Mesoporous sodalite: A novel, stable solid catalyst for base-catalyzed organic transformations

Article abstract of DOI:10.1016/j.jcat.2009.03.014

Mesoporous sodalite with a mesoporous/microporous hierarchical structure was successfully synthesized using an organosilane surfactant. It showed about 10-fold high surface area and 4-fold large pore volume, as compared with sodalite with solely microporous structure. The basicity of MPSOD was higher than that of CsNaX or KAlMCM-41. The catalytic activities of this mesoporous zeolite were evaluated for various base catalyzed reactions involving bulky and small substrates, viz. Knoevenagel condensation, Claisen-Schmidt condensation in liquid phase, and acetonylacetone cyclization in vapor phase. The catalyst showed higher activity and longer lifetime than CsNaX and KAlMCM-41.

Full text of DOI:10.1016/j.jcat.2009.03.014

Journal of Catalysis 264 (2009) 88–92
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Research Note
Mesoporous sodalite: A novel, stable solid catalyst for base-catalyzed
organic transformations
*
Ganapati V. Shanbhag, Minkee Choi, Jeongnam Kim, Ryong Ryoo
Center for Functional Nanomaterials and Department of Chemistry, Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology,
Daejeon 305-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Mesoporous sodalite with a mesoporous/microporous hierarchical structure was successfully synthe-
sized using an organosilane surfactant. It showed about 10-fold high surface area and 4-fold large pore
volume, as compared with sodalite with solely microporous structure. The basicity of MPSOD was higher
than that of CsNaX or KAlMCM-41. The catalytic activities of this mesoporous zeolite were evaluated for
various base catalyzed reactions involving bulky and small substrates, viz. Knoevenagel condensation,
Claisen–Schmidt condensation in liquid phase, and acetonylacetone cyclization in vapor phase. The cat-
alyst showed higher activity and longer lifetime than CsNaX and KAlMCM-41.
Received 26 February 2009
Revised 25 March 2009
Accepted 25 March 2009
Available online 26 April 2009
Keywords:
Mesoporous zeolite
Hierarchical
Sodalite
Ó 2009 Elsevier Inc. All rights reserved.
Basicity
Solid base
Knoevenagel
Claisen–Schmidt
Catalyst deactivation
1. Introduction
frameworks by modifications such as covalent grafting of amines
and impregnation of basic metal oxides [11–16]. However, such
The potential applications of heterogeneous base catalysts in
specialty and fine chemical production have expanded significantly
over the years [1–6]. Base-catalyzed condensation, addition, and
isomerization reactions are some of the important steps for build-
ing large and complex molecules for the synthesis of many fine
chemicals and pharmaceutical products. Basic solids such as Cs-
ZSM-5 and MgO have been used as catalysts in industrial processes
due to their activity, thermal stability, and reusability [7,8]. While
metal ion-exchanged zeolites possess basic sites of relatively low
strength, they can be easily regenerated from poisoning by air, as
compared with strong solid bases, such as alkaline earth oxides
[9]. Nevertheless, applications of basic zeolites are limited by slow
diffusion of substrates into their micropores for bulky molecular
reactions and rapid deactivation due to coke formation [10]. In
principle, alkali metals can be ion exchanged onto MCM-41-like
mesoporous aluminosilicate for application as a basic catalyst for
bulky substrates. However, mesoporous materials built with amor-
phous frameworks have serious drawbacks due to weak basicity
and low hydrothermal stability. Stronger basicity can be induced
in materials like mesoporous aluminosilicates and metal-organic
modified catalysts also carry limitations such as low hydrothermal
stability and leaching of active species, preventing them from find-
ing practical applications.
