Tailoring the catalytic activity of metal organic frameworks by tuning the metal center and basic functional sites

Article abstract of DOI:10.1039/c7nj01055a

In this study, zirconium, zinc, and copper-based metal organic framework catalysts were synthesized. In order to tune the catalytic activity, the coordinative unsaturated metal-organic frameworks were functionalized with different amines by an economical

Full text of DOI:10.1039/c7nj01055a

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Tailoring the catalytic activity of metal organic framework by tuning the metal centre and
basic functional sites
Poonam Rani and Rajendra Srivastava*
Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar-140001, India
_____________________________________________________________________________
Abstract
In this study zirconium, zinc, and copper based metal organic framework catalysts were
synthesized. In order to tune the catalytic activity, coordinative unsaturated metalꢀorganic
framework was functionalized with different amines by an economical and simple postꢀsynthetic
modification strategy. In this study, systematic investigation is made by the functionalization of
metal organic framework with primary, secondary, and tertiary amines via postꢀsynthesis
method. Furthermore, metal organic framework was also functionalized with one basic ionic
liquid. Materials were characterized by powder Xꢀray diffraction, nitrogen adsorption, scanning
electron microscopy, thermo gravimetric analysis, Fourier transform infrared, Xꢀray
photoelectron spectroscopy, and temperature programmed desorption techniques. Applications of
these biꢀfunctional catalysts were investigated in the best suited model reaction, Knoevenagel
condensation. Applicability of these catalysts was extended in the synthesis of jasminaldehyde
(Aldol condensation of 1ꢀheptanal and benzaldehyde) and cyclic carbonate (cycloaddition of
CO2 to epoxide). Catalysts can be easily recovered and reused with negligible loss in the
catalytic activity even after five recycles.
Keywords: Metal organic framework, amine base, postꢀsynthesis modified MOF, condensation
reaction, cyclic carbonate.
*Eꢀmail: rajendra@iitrpr.ac.in, Phone: +91ꢀ1881ꢀ242175; Fax: +91ꢀ1881ꢀ223395
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1. Introduction
Functional nanoporous materials fascinate catalysis researchers because of their possible
applications in catalysis, gas separation, energy applications and so on.1ꢀ3 Isolated metal centers,
tunable physicoꢀchemical properties, and ease of functionalization are keys for the success of
functional nanoporous materials. For example, microporous zeolites are robust materials and
play important role in petrochemical and fine chemical industries for reactions involving small
molecules.4,5 Due to the lack of external surface area, mesopores, and less functionalizability
(due to the present of very less surface silanol groups) this class of materials is difficult to use in
the fine chemical industry. With the development of mesoporous zeolites with large number of
surface silanol groups these problems have been solved and they can be used as robust functional
material.6ꢀ9 Another interesting example is the development of MCMꢀ41 and SBAꢀ15.
Hexagonal mesoporous silica MCMꢀ41 has large external surface, well defined mesopores, and
large number of surface silanol groups that make it easily functionalizable.10ꢀ12 However, less
stability under reaction condition discourages its numerous possible applications. With the
development of highly robust hexagonal mesoporous silica SBAꢀ15 this problem was also taken
care and even today after the 2 decades of its invention it is the choice of many catalysis
researchers.13ꢀ15
Porous metal–organic frameworks (MOFs) are emerging as a new class of functional
nanoporous materials. It is possible to prepare wide range of fascinating structures by the
bonding of metal ions with multifunctional organic ligands.16,17 Wide variety of organic and
inorganic subunits with varying chemical reactivity creates ample opportunity to use them in
various applications such as gas storage, adsorption, and heterogeneous catalysis.18ꢀ21 Due to
tunable microporous architecture, large surface area, and tunable reactivity they find important
role in gas adsorption and separation. Since the MOFs are built with organic subunits therefore it
is not suitable to use them in catalytic reactions which are operated at high temperature and
pressure condition. However, they can be used in liquid phase catalytic reactions operated under
mild reaction condition at a temperature below 200 °C. Study shows that structure of several
MOFs collapse in reaction medium even at low operating temperature (below 100 °C).22
Structures of several MOFs collapse on long storage or small exposure of solvents/humidity,
2

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which discourages their catalytic applications. Therefore, it is important to choose such MOFs
that are stable under liquid phase condition in different solvents and varied reaction condition.
It is important to tune the physical and chemical properties of MOFs with desired
functional groups in order to make them useful for the appointed catalytic applications. Similar
to other successful nanoporous materials, MOFs can also be functionalized with wide variety of
functional groups through direct or postꢀsynthesis approaches.23,24 Functional groups bearing
organic ligands are either not commercially available or they are more than 10 times costly than
conventional organic building units. Therefore, functional MOFs synthesized using direct
synthesis approach is very costly. However, postꢀsynthesis modifications are performed using
economical functional groups and therefore they are more attractive. In the direct synthesis
approach, functional sites are incorporated in the organic units before it is treated with metal
source. Postꢀsynthesis method is more versatile than directꢀsynthesis because the required
functional group can be incorporated through covalent bond with organic functional sites or
through coordinated bond with metal center of MOF without affecting the basic framework
structure. Several other strategies have been adopted to functionalize metal organic framework
that includes introduction of structural defects,25 solvent exchange,26 loading the metal
nanoparticles etc.27,28
Wide variety of heterogeneous nanoporous materials are known such as zeolites,
mesoporous alumnosilicates, metal oxides, heteropolyic acid, metal phosphates, ionic liquids
etc.29 However, only a few basic heterogeneous catalysts are known such as metal oxides and
hydrotalcites.30ꢀ32 Most of the time, they are not suitable for the fine chemical synthesis because
they require special organic amines. In order to get suitable base functionalization, mesoporous
materials have been functionalized using organic amines.33,34 Similar strategies can be adopted
for the MOF materials. Catalytic activity of amine functionalized MOFs such as MILꢀ53 and
IRMOFꢀ3 have been reported in various organic transformations.35ꢀ37 But these MOFs require
expensive ligands such as amine terphthalic acid or post synthetic modified amine group.
Recently, a few reports based on catalytic investigation of amine base containing zirconium
based MOF (NH2ꢀUiOꢀ66) have appeared in the literature.38,39 Conventional zirconium based
MOF has also been investigated in the ring opening of epoxides and hydroamination reactons.40
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In this study, systematic study is made by the functionalization of MOF with primary,
secondary and tertiary amines via postꢀsynthesis method. Wide range of robust MOFs based on
Zr, Zn, and Cu were prepared and then highly active MOF was functionalized with various
amines as mentioned above. Furthermore, the highly active MOF was also functionalized with
one basic ionic liquid. The catalytic activities of parent and functionalized MOFs were
systematically investigated in several model reactions such as condensation reactions and
cycloaddition reaction of CO2 to epoxides.
