Facile preparation of extra-large pore zeolite ITQ-37 based on supramolecular assemblies as structure-directing agents

Article abstract of DOI:10.1039/c5ce02312b

The chiral germanosilicate zeolite ITQ-37 was prepared using a readily-obtained, semi-rigid achiral organic structure-directing agent (SDA) 1,1′,1′′-(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)tris-(3-methyl-1H-imidazol-3-ium) (denoted tmbi). The synthetic factors, including crystallization temperature, water content, germanium and tmbi concentrations for the crystallization of ITQ-37, were studied by means of single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, liquid and ¹³C/¹⁹F/²⁹Si solid NMR and photoluminescence spectroscopy. The results showed that high Ge content, high tmbi concentration and low temperature (150 °C) conditions favor the formation of extra-large pore ITQ-37 when supramolecular interactions between tmbi molecules occur. On the other hand, a much diluted tmbi solution and a higher reaction temperature favor the crystallization of an unknown lamellar phase, wherein tmbi is present as monomers. These studies revealed that supramolecular assemblies of tmbi were formed during the zeolite synthesis and acted as SDAs for crystallization of ITQ-37, providing a general and applicable strategy for synthesizing large and extra-large pore zeolites. The Royal Society of Chemistry.

Full text of DOI:10.1039/c5ce02312b

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Facile preparation of extra-large pore zeolite ITQ-
37 based on supramolecular assemblies as
structure-directing agents†
Cite this: CrystEngComm, 2016, 18,
2735
a
b
c
a
Fei-Jian Chen,ab Zi-Hao Gao, Li-Li Liang, Jun Zhang and Hong-Bin Du
*
The chiral germanosilicate zeolite ITQ-37 was prepared using a readily-obtained, semi-rigid achiral organic
structure-directing agent (SDA) 1,1′,1″-(2,4,6-trimethylbenzene-1,3,5-triyl)trisIJmethylene)tris-(3-methyl-1H-
imidazol-3-ium) (denoted tmbi). The synthetic factors, including crystallization temperature, water content,
germanium and tmbi concentrations for the crystallization of ITQ-37, were studied by means of single
crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, liquid and 13C/19F/29Si solid
NMR and photoluminescence spectroscopy. The results showed that high Ge content, high tmbi concen-
tration and low temperature (150 °C) conditions favor the formation of extra-large pore ITQ-37 when su-
pramolecular interactions between tmbi molecules occur. On the other hand, a much diluted tmbi solution
and a higher reaction temperature favor the crystallization of an unknown lamellar phase, wherein tmbi is
present as monomers. These studies revealed that supramolecular assemblies of tmbi were formed during
the zeolite synthesis and acted as SDAs for crystallization of ITQ-37, providing a general and applicable
strategy for synthesizing large and extra-large pore zeolites.
Received 27th November 2015,
Accepted 4th March 2016
DOI: 10.1039/c5ce02312b
www.rsc.org/crystengcomm
be a key to the synthesis of large and extra-large pore zeo-
lites.8,9 A number of germanosilicate zeolites have recently
Introduction
Large pore (consisting of 12 tetrahedra, 12R) and extra-large
pore (consisting of more than 12 tetrahedra) zeolites have
attracted considerable interest because of their potential uses
in hydrocracking of heavy oil fractions,1,2 facilitating the pro-
duction of fine chemicals and biomass processes,3 preparing
materials in microelectronics with low values of the high-
frequency dielectric constant,4 manufacturing encapsulated
light-emitting devices (LEDs)5 and in medicine for diagnostic
treatments and controlled drug delivery.6 Although they are
still limited in number, the past decade has witnessed the mi-
raculous development and prosperity of the large and extra-
large pore zeolites, owing to the use of germanium in the con-
centrated fluoride system during the synthesis.7 The presence
of Ge and/or F aids the formation of the 3-membered ring
(3R) or double-4-membered ring (D4R), which is thought to
been synthesized, which constitute a very important group of
zeolites. Although most germanosilicates are unstable after re-
moving the organic templates at high temperature owing to
the easy hydrolysis of the Ge–O bonds, post-synthetic modifi-
cations by isomorphous substitution of Al or Si for Ge has
been successfully applied to some germanosilicates to yield
highly stable aluminosilicate or siliceous zeolites.10–12
In addition to Ge and F, organic cations, such as quater-
nary ammonium, known as structure-directing agents (SDAs),
also play an important, and in most cases, decisive role in
the formation of zeolites with special structural topology.