Among the various strategies to synthesize mesoporous zeo-
lites, very few were successful in obtaining high crystallinity with
tunable mesoporosity. In one such work, Choi et al. reported a di-
rect synthesis route to mesoporous zeolites with a tunable meso-
porous structure using amphiphilic organosilane surfactants as a
mesopore-directing agent [17]. The mesoporous MFI zeolite thus
synthesized exhibited much higher catalytic activities for the
conversion of bulky molecules than a conventional MFI zeolite,
providing evidence that the catalytic conversion occurred at the
mesopore walls [18]. In catalytic reactions involving small mole-
cules, these two kinds of zeolites initially showed no significant
difference, but the mesoporous zeolite exhibited remarkably
improved catalytic lifetimes. However, the successful catalytic
application has mostly been limited to high silica mesoporous
MFI zeolites, which are useful for acid-catalyzed reactions. It is
therefore of interest to develop a high aluminum-containing
mesoporous zeolite with a basicity similar to the existing basic
zeolites. Sodalite is a zeolite with high aluminum content (Si/
Al = 1) and high stability in basic solution. However, it thus far
has not found any significant catalytic applications due to its inac-
cessible cages with small pore openings (2.8 Å).
* Corresponding author. Fax: +82 42 350 8130.
E-mail address: rryoo@kaist.ac.kr (R. Ryoo).
0021-9517/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2009.03.014

G.V. Shanbhag et al. / Journal of Catalysis 264 (2009) 88–92
89
In the previous works, we had successfully synthesized meso-
2.3. Catalyst characterization
porous zeolites and zeolite-type solids such as MFI, BEA, LTA, and
AlPO via direct hydrothermal assembly methods [17–21]. In this
study, we report a new basic solid catalyst, viz. mesoporous soda-
lite with high aluminum content and highly crystalline zeolitic
walls. This basic mesoporous zeolite was synthesized using an
amphiphilc organosilane surfactant, followed by ion exchange with
K+. The catalytic activity was compared with that of a basic alkali-
exchanged NaX and NaAlMCM-41 (Si/Al = 1) for reactions involv-
ing bulky and small substrates. The K+-exchanged mesoporous
sodalite has been studied in detail, since K+ salts are inexpensive
and have better exchange ability than Cs+ salts. The mesoporous
sodalite was tested in C–C bond-forming reactions in liquid phase,
which involved bulky substrates. Knoevenagel condensation is a
key step in the preparation of several pharmaceutics including
the antimalarial drug lumefantrine, whereas Claisen–Schmidt con-
densation products such as 20-hydroxychalcone and flavanone
derivatives are used in the synthesis of anti-inflammatory, anti-
allergic, and anti-cancer drugs [22,23]. The catalyst has been fur-
ther tested in vapor phase intramolecular aldol condensation of
acetonylacetone to form a cyclopentenone derivative as the major
product. Cyclopentenone derivatives are used as intermediates in
the synthesis of perfumes and antibiotics [24].
X-ray diffraction (XRD) patterns were recorded with a Rigaku
Multiflex diffractometer equipped with Cu K radiation (40 kV,
a
40 mA). The textural properties of the samples were measured by
N2 sorption at liquid nitrogen temperature with a Quantachrome
AS-1MP volumetric adsorption analyzer. Samples were dried at
573 K in a dynamic vacuum for 2 h before the N2 physisorption
measurements. The specific surface area was determined using
the standard BET method on the basis of adsorption data. The pore
size distributions were calculated from both the adsorption and
desorption branches of the isotherms using the BJH method and
the Kelvin equation. Elemental analyses were performed by induc-
tively coupled plasma spectroscopy (ICP) using an OPTIMA 4300
DV (Perkin–Elmer) instrument. Nitrogen content was measured
by an elemental analyzer, EA-110 (Thermo Finnigan). Transmission
electron micrograph (TEM) images were obtained with a Tecnai G2
F30 microscope at an operating voltage of 300 kV. Scanning elec-
tron microscopy (SEM) was conducted using a Hitachi S-4800
microscope operating at 2 kV without a metal coating. 27Al MAS–
NMR spectra were recorded on a Bruker AM-300 NMR spectro-
meter (see Supplementary information (hereafter SI) for details).
