Ultra-high concentrations of amino group functionalized nanoporous polymeric solid bases: Preparation, characterization and catalytic applications

Article abstract of DOI:10.1016/j.catcom.2015.04.026

We report here that the amino-group functionalized nanoporous polydivinylbenzene (PDVB-2.0-NH₂, PDVB-NH₂), acts as an efficient solid base for catalyzing Knoevenagel condensation, which could be synthesized from nitration of nanoporo

Full text of DOI:10.1016/j.catcom.2015.04.026

Catalysis Communications 68 (2015) 25–30
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Ultra-high concentrations of amino group functionalized nanoporous
polymeric solid bases: Preparation, characterization and
catalytic applications
Bin Zhang , Chen Liu a,1, Lingjing Wang , Xianfeng Yi , Anmin Zheng , Wenshu Deng ,
b,1
a
c
c
a
a,
a,
Chenze Qi ⁎, Fujian Liu ⁎
a
Department of Chemistry, Shaoxing University, Shaoxing 312000, China
Zhejiang Pharmaceutical College, Ningbo, Zhejiang 315000, China
Wuhan Center for Magnetic Resonance, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences,
b
c
Wuhan 430071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
We report here that the amino-group functionalized nanoporous polydivinylbenzene (PDVB-2.0-NH , PDVB-
2
Received 31 January 2015
Received in revised form 13 April 2015
Accepted 22 April 2015
NH
nitration of nanoporous polydivinylbenzene (PDVB), reduction in the mixture containing SnCl
tivated with isopropylamine. The resultant solid bases of PDVB-2.0-NH and PDVB-NH have large BET surface
2
), acts as an efficient solid base for catalyzing Knoevenagel condensation, which could be synthesized from
2
and HCl, and ac-
2
2
Available online 23 April 2015
areas, abundant nanopores, controlled hydrophobic network and ultra-high concentrations of the amino
group. The above characteristics result in their excellent activities and good recyclability for catalyzing
Knoevenagel condensation of various aldehydes with malononitrile, much better than those of commercially
basic resin of Amberlite-400 and Amberlite-910, which was as comparable as that of the homogeneously strong
base of CaO. This work develops efficient nanoporous polymeric solid bases with controllable surface character-
istics and ultra high concentrations of basic sites.
Keywords:
Solid bases
Nanoporous polymers
Solvothermal synthesis
Knoevenagel condensation
Wettability
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
however, the drawbacks such as environmental concerns and difficult
regeneration from reaction media largely constrain their wide applica-
tions [1].
Acid and base catalytic processes showed an inseparable relation-
ship in the area of catalytic chemistry. In acid catalyzed reactions, reac-
tants act as bases toward catalysts which act as acids. On the contrary,
reactants act as acids toward catalysts in base catalyzed reactions [1],
and acid and base catalyzed reactions have been paid much attention
because of their wide applications for catalyzing production of various
useful chemicals [1–11]. Compared with acid catalysis, base catalysis
usually exhibits mild reaction conditions and high efficiency [6]. Typical
base catalyzed reactions such as aldolization, alkylation, Knoevenagel,
transesterification, glucose isomerization Michael condensations, and
Wadsworth–Emmons additions are very efficient tools for the fabrica-
tion of various fine chemicals and biofuels in the industry [12,13]. Con-
ventional base catalysts such as KOH, NaOH and CaO showed low cost,
strong base strength, and excellent activities in various reactions,
In recent times, the replacement of homogeneous bases with solid
bases for catalyzing production of fine chemicals and biofuels has re-
ceived considerable attention [6,14–16]. Up to now, the common solid
bases include alkaline earth oxides, basic zeolites, strong basic resins,
clay minerals and hydrotalcite, which have been widely used in various
base catalytic reactions, and showed relatively good catalytic activities
[1,6,12,17]. However, their relatively low BET surface areas result in
the low exposition degree of catalytically active sites and diffusion lim-
itation of reactants in various reactions, which constrains their catalytic
activities and lives [1,11,18–20]. Loading the basic active sites into high-
ly porous supports such as zeolites, mesoporous silicas and porous car-
bons basically overcomes the poor porosity problems of conventional
solid bases, and the resultant porous solid bases were active in various
base catalyzed reactions such as Knoevenagel reactions, toward
transesterification to biodiesel, and Michael addition etc. [1,15,21–24].
However, the reported porous solid bases showed the drawbacks
including: (i) the limited contents of basic sites could be loaded into
these porous materials and (ii) their sensitive basic sites could be easily
⁎
Corresponding authors.
E-mail addresses: qichenze@usx.edu.cn (C. Qi), fjliu1982@gmail.com (F. Liu).
These authors contributed equally to this work.
1
poisoned by molecules such as H
2 2
O and CO because of their unique
http://dx.doi.org/10.1016/j.catcom.2015.04.026
566-7367/© 2015 Elsevier B.V. All rights reserved.
1

