Direct synthesis and catalytic reactivity of highly ordered large-pore methylaminopropyl-functionalized SBA-15 materials

Article abstract of DOI:10.1071/CH05024

Highly ordered large-pore SBA-15 materials functionalized with a high loading of amino groups were synthesized for the first time by co-condensation of tetraethyl orthosilicate (TEOS) and [3-(methylamino)propyl]trimethoxysilane (MAPTMS) using an amphiphilic block copolymer. Addition of inorganic salt to the initial mixture greatly enhanced the mesostructure ordering and stability of the mesoporous materials. The materials thus obtained showed high catalytic activity and selectivity for the synthesis of flavanones by means of the Claisen-Schmidt condensation in the absence of solvent. CSIRO 2005.

Full text of DOI:10.1071/CH05024

Rapid Communication
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2005, 58, 507–510
Direct Synthesis and Catalytic Reactivity of Highly Ordered Large-
Pore Methylaminopropyl-Functionalized SBA-15 Materials
Xueguang WangA,B and Soofin ChengA
A
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
Corresponding author. Email: wxg228@yahoo.com; chem1031@ntu.edu.tw
B
Highlyorderedlarge-poreSBA-15materialsfunctionalizedwithahighloadingofaminogroupsweresynthesizedfor
the first time by co-condensation of tetraethyl orthosilicate (TEOS) and [3-(methylamino)propyl]trimethoxysilane
(MAPTMS) using an amphiphilic block copolymer.Addition of inorganic salt to the initial mixture greatly enhanced
the mesostructure ordering and stability of the mesoporous materials. The materials thus obtained showed high
catalytic activity and selectivity for the synthesis of flavanones by means of the Claisen–Schmidt condensation in
the absence of solvent.
Manuscript received: 10 January 2005.
Final version: 17 April 2005.
Organic functionalized mesoporous silica materials have
attractedgreatattentionbecauseoftheirpotentialapplications
in the fields of catalysis, separation, and nanotechnology.
prehydrolysis of TEOS. The materials thus obtained showed
high efficiency for the synthesis of flavanones in the absence
of solvent.
[
1–3]
These materials are usually prepared by incorporation of
organic groups through co-condensation or by grafting the
organic groups onto the surface of the mesoporous silica.
The small-angle XRD (X-ray diffraction) patterns of the
as-synthesized and the solvent-extracted materials containing
15 and 20 mol% [3-(methylamino)propyl]trimethoxysilane
(MAPTM) in the reaction mixture with TEOS prehydroly-
sis for 2 h are shown in Fig. 1. All the as-synthesized samples
exhibit one intense peak and two weak peaks indexed to
(100), (110), and (200) reflections, respectively (Fig. 1a).
The patterns are similar to that of pure siliceous SBA-15,
[
1,4]
The co-condensation method is often preferred to the post-
synthesis pathway because it minimizes processing steps
and provides a more uniform distribution of the organic
functionalities.[ In addition, one-pot co-condensation
synthesis often provides a higher loading of organic func-
5]
[
6]
tionalities without closing the framework mesopores.
Mesoporous silica functionalized with amino groups was
[
6,7]
(a)
found to be effective in base-catalyzed reactions
or fur-
(b)
ther post-synthesis functionalization.[ However, most of
8]
9]
(
100)
(
100)
the related work focussed on MCM-[ and HMS-type
[10]
mesoporous materials with relatively small mesopores,
which were synthesized under basic or neutral condi-
tions. In the large-pore SBA-15 system, the protonated
amino groups interfere with the self-assembly of the sil-
ica precursors and the surfactant; therefore, co-condensation
of tetraethyorthosilicate (TEOS) and amino silanes gave
only disordered materials, such as aminopropyltriethoxysi-
M15/SBA–NaCl
M15/SBA–NaCl
M20/SBA–NaCl
M20/SBA–NaCl
M15/SBA
[11]
lane (APTES), in an acidic environment.