2. Experimental Section
2.1. Catalyst preparation
Zirconium based MOF (designated as ZrꢀBDCꢀMOF) was prepared using 1, 4ꢀ
benzenedicarboxylic acid (H2BDC) as ligand and ZrOCl2.8H2O as inorganic unit by following
the reported procedure.40 A mixture of ZrOCl2.8H2O (6.4 g, 10 mmol), 1, 4ꢀbenzenedicarboxylic
acid (H2BDC) (3.2 g, 10 mmol), and 50 ml of DMF were taken in round bottom flask and stirred
for 15ꢀ20 min at ambient condition. HCl (1.6 ml, 19.2 mmol) was added into the reaction
mixture at ambient condition. Temperature of the reaction vessel was raised to 150 °C and the
reaction mixture was stirred at this temperature for 24 h. The resultant white product was
filtered, washed with DMF and dried in an oven at 100 °C for 12 h. The dried product was again
taken in 50 mL of DMF and stirred overnight at ambient condition to remove the unꢀreacted
ligand. Solvent exchange was carried out with methanol at ambient condition for 12 h. The
product was filtered and dried in an oven at 100 °C for 12 h. The solvent exchange process was
repeated 3 times to remove DMF from the reaction mixture, completely.
For comparative study, zinc based MOF (designated as ZnꢀBDCꢀMOF) was prepared by
following the reported procedure.41 Zn and Cu based MOFs were also prepared using trimesic
acid as organic linker by following the reported procedure and they are designated as ZnꢀBTCꢀ
MOF42 and CuꢀBTCꢀMOF43, respectively. Furthermore, widely investigated 2ꢀmethyl Imidazole
based ZnꢀMeIMIꢀMOF was also prepared for comparative catalytic investigation by following
the reported procedure.44
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2.1.1. Functionalization of Zr-BDC-MOF with amines
Amine grafted ZrꢀBDCꢀMOFs were prepared by postꢀsynthesis methodology. ZrꢀBDCꢀ
MOF was first activated at 220 °C for 24 h. Activated ZrꢀBDCꢀMOF (0.25 g) was suspended in
20 mL of methanol and the reaction mixture was stirred at ambient condition for 15 min. 1.3
mmol of amines were added, and the reaction mixture was stirred for 24 h at ambient condition.
The final product was centrifuged, washed with methanol and then dried in vacuum oven. Three
different amines Nꢀbutyl amine, diethylamine, 4ꢀdimethylaminopyridine, and one –OH
containing ionic liquid, butyl methyl imidazole were grafted and the resultant materials are
designated as NꢀbutylamineꢀZrꢀBDCꢀMOF, DiethylamineꢀZrꢀBDCꢀMOF, DMAPꢀZrꢀBDCꢀ
MOF, and [BMIM][OH]ꢀZrꢀBDCꢀMOF, respectively.
Procedure of catalytic reactions and details of methods and instruments used for the
characterization of MOF materials prepared in this study are provided in supporting information
section.
3. Results and discussion
Zirconium based metal organic framework [Zr6O4(OH)4(BDC)6] designated as ZrꢀBDCꢀ
MOF was prepared by the reaction of ZrOCl2.8H2O and terephthalic acid in DMF solvent using
HCl as a modulator. To enhance the catalytic activity of ZrꢀBDCꢀMOF, different amines were
grafted in the ZrꢀBDCꢀMOF framework via postꢀsynthesis method. ZrꢀBDCꢀMOF was first
activated and then reacted with amines in methanol to obtain amine functionalized ZrꢀBDCꢀ
MOF. Three different amines (Nꢀbutyl amine, diethylamine, 4ꢀdimethylaminopyridine) and one
ionic liquid [BMIM][OH]) were grafted in the ZrꢀBDCꢀMOF framework. Amines were
coordinativly bonded through unsaturated metal center of ZrꢀBDCꢀMOF to form the base
functionalized MOFs.
ZrꢀBDCꢀMOF possesses high thermal and chemical stability, which fulfills the requirement
of various catalytic organic transformations. In ZrꢀBDCꢀMOF, 12 terephthalate linkers are
present. Linker defect generates the coordinatively unsaturated metal sites as Lewis acid sites in
the framework. ZrꢀBDCꢀMOF is made up of the octahedral [Zr6(µ3ꢀO)4(µ3ꢀOH)4(µ2ꢀCOO)12]
clusters and their 3D porous systems feature alternating octahedral and tetrahedral cages sharing
triangular windows. Upon thermal activation, the cluster becomes [Zr6(µ3ꢀO)6(µ2ꢀCOO)12] by
releasing two water molecules, and the Zr centers change its coordination from eight to seven
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that generate potential Lewisꢀacid sites. In this study, electron rich amines were grafted to the
coordinated unsaturated metal sites to form biꢀfunctional catalysts.
1600
1200
800
400
0
(a)
Zr-BDC-MOF
80
Simulated-UiO-66
40
0
10
20
30
40
50
2θ (Degree
)
2400
1800
1200
600
1500
1000
500
(b)
(c)
[Bmim][OH]-Zr-BDC-MOF
Diethylamine-Zr-BDC-MOF
0
0
900
1600
1200
800
400
0
600
300
0
DMAP-Zr-BDC-MOF
N-butylamine-Zr-BDC-MOF
10
20
30
40
50
10
20
30
40
50
2θ (Degree
)
2θ (Degree
)
Fig. 1.Powder Xꢀray diffraction patterns of parent and base grafted ZrꢀBDCꢀMOF.
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3.1. Physico-chemical characterization
Powder XRD patterns of various catalysts prepared in this study are shown in Fig. 1 and
Fig. S1. XRD pattern of ZrꢀBDCꢀMOF matches well with the simulated XRD pattern of UiOꢀ66
(Figure 1a). XRD patterns of amine grafted ZrꢀBDCꢀMOF are similar to that of ZrꢀBDCꢀMOF,
which confirms that framework integrity of MOF was retained after the postꢀsynthesis
modification with different amines (Fig. 1). XRD peak intensities of DMAP and [BMIM][OH]
grafted ZrꢀBDCꢀMOF are similar to that of parent ZrꢀBDCꢀMOF. However, XRD peak
intensities of Nꢀbutylamine and diethylamine grafted ZrꢀBDCꢀMOF are lower than that of parent
ZrꢀBDCꢀMOF, which confirms that grafting influenced the crystallinity of resultant material.
XRD patterns of ZnꢀBDCꢀMOF, ZnꢀBTCꢀMOF, CuꢀBTCꢀMOF, and ZnꢀMeIMIꢀMOF match
well with the reported XRD patterns of MOFꢀ5, ZnꢀHKUSTꢀ1, CuꢀHKUSTꢀ1, and ZIFꢀ8,
respectively (Fig. S1).41ꢀ44
N2ꢀadsorption desorption measurements were performed to evaluate the textural
properties of various materials investigated in this study. N2ꢀadsorption isotherms of different Zn
based MOF exhibits type I isotherm (Fig. S2). Furthermore, it is interesting to observe that their
adsorption points begin with different adsorbed volume at yꢀaxis. Difference in the volume
adsorbed is directly proportional to the texture properties shown in Table 1 for various Zn based
MOFs. Catalytic activity data shows that (discussed in the following section) among the amine
grafted ZrꢀBDCꢀMOF investigated in this study, DAMPꢀZrꢀBDCꢀMOF exhibited the highest
activity. Therefore, N2ꢀadsorption desorption measurements were performed for ZrꢀBDCꢀMOF
and DAMPꢀZrꢀBDCꢀMOF (Fig. 2). ZrꢀBDCꢀMOF exhibits type I/IV isotherm with capillary
condensation at high P/P0 in the range of 0.45 to 0.9, which shows interꢀcrystalline mesoporosity
in the material. Microporeꢀsize distribution of ZrꢀBDCꢀMOF was determined using nonlocal
density functional theory (NLDFT). NLDFT shows pore size distribution in the range of 0.5ꢀ
0.87, 0.87ꢀ1.9, and 2.3ꢀ4.1 nm with peak maxima of 0.6, 1.1, and 3.6 nm, respectively. The
micropore volume for ZrꢀBDCꢀMOF was 0.36 cc/g. The poreꢀsize distribution obtained from
Barret–Joyner–Halenda (BJH) shows a narrow pore size distribution in the range of 1.5ꢀ3.5 nm
with a peak maximum of 1.9 nm. Textural properties obtained from N2ꢀadsorption desorption
measurements are shown in Table 1. DAMPꢀZrꢀBDCꢀMOF exhibited similar isotherm and pore
size distribution to that of ZrꢀBDCꢀMOF, however, their adsorption starts at relatively low
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adsorbs volume at yꢀaxis. The micropore volume for DAMPꢀZrꢀBDCꢀMOF was 0.28 cc/g.