26
B. Zhang et al. / Catalysis Communications 68 (2015) 25–30
1
1
1
1
1
0
0
.8
.6
.4
.2
.0
.8
.6
A 9
00
00
00
00
00
00
00
00
00
0
a
a
8
7
6
5
4
3
2
1
b
b
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
0.1
1
10
100
Relative pressure (p/p0)
Pore diameter (nm)
6
5
4
3
2
1
0
B 3
50
00
50
00
50
00
3
2
2
1
1
a
b
a
b
5
0
0.0
0.2
0.4
0.6
0.8
1.0
0
5
10
15
20
25
30
Relative pressure (p/p0)
Pore diameter (nm)
2 2 2
Fig. 1. N isotherms and pore size distribution of (A) PDVB-2.0 and PDVB-2.0-NH , and (B) PDVB and PDVB-NH .
hydrophilic frameworks. The above problems found in reported solid
bases strongly constrain their wide applications in various base-cata-
lyzed reactions [1,6,25,26].
Up to now, it is still challengeable to synthesize porous solid bases
with very high concentrations of basic sites and controllable hydropho-
bicity, which will be very important for the enhancement of catalytic ac-
tivities and recyclability of solid base catalysts. Recently, our group
successfully synthesized pyridine, imidazole and triazole functional,
nanoporous polymeric solid bases, which showed very good hydropho-
bicity and controlled wettability for various organic reactants. These
characters result in their very good stability in the air and good catalytic
activity in various reactions [6,17]. However, the limited contents of
basic sites that still constrain them are used as highly efficient solid
bases in various reactions.
A
B
2 2
Fig. 2. SEM images of (A) PDVB-2.0-NH and (B) PDVB-NH .