Basicity measurements were carried out by TPD of adsorbed CO2
using a Belcat-M instrument (see SI).
2. Experimental
2.4. Catalytic activity measurements
2.1. Synthesis of catalysts
Knoevenagel condensation of 4-isopropylbenzaldehyde (4-IPB)
with ethylcyanoacetate (ECA) was carried out in a Pyrex reactor
equipped with a reflux condenser (Eyela Chemistation) under a
N2 atmosphere to prevent the oxidation of aldehyde. No solvent
was used in the reaction. In a typical reaction, 10 mmol of 4-IPB
and 10 mmol of ECA were mixed with 0.05 g of catalyst and stirred
at 353 K. The products were analyzed by an Acme 6100 gas chro-
matograph fitted with a flame ionization detector and a HP-1 cap-
illary column.
A highly crystalline mesoporous sodalite was synthesized by
mixing an organosilane [(CH3O)3SiC3H6N(CH3)2C16H33]Cl (51.5
wt% methanol solution) with sodium metasilicate (Na2SiO3.9H2O),
sodium aluminate (53% Al2O3, 43% Na2O), NaOH, and H2O to
achieve a gel composition of 1.7 SiO2/15 Na2O/1 Al2O3/80 H2O/0.3
organosilane in mole ratio. The gel was heated at 423 K for 6 h in
a tumbling autoclave for precipitation of sodalite. The zeolite prod-
uct was collected by filtration, and washed with hot distilled water
until the pH of the filtrate was neutral. The product was then dried
and calcined in air at 823 K. This sample is designated by MPSOD.
Another sample of mesoporous sodalite was synthesized with a
gel composition of 1.5 SiO2/20 Na2O/1 Al2O3/160 H2O/0.5 organos-
ilane, by following the same hydrothermal procedure as MPSOD ex-
cept for 373 K. This sample was denoted as MPSOD-1. A third
sample of sodalite was synthesized by the same procedure as for
MPSOD, except that the organosilane surfactant was not used. This
sample without mesoporosity is denoted as SOD. NaAlMCM-41
with Si/Al = 1 was synthesized according to the procedure reported
elsewhere [25]. NaX zeolite was procured from Aldrich.
Claisen–Schmidt condensation of 20-hydroxyacetophenone (2-
HAcPh) with benzaldehyde was carried out in a Pyrex reactor
under N2 atmosphere. Five millimole of 2-HAcPh and 10 mmol of
benzaldehyde were heated at 423 K with 0.05 g of the catalyst.
After the reaction, the reaction mixture was diluted with 2 ml of
THF to confirm the dissolution of all the components, and was then
analyzed as described above.
Vapor phase cyclization of acetonylacetone (AcAc) was con-
ducted in a fixed bed, down flow reactor using 0.5 g of catalyst pel-
lets (20–35 mesh). The catalyst was pre-activated in a flow of air at
773 K for 2 h, and then cooled down to the reaction temperature.
High purity N2 (30 ml minꢀ1) was used as a carrier gas. The feed
(AcAc) was vaporized before passing into the reactor. The product
was analyzed with an Acme 6100 gas chromatograph fitted with
2.2. Cation exchange of catalysts
Supelco
a-Dex225 capillary column. Products of all the above-
Cation exchange of Na-form of all the catalyst samples was per-
formed with 0.5 M chloride solutions of K+ or Cs+. One gram of the
powder was stirred with 10 ml of the solution at 353 K for 3 h. The
resultant mixture was then cooled to RT, filtered, and washed
repeatedly with distilled water until it was free from Clꢀ and phys-
isorbed metal ions. This procedure was performed three times in
all to ensure maximum cation exchange. The resulting exchanged
materials, i.e., K+-exchanged MPSOD (hereafter KMPSOD), K+-ex-
changed microporous sodalite (KSOD), KAlMCM-41, and CsNaX,
were dried at 403 K for 12 h. They were subsequently calcined in
static air at 773 K for 4 h except for KAlMCM-41 (containing tem-
plate), which was calcined by a previously reported procedure [26].
