Molecular size- and shape-selective Knoevenagel condensation over microporous Cu3(BTC)2 immobilized amino-functionalized basic ionic liquid catalyst

Article abstract of DOI:10.1016/j.apcata.2014.03.041

A novel molecular size- and shape-selective catalyst, microporous metal-organic framework HKUST-1 immobilized amino-functionalized basic ionic liquid (ABIL-OH), was synthesized by facile impregnation and activation. Characterizations and catalytic results

Full text of DOI:10.1016/j.apcata.2014.03.041

Applied Catalysis A: General 478 (2014) 81–90
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Molecular size- and shape-selective Knoevenagel condensation over
microporous Cu3(BTC)2 immobilized amino-functionalized basic ionic
liquid catalyst
Qun-xing Luoa, Xue-dan Songa, Min Jia,∗, Sang-Eon Parkb, Ce Haoa, Yan-qin Lia
a School of Chemistry, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116023,
People’s Republic of China
b Laboratory of Nano-Green Catalysis and Nano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, Incheon 402-751,
Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel molecular size- and shape-selective catalyst, microporous metal-organic framework HKUST-1
immobilized amino-functionalized basic ionic liquid (ABIL-OH), was synthesized by facile impregna-
tion and activation. Characterizations and catalytic results revealed that the catalytically active species
ABIL-OH could be confined in well-defined HKUST-1 nanocavities via Cu NH2 coordination bond. The
resulting ABIL-OH/HKUST-1 heterogeneous catalyst showed comparable catalytic activity and enhanced
selectivity in liquid phase Knoevenagel condensation, and it could be recovered conveniently and reused
at least 5 times without significant loss of its catalytic efficiency. Moreover, ABIL-OH/HKUST-1 catalyst
demonstrated distinct size- and shape-selective properties for discrimination of reactants in Knoeve-
nagel condensation. It was supposed that diffusion kinetics of reactants might be controlling step and
play a more important role than the nature of the substituents in the confined microenvironment.
© 2014 Elsevier B.V. All rights reserved.
Received 24 February 2014
Received in revised form 27 March 2014
Accepted 29 March 2014
Available online 8 April 2014
Keywords:
Size and shape-selective catalysis
Metal-organic framework
Cu3(BTC)2 nanocavities
Amino-functionalized basic ionic liquid
Immobilization
1. Introduction
areas, exceptional porosity and tunability of pore structure offer
unprecedented possibilities for MOFs to host catalytically active
Molecular size- and shape-selective catalysis is a significant and
fascinating concept in the field of heterogeneous catalysis. It is
widely applied to produce target compounds with high selectiv-
ity. This characteristic catalysis is based on the sizes and shapes of
substrate molecules in comparison with the windows and channels
of nanoporous materials [1,2]. The traditional porous zeolites have
been investigated extensively and have achieved a few ground-
breaking successes [3–5]. Nevertheless, the available pore size of
zeolites are usually small (below 1 nm) and difficult to be tai-
lored. These inherent imperfections hinder application of zeolites
in liquid phase reactions where the substrates are relatively large.
Consequently, extending the size and shape-selective catalysis to
other nanoporous materials with larger pore sizes is highly desired.
In recent years, metal-organic frameworks (MOFs) or porous
coordination polymers (PCPs) can be considered as promising com-
plementing in expanding the molecular size and shape-selective
catalysis [6–8]. Compared with zeolites, the extra-large surface
guest molecules by post-synthetic modification strategy (PSM)
[9,10]. During the past decade, several catalytically active guest
species like metal nanoparticles [11,12], polyoxometalates [13,14],
organo-metallics [15,16] and biomimetic species [17] have been
successfully incorporated inside MOFs. Among various types of
MOFs, the well-known copper-based MOFs [Cu3(BTC)2] (HKUST-1)
(BTC = 1,3,5-benzenetricarboxylate) has been intensively studied.
HKUST-1 has a three dimensional square-shaped channel system
(1.0 nm × 1.0 nm) and accessible nanocavities [18]. Interestingly,
the coordinatively unsaturated Cu2+ sites (CUS) are homogeneously
distributed in the HKUST-1 framework, which would provide a fea-
sible concept to develop novel functionalized materials by surface
decoration with electron rich functional group (NH3, pyridine and
organic amine) [19,20].
The liquid-phase Knoevenagel condensation between an active
methylene compound and a carbonyl group (C O) is a very useful
C
C bond coupling reaction to prepare several important chemical
intermediates. In general, organic bases (alkylamine and ammo-
nium salts) [21,22] or Lewis acid catalysts [23] under homogeneous
system could effectively catalyze this reaction, but their utiliza-
tion is associated with the work-up of the reaction mixture and the
∗
Corresponding author. Tel.: +86 411 84986329; fax: +86 411 84986329.
E-mail address: jimin@dlut.edu.cn (M. Ji).
http://dx.doi.org/10.1016/j.apcata.2014.03.041
0926-860X/© 2014 Elsevier B.V. All rights reserved.

82
Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
Scheme 1. The schematic illustration for synthesizing ABIL-OH/HKUST-1 catalyst.
generation of considerable amounts of liquid waste. For this reason,
although several alternative heterogeneous catalysts have been
successfully applied in Knoevenagel condensation, such as zeolites
[24], mesoporous carbon nitride [25], organic-functionalized meso-
porous silicon [26] and MOFs materials [27–29], it usually requires
high reaction temperature or microwave irradiation. More recently,
task-specific ionic liquids (TSILs) as environmentally benign sol-
vent and/or co-catalyst have demonstrated excellent catalytic
performance in Knoevenagel condensation [30,31]. Unfortunately,
the homogeneous catalysis or liquid–liquid biphasic system using
TSILs as catalyst could not address problem in separation and recy-
cling of catalyst. On the other hand, the reaction mixture usually
contains inevitably some byproducts from the consecutive reaction
of the primary product over the homogeneous catalyst.