Studies show that the shape, size, rigidity, hydrophilicity, and
charge, as well as some other features of SDAs all make im-
portant impacts on their structure-directing roles. Therefore,
many efforts have been made to rationally design suitable
SDAs for zeolite synthesis.13
The rigidity of the SDA makes an impact on zeolite synthe-
sis. Flexible SDAs usually have good structure-directing ef-
fects and have been widely used for crystallizing zeolites13 as
they can easily adopt various conformations to fit the chan-
nels of zeolites. For instance, hexamethonium has been suc-
cessfully used to synthesize EU-1,14 ZSM-48,15 ITQ-13,16 ITQ-
17,17 IM-10,18 ITQ-22,19 ITQ-24,20 EMM-3 (ref. 21) and ITQ-
33.22 The drawback of flexible SDAs is, however, the lack of
structure-directing specificity for a particular zeolite. As a re-
sult, they often result in a mixture of different structures,
a State Key Laboratory of Coordination Chemistry, Collaborative Innovation
Center of Chemistry for Life Sciences, School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing, 210023, China.
E-mail: hbdu@nju.edu.cn
b Department of Chemistry, Bengbu Medical College, Bengbu 233030, PR China
c School of Materials and Chemical Engineering, Anhui University of Architecture,
Hefei, 230601, China
† Electronic supplementary information (ESI) available: TGA curves, PXRD, N2
sorption isotherms, crystallographic information data and file (CIF). CCDC
1437990. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c5ce02312b
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which makes it very difficult to separate and characterize
them. This is contrary to rigid SDAs, which are often of
higher specificity for directing the formation of a particular
zeolite structure. However, the rigid SDAs have their own lim-
itations because steric hindrance makes them less successful
in synthesizing zeolites. For the synthesis of large and extra-
large pore zeolites, a rigid and bulky SDA with an appropriate
polarity/hydrophilicity is usually required7 because in most
cases it acts as the space-filling agent to fill the voids of large
pores.23 However, there are some limitations for using bulky
SDAs in zeolite synthesis. First, bulky SDAs are not readily
available and are expensive; their preparations are tedious
and often involve multi-step reactions with low yields. Sec-
ond, as the size of an SDA increases, its hydrophobicity often
increases, which limits its solubility and thus results in the
formation of an amorphous phase during zeolite synthesis.24
ITQ-37 has so far the largest 30R (30-membered ring)
channel and is also the first chiral germanosilicate zeolite,25
which has long been sought after because it could be used to
Fig. 2 Synthesis of tmbiBr3.
mmol), paraformaldehyde (12.60 g, 420 mmol), sodium bro-
mide (74.08 g, 720 mmol), and acetic acid (96 mL), which
was first stirred at 60 °C for 2h and then the temperature was
slowly increased to 90–95 °C; the mixture was allowed to
stand overnight and then poured into water (2.0 L) at room
temperature. The white solid product was filtered, dried in vac-
uum, and recrystallized by ether-dichloromethane (1: 1 v/v) to
afford 34.13 g of product (94% yield). 1H NMR (500 MHz;
CDCl3, ppm): 2.46 (s, 9H, −CH3), 4.57 (s, 6H, −CH2). 13C NMR
(125 MHz; CDCl3, ppm): 15.3, 29.9, 133.4, and 138.1.
perform
shape-selective,
asymmetric
catalysis
and
The precursor tmbBr reacts with stoichiometric 1-methyl-
1H-imidazole under reflux in tetrahydrofuran for 2 d, to yield
the bromide salt of 1,1′,1″-(2,4,6-trimethylbenzene-1,3,5-triyl)-
separation.26–28 The SDA for ITQ-37 used by Corma et al.
(SDA1, Fig. 1) is a rigid, bulky and chiral quaternary ammo-
nium salt. The synthesis of SDA1 involves multi-step reac-
tions and a very long reaction time with a low total yield
(35%).25 Yu et al.29 successfully synthesized the chiral ITQ-37
using an achiral, yet asymmetric, SDA (SDA2, Fig. 1). Al-
though there are no chiral atoms within it, SDA2 is not com-
mercially available and its precursors are expensive. In this
study, we use a semi-rigid imidazolium, namely, 1,1′,1″-(2,4,6-
trimethylbenzene-1,3,5-triyl)-trisIJmethylene)trisIJ3-methyl-1H-
imidazol-3-ium) (denoted tmbi, Fig. 2), which is easily
obtained from inexpensive raw materials, as an efficient SDA
for ITQ-37 crystallization. It is noted that one isomer of tmbi
has previously been successfully applied in directing the crys-
tallization of zeolites LTA and ITQ-24.30 Herein, we show that
supramolecular self-assemblies of tmbi were formed during
the synthesis and acted as SDAs for crystallization of extra-
large pore ITQ-37, which provides a general strategy for syn-
thesizing extra-large pore zeolites.
trisIJmethylene)trisIJ3-methyl-1H-imidazol-3-ium)
(denoted
tmbiBr3) as a white precipitate (yield 96%). ESI-MS: M-Br
(m/z: 562.34, 30%), (M-2Br)/2 (m/z: 241.22, 55%), (M-3Br)/3
(m/z: 134.18, 100%).