Besides, as synthesized AlMCM-41 was used for cation exchange
since the calcined sample was not stable under the applied exper-
imental conditions.
mentioned reactions were identified with authentic samples and
GC combined with mass spectroscopy.
3. Results and discussion
3.1. Catalyst characterization
The percentage compositions of different metal ions present in
the catalyst are listed in Table 1. Nitrogen content was measured
by elemental analysis, and the result indicated that the N-contain-
ing groups (from the organosilane) were completely removed by
the work-up and calcination steps. Wide angle XRD patterns of
MPSOD and MPSOD-1 consisted of peaks that were typical of
microporous sodalite (Fig. 1B). The two prominent peaks at

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G.V. Shanbhag et al. / Journal of Catalysis 264 (2009) 88–92
Table 1
by-product. Therefore, in the following catalytic investigations, we
Physicochemical properties of the catalysts.
focused on the MPSOD sample which possessed high surface area
as well as sufficiently high stability. SEM images of KMPSOD
revealed the presence of particles of spherical morphology with
Catalyst
Si/Ala
M+ contenta (mol%)
SBET (m2 gꢀ1
)
Vpb (ml gꢀ1
)
Na
K
Cs
an average diameter of 1
[Fig. 2(c) and (d)].
lm, much smaller than that of KSOD
MPSOD
1.1
1.0
1.1
1.0
1.1
1.2
100
100
26
85
05
–
–
74
15
95
–
—
–
–
–
–
193
850
182
19
310
350
0.42
1.12
0.38
0.10
0.32
0.19
MPSOD-1
KMPSOD
KSOD
KAlMCM-41
CsNaX
27Al solid state MAS NMR spectra of MPSOD-1 and KMPSOD in a
fully rehydrated state after calcination at 823 K are depicted in
Fig. S2 (SI). The 27Al NMR spectra show two peaks. A peak at
ꢁ55 ppm is the tetrahedral Al signal. The second peak appearing
at ꢁ0 ppm with lower intensity is assigned to the octahedral Al
in the form of extra-framework species or the framework Al spe-
cies located at the defect sites. The spectra of MPSOD-1 and KMP-
SOD contained a major peak at 55 ppm and a negligibly small peak
at 0 ppm, which indicated that most of the Al atoms were located
inside the zeolite framework.
47
53
a
Determined by ICP analysis.
Total pore volume obtained at P/Po = 0.95.
b
2h = 13.9° and 24.3° represented (110) and (211) crystal planes,
respectively. XRD peak widths of mesoporous sodalite samples
were markedly broader than those of ordinary sodalite crystals,
which indicated a highly nanocrystalline nature of the framework.
Among the two mesoporous sodalite samples, MPSOD-1 showed
much broader XRD peaks, signifying that the material was built
with a thin sodalite framework. Notably, MPSOD-1 exhibited a sin-
gle broad peak in the low-angle XRD pattern [Fig. 1A(a)], indicating
a higher structural correlation in the mesopore arrangement. The
XRD pattern of KMPSOD suggested that the sodalite structure
was retained after ion exchange and calcination steps [Fig. 1B(c)].