2. Materials and methods
2.1. Materials
Toluene was dried with 5A molecular sieve. Other Reagents
were used without further purification. Cupric nitrate trihydrate
(Cu(NO3)2·3H2O), sodium hydroxide, 1-methylimidazole (99%),
acetonitrile, toluene and ethanol were purchased from Sinopharm
Chemical Reagent Co., Ltd. or Tianjin Kemiou Chemical Reagent Co.,
Ltd.
Other reagents were purchased from the following distributors:
1,3,5-Benzenetricarboxylic acid (H3BTC, 99%): Meryer Chemical
Technology Co., Ltd.
In this regard, supported ionic liquid catalysis (SILC) might be
an effective method to solve these major drawbacks. The novel
SILC would be likely to inspire distinct catalytic performance due
to combination the advantages of TSILs organocatalyst with those
of heterogeneous support [32–34]. Recently, the viability of this
concept has been confirmed by several investigations. Xia and co-
workers [35,36] reported hydroxyapatite-encapsulated ␥-Fe2O3
supported diethyl aliphatic amine basic ionic liquids, and this mag-
netic catalyst could be easily isolated from the reaction mixture by
simple magnetic decantation and reused four times without signif-
icant degradation. Hardacre et al. [37] prepared silica supported
basic ionic liquid catalyst that showed excellent recyclability in
Knoevenagel condensation. In addition, other solid supports like
silica-based materials (SiO2, SBA-15, MCM-41) [38–40], organic
polymers [41], carbon material (CNTs) [42,43] supported ionic liq-
uids catalyst by covalent or non-covalent attachment have also
been investigated in a variety of catalytic reactions. However, there
have been a handful of attempts on the investigation of metal-
organic framework supported ionic liquid.
Very recently, our group, for the first time, reported Brønsted
acidic ionic liquid-functionalized MIL-101 as a heterogeneous acid
catalyst for the acetalization of benzaldehyde with glycol. The cat-
alyst showed higher catalytic performance than its homogeneous
counterpart with excellent reusability [44]. Jhung and co-workers
reported MIL-101 supported 1-butyl-3-methylimidazolium chlo-
ride ionic liquid for adsorptive desulfurization from liquid fuel [45].
In this contribution, we reported a facile method to prepare micro-
porous HKUST-1 immobilized amino-functionalized basic ionic
liquid organocatalyst. This novel ABIL-OH/HKUST-1 heterogeneous
catalyst did not only exhibit remarkable catalytic performance and
recyclability, but also showed distinct size- and shape-selective
catalysis in Knoevenagel condensation.
2-Bromoethylamine hydrobromide (99%): J&K Scientific.
2.2. Preparation of metal-organic framework materials
Metal-organic framework HKUST-1 crystals were prepared by
a solvothermal reaction [18]. Typically, Cu(NO3)2·3H2O (4.5 mmol,
1.087 g) was dissolved in 15 mL deionized water and then mixed
with H3BTC (2.5 mmol, 0.525 g) dissolved in 15 mL ethanol. The
mixture was stirred for 30–60 min, and then transferred to a 50 mL
Teflon autoclave liner and sealed to heat at 120 ◦C for 12 h. The
obtained blue powder was filtered and washed several times with
deionized water and ethanol, and then dried in vacuum overnight
at 150 ◦C. MIL-101 material was provided by our previous synthesis
(SBET = 1873 m2 g−1, Vtotal = 0.906 cm3 g−1) [44].
2.3. Preparation of amino-functionalized basic ionic liquid
(ABIL-OH)
The amino-functionalized basic ionic liquid (ABIL-OH)
was prepared according to the literature, as illustrated in
Scheme S1 [46,47]. Methylimidazole (4.15 g, 0.05 mol) and
2-bromoethylamine hydrobromide (10.24 g, 0.05 mol) were
dissolved in 50 mL acetonitrile at 80 ◦C for 24 h under nitrogen
atmosphere with stirring. On completion, the solvent was removed
by rotary evaporation, and the residue was washed with ethanol
(3 × 10 ml). The solid residue was dissolved in water. Then the pH
value of the solution was adjusted to 8 by the addition of sodium
hydroxide. The obtained solution was concentrated by rotary
evaporation and the product 1 (ABIL-Br) was obtained.
During anion metathesis, the obtained product 1 and sodium
hydroxide (2 g, 0.05 mol) were added into ethanol–water (v/v, 1:1,
15.0 ml), and then the mixture was stirred for 24 h at ambient

Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
83
ABIL-OH/HKUST-1
As-synthesized HKUST-1
Scheme 2. The structural model of different catalyst.
temperature (30 ◦C). The upper suspension was extracted to
remove the precipitated bromide salt and the organic phase was
concentrated, and the product 2 was obtained.
Simulated
2.4. Catalyst preparation
The catalyst was prepared by a facile impregnation and acti-
vation, as illustrated in Scheme 1. In a round bottom flask, 0.3 g
ABIL-OH or ABIL-Br was dissolved in 25 ml ethanol solvent, respec-
tively. Metal-organic framework material (0.5 g) was suspended
in solution above, and the mixture was stirred at ambient tem-
perature (30 ◦C) for 24 h with magnetic stirring. The solvent was
separated by filtration and excess of amino-functionalized ionic
liquid was removed by washing with DMF (3 × 10 ml) and ethanol
(3 × 10 ml). The synthesized heterogeneous catalysts were termed
ABIL-OH/HKUST-1 and ABIL-Br/HKUST-1. Finally, the catalysts
were dried under vacuum at 80 ◦C for 12 h. The structural model
of catalyst was shown in Scheme 2.
5
10
15
20
25
30
35
40
45
50
2 Theta/ degree
Fig. 1. Powder X-ray diffraction (PXRD) patterns of ABIL-OH/HKUST-1 catalyst and
as-synthesized HKUST-1 sample.