Textural properties of DMAPꢀZrꢀBDCꢀMOF are lower than that of ZrꢀBDCꢀMOF which
confirms that surface area and porosity are influenced by the postꢀsynthesis modification.
700
3.5
(a)
(b)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
3.0
2.5
2.0
1.5
1.0
0.5
0.0
600
500
400
300
200
100
2
3 4 5 6 7 8
2
Pore size (nm)
4
6
8
Pore size (nm)
Zr-BDC-MOF
DMAP-Zr-BDC-MOF
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Relative pressure (P/P0)
Fig. 2. N2ꢀadsorption isotherms of ZrꢀBDCꢀMOF and DMAPꢀZrꢀBDCꢀMOF. Inset shows pore
size distribution determined using (a) Barret–Joyner–Halenda (BJH), (b) nonlocal density
functional theory (NLDFT).
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Table 1. Physicoꢀchemical properties of various catalysts investigated in this study.
VTotal
NH3-desorbed
Catalyst
SBET(m2/g)
SEA (m2/g)
(mmol/g)
(cc/g)
2.55
ZrꢀBDCꢀMOF
808
335
0.55
CuꢀBTCꢀMOF
ZnꢀBDCꢀMOF
831
655
4
4
33
0
0.43
0.37
0.24
0.71
0.39
0.37
ꢀ
2.92
1.32
0.039
ꢀ
ZnꢀBTCꢀMOF
ZnꢀMeIMIꢀMOF
DMAPꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOFa
1354
471
445
8
267
223
ꢀ
Amount of amine
grafted(mmol/g)
CO2-
Molecular formula
(Based on elemental
analysis)
desorbed
(based
Based on
Catalyst
Based on
TGA
elemental
analysis
(N content)
-
on TPD)
(mmol/g)
analysis
ZrꢀBDCꢀMOF
Zr6O4(OH)4(BDC)6
0.074
0.085
0.077
0.101
0.040
-
NꢀButylamineꢀZrꢀBDCꢀMOF
DiethylamineꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
1.72
1.33
1.20
0.77
1.68
Zr6(O)6(BDC)6(NB)3.2
.
1.30
Zr6(O)6(BDC)6 (DE)2.3
1.14
Zr6(O)6(BDC)6(DM)2.2
Zr6(O)6(BDC)6(BM)1.4
[BMIM][OH]ꢀZrꢀBDCꢀMOF
0.75
SBET = Total surface area, SEA = External surface area, VTotal = Total pore volume.
NB = NꢀButylamine, DE = Diethylamine, DM = DMAP, BM = [BMIM][OH].
aRecovered catalyst.
Surface morphology of the material was investigated using SEM (Fig. 3 and Fig. S3).
Irregular crystal morphology with different sizes is observed in the SEM micrograph of ZrꢀBDCꢀ
MOF (Fig. 3a). Morphologies of the different base grafted ZrꢀBDCꢀMOF are almost similar to
that of ZrꢀBDCꢀMOF (Fig. 3b and Fig. S3), which confirms that post synthetic modification with
base did not disturb the surface morphology of the material. The chemical composition of Zrꢀ
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BDCꢀMOF and DMAPꢀZrꢀBDCꢀMOF was investigated by EDS analysis (Fig. 3cꢀf). Zr, O, and
C elements are observed in the EDS spectrum of ZrꢀBDCꢀMOF whereas Zr, O, N, and C
elements are observed in the EDS spectrum of DMAPꢀZrꢀBDCꢀMOF which confirms the
grafting of ZrꢀBDCꢀMOF with DMAP.
Fig. 3. SEM and EDS images of ZrꢀBDCꢀMOF and DMAPꢀZrꢀBDCꢀMOF.
The presence of amine was also confirmed by Fourier transform infrared (FTꢀIR)
investigation. The carboxylate asymmetric stretching vibrations of ZrꢀBDCꢀMOF are observed at
1508 and 1572 cm−1, while the symmetric stretching vibration of ZrꢀBDCꢀMOF is observed at
1390 cm−1 (Fig. 4). Several bands in region of 1300–600 cm−1 are assigned to the outꢀofꢀplane
vibrations of H2BDC. All the characteristics peaks are observed in amine grafted ZrꢀBDCꢀMOF.
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NꢀbutylamineꢀZrꢀBDCꢀMOF shows two peaks at 3300 and 3250 cmꢀ1 which corresponds to NH2
stretching vibrations. Furthermore, absorption peaks at 1637 cmꢀ1 and 1107 cmꢀ1 are also
observed which correspond to NꢀH bending and CꢀN stretching vibrations, respectively.
DiethylamineꢀZrꢀBDCꢀMOF shows absorptions at 3350 cmꢀ1 and 1120 cmꢀ1 which correspond to
NꢀH stretching and CꢀN stretching, respectively. DMAPꢀZrꢀBDCꢀMOF shows absorptions at
1648 cmꢀ1 and 1220 cmꢀ1 which correspond to C=N stretching and CꢀN stretching, respectively.
NꢀbutylamineꢀZrꢀBDCꢀMOF and DiethylamineꢀZrꢀBDCꢀMOF exhibit peaks at 2950 and 2850
cmꢀ1 that correspond to aliphatic CꢀH stretching vibrations. In addition to these peaks, FTꢀIR
peaks correspond to ZrꢀBDCꢀMOF is observed in all these grafted bases. [BMIM][OH]ꢀZrꢀBDCꢀ
MOF shows absorptions at 2985 cmꢀ1 and 2881cmꢀ1 which correspond to aliphatic asymmetric
and symmetric (CꢀH) stretching vibration of methyl group. OH peak and quaternary amine salt
peaks are merged with the carboxylate peak of H2BDC in ZrꢀBDCꢀMOF. The characteristic
peaks of [BMIM] such as C=C and C=N are merged with the carboxylate asymmetric stretching
vibrations of ZrꢀBDCꢀMOF. Based on FTꢀIR investigation one can conclude that amines and
[BMIM][OH] were successfully grafted on the surface of ZrꢀBDCꢀMOF.