N2-sorption measurements of MPSOD and MPSOD-1 samples
exhibited type IV isotherms with a H1-type hysteresis loop, which
was typical of mesoporous solids (Fig. 1C). Table 1 represents the
structural and textural properties of the materials. The higher spe-
cific surface area and larger pore volume were attributed to the
presence of highly mesoporous structures in the MPSOD and
MPSOD-1. The KMPSOD catalyst showed about 10-fold higher sur-
CO2 is often used as a probe molecule in TPD due to its small
size, good thermal stability, and weak acidic character. The amount
of desorbed CO2 and the temperature of maximum desorption of
CO2 are the criteria for the concentration and strength of basic
sites, respectively. The basicity data of the catalysts are presented
in Fig. 1D. While the total basicity of MPSOD after K+ exchange
remained unchanged (109 l
mol gꢀ1), the basic strength increased
as expected. The temperature of peak maximum of CO2 desorption
indicated that the basic strength of KMPSOD was greater than that
of KAlMCM-41 (553 and 473 K, respectively). The intrinsic basicity
of porous materials depends on the framework oxygen atoms bear-
ing negative charges. The electron density on these oxygen atoms
is a measure of basic strength, which depends on porous structure,
nature of cations, and their location. Al sites of KAlMCM-41 are lo-
cated on amorphous mesopore walls, whereas in KMPSOD they are
situated mostly on crystalline mesopore walls. It is worth noting
that the temperature of peak maximum for KMPSOD (553 K) was
slightly higher than that of CsNaX (508 K).
face area (182 m2 gꢀ1) and 4-fold larger pore volume (0.38 ml gꢀ1
)
than KSOD (19 m2 gꢀ1and 0.1 ml gꢀ1). A small decrease in the sur-
face area of MPSOD after ion exchange was attributed to an in-
crease in the weight of the sample when Na+ ions were replaced
with K+.
3.1.1. Catalytic activity study
Knoevenagel condensation of 4-IPB with ECA is catalyzed by
mild basic catalysts. The activity of KMPSOD was compared with
that of KAlMCM-41 and CsNaX which contained similar Si/Al ratios
but differed in pore size, pore structure, and basicity. The activity
and selectivity of the catalysts are listed in Table S1 (SI). KMPSOD
was the most active catalyst (78%) followed by MPSOD (70%), KAl-
MCM-41 (46%), and CsNaX (35%) after 1 h reaction. The higher
activity of KMPSOD was attributed to the basic sites located in
TEM images [Fig. 2(a) and (b)] revealed that both MPSOD and
MPSOD-1 possessed disordered mesoporous structures. The
MPSOD-1 sample was built with a much thinner framework
(2.5 nm) than the MPSOD sample (8 nm). The thin framework of
MPSOD-1 provided the highest surface area and pore volume
among the three sodalite samples. Unfortunately, this thin frame-
work collapsed under the reaction conditions generating water as a
Fig. 1. (A) Low-angle and (B) wide angle XRD patterns: (a) MPSOD-1, (b) MPSOD, (c) KMPSOD, and (d) KSOD. (C) N2 sorption isotherms: (a) MPSOD-1, (b) KMPSOD, and (c)
KSOD. Inset: Pore size distribution. (D) TPD profiles of CO2 desorption: (a) MPSOD, (b) KMPSOD, (c) KAlMCM-41, and (d) CsNaX. The data on each plot represent the total
basicity in l .
mol gꢀ1

G.V. Shanbhag et al. / Journal of Catalysis 264 (2009) 88–92
91
Fig. 2. TEM images: (a) MPSOD, and (b) MPSOD-1. SEM images: (c) KMPSOD, and (d) KSOD.
their mesopores, which facilitated the diffusion of bulky molecules.
On the other hand, CsNaX showed comparatively low activity, as
expected, since the bulky product should be formed not at the ba-
sic sites located inside the cavities, but preferentially at the sparse
sites situated on the zeolite external surface. KAlMCM-41 showed
a higher activity than CsNaX, but its structure collapsed as a result
of the water produced during the reaction, as evident by XRD.
Although KAlMCM-41 contained a high number of basic sites (Si/
Al = 1.1), it exhibited a poor hydrothermal stability, whereas KMP-
SOD showed a good recyclability and retained its structural charac-
teristics even after 3 cycles.
The condensation of 2-HAcPh and benzaldehyde involves Clais-
en–Schmidt condensation in the first step to yield 20-hydroxychal-
cone, followed by isomerization and ring closure to give flavanone.