2.8. Characterization techniques
The Powder X-ray diffraction (PXRD) data was recorded on a
Rigaku diffractormeter (D/MAX-IIIA, 3 kW) using Cu K␣ radiation,
scanning angle from 5◦ to 50◦. The nitrogen adsorption–desorption
was performed at 77 K using a Quantachrome AUTOSORB 1C appa-
ratus. Before the analysis, the samples were evacuated at 150 ◦C
for 12 h. Fourier transform infrared (FT-IR) spectroscopy was per-
formed on Bruker-Tenson 27 infrared spectrometer in the range
400–4000 cm−1 using KBr pellets. DRS UV–vis spectroscopy was
performed on Agilent Cary 5000 spectrophotometer. Scanning elec-
tron microscopy images (SEM) and energy dispersive analysis
of X-ray (EDX) were obtained on JSM-5600LV instrument. X-ray
photoelectron spectroscopy (XPS) was recorded using Al K Alpha
source. Thermogravimetric analysis (TGA) was carried out on TA
instrument from room temperature to 800 ◦C with a heating rate
of 10 ◦C min−1 under a flow of N2. Elemental analysis (EA) was
performed on vario EL III.
2.5. General procedure for Knoevenagel condensation
Knoevenagel condensation of aromatic aldehydes with mal-
ononitrile was carried out in self-made glass microreactor under
batch reaction conditions (Scheme 3). In a typical experiment, 2 ml
toluene, 2 mmol aromatic aldehydes, 4 mmol malononitrile, 50 mg
catalysts were placed into a magnetically stirred glass reactor under
ambient temperature (30 ◦C). When the reaction was completed,
the product of Knoevenagel condensation was separated by cen-
trifugation. The catalytic activity and selectivity were determined
by GC–MC (Agilent 6890, HP-5 capillary column 25 m, 0.32 mm).
2.6. Reusability of catalyst and the hot filtration test
After every reaction, the catalysts were washed with toluene
(2 × 5 ml) and dried at 80 ◦C for 2 h, and reused in a subsequent reac-
tion under identical condition. The hot filtration test was carried out
by stopping a standard reaction after 30 min. The reaction mixture
was separated from the suspended catalyst. The liquid phase was
then transferred to another flask and again allowed to react.
3. Results and discussions
3.1. Catalyst characterization
3.1.1. Powder X-ray diffraction (PXRD)
For synthesized ABIL-OH/HKUST-1 catalyst, initial evidence of
intrinsic crystalline structures was confirmed by Powder X-ray
diffraction, as shown in Fig. 1. The PXRD patterns of ABIL-
OH/HKUST-1 catalyst show that almost all the main diffraction
peaks are observed in accordance with simulated pattern and as-
synthesized HKUST-1 sample, apart from some slight variations in
the Bragg intensities. These results clearly indicate that the crys-
talline structure of HKUST-1 is unchanged and intact during the
synthetic process.
2.7. Molecular simulation and calculation of substrates
dimension
The ground state geometric optimizations of all molecules
were performed with the density functional theory (DFT) method
through Gaussian 09 program suites. We employed the B3LYP func-
tional in Gaussian 09 and the relativistic effects were taken into
account by using the 6-311G basis sets for the simulation.
Scheme 3. Knoevenagel condensation of aromatic aldehyde with malononitrile under ambient temperature (30 ◦C).

84
Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
Table 1
The physical and chemical properties of all samples.
Sample
Textural propertiesa
Cub (%)
Loading amount of ABIL-OH/mmol g−1c
SBET/m2 g−1
Vtotal/cm3 g−1
As-synthesized HKUST-1
ABIL-OH/HKUST-1
1158
338
0.50
0.21
9.0
6.6
–
1.07
a
The N2 physical adsorption–desorption at 77 K.
SEM-EDX.
b
c
Measured by elemental analysis, nitrogen content = 3.21 mmol g−1
.
3.1.2. Scanning electron microscopy (SEM-EDX)
wavenumbers region over ABIL-OH/HKUST-1 catalyst is observed.
The characteristic peak at 3149 cm−1 is due to sp2
H stretch-
The surface morphology and chemical composition of all sam-
ples were characterized by SEM-EDX (Fig. S1). The as-synthesized
HKUST-1 sample is octahedral crystal morphology with smooth
surface, and particles size is about 20–25 ␮m. The Cu content is 9.0%
by EDX analysis. The surface of ABIL-OH/HKUST-1 catalyst tends to
be rough, but the octahedral crystal morphology is still observed.
Meanwhile, particle size of octahedral crystallites could remain the
same (20–25 ␮m). The corresponding Cu content decreases to 6.6%
(Table 1) which could be attributed to a handful leaching of transi-
tion metal Cu ions from framework under weak alkaline solution.
C
ing vibrations of imidazole moiety. The band at 2962 cm−1 and
2875 cm−1 are assigned to aliphatic C H asymmetric and symmet-
rical stretching vibrations of alkyl chain. In the low wavenumbers
region, the peak at 1569 cm−1 and 1643 cm−1 can be ascribed
to the C C and C N vibrations of the imidazole ring. The band
at 1170 cm−1 is assigned to the C C skeleton stretching vibra-
tion of alkyl chain. Moreover, two important peaks at 837 cm−1
and 1109 cm−1 are observed, which could be attributed to N
H
out-of-plane bending vibration and C N stretching vibration of
amino-alkyl chain [38,39]. It is interesting to note that the
wavenumber of N H out-of-plane bending vibration is shifted to
lower values (808 cm−1), which is tentatively ascribed to interac-
tion (coordination bond N Cu) between NH2 and coordinatively
unsaturated metal sites Cu(II) in HKUST-1 frameworks.