Recently, we
M15/SBA
M20/SBA
have successfully synthesized well ordered aminopropyl-
functionalized SBA-15 by the prehydrolysis of TEOS before
the addition of APTES.[
12]
M20/SBA
This report outlines the syn-
thesis of highly ordered SBA-15 mesoporous silica con-
1
2
3
2u [Њ]
4
5
1
2
3
2u [Њ]
4
5
−1
taining up to 2.37 mmol g of methylaminopropyl groups,
with high surface area and narrow pore size distribution,
by a one-pot method using triblock copolymer Pluronic
P123 (EO20PO70EO20) as the pore-directing agent under
strong acidic conditions with the aid of inorganic salts and
Fig. 1. XRD patterns of (a) as-synthesized and (b) solvent-extracted
materials containing 15 and 20% of MAPTMS withTEOS prehydrolysis
for 2 h in the absence of, or in the presence of, NaCl in the reaction
mixture.
©
CSIRO 2005
10.1071/CH05024
0004-9425/05/070507

5
08
X. Wang and S. Cheng
Q4
indicating that the prepared materials contain well ordered
hexagonal arrays of one-dimensional channel structure.
(a)
[
13]
Q3
After the removal of the template by solvent extraction, the
samples prepared without NaCl show only one very broad
◦
peak at 2θ around 1.0–1.2 (Fig. 1b), demonstrating that the
ordered mesostructures were destroyed under the extraction
conditions. In contrast, the samples prepared in the presence
of NaCl still retain three well resolved reflections. The cell
parameter (a0) of 10.5 nm calculated from the d-spacings of
the (100) reflection peaks was close to the value of 10.8 nm
for pure siliceous SBA-15. These results indicate that the
addition of NaCl to the reaction mixture greatly improves
the structural ordering and stability of the functionalized
silica framework. A similar salt effect was also observed
T3
Q2
T2
15% MAPTMS
20% MAPTMS
[
14]
in the synthesis of periodic mesoporous organosilicas.
Ϫ20
(b)
Ϫ40
Ϫ60
Ϫ80 Ϫ100 Ϫ120 Ϫ140 Ϫ160 Ϫ180
The slight shift of the diffraction peaks of the extracted
materials toward larger 2θ angles indicates a slight shrink-
age of the cell dimension upon extraction. Transmission
electron microscopic (TEM) analysis (Accessory Materi-
als, Fig. S1) further confirms the ordered channels in the
structure of the M15/SBA–NaCl sample and the rather dis-
ordered structure for M15/SBA. The morphology of the
functionalized materials with the addition of inorganic salt
was also transformed from rod-shaped particles to fibre-
like materials (Accessory Materials, Fig. S2). It should be
noted that the prehydrolysis of TEOS before addition of
MAPTMS was a very important step for the formation of
mesoporous silica using P123 as pore-directing agent under
acidic conditions. No precipitate was observed in the reaction
mixture of TEOS and MAPTMS if TEOS was not pre-
hydrolyzed, a result which is different from that reported
in the synthesis of mesoporous amine-functionalized silica
Chemical shift [ppm]
C2
C3
C4
Si–CH –CH –CH –NH–CH
C1
2
2
2
2
1
2
3
4
160
120
80
40
0
Chemical shift [ppm]
Fig. 2. (a) 29Si MAS NMR spectra of the extracted M15/SBA–NaCl
1
3
1
and M20/SBA–NaCl and (b) C{ H} CP-MAS NMR spectrum of the
extracted M15/SBA–NaCl.
[9a,10,15]
under neutral and basic conditions.
This may be due
to the strong interaction between the protonated aminopropyl
groups and the ethoxy groups on the silane through hydrogen
analysis showed that most of the methylaminopropyl groups
in the reaction mixture are effectively (above 86 mol% of the
theoretical contents) incorporated into the silica framework
(Table 1).
+
bonding (−CH3NH · · · OC2H5Si), so that the hydrolysis of
2
[11a]
ethoxysilane is inhibited.
