt)h-1.
optical emission spectroscopy (ICP-OES), with a Jarrell-Ash
1100 ICP analyzer (Canada). X-ray photoelectron spectroscopy
(XPS) was carried out using an ESCA M-Probe system from
Surface Science Instruments equipped with a monochromatic
Al Kα excitation source (λ= 8.33 Å). Measurements were
conducted at a pressure in the 10-9 mbar range. Survey scans
were acquired with a detector pass energy of 158.9 eV,
whereas high-resolution spectra were recorded with a pass
energy of 22.9 eV. Spectral corrections and peak
deconvolution were done with CasaXPS software (Casa
Software Ltd.). Binding energies were charge-corrected in
reference to the C 1s signal for adventitious carbon (284.8 eV).
All spectra were fitted with Shirley or, where necessary, Spline
Shirley backgrounds using a GL(30) line shape for non-
conductive synthetic components and an asymmetric A(0.4,
0.38, 20)GL(20) line shape for C=C contributions. EPR spectra
were recorded on solid samples in the X-band on a Bruker
Experimental Section
Materials and Instrumentation
All reagents were purchased as ACS reagent grade from Merck
(Germany) or Fluka (Switzerland). Powder X-ray diffraction
(PXRD) analysis was conducted using a D8 Advance instrument
from Bruker (Germany) using Cu Kα (λ = 1.5406 Å) radiation. N2
adsorption-desorption isotherms at 77
adsorption isotherms at 273 were obtained on
Micromeritics Tristar instrument (France) equipped with a
Smart VacPrep outgassing unit. The Brunauer-Emmett-Teller
(BET) method and the Barrett, Joyner, and Halenda (BJH)
method were used for calculation of the specific surface areas
and the pore distribution, respectively. The chemical
composition was determined using inductively coupled plasma
K and CO2 gas
K
a
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(Germany) System ELEXSYS 500E equipped with a Bruker reaction, aliquots were periodically collected forViGewCAratinclealOynsliinse.
Variable Temperature Unit ER 4131VT (500 to 100 K); the g Valeric acid was used as an internal standard and the yield of
DOI: 10.1039/C9NJ02607J
values were calibrated using a dpph sample. The progress of the reaction was reported based on the amount of acetic acid.
the reactions was monitored using GC analysis with an Agilent The catalyst was separated via centrifugation prior to gas
(USA) GC6890 equipped with a 19096C006 80/100 WHP chromatography analysis. To avoid any additional conversion
packed column and a flame ionization detector. NH3 and CO2 in the reaction mixture, the analysis was carried out directly
temperature programmed desorption (TPD) experiments were after sampling. For the recycling tests, the catalyst Co-
carried out using a NanoSORD NS91 (Sensiran, Iran) apparatus. POM@MIL-101(3) was recovered by filtration, washed with
water and chloroform, and dried under vacuum at 100 °C. The
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Synthesis of the Co-POM@MIL-101 catalysts
recovered catalyst was directly used for the next run.
Co-POM was synthesized according to the literature72 and the
Co-POM@MIL-101 catalysts were prepared according to our
previously reported procedure.14 Briefly, the catalyst was
synthesized by adding the MIL-101(Cr) precursor, including
Cr(NO3)3⋅9H2O (2.0 g, 5 mmol), terephthalic acid (0.83 g, 5
mmol), and Co-POM (0.4 g (0.129 mmol), 0.8 g (0.258 mmol),
1.0 g (0.323 mmol), 2.0 g (0.645 mmol), and 2.5 g (0.806
mmol)) and deionized water (20 mL) in a Teflon-lined
autoclave reactor. After sonicating for a short time, the
mixture was put in the oven at 218 °C for 18 h without stirring.
The resulting solid Co-POM@MIL-101 was filtered off by
centrifugation and washed with water, ethanol, and acetone,
followed by drying and activation at 100 °C under vacuum
overnight.
Conclusions
The effect of the encapsulation of the Keggin anion
[Co(III)W12O40]5‒ (Co-POM) in the MOF MIL-101(Cr) on the
catalytic activity of Co-POM@MIL-101 catalysts in the
cycloaddition of CO2 with epoxides, as well as in the
esterification of acetic acid with alcohol was investigated in
this study.