3.1.3. N2 physical adsorption–desorption
The N2 adsorption–desorption isotherms of all samples were
exhibited in Fig. S2. Compared with the as-synthesized HKUST-
1 sample, the ABIL-OH/HKUST-1 catalyst shows a significant
decrease in the adsorbed N2 amount. The as-synthesized HKUST-1
shows a BET surface area and a total pore volume of 1158 m2 g−1
and 0.50 cm3 g−1, whereas ABIL-OH/HKUST-1 catalyst has cor-
responding values of 338 m2 g−1 and 0.21 cm3 g−1. Additionally,
the N2 adsorption–desorption curve of ABIL-OH/HKUST-1 catalyst
shows I/IV mixed type isotherm with H2 hysteresis loop, which is
indicative of existing microporous and mesoporous structures. The
pore size distribution curves are obtained by using the methods of
Density Functional Theory (DFT), as shown in Fig. S2. The formed
mesoporosity is usually ascribed to stacking of nanoparticles. It is
worthwhile to note that microporous size decreased from 1.1 nm to
0.8 nm and 0.6 nm, which could be attributed to the incorporation
of ABIL-OH organocatalyst inside HKUST-1 nanocavities.
3.1.5. DRS UV–vis spectra
Since bivalent copper species Cu2+ (3d9) presents in HKUST-
1 framework, it would involve d–d transitions in changed local
coordination environment of central Cu2+ ion in electronic spectra
analysis. Fully hydrated sample shows a azure color. Upon acti-
vation (dehydration), its color changs drastically into dark blue.
However, ABIL-OH/HKUST-1 catalyst exhibits pale blue color (Fig. 3.
Inset image A, B and C). This behavior reflects unequivocally the
change in the close surrounding of copper species as the color is
associated with d–d transitions of Cu2+ ions. The corresponding DRS
UV–vis spectra are illustrated in Fig. 5. All samples demonstrate an
edge around 350 nm due to a ligand to metal charge transfer (LMCT)
transition from oxygen to copper atoms (O → Cu). In addition, it is
obvious to observe that as-synthesized HKUST-1 (hydration) sam-
ple shows a band centered at 586 nm because of characteristic of
3.1.4. FT-IR spectroscopy
FT-IR spectra of all samples were shown in Fig. 2. Compared
with as-synthesized HKUST-1, the presence of new bands in high
Fig. 2. Partial enlarged view of FT-IR spectra. Low wavenumber (left); high wavenumber (right). Amino-functionalized basic ionic liquid ABIL-OH (a); as-synthesized HKUST-1
(b); ABIL-OH/HKUST-1 (c).

Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
85
Fig. 3. The DRS UV–vis spectra of all samples (left) and splitting of bivalent copper species Cu2+ in the filed of ligand in different coordination environments (right). Activated
HKUST-1 (a); As-synthesized HKUST-1 (b); ABIL-OH/HKUST-1 (c).
the d–d transition for Cu(II) species in a distorted octahedral local
geometry.
and 953.5 eV, corresponding to Cu 2p3/2 and Cu 2p1/2, respec-
tively. Meanwhile, the well-known “shake-up satellite bands” (at
the 938–946 eV and 961–965 eV regions) are observed [50–52].
However, it is worthwhile to note that the Cu 2p3/2 and Cu 2p1/2
bind energy of ABIL-OH/HKUST-1 catalyst shift from 933.8 eV to
933.3 eV and 953.5 eV to 953.0 eV, respectively. This slightly reduc-
tion of binding energy is because of Cu2+ center accepting the lone
pair electrons from donating NH2 group. Additionally, the inten-
sity of “shake-up satellite bands” is also decreased slightly. As a
consequence, it is supposed that the coordination environment of
Cu2+ center has changed slightly due to the interaction between the
CUS and NH2 group.
The distortion of octahedral complexes is commonly explained
from the crystal field theory. Splitting of bivalent copper species
Cu2+ in the filed of ligand (Jahn-Teller effect) causing a distortion
of the octahedral Cu2+ complex. The corresponding band of acti-
vated HKUST-1 is shifted to 517 nm due to removing of coordinated
water. Interestingly, the spectrum tends to restore original state
over ABIL-OH/HKUST-1 catalyst, apart from some extent red shift
in the d–d band (∼645 nm) [20,48,49]. One reasonable explanation
for this phenomenon is that ABIL-OH molecules are re-adsorbed
onto bivalent copper species Cu2+. This change in local coordina-
tion environment of central Cu2+ ion is sufficient to cause a visually
color change.
3.1.7. Thermogravimetric analysis (TGA)
The thermogravimetric analysis (TGA) were also carried out
from 30 ◦C to 800 ◦C with a heating rate of 10 ◦C min−1 under
N2 flow, as depicted in Fig. 5. The TGA curve of as-synthesized
HKUST-1 indicates an initial weight loss of about 22% up to 150 ◦C
corresponding to the adsorbed water inner and outer surfaces
of HKUST-1. However, ABIL-OH/HKUST-1 catalyst loses only ∼7%
weight at <150 ◦C because adsorption sites are occupied by ABIL-
OH group. In the second step, there is about 23% weight loss at
3.1.6. X-ray photoelectron spectroscopy (XPS)
The X-ray photoelectron spectroscopy (XPS) was performed to
investigate the surface characteristic (Fig. 4). The presence of new
peak (BE at ∼399 eV) in ABIL-OH/HKUST-1 catalyst is attributed to
N 1s of the ABIL-OH group. The copper specie Cu 2p XPS spectrum of
as-synthesized HKUST-1 is depicted around the range from 925 eV
to 965 eV. Two characteristic peaks of Cu2+ are observed at 933.8 eV
933.8
O 1s
Cu 2p
3/2
Cu 2p
Cu 2p
1/2
953.5
(a)
933.3
C 1s
(b)
953.0
N 1s
(a)
(b)
Shake-up
(satellite bands)
0
300
600
900 1200 1500
920
930
940
950
960
970
Binding energy (eV)
Binding energy (eV)
Fig. 4. X-ray photoelectron spectroscopy (XPS) of all samples. Survey XPS spectra (left); Cu 2p XPS spectra (right). As-synthesized HKUST-1 (a); ABIL-OH/HKUST-1 (b).