Thermograms of various catalysts prepared in this study are shown in Fig. 5. The amount
of amine grafted on ZrꢀBDCꢀMOF can be calculated by TGA analysis. Three characteristic
weight losses are observed in ZrꢀBDCꢀMOF. The first weight loss is related to removal of
physisorbed H2O molecules between 25 °C and 100 °C, the second weight loss between 100 °C
and 300 °C is attributable to the removal of solvent molecules occluded in MOF framework.
Finally, the third weight loss between 300 °C and 580 °C corresponds to the degradation of the
framework to produce ZrO2 The decomposition temperature for amine grafted ZrꢀBDCꢀMOF
.
was shifted. The weight loss between 100ꢀ400 °C corresponds to the removal of base from Zrꢀ
BDCꢀMOF framework (for amine functionalized ZrꢀBDCꢀMOF). The difference in the weight
loss for different amine grafted MOFs corresponds to the amount of base incorporated in Zrꢀ
BDCꢀMOF (Table 1). Elemental analysis was also performed to evaluate the amount of amine
grafted in these materials and data is presented in Table 1. Based on the amount of amine grafted
on MOFs, the molecular formula of the amine functionalized MOF was determined (Table 1).
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(d)
(c)
(b)
2881
2985
C-H stretching
Asymmetric
stretching/
C=C and C=N
stretching
(e)
Asymmetric
stretching
4000 3500 3000 2500 2000 1500 1000
OOP
Symmetric
stretching
(a)
Wavenumber (cm-1)
3600 3000 2400 1800 1200 600
Wavenumber (cm-1)
(C=N Stretching)
1646
(d)
(d)
(c)
(b)
(a)
(d)
(c)
(b)
1220
(C-N stretcing)
(NH Stretching)
3350
1120
(C-N stretcing)
(c)
(NH2 Stretching)
(N-H Bending)
1637
3300
3250
(b)
1107
(C-N stretcing)
(a)
3400
(a)
1250
1680
3200
1640
1600
3300
1200
1150
1100
1050
Wavenumber (cm-1)
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 4. FTꢀIR spectra of (a) ZrꢀBDCꢀMOF and (bꢀe) N–butyl amine, diethylamine, DMAP, and
[BMIM][OH] grafted ZrꢀBDCꢀMOF, respectively.
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100
90
80
70
60
50
40
30
20
10
51.9
12.6
14.7
Zr-BDC-MOF
DMAP-Zr-BDC-MOF
Diethylamine-Zr-BDC-MOF
[BMIM][OH]-Zr-BDC-MOF
N-butylamine-Zr-BDC-MOF
13.4
9.7
100 200 300 400 500 600 700
Temperature ( 0C)
Fig. 5. Thermogravimetric analysis of parent and different base grafted ZrꢀBDCꢀMOF.
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DMAP-Zr-BDC-MOF
DMAP-Zr-BDC-MOF
Zr 3d
C 1s
183.2
183.6
180.7
283.3
181
181
283.3
Zr-BDC-MOF
183.2
Zr-BDC-MOF
188 186 184 182 180 178 176
286
284
282
280
278
Binding energy (eV)
Binding energy (eV)
N 1s
Zr-BDC-MOF
Zr-BDC-MOF
O 1s
530.5
528.7
DMAP-Zr-BDC-MOF
DMAP-Zr-BDC-MOF
530.9
397.9
528.6
400.1
402
400
398
396
536
534
532
530
528
526
Binding energy (eV)
Binding energy (eV)
Fig. 6. High resolution XPS spectra of Zr 3d, C 1s, N 1s, and O 1s for ZrꢀBDCꢀMOF and
DMAPꢀZrꢀBDCꢀMOF.
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Xꢀray photoelectron spectroscopy (XPS) is a very useful technique to verify the chemical
constituents and the oxidation state of the elements present in the functionalized material. The
XPS measurements were performed for ZrꢀBDCꢀMOF and highly active catalyst DMAPꢀZrꢀ
BDCꢀMOF. Figure 6 shows the individual high resolution XPS spectra for Zr 3d, O 1s, C 1s, and
N 1s energy levels. The high resolution XPS spectrum for Zr 3d exhibits two peaks at 183.2 and
181.0 eV that correspond to Zr 3d3/2 and Zr 3d5/2, respectively, for ZrꢀBDCꢀMOF. DMAPꢀZrꢀ
BDCꢀMOF also exhibits peaks corresponding to Zr 3d3/2 and Zr 3d5/2. In addition to these two
peaks, additional less resolved peaks at 183.6 and 180.7 eV are also observed. These additional
peaks are due to the DMAP coordination with some of the Zr sites in DMAPꢀZrꢀBDCꢀMOF.
Two peaks at 397.9 and 400.1 eV are observed in the high resolution spectrum of N 1s in
DMAPꢀZrꢀBDCꢀMOF. However, no peak corresponding to N 1s was observed for ZrꢀBDCꢀ
MOF. The high resolution XPS spectrum for O 1s shows two distinguished peaks.
Deconvolution of spectrum shows that peaks maxima are at 531.0 and 528.8 eV that can be
attributed to the carboxylate and hydroxylated species (Zr(OH)Zr), respectively, present in the
ZrꢀBDCꢀMOF. Changes in the signature of O 1s XPS spectrum can be observed in the DMAPꢀ
ZrꢀBDCꢀMOF. Intensity of the peak corresponding to hydroxylated species is significantly
reduced which confirms the removal of water and coordination of DMAP with Zr sites in
DMAPꢀZrꢀBDCꢀMOF. The high resolution XPS spectrum of C 1s exhibits one peak at 283.3 eV
that corresponds to the SP2 hybridized carbon atom in the framework of ZrꢀBDCꢀMOF and
DMAPꢀZrꢀBDCꢀMOF. XPS investigation provides convincing evidence about the local structure
of metal center of ZrꢀBDCꢀMOF and its coordination with DMAP in the DMAPꢀZrꢀBDCꢀMOF.
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800
600
400
200
0
(b)
29.7
(a)
Zn-MeIMI-MOF
19.8
9.9
0.0
540
360
180
0
Zn-BTC-MOF
Zn-BDC-MOF
1290
860
430
0
Zr-BDC-MOF
300 400
100
150
200
250
100
200
Temperature (°C)
Temperature (°C)
(c)
Zr-BDC-MOF
N-Butylamine-Zr-BDC-MOF
Diethylamine-Zr-BDC-MOF
DMAP-Zr-BDC-MOF
[BMIM][OH]-Zr-BDC-MOF
50
100
150
200
Temperature (°C)
Fig. 7. NH3ꢀTPD profiles of (a) ZrꢀBDCꢀMOF, (b) Zn based metal organic framework and (c)
CO2ꢀTPD profiles of parent and base grafted ZrꢀBDCꢀMOF materials.
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Acidity (amount and strength) of the catalyst was determined by NH3ꢀTPD measurement
(Fig. 7). NH3 is a base probe molecule that can be adsorbed on the acid sites of the catalyst. TPD
measurements are based on the thermal stability of MOF materials. Thermal stability of ZrꢀBDCꢀ
MOF was more than that of the thermal stability of Zn based MOF. Therefore, NH3ꢀTPD for Zn
based MOFs was performed up to 250 °C. NH3 was adsorbed at 50 °C on the catalyst surface and
then desorbed in the range of 50–250 °C. NH3ꢀTPD for ZrꢀBDCꢀMOFs was performed up to 450
°C. NH3ꢀTPD experiment shows that NH3 is desorbed in the temperature range of 50–450 °C
with two peak maxima at 135 °C and 300 °C (Fig. 7). TCD signals observed during the NH3
desorption experiments clearly shows that large amount of NH3 was desorbed from ZnꢀBDCꢀ
MOF when compared to various Zn based MOFs investigated in this study. Furthermore, the
acid strength of ZrꢀBDCꢀMOF is more when compared to Zn based MOFs investigated in this
study. Total acidity of various MOF samples investigated in this study is presented in Table 1.