The 29Si MAS (magic angle spinning) NMR spectra
(
Fig. 2a) of the extracted M15/SBA–NaCl and M20/SBA–
The N2 sorption isotherms of the extracted materials
synthesized with NaCl in the initial mixture display the char-
acteristic type IV isotherms with clear H1 type hysteresis at
high relative pressure similar to that of pure siliceous SBA-15
(Accessory Materials, Fig. S4), while those of the materials
synthesized without NaCl have a very small hysteresis loop
of H2 type. BJH (Barrett–Joyner–Halenda) pore size anal-
ysis shows that the materials synthesized with NaCl have
narrow pore size distributions, with the diameter ranging
from 5.1 to 7.5 nm, but the materials synthesized without
NaCl have broad pore size distributions with a smaller pore
diameter range. Table 1 shows that the pore diameters, BET
(Brunauer–Emmett–Teller) surface areas, and pore volumes
of the functionalized materials decrease with N content due to
the occupation of space inside the pore by the organic groups.
Nevertheless, the materials synthesized with NaCl have much
higher surface areas than those without NaCl. When the N
NaCl show three resonance peaks in the upfield region
4
3
corresponding to Q (δ −111 ppm), Q (δ −101 ppm), and
2
Q (δ −91 ppm), and two downfield peaks were assigned
3
2
[11a]
4−n
to T (δ −67 ppm) and T (δ −58 ppm),
where Q
=
3
−m
Si(OSi)4−n(OH)n andT
= RSi(OSi)3−m(OH)m.The pres-
ence of T peaks confirms the incorporation of organosilane
1
3
1
moieties as a part of the silica wall structure. The C{ H}
CP-MAS (cross-polarization magic angle spinning) NMR
spectrum (Fig. 2b) of the extracted M15/SBA–NaCl clearly
displayed four peaks at 10, 20, 34, and 51 ppm, corresponding
to the C atoms on the Si–CH2–CH2–CH2–NH–CH3 chain
in sequence from left to right. These results show that the
methylaminopropyl groups did not decompose during the
synthesis. In addition, no resonance peaks corresponding to
the surfactant P123 were observed in the range 67–77 ppm,
indicating that the surfactant was completely removed dur-
ing the extraction.[ These results were also supported by
the thermogravimetric analysis (TGA; Accessory Materi-
als, Fig. S3). The nitrogen content determined by elemental
16]
content is up to 2.37 mmol g (17.2 mol% MAPTMS), the
−1
material synthesized with NaCl still retains a surface area of
2
−1
.
200 m g

Large-Pore Methylaminopropyl-Functionalized SBA-15 Materials
509
Table 1. Physical–chemical properties of the extracted MAPTMS-functionalized SBA-15 silicas
prepared with or without NaCl
Sample
a0
nm]
SBET
[m g
DpA
[nm]
Vp
[cm g
WtB
[nm]
N contentC
2
−1
3
−1
−1
[
]
]
[mmol g
]
SBA-15
M15/SBA
M15/SBA–NaCl
M20/SBA
M20/SBA–NaCl
10.8
–
10.5
–
769
280
384
56
7.8
–
6.7
–
1.04
0.23
0.50
0.06
0.29
3.0
3.8
–
1.97 (2.15)
1.95 (2.15)
2.30 (2.75)
2.37 (2.75)
10.5
200
6.0
4.5
A
B
C
Peak BJH pore diameter calculated from the adsorption branch.
elemental analysis. Values in parentheses refer to theoretical values.
Wall thickness.