86
Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
100
90
80
70
60
50
40
30
20
10
0
100
93%
H2O
80
60
40
20
0
ABIL-OH
ABIL-Br
78%
70%
As-synthesized HKUST-1
ABIL-Br/HKUST-1
ABIL-OH/HKUST-1
HKUST-1
(a)
(b)
31%
200
0
30
60
90 120 150 180 210 240
Time on Stream (min)
100
300
400
500
600
700
800
º
Fig. 7. Verification experiment of CUS-NH2 interaction. Reaction condition: 2 ml
toluene, 2 mmol benzaldehyde, 4 mmol malononitrile, reaction temperature = 30 ◦C,
mcat = 50 mg ABIL-OH/HKUST-1 or ABIL-Br/HKUST-1, 8 mg ABIL-OH or ABIL-Br,
respectively.
Temperature/ C
Fig. 5. The thermogravimetric analysis (TGA) curves of ABIL-OH/HKUST-1
catalyst and as-synthesized HKUST-1 sample. As-synthesized HKUST-1 (a); ABIL-
OH/HKUST-1 (b).
comparison, homogeneous counterpart ABIL-OH organocatalyst
was also examined under the same total number of OH− active
species. The employment of ABIL-OH organocatalyst presents
admirable catalytic activity with 100% conversion only after
120 min. Nevertheless, it must be recognized that free NH2 group
of ABIL-OH organocatalyst could serve as a Lewis basic site to make
a contribution to the catalytic activity.
In order to further verify CUS-NH2 interaction, homogeneous
ABIL-Br organocatalyst and ABIL-Br/HKUST-1 heterogeneous cata-
lysts were prepared and also evaluated under the same conditions,
as depicted in Fig. 7. The ABIL-Br organocatalyst demonstrates
high benzaldehyde conversion (94.1%) after 240 min because free
NH2 group could serve as a Lewis basic site to catalyze Kno-
evenagel condensation. Nevertheless, ABIL-Br/HKUST-1 catalyst
exhibits comparative catalytic activity with as-synthesized HKUST-
1, but it is still lower than that of ABIL-Br and ABIL-OH/HKUST-1
catalysts. These results clearly indicate that lone pair electrons of
free NH2 group interact with coordinatively unsaturated metal
sites, and Lewis basic sites are shielded.
150–290 ◦C, which is probably due to the decomposition of the
ABIL-OH organocatalyst inside HKUST-1 nanocavities. Finally, the
weight loss at ∼300 ◦C is attributed to the complete collapse of
HKUST-1 framework. In addition, the weight of residual solid ABIL-
OH/HKUST-1 is lower than as-synthesized HKUST-1 sample. This
result agrees with the previous observation from SEM-EDX analy-
sis.
3.2. Catalytic performance
3.2.1. Catalytic activity study
As for synthesized ABIL-OH/HKUST-1 catalyst, the loading
amount of ABIL-OH group is measured to be 1.07 mmol g−1 by
elemental analysis (Table 1). The catalytic performance was eval-
uated by using Knoevenagel condensation of benzaldehyde with
malononitrile as a probe reaction under ambient temperature.
Kinetic curves (dependence of conversion on reaction time) are
depicted in Fig. 6. A blank experiment, Knoevenagel condensa-
tion cannot proceed in absence of catalyst. The as-synthesized
HKUST-1 gives
a maximum benzaldehyde conversion of ca.
3.2.2. Recyclability and hot filtration tests
55.3% after 240 min. Bracingly, ABIL-OH/HKUST-1 catalyst Exhibits
100% benzaldehyde conversion after 210 min. For the sake of
The recyclability of ABIL-OH/HKUST-1 catalyst was investigated
under same reaction condition. After every reaction, the catalyst
was washed with toluene and dried under vacuum. As shown
in Fig. 8, it could maintain high catalytic activity (>90% conver-
sion) and 100% selectivity after five times recycle, but the slightly
decrease of conversion in continuing recycle of the reaction is
observed. PXRD characterizations of fresh catalyst and reused cat-
alyst were attempted to investigate the reason for the loss of the
catalytic activity, as shown in Fig. S3. It is found that the main
diffraction peaks of reused catalyst are observed, but several peaks
at high angle region disappear. The reasonable interpretation for
collapse of partial framework might be the reduction of Cu(II) in
HKUST-1 framework by the aldehyde group of reactant [53,54]. The
resulting catalytically active ABIL-OH group could leak out from
nanocavities. The hot filtration test was also carried out by stop-
ping a standard Knoevenagel condensation after 30 min. Negligible
increase in conversion is observed (Fig. 9). These results reveal that
the catalytic reaction is truly heterogeneous process.
100
80
Blank
As-synthesized HKUST-1
ABIL-OH/HKUST-1
60
ABIL-OH
ABIL-OH/MIL-101
40
20
0
0
30
60
90 120 150 180 210 240
Time on Stream (min)
3.2.3. Size- and shape-selective catalysis
Fig. 6. Kinetic curves of Knoevenagel condensation using different catalyst. Reac-
tion condition: 2 ml toluene, 2 mmol benzaldehyde, 4 mmol malononitrile, reaction
temperature = 30 ◦C, mcat = 50 mg ABIL-OH/HKUST-1, 8 mg ABIL-OH, 73 mg ABIL-
OH/MIL-101, respectively.
In general, the aromatic aldehydes with electron-donating or
electron-withdrawing groups would have an effect on the catalytic
performance under homogeneous catalysis, and higher catalytic

Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
87
Table 2
Conversion
Selectivity
The calculation of different molecular size by ground state geometric optimizations
and simulation.