Basicity of the parent and functionalized ZrꢀBDCꢀMOF was determined using CO2ꢀTPD
(Figure 7c). In this study, catalytic reactions (discussed in the following section) were performed
in the temperature range of 30ꢀ100 °C. Considering the stability and reaction temperature, CO2ꢀ
TPD was performed up to 200 °C to examine the basic characteristics of the amine
functionalized MOFs. CO2 was adsorbed at 25 °C and then desorbed in the range of 25–200 °C.
ZrꢀBDCꢀMOF shows the CO2ꢀdesorption with peak maxima around 140 °C which was probably
due to ZrꢀO/Zrꢀ(OH) of the ZrꢀBDCꢀMOF framework. Amine functionalized MOF shows
different CO2 desorption profiles when compared to the parent ZrꢀBDCꢀMOF. Among the
different amines functionalized MOF, DMAPꢀZrꢀBDCꢀMOF exhibited the highest CO2
desorption. The order of basicity was determined using the amount of CO2 desorbed (Table 1).
Based on CO2ꢀTPD, the order of basicity of different functionalized MOFs was: DMAPꢀZrꢀ
BDCꢀMOF > NꢀButylamineꢀZrꢀBDCꢀMOF > DiethylamineꢀZrꢀBDCꢀMOF > ZrꢀBDCꢀMOF >
[BMIM][OH]ꢀZrꢀBDCꢀMOF (Table 1). In order to further validate our results, CO2 adsorption
experiments were performed at ambient condition for ZrꢀBDCꢀMOF and DMAPꢀZrꢀBDCꢀMOF.
Adsorption isotherm obtained at 298 K clearly shows that with increase in the CO2 pressure,
adsorption increases. From the isotherm, it is clearly evident that CO2 was adsorbed more on
DMAPꢀZrꢀBDCꢀMOF when compared to the parent ZrꢀBDCꢀMOF at all pressure (0 to 1 atm)
(Fig. S4)
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3.2 Catalytic activity
Condensation reactions are catalyzed by the acid or base catalysts. However, some
condensation reaction proceeds well if acid and base both sites are present in the same catalyst.
Knoevenagel condensation is a wellꢀestablished model reaction to demonstrate the effectiveness
of acidꢀbase biꢀfunctional catalyst. In this study acidic MOF such as ZrꢀBDCꢀMOF, CuꢀBTCꢀ
MOF, ZnꢀBTCꢀMOF, and ZnꢀBDCꢀMOF were investigated. ZnꢀMeIMIꢀMOF was also chosen
in this study because it has demonstrated good activity in CO2 activation reaction for the
synthesis of cyclic carbonate from epoxide which is known to be promoted by biꢀfunctional
catalyst.45 Activity of various MOF investigated in this study was evaluated in Knoevenagel
condensation under identical reaction condition (Table 2). Benzaldehyde and malononitrile were
chosen as model substrates for this reaction. ZrꢀBDCꢀMOF exhibited the best activity among the
MOFs investigated in this study. In ZnꢀMeIMIꢀMOF, MeIMI electrons participate in the bond
formation to generate the MOF framework structure. NH3ꢀTPD study shows that ZnꢀMeIMIꢀ
MOF exhibits the lowest acidity, which is due to the absence of unsaturated metal sites. Due to
very weak acidity ZnꢀMeIMIꢀMOF exhibits the lowest activity. Excellent acidity (especially the
strong acid sites) of ZrꢀBDCꢀMOF is responsible for the high activity in Knoevenagel
condensation. Order of the catalytic activity is consistent with the order of acidity obtained from
NH3ꢀTPD study for various Zn based MOF investigated in this study.
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Table 2. Knoevenagel condensation of benzaldehyde with malononitrile over various MOFs
investigated in this study.
E. No.
Catalyst
Product yield (%)
TOF (h-1)
1
2
3
4
5
ZrꢀBDCꢀMOF
ZnꢀBTCꢀMOF
ZnꢀBDCꢀMOF
ZnꢀMeIMIꢀMOF
CuꢀBTCꢀMOF
39.2
17.2
25.1
6.3
50
24
31.6
8
21.6
27.4
Reaction conditions: Catalyst (0.015 mmol), benzaldehyde (1.9 mmol), malononitrile (3.8
mmol), temperature (30 °C), time (1h).
TOF (hꢀ1) = moles of benzaldehyde converted per mole of active metal per hour.
In order to further improve the catalytic activity, various amines (primary, secondary,
tertiary) and Brönsted base [BMIM][OH] were grafted on the highly active ZrꢀBDCꢀMOF by
following oneꢀstep, postꢀsynthetic modification. In this study, ZrꢀBDCꢀMOF was grafted with
three amines, Nꢀbutylamine, diethylamine, 4ꢀdimethylaminopyridine. Presence of amine
functionality along with Lewis acidity of ZrꢀBDCꢀMOF provides biꢀfunctionality in the resultant
material which would be more suitable for Knoevenagel condensation. Among the amine grafted
ZrꢀBDCꢀMOFs, DMAPꢀZrꢀBDCꢀMOF exhibited the highest activity (Table 3). Catalytic activity
shows that the presence of free lone pair of electrons on the tertiary nitrogen atoms in DMAPꢀZrꢀ
BDCꢀMOF provides more basicity required for this reaction, which is consistent with the
basicity order obtained from CO2ꢀTPD.
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Table 3. Knoevenagel condensation of benzaldehyde with malononitrile over various amine
grafted ZrꢀBDCꢀMOF catalysts.
Benzaldehyde
TOF (h-1)
Catalyst
conversion (%)
Based on Zr
Based on amine
ZrꢀBDCꢀMOF
15.3
55.2
61.5
98.9
80.5
95.4
143
599
ꢀ
NꢀbutylamineꢀZrꢀBDCꢀMOF
DiethylamineꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
187
274
495
628
453
644
1095
891
[BMIM][OH]ꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOFa
1056
Reaction conditions: Catalyst (20 mg), benzaldehyde (1.9 mmol), malononitrile (3.8 mmol),
temperature (30 °C), time (10 minutes). aCatalytic data obtained after the fifth recycles.
TOF (hꢀ1) = moles of benzaldehyde converted per mole of active species per hour.
Influence of solvent was investigated using highly active catalyst DMAPꢀZrꢀBDCꢀMOF
and catalytic activity data is presented in Table S1. Polar solvents facilitate the rate of proton
transfer which resulted higher yield of the product. Furthermore, the amphiprotic property of
protic polar solvents such as water and ethanol makes it more active than CH3CN/DMF (Table
S1). Very low yield of the product was obtained in the aprotic solvent such as toluene. However,
reaction proceeded equally well in neat condition (Table S1). As per the green chemistry
principle, noꢀsolvent is the best condition to perform the reaction. Therefore, neat condition was
chosen as optimum reaction medium.