Estimated by
ꢀ
Table 2. Condensation reaction of substituted benzaldehyde A (15 mmol) and substituted 2 -hydroxy-
acetophenone B (10 mmol) in the absence of solvent over methylaminopropyl-functionalized SBA-15 (0.15 g)
◦
at 140 C for 10 h
Reaction products were identified by GC–MS. Products in reaction mixtures were analyzed by GC. Products
were diluted with chlorobenzene, and subjected to GC analysis
R
HO
O
OH
H
O
O
R
ϩ
O
O
R
R؅
R؅
R؅
A
B
C
D
ꢀ
R
H
R
Catalyst
Conversion of B [%]
Selectivity for D [%]
H
M15/SBA
41
52
45
45
72
23
40
35
50
70
69
75
62
61
74
75
87
86
M15/SBA–NaCl
Spent M15/SBA–NaCl
M15/SBA
M15/SBA–NaCl
M15/SBA
M15/SBA–NaCl
M15/SBA–NaCl
M15/SBA–NaCl
CH3O
Cl
H
H
H
NO2
H
CH3O
Flavanone is an important intermediate in many phar-
maceutical syntheses, and members of the flavanoid fam-
ily were documented to have various pharmacological
activities.[ Flavanones are commonly synthesized by the
recovered by filtration, washed with methanol, and finally
dried at 120 C for one day. The physical properties, tex-
◦
ture, and N content of the treated materials were found to be
almost unchanged (Accessory Materials, Fig. S5). Pure sili-
caceous SBA-15, which had been treated in the same manner
as that described above, was first used in the condensa-
17]
Claisen–Schmidt condensation between benzaldehyde and
ꢀ
2
-hydroxyacetophenone either in basic or acidic media under
[18]
ꢀ
homogeneous conditions. In the past decade, various solid
tion of benzaldehyde and 2 -hydroxyacetophenone, and gave
[19]
[20]
catalysts, such as magnesium oxide,
alumina,
bar-
negligible conversion (<3%). Table 2 shows that the amino-
functionalized silica materials with 15 mol% MAPTMS gave
good conversions of acetophenones B into flavanones D;
these results are the most highly selective reported to date
for the Claisen–Schmidt condensations over various catalysts
with or without solvent. On the other hand, use of M15/SBA–
NaCl resulted in much higher conversions than those for
M15/SBA. This may be because the high surface area and
well ordered mesopores of the former facilitate the diffu-
sion of the reactant and product molecules in liquid-phase
reactions.
ium hydroxides,[ hydrotalcites,
21]
[22]
and natural phosphates
modified with sodium nitrate or with KF,[ have been used
in the synthesis of flavanones. However, most of them require
rathercomplicatedproceduresoruseexpensivetoxicsolvents
to facilitate liquid-phase reactions by improving the heat
and mass transfer characteristics of the system.[ Here, the
extracted M15/SBA-15 materials are used as solid basic cat-
alysts to test the condensation and subsequent intramolecular
Michael addition of substituted acetophenones and benz-
aldehyde derivatives in the absence of solvent. Before the
catalytic reaction, the mesoporous silica was treated with a
23]
19]
After the used M15/SBA–NaCl catalyst was refluxed with
◦
methanol solution of 0.2 M tetramethylammonium hydroxide
CH3OH in a Soxhlet apparatus for 4 h and dried at 100 C
−
(
TMAOH) to remove the residual Cl ions and to neutralize
overnight, the spent catalyst was re-tested in the Claisen–
Schmidt condensation and was found to retain its activity,
the protonated amine groups in the sample. The solid was

5
10
X. Wang and S. Cheng
resulting in 45% conversion of acetophenone and 75% selec-
tivity to flavanone.This result indicates that most of the active
sites could be regenerated by a simple solvent treatment.
To conclude, highly ordered large-pore mesoporous SBA-
[5] A. Walcarius, C. Delacote, Chem. Mater. 2003, 15, 4181.
doi:10.1021/CM031089L
[
6] D. J. Macquarrie, D. B. Jackson, Chem. Commun. 1997, 1781.
doi:10.1039/A704156J
[
7] (a) J. E. Mdoe, G. J. H. Clark, D. J. Macquarrie, Synlett 1998,
1
5 with high loadings of methylaminopropyl groups has been
6
25.
prepared with the addition of NaCl and the aid of TEOS pre-
hydrolysis. The resultant materials are highly efficient in
(b) G. Sartori, F. Bigi, R. Maggi, R. Sartorio, D. J. Macquarrie,
M. Lenarda, L. Storaro, S. Coluccia, G. Martra, J. Catal. 2004,
2
22, 410. doi:10.1016/J.JCAT.2003.11.016
catalyzingthesynthesisofflavanonesfrombenzaldehydeand
[
[
8] D. Brunel, F. Fajula, J. B. Nagy, B. Deroide, M. J. Verhoef,
ꢀ
2
-hydroxyacetophenone in the absence of solvent.