100
80
60
40
20
0
100
80
60
40
20
0
˚
Substrate
Aromatic aldehyde
Molecular size (Å × A)
1
6.64 × 4.64
2
3
7.25 × 4.64
8.12 × 4.69
Run1 Run2 Run3 Run4 Run5 Run6
Recyling Times
4
5
8.94 × 4.86
9.08 × 4.85
Fig. 8. The recyclability of ABIL-OH/HKUST-1 catalyst for Knoevenagel condensation
of benzaldehyde with malononitrile.
activities are obtained for aromatic aldehydes with electron-
withdrawing groups. For another thing, however, the aromatic
aldehydes with different substituted groups would lead to differ-
ent molecular size and shape, which might also play an important
role on catalytic activities over heterogeneous catalyst. Therefore,
we attempted to extend the Knoevenagel condensation reac-
tions to a series of aromatic aldehydes with different substituted
groups. The corresponding reactant molecular sizes were calcu-
lated by ground state geometric simulation and optimization,
as illustrated in Table 2. The catalytic activities are depicted in
Fig. 10.
6
7
6.65 × 5.41
7.60 × 6.43
The Knoevenagel condensation reactions proceed smoothly
over homogeneous ABIL-OH organocatalyst. The conversion of 4-
(dimethylamino) benzaldehyde (substrate 5) decreases slightly
(97%) due to existence of +I (electron donating inductive effect)
effect. The rest of all substrates show 100% conversion, but the
products selectivity of substrate 2 and 4 are decreased to 82% and
95%, respectively. These results indicate that ABIL-OH organocat-
alyst exhibits excellent generality for Knoevenagel condensation.
Interestingly, it is obvious to note that the increase in reactants
sizes have a great influence on the catalytic activities over the ABIL-
OH/HKUST-1 heterogeneous catalyst. The smallest benzaldehyde
˚
dimensions of 7.25 × 4.64 A demonstrates 82% conversion. The con-
versions of p-methoxybenzaldehyde and p-isopropylbenzaldehyde
˚
(substrate 3 and 4) with molecular dimensions of 8.12 × 4.69 A
˚
and 8.94 × 4.86 A are decreased to 56% and 48%, respectively.
The reactant 4-(dimethylamino) benzaldehyde (substrate 5) with
Selectivity
Conversion
Homogeneous Catalyst
Heterogeneous Catalyst
Homogeneous Catalyst
Heterogeneous Catalyst
˚
molecule (substrate 1) with dimensions of 6.64 × 4.64 A shows
100% conversion. The p-chlorobenzaldehyde (substrate 2) with
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
Hot filtration test
40
20
0
0
30
60
90 120 150 180 210 240
Time on Stream (min)
Fig. 10. Results for Knoevenagel condensation of aromatic aldehydes with mal-
ononitrile using ABIL-OH/HKUST-1 as catalyst. Reaction condition: 2 ml toluene,
2 mmol aromatic aldehydes, 4 mmol malononitrile, reaction time = 3.5 h reaction
temperature = 30 ◦C, mcat = 50 mg ABIL-OH/HKUST-1, 8 mg ABIL-OH, respectively.
Fig. 9. The hot filtration test over ABIL-OH/HKUST-1 catalysts.

88
Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
30°C
60°C
30°C
60°C
Selectivity=100%
Selectivity=100%
100
80
60
40
20
0
100
80
60
40
20
0
Fig. 11. Knoevenagel condensation of aromatic aldehydes with malononitrile over
Fig. 13. Knoevenagel condensation of aromatic aldehydes with malononitrile over
ABIL-OH/HKUST-1 catalyst under different temperature.
ABIL-OH/MIL-101 catalyst under different temperature.
˚
(substrates 2, 3, and 4) are increased significantly. From these
results, it is supposed that these reactants could diffuse through the
nanocavities and catalytic activities are also affected by thermody-
namics. However, substrate 5 with larger size has no increase in
conversion indicating that diffusion of reactants might be the
controlling step in confined microenvironment. In addition, there
is still no any obvious catalytic activity for substrate 6 and substrate
7. In this case, the catalytic activities seem to depend on the size
and shape of the reactants.
dimensions of 9.08 × 4.85 A displays only 12.1% conversion. For all
of the above aromatic aldehydes substrates, the products selectiv-
ity maintains 100%. In addition, there is no any catalytic activity for
˚
reactant o-hydroxybenzaldehyde (6.65 × 5.41 A) and 3-methoxy-
˚
4-hydroxybenzaldehyde (7.60 × 6.43 A), which could be attributed
to a difficult rotation and steric factor in confined microenviron-
ment.
N2 physical adsorption–desorption has demonstrated that the
pore size distribution of ABIL-OH/HKUST-1 catalyst is about
0.6–0.8 nm. It is thereby reasonable that the reactants with
matched sizes could diffuse smoothly through the nanocavities.
Therefore, diffusion of reactants might be an important factor
for catalytic activity. Further considering thermodynamics, differ-
ent reactants must meet certain activation energies over specified
catalyst. For this reason, the Knoevenagel condensation was fur-
ther investigated under higher temperature (Fig. 11). As seen
from the figure, the conversions of reactants with matched sizes
To better discern the molecule size and shape-selective catal-
˚
ysis, another MOFs material with large pore window (12–16 A)
˚
and mesoporous cages (29–34 A) so-called MIL-101 was employed
to immobilize ABIL-OH organocatalyst. The representative 3D
pore network was illustrated in Fig. 12. The loading amount
of ABIL-OH within MIL-101 nanocages is 0.73 mmol g−1. And it
was also tested under the same total number of OH− active
species. The corresponding catalytic activities of different aro-
matic aldehydes are shown in Fig. 13. As expected, conversions
of all aromatic aldehydes are improved significantly over ABIL-
OH/MIL-101 catalyst, and products selectivity also to maintain
100%. Similarly, the substrate 5 displays lower conversion (58.5%)
than others. It is interesting to note that the substrate 6 and
substrate 7 show excellent conversions. A reasonable explana-
tion for this result should be that reactant molecules with smaller
˚
˚
size (6.65 × 5.41 A and 7.60 × 6.43 A) are able to rotate freely and
interact with active species inside open mesoporous nanocages.
Furthermore, Knoevenagel condensation over ABIL-OH/MIL-101
catalyst was also investigated under higher temperature. It is
clearly observed that all aromatic aldehyde exhibit 100% conver-
sions.