The template tmbiBr3 was converted into the correspond-
ing hydroxides tmbiIJOH)3 by anion exchange. The final con-
centration of the hydroxide solution was determined by titra-
tion with HCl with phenolphthalein as the indicator.
Zeolite synthesis
Unless otherwise stated, all the SDAs were used in OH− forms
for zeolite synthesis. In a typical synthesis of ITQ-37, 0.2615 g
(2.5 mmol) of GeO2 (Sigma-Aldrich, >98%) were added to a
2.5 mmol (based on OH− concentration) SDAOH solution and
stirred for half an hour. Then, 0.7315 g (2.5 mmol) of tetra-
ethylorthosilicate (TEOS, Sigma-Aldrich, >99%) were added
to the solution. After the mixture was stirred for 2 h for ade-
quate hydrolysis of the TEOS, 0.1250 g (2.5 mmol) of HF solu-
tion (40 wt%) were added. The mixture was allowed to reach
the desired water ratio by evaporation of ethanol and some
water at 80 °C. The obtained gel (1.0224 g) with a molar com-
position of 1SiO2 : 1GeO2 : 1SDA1/3(OH) : 1HF : 3H2O was trans-
ferred into a 15 mL Teflon lined vessel in a steel autoclave
and heated at 150 or 175 °C in static conditions for 15 days.
The final powder was filtered, washed with distilled water
and ethanol, and dried in air.
Experimental
Synthesis of the SDAs
1,3,5-TrisIJbromomethyl)-2,4,6-trimethylbenzene
(denoted
tmbBr) was synthesized by a modified procedure reported by
Alexander et al.31 As shown in Fig. 2, typically, a mixture of
concentrated sulfuric acid and acetic acid (1 : 1 v/v, 90 mL)
was added dropwise to a mixture of mesitylene (12.48 mL, 90
Characterization
Elemental analyses of C, H, and N were performed on an
Elementar Vario MICRO Elemental Analyzer. The inductively
coupled plasma (ICP) analysis was carried out on a Perkin-
Elmer Optima 3300 DV. Powder X-ray diffraction (PXRD) data
were collected on a Bruker D8 Advance instrument using Cu-
Fig. 1 SDAs used for synthesis of ITQ-37.
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Table 1 Survey of zeolite synthesis with tmbi as an SDA
Kα1 radiation (λ = 1.54056 Å) at room temperature. Scanning
electron microscopy (SEM) images of the products were
obtained on a field emission scanning electron microanalyser
(Hitachi S-4800), employing an accelerating voltage of 10 kV.
Electrospray ionization mass spectrometry (ESI-MS) was
recorded in positive ion mode (LC–ESI-MS, ThermoQuestLCQ
Duo, USA) without a liquid chromatography (LC) process.
Fluorescence measurements were performed on a FluoroMax-
4 spectrofluorometer with a 3 nm slit. Thermogravimetric
(TG) analyses were performed on a Perkin-Elmer thermal ana-
lyzer under air with a heating rate of 5 °C min−1. A Micro-
meritics ASAP 2020 surface area porosimetry system was used
to measure N2 gas adsorption at 77 K. Solid state NMR spec-
tra were obtained on a Bruker Av-400 spectrometer using the
magic-angle spinning (MAS) technique at room temperature.
19F spectra were obtained using a Bruker Av-400 spectrometer
at 376.47 MHz in 4.0 mm diameter zirconia rotors at a spin-
ning rate of 14 kHz. The spectra were obtained using 2.1 μs
pulses, which correspond to a magnetization flip angle of π/2
rad and a recycle delay of 15 s. The spectra were referenced
to CFCl3. The 13C spectra were obtained at a 100.62 MHz res-
Ge/Si
Si/OH− H2O/Si
1
3
0.5
3
0.2
5
10
5
10
3
5
10
2
2
1
1
150 °C ITQ-37 U1
175 °C ITQ-37
150 °C ITQ-37 ITQ-37
175 °C ITQ-37
U1
—
—
—
—
—
U1
—
U1
—
—
—
—
—
—
—
—
—
—
—
—
—
—
ITQ-37 ITQ-37 U1
ITQ-37
—
—
—
“—” represents an amorphous phase.
the water content or decreasing the Ge content, however, an
unknown phase, U1, which appeared to be a lamellar phase
(as shown in Fig. 3) was formed at 150 °C and an amorphous
phase was obtained at 175 °C. On the other hand, when the
syntheses were carried out with a higher concentration of
tmbi, i.e. Si/OH− = 1 (Table 1), ITQ-37 was obtained in a
broader range of synthetic conditions, e.g. under lower Ge
concentration and higher water content. The phase U1 was
only formed at conditions of Ge/Si = 0.5 and H2O/Si = 10 at
150 °C, whereas the other systems with low Ge concentration
and very high water content led to the formation of amor-
phous phases. It is clear that a high concentration of tmbi, a
higher Ge content, and much less water content together
with a lower temperature (150 °C) favor the formation of the
extra-large pore zeolite ITQ-37.