L. Veum, J. A. Peters, H. Van Bekkum, Appl. Catal. A: General
2
001, 213, 73. doi:10.1016/S0926-860X(00)00886-3
9] (a) T. Yokoi, H. Yoshitake, T. Tatsumi, J. Mater. Chem. 2004, 14,
51. doi:10.1039/B310576H
b) S. Huh, J. W. Wiench, J. C.Yoo, M. Pruski, V. S.Y. Lin, Chem.
Mater. 2003, 15, 4247. doi:10.1021/CM0210041
c) S. Sadasivan, D. Khushalani, S. Mann, J. Mater. Chem. 2003,
3, 1023. doi:10.1039/B300851G
Experimental
9
(
In the typical synthesis, Pluronic 123 (P123, 4 g) and NaCl (11 g) were
dissolved in aqueous HCl (2 M; 125 g) with stirring at room temperature.
◦
After TEOS was added, the resultant solution was hydrolyzed at 40 C
(
1
for 2 h, and then [3-(methylamino)propyl]trimethoxysilane was slowly
added to the solution. The molar composition of the mixture was (1 − x)
TEOS : x MAPTMS : 6.1 HCl : 4.7 NaCl : 0.017 P123 : 165 H2O, where
x = 0.15 and 0.20 for samples M15/SBA–NaCl and M20/SBA–NaCl,
[
[
10] D. J. Macquarrie, D. B. Jackson, J. E. G. Mdoe, J. H. Clark,
New J. Chem. 1999, 23, 539. doi:10.1039/A900839J
11] (a) A. S. M. Chong, X. S. Zhao, J. Phys. Chem. B 2003, 107,
◦
respectively.The resultant mixture was stirred at 40 C for 20 h, and then
1
2650. doi:10.1021/JP035877+
◦
heated at 90 C for 24 h under static conditions. The solid product was
(
b) H. H. P. Yiu, P. A. Wright, N. P. Botting, J. Mol. Catal., B
recovered by filtration and dried at room temperature overnight. The
template was removed from the as-synthesized material by refluxing
the latter in ethanol for 24 h. Finally, the material was filtered off again,
Enzym. 2001, 15, 81. doi:10.1016/S1381-1177(01)00011-X
12] (a) X. G. Wang, K. S. K. Lin, J. C. C. Chan, S. Cheng, Chem.
Commun. 2004, 2762. doi:10.1039/B408022J
[
◦
washed several times with water and ethanol, and dried at 50 C. For
(
2
b) X. G. Wang, K. S. K. Lin, J. C. C. Chan, J. Phys. Chem. B
005, 109, 1763. doi:10.1021/JP045798D
comparison, the samples synthesized without the addition of NaCl in the
initial solutions were also prepared and termed M15/SBA and M20/SBA
for x = 0.15 to 0.20, respectively.
[
[
13] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Frederichson, B. F.
Chmelka, G. D. Stucky, Science 1998, 279, 548. doi:10.1126/
SCIENCE.279.5350.548
14] (a) Y. Wang, B. Zibrowius, C. M. Yang, B. Spliethoff, F. Schuth,
Chem. Commun. 2004, 46. doi:10.1039/B309578A
Accessory Materials
Figures showing TEM, SEM, TGA, N2 adsorption–
desorption, and XRD images of M15/SBA–NaCl treated with
TMAOH are available from the author or, until July 2010, the
Australian Journal of Chemistry.