B. Zhang et al. / Catalysis Communications 68 (2015) 25–30
27
with isopropylamine (As shown in Scheme S1). Typically, 1.5 g of PDVB
or PDVB-2.0 powder was added into a mixture containing 61.8 g of
A
H
2
SO
the mixture for 72 h under vigorous stirring. Then, the reaction mixture
was diluted with 800 mL of H O, the resultant PDVB-NO could be ob-
tained from filtration, washing with a large amount of water and drying
at 60 °C under vacuum condition. To synthesize PDVB-NH , PDVB-NO
was dispersed into a mixture containing 6.4 g of SnCl and 60 mL of
4 3
and 13.88 g of HNO under ice bath condition, after stirring of
2
2
2
2
2
HCl, after stirring the mixture at room temperature for 72 h, which
was dispersed into 800 mL of water, filtration, washing with large
amount of water and drying at 60 °C under vacuum condition. Then,
the dried sample was activated with a mixture containing 20 mL of
isopropylamine and 150 mL of ethanol for 30 min at room temperature.
a
b
PDVB-NH
2
could be obtained from repeating this treatment for two
294
292
290
288
286
284
282
times and drying at 60 °C under vacuum condition.
Binding energy (eV)
2
.2. Catalytic reactions
B
The Knoevenagel condensation of benzaldehyde with malononitrile
was performed in a flask equipped with a reflux condenser and magnet-
ic stirrer. Typically, 2 mmol of aldehydes (benzaldehyde, cyclohexa-
none, 4-nitrobenzaldehyde, salicylaldehyde or furfural) and 2 mmol of
malononitrile were dispersed into 5 mL of ethanol solvent, then 0.02 g
of catalyst was rapidly added. After stirring of the mixture at 80 °C
for 2 h, the reaction was finished. The products were analyzed by
using gas chromatography systems (Agilent 7890) with a flame ion-
ization detector (FID). The initial temperature of the column was
100 °C, ramping rate was 20 °C/min, and the final temperature was
a
b
2
3
80 °C; the temperatures of the inlet and detector were 300 and
50 °C, respectively. In this reaction, the concentrations of products
4
10
408
406
404
402
400
398
396
394
392
were calculated through the internal standard (dodecane) method.
In the meanwhile, the catalysts could be regenerated from centrifu-
gation, washing with large amount of ethanol, reactivated with
isopropylamine and drying at 60 °C. The regenerated catalyst was di-
rectly used for the next run.
Binding energy (eV)
2 2
Fig. 3. XPS spectra of (A) C1s and (B) N1s of (a) PDVB-2.0-NH and (b) PDVB-NH .
Herein, we report novel amino-group functionalized, super-
hydrophobic nanoporous polydivinylbenzene (PDVB-2.0-NH , PDVB-
NH ), which could be synthesized from nitration of superhydrophobic
nanoporous polydivinylbenzene (PDVB), reduction in the mixture
containing SnCl and HCl, and activated with isopropylamine. The
3. Results and discussion
2
2
Fig. 1 showed N
PDVB, PDVB-2.0, PDVB-NH
showed typical IV adsorption curves. For the samples of PDVB-2.0 and
PDVB-2.0-NH , which gave the sharp capillary condensation step at rel-
ative pressure P/P = 0.85–1.0. Meanwhile, PDVB and PDVB-NH gave
the sharp capillary condensation step P/P = 0.4–0.7. These results indi-
cate the formation of abundant nanopores in these samples. Corre-
spondingly, the pore sizes of PDVB-2.0 and PDVB-2.0-NH were
centered at 3.5 & 16.3 and 24.1 nm (Fig. 1A), and the pore sizes of
PDVB and PDVB-NH were centered at 3.85 and 3.83 nm (Fig. 1B). Com-
pared with PDVB and PDVB-2.0 (460 and 700 m /g), the decreased BET
2
isotherms and pore size distribution of nanoporous
2
and PDVB-2.0-NH . All of these samples
2
2
nanoporous PDVB support could be obtained through one-step
solvothermal synthesis without using any organic templates. PDVB-
2
0
2
NH
2
showed unique characteristics including large BET surface areas,
0
good thermal stability, ultra-high concentrations of amino group,
superhydrophobic network and controllable wettability for various
organic substrates, which result in their good ability for anti-poison
2
for H
2
O and CO
2
in the air. The above characteristics make PDVB-
show excellent catalytic activity and good
2
2
2
.0-NH
2
and PDVB-NH
2
2
recyclability in the reactions of Knoevenagel condensation, much
better than those of conventional solid bases including conventional
solid bases of Amberlite 400, Amberlite 910 and zeolite L, which was
as comparable as that of homogeneous CaO. The preparation of
2 2
surface areas in PDVB-NH and PDVB-2.0-NH (186 and 429 m /g,
Table S1) should be resulted from the grafting of amino group in
PDVB and PDVB-2.0 supports, which largely increase the weight of
their network, similar results have also been reported previously [27].
Compared with PDVB, the decreased volume adsorption could not be
2 2
PDVB-2.0-NH and PDVB-NH will develop a new way to the synthe-
sis of nanoporous polymer based solid bases with controllable hy-
drophobicity, ultrahigh contents of basic sites, which will be very
important for them used as highly efficient solid base catalysts in
various base catalyzed reactions.
2
observed in PDVB-NH in microporous region, which may be attributed
to decomposition of unstable units such as oligomers during nitration
and reduction processes. Alternatively, the decomposition of unstable
units leads to the enlarged pore diameter in PDVB-2.0-NH
2
(Fig. 1B).
may
The different structural changes in PDVB-2.0-NH and PDVB-NH
2
2
2
. Experimental section
be attributed to their obviously different nanoporous structures and
cross linking degree of their supports. On the other hand, the concentra-
2
.1. Synthesis of PDVB-2.0-NH
2
and PDVB-NH
2
2 2
tions of nitrogen (basic site) in PDVB-NH and PDVB-2.0-NH were 10.1
and 10.8 mmol/g respectively, which was much higher than those of
commercial basic resin of Amberlite 400 (5.18 mmol/g), Amberlite
IRA910 (3.5 mmol/g) and reported sold bases [15,21,28].
PDVB-NH
2
and PDVB-2.0-NH
2
were synthesized from nitration of
and HCl, and activated
PDVB, reduction in the mixture containing SnCl
2