DMAPꢀZrꢀBDCꢀMOF was recycled for five times. At the end of each reaction, catalyst
was recovered by filtration, washed with ethyl acetate, dried in vacuum oven at 100 °C for 4 h
and then used in next cycle Recycling experiments confirmed that no significant change in the
.
activity was observed even after five recycles (Table 3). Recycled catalyst exhibits similar XRD
pattern to that of the fresh catalyst (Fig. S5). Textural properties of the recycled catalyst were
only marginally low when compared to the fresh catalyst (Table 1). In order to confirm the
stability of grafted bases, leaching experiments were conducted in ethanol medium for the easy
separation of the catalyst. Reaction was stopped after 2/5 minutes, catalyst was removed and then
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the reaction was continued. No significant increase in the conversion of benzaldehyde was
observed (Fig. S6), which confirms that active components were not leached to the reaction
mixture and the catalyst was stable.
A wide range of benzaldehyde derivatives and active methylenic compounds could be
converted into the corresponding condensed product (Table 4). Most of the MOF based catalysts
reported in the literature are active for malononitrile. However, only a few catalysts based on
MOF is reported which is active for ethyl cyanoacetate.45ꢀ48 It would be worthy to note that we
did not come across any report in which MOF based catalyst is shown active for Knoevenagel
condensation with diethyl malonate (Table S2). At optimized reaction condition, significantly
low product yield was obtained using ethyl cyanoacetate (Table 4). Negligible activity was
observed when diethyl malonate is used at the optimized reaction condition for malononitrile. In
order to increase the product yield, catalyst amount, reaction temperature, and reaction time were
increased (Table 4). Inꢀorder to get good activity, reaction was performed at 100 °C for 6 h/16 h
using 50 mg of catalyst. Comparative catalytic activity data shows that this catalyst exhibits
higher or comparable catalytic activity when compared to various MOF based catalysts reported
in the literature (Table S2). Based on the results obtained and the literature reports,49 the
plausible mechanism for the Knoevenagel condensation reaction is proposed in Scheme S1a. In
this mechanism, base grafted ZrꢀBDCꢀMOF acts as a biꢀfunctional catalyst. Carbonyl group of
the benzaldehyde is activated by the Lewis acid site of the catalyst, whereas the basic site of the
catalyst activates the active methylene group of malononitrile. Simultaneous activation of these
two reactants is required to facilitate the reaction in very less time. Proton migration followed by
dehydration leads to form the condensed product. Proton migration is promoted in protic polar
solvents therefore the activity of this catalyst was more in ethanol/water medium when compared
to toluene/ CH2Cl2.
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Table 4. Influence of substrate in the Knoevenagel condensation reactions using DMAPꢀZrꢀ
BDCꢀMOF.
E. No.
Substrate
Catalyst
(mg)
Time
Product
yield (%)
1
2
20
20
10 min
10 min
94.7
91.4
3
4
20
20
20
50
50
50
10 min
10 min
10 min
10 min
6 h
99.8
99.8
10.8
24.6
94.6
92.5
5
6
7a
8a
16 h
Reaction conditions: Benzaldehyde (1.9 mmol), methylene compound (3.8 mmol), reaction
temperature (30 °C).
a Temperature (100 °C)
After achieving excellent activity in the Knoevenagel condensation reaction, the
applicability of this catalyst was investigated in the synthesis of jasminaldehyde (αꢀpentyl
cinnamaldehyde). Jasminaldehyde is produced by the Aldol condensation of benzaldehyde with
1ꢀheptanal. This reaction is known to be catalyzed by solid acid as well as solid base
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catalysts.50,51 Amineꢀgrafted ZrꢀBDCꢀMOF based biꢀfunctional catalyst could be interesting to
investigate this reaction. To explore the catalytic activity of amine grafted metal organic
framework, aldol condensation reaction of benzaldehyde and 1ꢀheptanal was performed. Under
the optimized reaction condition, ZrꢀBDCꢀMOF exhibited low 1ꢀheptanal conversion (Table 5).
In this case, no selfꢀcondensation product of 1ꢀheptanal was observed. However, oxidized
products 1ꢀheptanoic acid and benzoic acid were identified in the reaction mixture. Amine
grafted ZrꢀBDCꢀMOF materials were more active than parent ZrꢀBDCꢀMOF. In contrast to
Knoevenagel condensation, in this case NꢀbutylamineꢀZrꢀBDCꢀMOF exhibited more
jasminaldehyde yield. It is interesting to note that selectivity of jasminaldehyde follows the
following order: NꢀbutylamineꢀZrꢀBDCꢀMOF> DiethylamineꢀZrꢀBDCꢀMOF> DMAPꢀZrꢀBDCꢀ
MOF. This confirms that primary amine grafted bases are more favorable for the crossꢀ
condensation reaction. In order to verify this observation, reactions were performed in the
presence of various amine bases (only). In all these cases, more than 95% 1ꢀheptanal conversion
was obtained but selectivity for jasminaldehyde was the highest when Nꢀbutylamine was used as
base catalyst. The yield of jasminaldehyde follows the order: Nꢀbutylamine> Diethylamine>
DMAP. Based on the jasminaldehyde yield, one can conclude that the primary amine is more
suitable for the formation of crossꢀcondensation product. Furthermore, if we compare the
jasminaldehyde yield in homogenous base catalysts and amineꢀgrafted ZrꢀBDCꢀMOF catalysts,
one can conclude that optimum basicity and acidity are required for high jasminaldehyde yield.
When the yields of jasminaldehyde obtained in the case of Nꢀbutylamine and NꢀbutylamineꢀZrꢀ
BDCꢀMOF are compared, the selectivity for jasminaldehyde was more in the case of Nꢀ
butylamineꢀZrꢀBDCꢀMOF. Since Nꢀbutylamine coordinates to the Zr metal sites therefore only
partial basicity is available to catalyze this reaction and hence more selectivity towards crossꢀ
condensed product is obtained. Based on the results obtained, mechanism for the synthesis of
jasminaldehye is proposed (Scheme S1b). Mechanism of the Aldol condensation is similar to the
Knoevenagel condensation. The carbonyl group of benzaldehyde is activated by the acid sites of
catalyst whereas basic sites of the catalyst favor the formation of carbanion of 1ꢀheptanal.
Carbanion of 1ꢀheptanal reacts with activated benzaldehyde to form crossꢀcondensed product
jasminaldehyde. Carbanion of 1ꢀheptanal can also react with the carbonyl groups of 1ꢀheptanal to
form selfꢀcondensation product 2ꢀpentylꢀ2ꢀnonenal as a byꢀproduct. Since the reactivity of
benzaldehyde is very high and it can be more easily polarized by the acid sites therefore the
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crossꢀcondensed product is preferred in NꢀbutylamineꢀZrꢀBDCꢀMOF. Based on the results
obtained using amine grafted ZrꢀBDCꢀMOF, one can conclude that tuning the basicity of amines
could lead to produce more selectivity for the desired product.
Table 5. Catalytic condensation of benzaldehyde with 1ꢀheptanal over parent and amine grafted
ZrꢀBDCꢀMOF.