In addition, kinetic curve of Knoevenagel condensation between
benzaldehyde and malononitrile over ABIL-OH/MIL-101 catalyst
was also investigated, as depicted in Fig. 6. Unexpectedly, the ini-
tial reaction rate over ABIL-OH/MIL-101 catalyst is slower than
that over ABIL-OH/HKUST-1 catalyst before 120 min. And then,
both catalytic activity and reaction rate are almost same. This
deviant phenomenon could be ascribed to confinement effect. In
the confined microenvironment, the benzaldehyde molecule with
˚
matched dimensions (6.64 × 4.64 A) is more favorable to interact
Fig. 12. The three-dimensional (3D) pore network of metal-organic framework
HKUST-1 (left) and MIL-101 (right).
with active species.

Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
89
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (21076031 and 21356001) and Fundamen-
tal Research Funds for the Central Universities (DUT12ZD219).
Prof. Sang-Eon Park thanks Dalian University of Technology for the
“Seasky” professorship.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2014.03.041.
References
[1] B. Smit, T.L. Maesen, Nature 451 (2008) 671–678.
[2] Y. Shin, J. Liu, L.Q. Wang, Z. Nie, W.D. Samuels, G.E. Fryxell, G.J. Exarhos, Angew.
Chem. 112 (2000) 2814–2819.
[3] A. Corma, J. Catal. 216 (2003) 298–312.
[4] T.L. Maesen, R. Krishna, J.M. van Baten, B. Smit, S. Calero, J.M. Castillo Sanchez,
J. Catal. 256 (2008) 95–107.
[5] Y. Iwase, Y. Sakamoto, A. Shiga, A. Miyaji, K. Motokura, T.-R. Koyama, T. Baba, J.
Phys. Chem. C 116 (2012) 5182–5196.
[6] S. Horike, M. Dinca, K. Tamaki, J.R. Long, J. Am. Chem. Soc. 130 (2008)
5854–5855.
Scheme 4. The schematic mechanism in different catalytic microenvironment. (A)
Homogeneous ABIL-OH organocatalyst; (B) ABIL-OH/HKUST-1 heterogeneous cata-
lyst; (C) ABIL-OH/MIL-101 heterogeneous catalyst.
[7] L.G. Qiu, A.J. Xie, L.D. Zhang, Adv. Mater. 17 (2005) 689–692.
ˇ
[8] A. Dhakshinamoorthy, M. Opanasenko, J. Cejka, H. Garcia, Catal. Sci. Technol. 3
(2013) 2509–2540.
[9] S.M. Cohen, Chem. Rev. 112 (2011) 970–1000.
[10] S.M. Cohen, Chem. Sci. 1 (2010) 32–36.
[11] G. Lu, S. Li, Z. Guo, O.K. Farha, B.G. Hauser, X. Qi, Y. Wang, X. Wang, S. Han, X.
Liu, Nat. Chem. 4 (2012) 310–316.
[12] H.-L. Jiang, B. Liu, T. Akita, M. Haruta, H. Sakurai, Q. Xu, J. Am. Chem. Soc. 131
(2009) 11302–11303.
[13] C.-Y. Sun, S.-X. Liu, D.-D. Liang, K.-Z. Shao, Y.-H. Ren, Z.-M. Su, J. Am. Chem. Soc.
131 (2009) 1883–1888.
[14] J. Song, Z. Luo, D.K. Britt, H. Furukawa, O.M. Yaghi, K.I. Hardcastle, C.L. Hill, J.
Am. Chem. Soc. 133 (2011) 16839–16846.
[15] A. Yperen-De Deyne, V. Speybroeck, P. Der Voort, Chem. Commun. 49 (2013)
8021–8023.
[16] M.H. Alkordi, Y. Liu, R.W. Larsen, J.F. Eubank, M. Eddaoudi, J. Am. Chem. Soc.
130 (2008) 12639–12641.
[17] R.W. Larsen, L. Wojtas, J. Perman, R.L. Musselman, M.J. Zaworotko, C.M. Vetro-
mile, J. Am. Chem. Soc. 133 (2011) 10356–10359.
[18] S.S.-Y. Chui, S.M.-F. Lo, J.P. Charmant, A.G. Orpen, I.D. Williams, Science 283
(1999) 1148–1150.
Based on the foregoing results and related literatures [25,55,56],
it is found that catalytic microenvironment could have a profound
effect on Knoevenagel condensation. We propose the catalytic
mechanism over different catalyst, as illustrated in Scheme 4. In
the case of homogeneous catalysis, the catalytically active species
as mono-molecule are dispersed in reactive medium, which is
beneficial to interact with reactants. The ABIL-OH organocatalyst
exhibits excellent catalytic activity and generality for Knoeve-
nagel condensation. As a consequence, the nature of substituent
group might play a critical role. In the confined microenviron-
ment of ABIL-OH/HKUST-1 catalyst, the diffusion of reactants
might be controlling steps and play a leading role for Knoeve-
nagel condensation. In other words, the molecular size and shape
of reactants could serve as a more important factor than nature
of substituent group for Knoevenagel reaction. In open microenvi-
ronment, the nature of substituent group (thermodynamics) and
diffusion of reactant might be a co-leading role for Knoevenagel
condensation.
[19] A. Demessence, D.M. D’Alessandro, M.L. Foo, J.R. Long, J. Am. Chem. Soc. 131
(2009) 8784–8786.
[20] E. Borfecchia, S. Maurelli, D. Gianolio, E. Groppo, M. Chiesa, F. Bonino, C. Lam-
berti, J. Phys. Chem. C. 116 (2012) 19839–19850.
[21] S. Balalaie, M. Sheikh-Ahmadi, M. Bararjanian, Catal. Commun.
1724–1728.
8 (2007)
[22] Y. Kubota, Y. Nishizaki, Y. Sugi, Chem. Lett. 29 (2000) 998–999.
[23] P. Shanthan Rao, R. Venkataratnam, Tetrahedron Lett. 32 (1991) 5821–5822.