This reaction requires a catalyst having moderate basicity. KMP-
SOD showed high activity (67% conversion) and good selectivity
for flavanone (52%) after 5 h of reaction, exceeding CsNaX and KAl-
MCM-41 as shown in Table S2 (SI). The higher activity of KMPSOD
in this case is due to its mesoporous structure as well as moderate
basicity. KAlMCM-41 though contains mesopores, its lower activity
can be attributed to its relatively weak basicity.
Solid base-catalyzed vapor phase condensation of AcAc involves
intramolecular aldol condensation and cyclization to give 3-
methyl-2-cyclopenten-1-one (ketone) as the major product and
2,5-dimethylfuran (ether) as the minor product. Apart from com-
mercial importance, this reaction is also studied to identify the
basicity present in the catalyst containing acid base pairs [27].
The reaction was carried out in a down flow reactor at 623 K with
WHSV 1.9 hꢀ1. This reaction also involves smaller organic mole-
cules that are easily formed and diffused through the micropores
of large pore zeolites such as CsNaX. The blank experiment gave
5% conversion with 0% selectivity for ketone at 1 h. The KMPSOD
catalyst converted 91% of AcAc into products: ketone (88%) and
ether (4%) at 2 h. The high selectivity for ketone reflected the basic
character of KMPSOD, since the product, ketone, was formed by
base catalysis [27]. All the catalysts exhibited some level of deacti-
vation, which was evident by a loss in the conversion with time on
stream. During the initial period of reaction (at 1 h), the activities
of KMPSOD and CsNaX were almost the same (ꢁ90%) (Fig. 3).
Fig. 3. Vapor phase condensation of acetonylacetone with different catalysts.
Conversion: KMPSOD (j), CsNaX (d), and KAlMCM-41 (
with KMPSOD: ketone (w) and ether (q). Reaction conditions: temperature = 623 K,
WHSV = 1.9 hꢀ1
N
). Selectivity obtained
.
While KMPSOD showed a slow deactivation with time (conversion
decreased to 75% in 7 h), the activity of CsNaX decreased rapidly
with time (conversion dropped to 11% in 7 h). The retention of
activity of mesoporous sodalite for a longer period can be attrib-
uted to the facile diffusion of the products from its mesopores. In
contrast, for microporous zeolites, such as CsNaX, the organic com-
pounds undergo side reactions, leading to coke formation inside
the channels which blocks the active sites. Moreover, the activity
of KAlMCM-41 decreased rapidly than that of KMPSOD. The KAl-
MCM-41 catalyst showed a 90% loss of small angle XRD peaks
when measured after the reaction. As indicated by this change,
the catalytic deactivation of KAlMCM-41 seemed to be due to the

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G.V. Shanbhag et al. / Journal of Catalysis 264 (2009) 88–92
collapse of the mesoporous structure during the water-generating
reaction.
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The mesoporous sodalite investigated in this study contains
mesoporous–microporous hierarchical structure. It showed about
10-fold higher surface area and 4-fold larger pore volume than
microporous sodalite. The basicity of the mesoporous sodalite
was higher than that of CsNaX or KAlMCM-41 when compared un-
der similar Al concentrations. The mesoporous sodalite showed
high catalytic activity with good recyclability in liquid phase Knoe-
venagel condensation and Claisen–Schmidt condensation reac-
tions. It also exhibited high activity and stability toward
deactivation in a vapor phase acetonylacetone condensation reac-
tion and therefore could be used for longer reaction time, whereas
CsNaX deactivated rapidly due to coke formation. In conclusion,
mesoporous sodalite is a stable and versatile basic catalyst for a
range of bulky and small molecular reactions. Given its now estab-
lished physicochemical properties, it can also be used as a stable
support for further surface modifications, which will expand its
applicability.
Acknowledgement
This work was supported by National Honor Scientist Program
of the Ministry of Education, Science and Technology in Korea.
Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jcat.2009.03.014.