The thorough characterization of the catalyst materials
revealed good encapsulation and distributions of the Co-POM
in the MOF (SEM, TEM, EDX). The low Co content of less than
1% from EDX was confirmed by XPS alongside with an
increased tendency of electron transfer from Cr(III) of MIL-101
to Co(III) with increasing Co-POM contents resulting in the
observation of Cr(IV) and Co(II) in XPS and EPR spectra.
The facile Co(III)/Co(II) electron transfer seems to be
important for the two studied reactions. For the cycloaddition
of CO2 with epoxides a Co(III)/Co(II) mediated reaction
mechanism could be proposed based on the observation that
the Lewis acid-base character of the components MIL-101(Cr)
and Co-POM as determined from NH3 and CO2 temperature
programmed desorption (TPD) experiments do not correlate
with the observed catalytic efficiency. The same is true for the
esterification of acetic acid and various alcohols. Trapping
experiments using radical scavengers as acrylonitrile and 2,6-
General procedure for the cycloaddition of CO2 with epoxides
The reactions were conducted in a 75 mL stainless steel
autoclave equipped with a magnetic stirrer. For a typical
catalytic reaction, catalyst (200 mg including 0.002 mmol of
Co-POM, calculated based on Co), epoxide (15 mmol) and
tetrabutylammonium bromide (1 mmol) were placed in the
reactor. The autoclave was charged three times with CO2 to
deplete air, then pressurized with the appropriate amount of
CO2 and heated to the desired temperature in an oil bath for
the designated period of time. After the reaction was
complete, the autoclave was cooled to 0 °C in an ice-water
bath, and the remaining CO2 was slowly released. The product
was diluted with ethyl acetate and the reaction yield was
determined by GC analysis. The catalysts were separated via
centrifugation, washed with ethyl acetate and DMF, dried
under vacuum at 150 °C and then reused directly for the next
run.
di-tert-butylphenol
support
strongly
electron-transfer
triggered mechanisms for both reactions.
The easy-to-make catalyst system Co-POM@MIL-101
allows to carry out these interesting reactions using a plethora
of substrates, under solvent-free conditions, low conversion
times, high TOF and selectivity, at low temperature and the
catalyst can be easily recycled and has been reused several
times. This success underlines that the encapsulation of POM
catalysts in MOF or related porous materials is an interesting
approach to design highly active, selective and easily
recoverable catalysts.
General procedure for the esterification reaction
Acetic acid and alcohol were introduced into a two-necked
round bottom flask connected to a reflux condenser and a
thermometer. The reaction mixture was heated using an oil
bath at 70 °C and then the catalyst was added. To follow the
.
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Table 8. Comparison of catalytic performance of Co-POM@MIL-101 and reported catalysts for esterification of acetic acid.
entry
catalyst
Co-POM/UiObpy a
HPW@MIL-101(Cr) b
MIL-125s
alcohol
1-propanol
n-hexanol
T (°C)
60
time (h)
yield (%)
30
reusability (runs)
Ref
1
2
3
4
5
6
7
8
7
6
2
11
110
90
58.3
75.2
97.4
95
5
73
butanol
7
3
45
poly(VMPS)-PW c
Fe(ClO4)3
butanol
110
R.T
100
50
1.5
15
6
74
benzyl alcohol
benzyl alcohol
benzyl alcohol
benzyl alcohol
homogeneous
75
POM-IL d
6
89.2
94
8
no data
7
76
77
p-phenolsulfonic acid
formaldehyde resins
12
Co-POM@MIL-101(3)
70
25 min
84
present work
a UiO-bpy: Zr-MOFs connected by 2,2′-bipyridine-5,5′-dicarboxylic acid linkers. b HPW = [PW12O40]3- c SO3H functionalized [PW12O40]3‒. d POM = [HPW12O40]2‒.
7. N. Maksimchuk, M. Timofeeva, M. Melgunov, A. Shmakov, Y. A.
Chesalov, D. Dybtsev, V. Fedin and O. Kholdeeva, J. Catal., 2008,
257, 315–323.
Conflicts of interest
8. J. Juan-Alcañiz, J. Gascon and F. Kapteijn, J. Mater. Chem., 2012,
22, 10102–10118.
There are no conflicts to declare.
9. D.-Y. Du, J.-S. Qin, S.-L. Li, Z.-M. Su and Y.-Q. Lan, Chem. Soc.
Rev., 2014, 43, 4615–4632.