(b) W. Guo, J. Y. Park, M. O. Oh, H. W. Jeong, W. J. Cho, I. Kim,
C. S. Ha, Chem. Mater. 2003, 15, 2295. doi:10.1021/CM0258023
15] S. R. Hall, C. E. Fowler, B. Lebeau, S. Mann, Chem. Commun.
[
[
1
999, 201. doi:10.1039/A809008D
16] C. Yang, B. Zibrowius, F. Schuth, Chem. Commun. 2003, 1772.
doi:10.1039/B304626E
Acknowledgment
[17] S. Makela, M. Poutanen, M. L. Kostian, N. Lehtimaki, L. Strauss,
R. Santti, R. Vihko, Proc. Soc. Exp. Biol. Med. 1998, 217, 310.
This project was supported by the National Science Council,
Taiwan.
[
[
18] (a) J. B. Harbone, T. J. Mabry, H. Mabry, The Flavonoids 1976
(Academic Press: New York, NY).
(
b) D. N. Dahr, The Chemistry of Chalcones and Related Com-
pounds 1981 (Wiley: New York, NY).
References
19] M. T. Drexler, M. D. Amiridis, J. Catal. 2003, 214, 136.
doi:10.1016/S0021-9517(02)00013-1
[
[
[
1] A. P. Wight, M. E. Davis, Chem. Rev. 2002, 102, 3589.
doi:10.1021/CR010334M
2] I. K. Mbaraka, D. R. Radu, V. S.-Y. Lin, B. H. Shanks, J. Catal.
[20] R. S. Varma, G. W. Kabalka, L. T. Evans, R. M. Pagni, Synth.
Commun. 1985, 15, 279.
[21] A. Aguilera, A. R. Alcantara, J. M. Marinas, J. V. Sinisterra, Can.
J. Chem. 1987, 65, 1165.
[22] (a) M. J. Climent, A. Corma, S. Iborra, J. Primo, J. Catal. 1995,
151, 60. doi:10.1006/JCAT.1995.1008
2
003, 219, 329. doi:10.1016/S0021-9517(03)00193-3
3] (a) S. Dai, M. C. Burleigh, Y. Shin, C. C. Morrow, C. E. Barnes,
Z. Xue, Angew. Chem. Int. Ed. 1999, 38, 1235. doi:10.1002/
(
SICI)1521-3773(19990503)38:9<1235::AID-ANIE1235>3.0.
CO;2-X
b) V. S. Y. Lin, C. Y. Lai, J. Huang, S. A. Song, S. Xu, J. Am.
Chem. Soc. 2001, 123, 11510. doi:10.1021/JA016223M
c) C. Baleizão, B. Gigante, D. Das, M. Álvaro, H. Garcia,
A. Corma, J. Catal. 2004, 223, 106. doi:10.1016/J.JCAT.
004.01.016
(b)A. Guida, M. H. Lhouty, D.Tichit, F. Figueras, P. Geneste,Appl.
Catal. A 1997, 164, 251. doi:10.1016/S0926-860X(97)00175-0
(c) M. J. Climent, A. Corma, S. Iborra, J. Primo, J. Catal. 2004,
221, 474. doi:10.1016/J.JCAT.2003.09.012
(
(
[23] (a) S. Sebti, A. Solhy, R. Tahir, S. Abdelatif, S. Boulaajaj,
J. A. Mayoral, J. I. Garcia, J. M. Fraile, A. Kossir, H. Oumimoun,
J. Catal. 2003, 213, 1. doi:10.1016/S0021-9517(02)00017-9
(b) D. J. Macquarrie, R. Nazih, S. Sebti, Green Chem. 2002, 4,
56. doi:10.1039/B109015C
2
[
4] D. Margolese, J. A. Melero, S. C. Christiansen, B. F. Chmelka,
G. D. Stucky, Chem. Mater. 2000, 12, 2448. doi:10.1021/
CM0010304