28
B. Zhang et al. / Catalysis Communications 68 (2015) 25–30
A
CA<5°
B
CA<5°
CA<5°
CA<5°
C
D
E
CA 150°
F
CA 140°
2 2 2 2
Fig. 4. Contact angles of a malononitrile droplet on (A) PDVB-2.0-NH and (B) PDVB-NH , a benzaldehyde droplet on (C) PDVB-2.0-NH and (D) PDVB-NH , and A water droplet on
(
E) PDVB-2.0-NH and (F) PDVB-NH
2
2
.
Fig. 2 showed SEM images of PDVB-2.0-NH
an efficient technique to determine the surface characteristics of various
nanomaterials. Notably, PDVB-2.0-NH and PDVB-NH showed rough
surface with sponge-like structures, which exhibited abundant porosity
with nanoscaled pore diameters, in agreement with the result obtained
2
and PDVB-NH
2
, which is
water, which indicates its superhydrophobic surface characteristics.
Alternatively, PDVB-2.0-NH shows the contact angles lower than
5° for both malononitrile and benzaldehyde, which indicate its
superwettability for these organic substrates. Similar results could
2
2
2
also be found in the samples of PDVB and PDVB-NH
drophobic network in PDVB-2.0-NH and PDVB-NH
for enhancement of its anti-poison ability for H O and CO
2
2
. The unique hy-
was favorable
during
from N
2
isotherms and TEM results (Fig. S1). Abundant nanoporosity
2
2
was favorable for the decreasing of diffusion limitation of various organ-
ic substrates in these samples [6].
2
various base catalyzed reactions [6]. On the other hand, their
superwettability for malononitrile and benzaldehyde largely de-
creases the diffusion limitation of the reactants in the samples, fur-
ther resulting in their enhanced exposure degree of catalytically
active sites [6], which largely improves its catalytic activity for con-
version of these substrates through Knoevenagel condensation.
Table 1 presents catalytic performances of various catalysts in
2 2
Fig. 3 showed XPS spectra of PDVB-NH and PDVB-2.0-NH . Notably,
the peaks associated with C1s (284.8 eV) and N1s (402.1 eV) could be
clearly observed in these samples. Furthermore, the broaden C1s spectra
could be fitted and deconvoluted into two peaks, centered at around
2
84.8 and 286.1 eV, which should be assigned to C\\C and C\\N
bonds in these samples [28]. Correspondingly, the N1s spectrum could
also be fitted and deconvoluted into two peaks centered at around
Knoevenagel condensation. Notably, both PDVB-2.0-NH
2
and PDVB-
3
98.4 and 401.8 eV, which may be attributed to\\NH
dation of\\NH on the surface of the samples. These results confirm
the successful grafting of\\NH group onto the network of PDVB and
PDVB-2.0, in agreement with FT-IR and C NMR results (Figs. S2&3)
28].
Fig. 4 showed contact angle of PDVB-2.0 and PDVB for water, and
PDVB-2.0-NH and PDVB-NH for malononitrile and benzaldehyde.
Notably, PDVB-2.0 support gives the contact angle up to 150° for
2
and partial oxi-
NH were very active for catalyzing Knoevenagel condensation of
malononitrile with benzaldehyde (Table 1 Runs 1 & 3), much higher
than those of basic resins of Amberlite 400, Amberlite 910 amino
2
2
2
13
2
group functionalized ordered mesoporous silica (OMS-NH ) and zeolie
[
L (Table 1, Runs 8–12), which were as comparable as that of homoge-
neous base of CaO (Table 1, Run 13). For example, in the reaction of
malononitrile with benzaldehyde, the product yield catalyzed by
2
2
2 2
PDVB-2.0-NH and PDVB-NH were up to 99.1 and 98.6% only after