10. W. Xie and F. Wan, Chem. Engin. J. 2019, 365, 40–50.
11. X. Song, D. Hu, X. Yang, H. Zhang, W. Zhang, J. Li, M. Jia, and J.
Yu, ACS Sustainable Chem. Eng. 2019, 7, 3624–3631.
12. M. Stuckart and K. Y. Monakhov, J. Mater. Chem. A, 2018, 6,
17849–17853.
13. N. V. Maksimchuk, O. A. Kholdeeva, K. A. Kovalenko, and V. P.
Fedin, Isr. J. Chem. 2011, 51, 281–289.
14. A. Marandi, S. Tangestaninejad, M. Moghadam, V. Mirkhani, A.
Mechler, I. Mohammadpoor-Baltork and F. Zadehahmadi, Appl.
Organomet. Chem., 2018, 32, e4065
15. C.-Y. Sun, S.-X. Liu, D.-D. Liang, K.-Z. Shao, Y.-H. Ren and Z.-M.
Su, J. Am. Chem. Soc., 2009, 131, 1883–1888.
16. L. H. Wee, S. R. Bajpe, N. Janssens, I. Hermans, K. Houthoofd, C.
E. Kirschhock and J. A. Martens, Chem. Commun., 2010, 46,
8186–8188.
17. L. H. Wee, N. Janssens, S. R. Bajpe, C. E. Kirschhock and J. A.
Martens, Catal. Today, 2011, 171, 275–280.
18. B. Gagea, Y. Lorgouilloux, Y. Altintas, P. Jacobs and J. Martens, J.
Catal., 2009, 265, 99–108.
19. I. A. Weinstock, Chem. Rev., 1998, 98, 113–170.
20. C. Saux, L. R. Pizzio, L. B. Pierella, Appl. Catal. A: Gen., 2013, 452,
17–23.
Acknowledgments
We are thankful to the Research Council of the University of
Isfahan for financial support of this work. AK acknowledges the
German Academic Exchange Service (DAAD), KD-0001052598-
2 for a short-time guest lectureship and the University of
Shiraz. AS, RF, AK, and SM kindly acknowledge support from
the University of Cologne.
Notes and references
1. R. M. Ladera, J. L. G. Fierro, M. Ojeda and S. Rojas, J. Catal.,
2014, 312, 195–203.
2. S. S. Balula, I. C. Santos, L. Cunha-Silva, A. P. Carvalho, J. Pires, C.
Freire, J. A. Cavaleiro, B. de Castro and A. M. Cavaleiro, Catal.
Today, 2013, 203, 95–102.
3. Y. Yang, Y. Guo, C. Hu, Y. Wang and E. Wang, Appl. Catal. A:
Gen., 2004, 273, 201–210.
4. O. Kholdeeva, N. Maksimchuk and G. Maksimov, Catal. Today,
2010, 157, 107–113.
5. R. R. Ozer and J. L. Ferry, J. Phys. Chem. B, 2002, 106, 4336–
4342.
6. G. Ferey, Science, 2005, 310, 1119–1119.
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 12 of 13
ARTICLE
New J. Chem.
1
2
3
4
5
6
7
8
9
21. E. N. Glass, J. Fielden, Z. Huang, X. Xiang, D. G. Musaev, T. Lian 51. M. C. Biesinger, B. P. Payne, A. P. Grosvenor, L. W. M. Lau, A. R.
and C. L. Hill, Inorg. Chem., 2016, 55, 4308–4319.
Gerson, R. St. C. Smart, Appl. Surf. Sci., 2011, 257, V2i7ew17Ar‒ti2cl7e3O0n.line
DOI: 10.1039/C9NJ02607J
22. S. Mukhopadhyay, J. Debgupta, C. Singh, A. Kar and S. K. Das, 52. T. H. Fleisch, G. W. Zajac, J. O. Schreiner and G. J. Mains, Appl.
Angew. Chem., Int. Ed., 2018, 57, 1918–1923. Surf. Sci., 1986, 26, 488‒497.
23. J. Juan-Alcañiz, E. V. Ramos-Fernandez, U. Lafont, J. Gascon and 53. Y. Xie, Z. Fang, L. Li, H. Yang and T.-F. Liu, ACS Appl. Mater.