Product Selectivity
(%)
TOF (h-1)
1-heptanal
conv. (%)
Catalyst
Based on Based on
A
B
C
35.8
ꢀ
Zr
amine
ZrꢀBDCꢀMOF
NꢀbutylamineꢀZrꢀBDCꢀMOF
DiethylamineꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
[BMIM][OH]ꢀZrꢀBDCꢀMOF
Nꢀbutylaminea
66.1
90.3
94.4
98.7
84.2
98.5
98.9
96.7
63.2
89.8
73.7
82.8
66.5
77.4
45.6
36.7
ꢀ
10.2
26.3
ꢀ
6.6
ꢀ
10.4
10.5
11.7
9.8
66
3.2
4.3
ꢀ
17.2
33.5
5.2
ꢀ
7.1
9.8 12.8
42.8 11.6
35.7 25.6
0.64
0.65
1.06
Diethylaminea
66
DMAPa
65
Reaction conditions: Catalyst (15 mg), benzaldehyde (1.32 mmol), heptanal (0.09 mmol),
temperature (100 °C), time (1h).
a Catalyst (10 mg)
TOF (hꢀ1) = moles of 1ꢀheptenal converted per mole of active species per hour.
Having shown the applicability of amine grafted ZrꢀBDCꢀMOF in different condensation
reactions; the aim was to extend its application in another interesting reaction, cycloaddition of
CO2 to epoxide. First, the activity of various MOF was investigated in the cycloaddition of
epichlorohydrin to CO2 in order to obtain the best MOF for this reaction (Table 6). Reaction did
not proceed in the absence of catalyst. All catalysts investigated in this study were active for this
reaction. ZrꢀBDCꢀMOF exhibited the highest epichlorohydrin conversion and good selectivity
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for cyclic carbonate. The activity of ZnꢀMeIMIꢀMOF was comparatively low but it exhibited
somewhat better selectivity for cyclic carbonate. In all the cases, along with the cyclic carbonate;
minor amount of side product (3ꢀchloro propanol or 2ꢀchloro propanol) was obtained. Influence
of reaction parameters such as CO2 pressure, reaction temperature, and catalyst amounts were
studied and the obtained results are presented in Fig. S7. In order to evaluate the comparative
catalytic activity of various amine grafted ZrꢀBDCꢀMOF, following mild reaction condition was
adopted: epichlorohydrin (38 mmol), temperature (100 °C), time (1h), catalyst (100 mg).
Table 6. Cycloaddition of CO2 to epoxide over various MOFs investigated in this study.
Catalyst
Epichlorohydrin
conv. (%)
Product
Selectivity
(%)
TOF (h-1)
Based on
Based on
amine
ꢀ
metal
None
ꢀ
ꢀ
ꢀ
ZrꢀBDCꢀMOF
51.5a
88
326.2
ꢀ
ZnꢀBTCꢀMOF
ZnꢀBDCꢀMOF
35.2a
42.1a
48.4a
8.6a
63.1a
70.4a
79.6a
55.9a
18.6b
92.8b,d
12.3c
86.5c,d
75.3a,e
82
84
89
64
86
90
91
92
95
96
93
97
90
110.5
122.7
42.5
ꢀ
ꢀ
ZnꢀMeIMIꢀMOF
ꢀ
CuꢀBTCꢀMOF
18.4
ꢀ
NꢀbutylamineꢀZrꢀBDCꢀMOF
DiethylamineꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
[BMIM][OH]ꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
DMAPꢀZrꢀBDCꢀMOF
460.4
495.4
593.1
409.3
138.6
57.7
142.5
205.8
265.3
312.1
62.0
25.8
40.9
24.0
243.4
91.6
53.7
561.1
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Reaction conditions: Catalyst (100 mg), epoxide (38 mmol), CO2 pressure (10 bar), reaction
temperature (100 °C), reaction time (1h)
aEpichlorohydrin,bpropylene oxide, cstyrene oxide, dreaction time (12 h), edata obtained after five
recycles.
TOF (hꢀ1) = moles of epoxide converted per mole of active species per hour.
Literature reports suggest that various heterogeneous catalysts have been investigated for this
reaction.52ꢀ54 However, in most of these catalysts, quaternary ammonium salts or DMAP were
used as additional coꢀcatalyst. For this reaction to proceed, simultaneous activation of epoxide
and CO2 are needed. Since CO2 is an acidic molecule, therefore several bases have been used as
coꢀcatalyst or grafted on the surface of active solid catalyst to catalyze this reaction.55ꢀ57 These
studies encouraged us to investigate the role of various amine grafted MOF catalysts investigated
in this study for the synthesis of cyclic carbonate. Various amine grafted ZrꢀBDCꢀMOF catalysts
were investigated in the cycloaddition reaction of epichlorohydrin and CO2 under the mild
optimized reaction condition and the results are summarized in Table 6. Among various amine
grafted ZrꢀBDCꢀMOF, DMAPꢀZrꢀBDCꢀMOF exhibited the highest activity. Having optimized
the reaction condition (Fig. S7), applicability of DMAPꢀZrꢀBDCꢀMOF was investigated in the
synthesis of cyclic carbonates with different epoxides under mild condition (Table 6). Among the
epoxides investigated, the order of reactivity was found to be epichlorohydrin >propylene oxide
> styrene oxide. Further, the stability of the catalyst in the liquid phase reaction was also
evaluated with recycling experiment. After the reaction, catalyst was recovered by filtration,
washed with ethyl acetate, dried in vacuum oven at 100 °C for 4 h and then used in next cycle.
The activity of reused catalyst was almost similar to that of fresh catalyst even after five cycles
(Table 6). The presence of base enhances the uptake of CO2 which leads to an increase in the
concentration of CO2 near the catalytic site. In this case, basic sites of the catalyst adsorb and
activate the CO2 molecules whereas acid sites of the catalyst adsorb and activate the epoxide.
Activated CO2 attacks the least hindered site of the epoxide which is polarized by the Zr moieties
of ZrꢀBDCꢀMOF [due to large ionic radius (0.73 Å) and electronegative difference between Zr
and oxygen attached to epoxide ring (2.11)], which is followed by ring closing to give cyclic
carbonate and regenerates the catalyst (Scheme S2). Catalytic activity of DMAPꢀZrꢀBDCꢀMOF
was found to be more or similar when compared to various MOF based catalyst reported in the
literature under mild reaction condition (Table S3).58ꢀ65 However, it may be noted that most of
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the MOF based catalysts were active only in the presence of coꢀcatalyst or they require high
pressure and temperature (Table S3)
4. Conclusions
Zirconium, zinc, and copper based robust metal organic framework catalysts were
successfully synthesized. Catalytic activity of highly active Zr metalꢀorganic framework was
tailored by functionalization of different amines and one basic ionic liquid by an economical and
simple postꢀsynthetic modification strategy. FTꢀIR, TGA, elemental, and EDS analysis
confirmed that MOF was functionalized by different active functional groups. Surface area and
pore volume were reduced after the functionalization. Catalytic investigation shows that tertiary
amine (DMAP) grafted zirconium MOF exhibited the best activity in Knoevenagel condensation
whereas primary amine (Nꢀbutylamine) grafted zirconium MOF exhibited the best activity in the
crossꢀcondensed Aldol reaction for the synthesis of jasminaldehyde. Catalytic activity based on
CO2 activation shows that CO2 adsorption and cycloaddition reaction were significantly favored
in tertiary amine (DMAP) grafted zirconium MOF. Catalyst exhibited better or similar activity
when compared to various catalysts reported in literature. Catalysts were stable and exhibited
excellent activity even after five recycles. Leaching experiments confirmed that functionalized
bases were stable during the reaction. XRD and N2ꢀadsorption investigation shows that
recovered catalyst was stable and exhibited only a marginal change in the physical property of
the recovered catalyst. These model reactions clearly demonstrate that optimum functionalization
of MOF can leads to provide desired catalyst by tuning the physicoꢀchemical properties of the
catalyst required for appointed reactions. We are sure that such strategy can be used to develop
desired sustainable catalyst based on MOF.