B. Zhang et al. / Catalysis Communications 68 (2015) 25–30
29
Table 1
a
Catalytic data in Knoevenagel condensation over various samples.
Run
1
Catalysts
Substrates
Products (sel. %)
Conv. (%)
99.1
TOF (h−1) d
PDVB-2.0-NH
2
2
N99.0
N99.0
N99.0
4.6
4.6
4.9
b
2
3
PDVB-2.0-NH
95.3
98.6
PDVB-NH
2
4
5
PDVB-2.0-NH
PDVB-2.0-NH
2
2
N99.0
N99.0
95.6
90.5
4.4
4.2
6
7
PDVB-2.0-NH
PDVB-2.0-NH
2
2
N99.0
N99.0
89.3
96.8
4.1
4.5
8
9
Amberlite 400 (OH form)
Amberlite 910 (OH form)
N99.0
N99.0
75.2
86.3
7.3
11.7
1
1
0
1
Amberlite 910 (OH form)
N99.0
N99.0
81.9
75.7
11.1
Zeolite L
–
c
1
2
3
OMS-NH
2
N99.0
N99.0
86.4
99.2
36.0
2.8
1
CaO
a
Reaction conditions: 2 mmol of aldehydes, 2 mmol of malononitrile, 5 mL of ethanol solvent, and 0.02 g of catalyst. Reaction temperature: 80 °C. Reaction time: 2 h. The products were
analyzed by using gas chromatography systems (Agilent 7890) with a flame ionization detector (FID). The conversions of various reactants were determined by using internal standard (n-
dodecane) method.
b
The catalyst has been recycled for 5 times.
Typical mesoporous solid bases synthesized as in Ref. [27].
Turn over frequency.
c
d
reacting for 2 h, which showed very good selectivity (N99%). On the
contrary, the product yields catalyzed by Amberlite 400, Amberlite
1
00
910, zeolite L and OMS-NH
spectively. The product yield catalyzed by strongly homogeneous CaO
was 99.2%, similar with those of PDVB-2.0-NH and PDVB-NH . More
importantly, PDVB-2.0-NH showed good reusability, even after being
reused for 5 times, the regenerated PDVB-2.0-NH still gave superior ac-
tivity (Table 1, Run 2), which was as comparable as that of fresh PDVB-
.0-NH (Table 1, Run 1). Correspondingly, the dependences of catalytic
2
were only 75.2, 86.3, 75.7 and 86.4%, re-
a
2
2
8
6
4
2
0
0
0
0
0
b
c
2
d
2
e
f
2
2
activities on reaction time in Knoevenagel condensation of benzalde-
hyde with malononitrile catalyzed by various catalysts have also been
investigated in Fig. 5, which further confirms very good activity and
2 2
reusability of PDVB-2.0-NH and PDVB-NH in comparison with those
of Amberlite 910, OMS-NH , Zeolite L and Amberlite 400, in good agree-
2
ment with the results obtained in Table 1. Meanwhile, their high activ-
ities could also be expanded to other substrates, which include the
reactions of malononitrile with other substrates such as cyclohexanone,
p-nitrobenzaldehyde, salicylaldehyde and furfural (Table 1 Runs 4–7).
Compared with Amberlite 400, Amberlite 910, the better catalytic
0
20
40
60
80
100
120
Reaction time (min)
Fig. 5. Dependences of catalytic activities on the time in Knoevenagel condensation of
benzaldehyde with malononitrile catalyzed by (a) PDVB-2.0-NH , (b) PDVB-2.0-NH
recycled for 5 times, (c) Amberlite 910, (d) OMS-NH , (e) Zeolite L and (f) Amberlite 400.
2 2
activities found in PDVB-2.0-NH and PDVB-NH should be attributed
2
2
2
to their large BET surface areas, controllable hydrophobicity and

30
B. Zhang et al. / Catalysis Communications 68 (2015) 25–30
wettability for the reactants (as shown in Fig. 4), and ultra high concen-
trations of amino groups, which largely increase the exposure degree of
catalytically active sites. Alternatively, a relatively lower activity of
zeolie L should be attributed to its constrained micropores, which re-
sults in the difficult accessibility of bulky substrates to catalytically
active sites. On the other hand, the hydrophilic framework and low
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.04.026.
concentration of basic site of OMS-NH
comparison with those of PDVB-2.0-NH
noteworthy that PDVB-2.0-NH and PDVB-NH
2
result in its lower activity in
and PDVB-NH [6,20]. It is
showed relatively
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This work was supported by the National Natural Science Founda-
tion of China (21203122), the Natural Science Foundation of Zhejiang
Province (LY15B030002), the Foundation of Science Technology
Department of Zhejiang Province (2013C31030) and the Foundation
of State Key Laboratory of Magnetic Resonance and Atomic and Molec-
ular Physics (T151303).
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