F. Kapteijn, J. Catal., 2010, 269, 229–241. Interfac., 2019, 11, 27017−27023.
24. L. Bromberg, Y. Diao, H. Wu, S. A. Speakman and T. A. Hatton, 54. F. Soltanolkottabi, M. R. Talaie, S. Aghamiri and S.
Chem. Mater., 2012, 24, 1664–1675.
Tangestaninejad, J. Iran. Chem. Soc., 2019 published online,
https://doi.org/10.1007/s13738-019-01746-8.
55. J. Graciani, K. Mudiyanselage, F. Xu, A. E. Baber, J. Evans, S. D.
Senanayake, D. J. Stacchiola, P. Liu, J. Hrbek, J. Fernández Sanz
and J. A. Rodriguez, Science, 2014, 345, 546‒550.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
25. G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S.
Surblé and I. Margiolaki, Science, 2005, 309, 2040–2042.
26. M. North, R. Pasquale and C. Young, Green Chem., 2010, 12,
1514–1539.
27. M. M. Halmann, Chemical Fixation of Carbon Dioxide – Methods 56. A. K. Opitz, A. Nenning, C. Rameshan, M. Kubicek, T. Götsch, R.
for Recycling CO2 into Useful Products, CRC Press, Boca Raton,
2018.
28. Y. Leng, D. Lu, C. Zhang, P. Jiang, W. Zhang and J. Wang, Chem.
Eur. J., 2016, 22, 8368–8375.
29. J. A. Kozak, J. Wu, X. Su, F. Simeon, T. A. Hatton and T. F.
Jamison, J. Am. Chem. Soc., 2013, 135, 18497–18501.
Blume, M. Hävecker, A. Knop-Gericke, G. Rupprechter, B.
Klötzer and J. Fleig, ACS Appl. Mater. Interfaces, 2017, 9,
35847−35860.
57. J. Kim, S.-N. Kim, H.-G. Jang, G. Seo and W.-S. Ahn, Appl. Catal.
A: General, 2013, 453, 175–180.
58. K. Kamata and K. Sugahara, Catalysts, 2017, 7, 345 (1‒24).
30. Y. Wang, Y. Qin, X. Wang and F. Wang, Catal. Sci. Technol., 2014, 59. L. Zhu, X.-Q. Liu, H.-L. Jiang and L.-B. Sun, Chem. Rev., 2017, 117,
4, 3964–3972. 8129–8176.
31. F. Liu, K. Huang, A. Zheng, F.-S. Xiao and S. Dai, ACS Catal., 2018, 60. M. North and R. Pasquale, Angew. Chem., 2009, 121, 2990–
8, 372–391. 2992.
32. K. Huang, J.-Y. Zhang, F. Liu and S. Dai, ACS Catal., 2018, 8, 61. S.-S. Wu, X.-W. Zhang, W.-L. Dai, S.-F. Yin, W.-S. Li, Y.-Q. Ren and
9079–9102. C.-T. Au, Appl. Catal. A: Gen., 2008, 341, 106–111.
33. F. Liu, K. Huang, C.-J. Yoo, C. Okonkwo, D.-J. Tao, C. W. Jones 62. L.-F. Xiao, F.-W. Li, J.-J. Peng and C.-G. Xia, J. Mol. Catal. A:
and S. Dai, Chem. Eng. J., 2017, 314, 466–476. Chemical, 2006, 253, 265–269.
34. F. Liu, K. Huang, Q. Wu and S. Dai, Adv. Mater., 2017, 29, 63. J. Sun, L. Han, W. Cheng, J. Wang, X. Zhang and S. Zhang,
1700445 (1‒8). ChemSusChem, 2011, 4, 502–507.
35. K. Huang, F. Liu and S. Dai, J. Mater Chem. A, 2016, 4, 64. O. V. Zalomaeva, A. M. Chibiryaev, K. A. Kovalenko, O. A.
13063‒13070.
Kholdeeva, B. S. Balzhinimaev and V. P. Fedin, J. Catal., 2013,
298, 179–185.
65. R. Babu, A. C. Kathalikkattil, R. Roshan, J. Tharun, D.-W. Kim and
D.-W. Park, Green Chem., 2016, 18, 232–242.
36. F. Liu, K. Huang, S. Ding and S. Dai, J. Mater. Chem. A, 2016, 4,
14567‒14571.