Acknowledgements
Authors are thankful to SERB, Department of Science and Technology, New Delhi
(EMR/2016/001408) for financial support. PR acknowledged financial assistance from MHRD,
New Delhi. Authors thank Mr. Sandeep and Dr. C. M. Nagaraja, IIT Ropar for their help in the
measurement of CO2 adsorption at ambient temperature. Authors are grateful to Prof. Sanjeev
Kumar Srivastava and DSTꢀFIST funded XPS facility of Department of Physics, IIT Kharagpur.
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References
1
2
A. Thomas, Angew. Chem. Int. Ed., 2010, 49, 8328ꢀ8344.
A. V. Perdikaki, O. C. Vangeli, G. N. Karanikolos, K. L. Stefanopoulos, K. G. Beltsios,
P. Alexandridis, N. K. Kanellopoulos and G. E. Romanos, J. Phys. Chem. C, 2012, 116,
16398ꢀ16411.
3
4
Y. Li, Z. Y. Fu and B. L. Su, Adv. Funct. Mater., 2012, 22, 4634–4667.
W. F. Hölderich, J. Röseler, G. Heitmann and A.T. Liebens, Catal. Today, 1997, 37, 353ꢀ
366.
5
I. I. Ivanova and E. E. Knyazeva, Chem. Soc. Rev., 2013, 42, 3671–3688.
Y. Tao, H. Kanoh, L. Abramsand and K. Kaneko, Chem. Rev., 2006, 106, 896–910.
K. M. Reddy and C. Song, Catal. Today, 1996, 31, 137ꢀ144.
C. S. Cundy and P. A. Cox, Chem. Rev., 2003, 103, 663–702.
K. Moller and T. Bein, Chem. Soc. Rev., 2013, 42, 3689ꢀ3707.
M. V. Regi, A. Ramila, R. P. d. Real and J. P. Pariente, Chem. Mater. 2001, 13, 308ꢀ311.
A. Taguchi and F. Schuth, Microporous Mesoporous Mat., 2005, 77, 1ꢀ45.
J. S. Choi, D. J. Kim, S. H. Chang and W. S. Ahn, Appl. Catal. A: General, 2003, 254,
225ꢀ237.
6
7
8
9
10
11
12
13
D. Margolese, J. A. Melero, S. C. Christiansen, B. F Chmelka and G. D Stucky, Chem.
Mater., 2000, 12, 2448ꢀ2459.
14
15
M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun., 2003, 1340ꢀ1341.
X. Wang, K. S. K. Lin, J. C. C. Chan and S. Cheng, J. Phys. Chem. B, 2005, 109, 1763ꢀ
1769.
16
17
H. C. Zhou, J. R. Long and O. M. Yaghi, Chem. Rev., 2012, 112, 673ꢀ674.
M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M. Reineke, M. O’Keeffe and O. M.
Yaghi, Acc. Chem. Res., 2001, 34, 319ꢀ330.
18
J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen and J. T. Hupp, Chem. Soc.
Rev., 2009, 38, 1450ꢀ1459.
19
20
B. Li, H. M. Wen, W. Zhou and B. Chen, J. Phys Chem Lett, 2014, 5, 3468ꢀ3479.
R. J. Kuppler, D. J. Timmons, Q. R. Fang, J. R. Li, T. A. Makal, M. D. Young, D. Q.
Yuan, D. Zhao, W. J. Zhuang and H. C. Zhou, Coord. Chem. Rev., 2009, 253, 3042ꢀ
3066.
28

Page 29 of 32
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ01055A
21
22
H. Furukawa, K. Cordova, M. Okeeffe and O. Yaghi, Science, 2013, 341, 1230444.
P. Guo, D. Dutta, A. G. WongꢀFoy, D. W. Gidley and A. J. Matzger, J. Am. Chem. Soc.,
2015, 137, 2651ꢀ2657.
23
M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. Okeeffe and O. M. Yaghi,
Science, 2002, 295, 469ꢀ472.
24
25
Z. Q. Wang and S. M. Cohen, Chem. Soc. Rev., 2009, 38, 1315ꢀ1329.
U. Ravon, M. E. Domine, C. Gaudillere, A. D. Chomel and D. Farrusseng, New J. Chem.,
2008, 32, 937ꢀ940.
26
27
28
K. Koh, J. D. V. Oosterhout, S. Roy, A. G. WongꢀFoy and A. J. Matzger, Chem. Sci.,
2012, 3, 2429ꢀ2432.
M. Meilikhov, K. Yusenko, D. Esken, S. Turner, G. V. Tendeloo and R. A. Fischer, Eur.
J. Inorg. Chem., 2010, 3701–3714.
Y. K. Park, S. B. Choi, H. J. Nam, D. Y. Jung, H. C. Ahn, K. Choi, H. Furukawa and J.
Kim, Chem. Commun., 2010, 46, 3086–3088.
29
30
31
32
33
34
S. De, S. Duttab and B. Saha, Catal. Sci. Technol., 2016, 6, 7364–7385.
G. Centi and S. Perathoner, Microporous Mesoporous Mater., 2008, 107, 3ꢀ15.
Y. C. Sharma, B. Singh and J. Korstad, Fuel, 2011, 90, 1309ꢀ1324.
Y. Ono, J Catal, 2003, 216, 406ꢀ415.
D. Rath, S. Ranab and K. M. Parida, RSC Adv., 2014, 4, 57111–57124.
M. C. Burleigh, M. A. Markowitz, M. S. Spector and B. P. Gaber, Chem. Mater., 2001,
13, 4760ꢀ4766.
35
36
37
Z. Qiao, N. Wang, J. Jiangc and J. Zhou, Chem. Commun., 2016, 52, 974ꢀ977.
Y. Lin, C. Kong and L. Chen, RSC Adv., 2016, 6, 32598ꢀ32614.
S. Couck, J. F. M. Denayer, G. V. Baron, T. Remy, J. Gascon and F. Kapteijn, J. Am.
Chem. Soc., 2009, 131, 6326ꢀ6327.
38
39
Y. Luan, Y. Qi, H. Gao, N. Zheng and G. Wang, J. Mater. Chem. A, 2014, 2, 20588ꢀ
20596.
J. Long, S. Wang, Z. Ding, S. Wang, Y. Zhou, L. Huang and X. Wang, Chem. Commun.,
2012, 48, 11656ꢀ11658.
40
41
P. Rani and R. Srivastava, RSC Adv., 2015, 5, 28270ꢀ28280.
H. Li, W. Shi, K. Zhao, H. Li, Y. Bing and P. Cheng, Inorg. Chem., 2012, 51, 9200ꢀ9207.
29