[24] S. Saravanamurugan, M. Palanichamy, M. Hartmann, V. Murugesan, Appl. Catal.
A 298 (2006) 8–15.
[25] M.B. Ansari, H. Jin, M.N. Parvin, S.-E. Park, Catal. Today 185 (2012) 211–216.
[26] Y. Peng, J. Wang, J. Long, G. Liu, Catal. Commun. 15 (2011) 10–14.
[27] J. Gascon, U. Aktay, M.D. Hernandez-Alonso, G.P. van Klink, F. Kapteijn, J. Catal.
261 (2009) 75–87.
4. Conclusions
In summary, we demonstrated
a novel molecular size-
ˇ
[28] A. Dhakshinamoorthy, M. Opanasenko, J. Cejka, H. Garcia, Adv. Synth. Catal. 355
and shape-selective catalyst by immobilization of amino-
functionalized basic ionic liquid onto microporous metal-organic
framework HKUST-1. The catalytically active groups ABIL-OH are
confined inside well-defined HKUST-1 nanocavities via Cu NH2
coordination bond. The resulting ABIL-OH/HKUST-1 catalyst
shows comparable catalytic activity and enhanced selectivity, and
it could be reused at least 5 times. More importantly, the confined
microenvironment of ABIL-OH/HKUST-1 catalyst provides distinct
size- and shape-selective catalytic properties for discrimination
of reactants. The knowledge from this contribution opens up
new possibility to design and develop highly active and selective
catalyst based on nanoporous metal-organic framework materials.
Meanwhile, this strategy would bridge the distance between
heterogeneous and homogeneous catalysis by combination of
MOFs and task-specific ionic liquid organocatalyst.
(2013) 247–268.
[29] M. Opanasenko, A. Dhakshinamoorthy, M. Shamzhy, P. Nachtigall, M. Horácˇek,
ˇ
H. Garcia, J. Cejka, Catal. Sci. Technol. 3 (2013) 500–507.
[30] R.V. Hangarge, D.V. Jarikote, M.S. Shingare, Green Chem. 4 (2002) 266–268.
[31] D.-Z. Xu, Y. Liu, S. Shi, Y. Wang, Green Chem. 12 (2010) 514–517.
[32] C.P. Mehnert, Chem. Eur. J. 11 (2005) 50–56.
[33] M. Valkenberg, W. Hölderich, Green Chem. 4 (2002) 88–93.
[34] H. Li, P.S. Bhadury, B. Song, S. Yang, RSC Adv. 2 (2012) 12525–12551.
[35] Y. Zhang, C. Xia, Appl. Catal. A 366 (2009) 141–147.
[36] Y. Zhang, Y. Zhao, C. Xia, J. Mol. Catal. A 306 (2009) 107–112.
[37] C. Paun, J. Barklie, P. Goodrich, H. Gunaratne, A. McKeown, V. Parvulescu, C.
Hardacre, J. Mol. Catal. A 269 (2007) 64–71.
[38] Q. Zhang, J. Luo, Y. Wei, Green Chem. 12 (2010) 2246–2254.
[39] M.N. Parvin, H. Jin, M.B. Ansari, S.-M. Oh, S.-E. Park, Appl. Catal. A 413 (2012)
205–212.
[40] B. Karimi, M. Vafaeezadeh, Chem. Commun. 48 (2012) 3327–3329.
[41] Y. Shen, Y. Zhang, Q. Zhang, L. Niu, T. You, A. Ivaska, Chem. Commun. 33 (2005)
4193–4195.
[42] S. Guo, S. Dong, E. Wang, Adv. Mater. 22 (2010) 1269–1272.

90
Q.-x. Luo et al. / Applied Catalysis A: General 478 (2014) 81–90
[43] B. Wu, D. Hu, Y. Kuang, B. Liu, X. Zhang, J. Chen, Angew. Chem. Int. Ed. 48 (2009)
4751–4754.
[50] S. Poulston, P. Parlett, P. Stone, M. Bowker, Surf. Interface Anal. 24 (1996)
811–820.
[44] Q.-X. Luo, M. Ji, M.-G. Lu, C. Hao, J.-S. Qiu, Y.-Q. Li, J. Mater. Chem. A 1 (2013)
6530–6534.
[45] N.A. Khan, Z. Hasan, S.H. Jhung, Chem. Eur. J. 20 (2014) 376–380.
[46] E.D. Bates, R.D. Mayton, I. Ntai, J.H. Davis, J. Am. Chem. Soc. 124 (2002) 926–927.
[47] Z. Zhang, Y. Xie, W. Li, S. Hu, J. Song, T. Jiang, B. Han, Angew. Chem. Int. Ed. 47
(2008) 1127–1129.
[48] C. Prestipino, L. Regli, J. Vitillo, F. Bonino, A. Damin, C. Lamberti, A. Zecchina, P.
Solari, K. Kongshaug, S. Bordiga, Chem. Mater. 18 (2006) 1337–1346.
[49] F. Giordanino, P.N. Vennestrøm, L.F. Lundegaard, F.N. Stappen, S.L. Mossin, P.
Beato, S. Bordiga, C. Lamberti, Dalton Trans. 42 (2013) 12741–12761.
[51] L. Kundakovic, M. Flytzani-Stephanopoulos, Appl. Catal. A 171 (1998) 13–29.
[52] H. Chen, L. Wang, J. Yang, R.T. Yang, J. Phys. Chem. C 117 (2013) 7565–
7576.
[53] A. Dhakshinamoorthy, M. Alvaro, P. Concepcion, H. Garcia, Catal. Commun. 12
(2011) 1018–1021.
[54] K. Schlichte, T. Kratzke, S. Kaskel, Micropor. Mesopor. Mater. 73 (2004)
81–88.
[55] K. Parida, S. Mallick, P. Sahoo, S. Rana, Appl. Catal. A 381 (2010) 226–232.
[56] J. Mondal, A. Modak, A. Bhaumik, J. Mol. Catal. A 335 (2011) 236–241.