37. W. Ge, X. Wang, L. Zhang, L. Du, Y. Zhou and J. Wang, Catal. Sci.
Technol., 2016, 6, 460–467.
66. B. Yu, B. Zou and C.-W. Hu, J. CO2 Util., 2018, 26, 314–322.
38. F. Chen, X. Li, B. Wang, T. Xu, S. L. Chen, P. Liu and C. Hu, Chem. 67. M.-Y. Wang, R. Ma and L.-N. He, Sci. China: Chem., 2016, 59,
Eur. J., 2012, 18, 9870–9876. 507–516.
39. Q. Han, B. Qi, W. Ren, C. He, J. Niu and C. Duan, Nat. Commun., 68. X.-B. Lu and D. J. Darensbourg, Chem. Soc. Rev., 2012, 41, 1462–
2015, 6, 10007 (1‒8). 1484.
40. Y.-B. Huang, J. Liang, X.-S. Wang and R. Cao, Chem. Soc. Rev., 69. J. Zhao, H. Guan, W. Shi, M. Cheng, X. Wang and S. Li, Catal.
2017, 46, 126–157. Commun., 2012, 20, 103–106.
41. T. S. Reddy, M. Narasimhulu, N. Suryakiran, K. C. Mahesh, K. 70. B. Yu, B. Zou and C.-W. Hu, J. CO2 Util., 2018, 26, 314–322.
Ashalatha and Y. Venkateswarlu, Tetrahedron Lett., 2006, 47, 71. Y. Cao, Q. Chen, C. Shen and L. He, Molecules 2019, 24, 2069
6825–6829.
(1‒26).
42. N. G. Khaligh, J. Mol. Catal, A: Chemical, 2012, 363, 90–100.
43. G. Bartoli, M. Bosco, R. Dalpozzo, E. Marcantoni, M. Massaccesi
and L. Sambri, Eur. J. Org. Chem., 2003, 2003, 4611–4617.
72. M. H. Habibi, S. Tangestaninejad, I. Mohammadpoor-Baltork, V.
Mirkhani and B. Yadollahi, Tetrahedron Lett., 2001, 42,
6771‒6774.
44. M. Popova, H. Lazarova, Y. Kalvachev, T. Todorova, Á. Szegedi, 73. Y. Zang, J. Shi, X. Zhao, L. Kong, F. Zhang and Y. Zhong, React.
P. Shestakova, G. Mali, V. D. Dasireddy and B. Likozar, Catal.
Commun., 2017, 100, 10–14.
Kinet., Mech. Catal., 2013, 109, 77–89.
74. Y. Leng, P. Jiang and J. Wang, Catal. Commun., 2012, 25, 41–44.
45. E. Yılmaz, E. Sert and F. S. Atalay, Catal. Commun., 2017, 100, 75. M. M. Heravi, F. K. Behbahani, R. H. Shoar and H. A. Oskooie,
48–51. Catal. Commun., 2006, 7, 136–139.
46. Q.-X. Luo, M. Ji, M.-H. Lu, C. Hao, J.-S. Qiu and Y-Q. Li, J. Mater. 76. H. Li, Y. Qiao, L. Hua, Z. Hou, B. Feng, Z. Pan, Y. Hu, X. Wang, X.
Chem. A, 2013, 1, 6530‒6534. Zhao and Y. Yu, ChemCatChem, 2010, 2, 1165–1170.
47. B. Babu, Ch. R. Krishna, Ch. V. Reddy, V. P. Manjari and R. V. S. S. 77. M. Minakawa, H. Baek, Y. M. Yamada, J. W. Han and Y. Uozumi,
N. Ravikumar, Spectrochim. Acta A: Molecular and Biomolecular
Spectroscopy, 2013, 109, 90–96.
Org. Lett., 2013, 15, 5798–5801.
48. K. Ravindranadh, K. D. V. Prasad and M. C. Rao, AIMS Mater. Sci.
2016, 3, 796‒807.
49. W. E. Antholine, S. Zhang, J. Gonzales and N. Newman, Int. J.
Mol. Sci. 2018, 19, 3532 (1‒7).
50. A. G. Shard, Surf. Interface Anal., 2014, 46, 175‒185.
12 | New. J. Chem., 2019, 00, 00-00
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DOI: 10.1039/C9NJ02607J
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