1
onance frequency using a CP-MAS sequence, with a 3.0 μs H
excitation pulse, 2.0 ms contact time, 5 s recycle delay and
100 kHz spectral width, using proton decoupling at 60 kHz
spinal-64 during acquisition. The 29Si spectra were obtained
at a resonance frequency of 79.49 MHz with a π/2 pulse at 56
kHz, spectral width of 100 kHz and a 150 s relaxation delay.
X-ray crystal structure determination. The data collections
for single crystal X-ray diffraction were carried out on a
Bruker Smart APEX II CCD diffractometer at 296 K, using
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å).
Data reduction and absorption correction were performed
using the SAINT and SADABS programs,32 respectively. The
structures were solved by direct methods using the SHELXS-
97 program and refined with full-matrix least squares on F2
using the SHELXL-97 program.33 All non-hydrogen atoms
were refined anisotropically and the hydrogen atoms were
placed in geometrically calculated positions and refined
using the riding model.
Characterization of ITQ-37
As shown in Fig. 4, the powder XRD patterns of the as-
synthesized ITQ-37 are consistent with the simulated one
based on the reported crystal structure data,25 proving that
the as-synthesized ITQ-37 is a pure phase.
19F MAS NMR spectra of both ITQ-37 and U1 (Fig. 5) show
strong resonance bands at −7.8 ppm for ITQ-37 and −8.3
ppm for U1, characteristic of fluoride anions entrapped in
germanium-rich double-4-rings (D4R).34 Another band at
Results and discussion
Crystallization of ITQ-37
Zeolite syntheses were carried out in the presence of Ge and
F because both are thought to be beneficial for the formation
of large and extra-large pore zeolites.8,9 The typical gel molar
compositions are in the form of 1SiO2 : xGeO2 : ySDA1/3(OH) :
yHF: zH2O, where x = 1, 0.5, 0.2; y = 1, 0.5; z = 3, 5, 10. The
crystallization occurred at either 150 °C or 175 °C for up to
45 d. In addition to crystallization temperature, the effects of
water content, germanium and SDA concentrations were
studied. Table 1 lists various synthetic parameters that we
have surveyed using the designed SDA.
As shown in Table 1, when Si/OH− is 2, ITQ-37 can be pro-
duced only with a high Ge content (Si/Ge = 1) and a low water
content (H2O/Si = 3) either at 150 or 175 °C. Upon increasing
Fig. 3 XRD pattern and SEM image of as-synthesized phase U1.
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charge-balancing counterparts for the tmbi cations. The pres-
ence of the strong peak owing to the mobile fluoride in the
as-synthesized ITQ-37 is different from that of Corma's ITQ-
37 (ref. 25) and implies that there were many more fluorides
in our as-synthesized ITQ-37, which may be attributed to the
use of the tmbi tri-cations.
The solid-state 13C NMR spectra of the as-synthesized
ITQ-37 and U1 are in good agreement with that of the liq-
uid tmbi (Fig. 6), indicating that the organic tmbi cations
are maintained intact in both products. In comparison to
that of the liquid, however, peak broadening in both mate-
rials occurred. Such a phenomenon usually occurs in the
solid state, which arises from decreased mobility of the
tmbi molecule within the framework due to steric restric-
tions or some strong intermolecular interactions.36 In U1,
peak splittings for C1 and C3 are observed, which indicate
that tmbi may locate in different chemical environments
in U1.
Fig. 4 (a) Experimental and (b) simulated PXRD patterns for ITQ-37.
ICP analyses of the as-synthesized ITQ-37 show a Ge: Si mo-
lar ratio of 1 : 1. CHN analyses of the as-synthesized ITQ-37 and
U1 give C : N molar ratios of 4.2 and 4.3, respectively,
which are in accordance with the expected C : N ratio of 4.0
in the tmbi. The TG curve of the as-synthesized U1 (Fig.
S1, ESI†) shows a total weight loss of ca. 15.6% in the re-
gion of 200–800 °C, whereas that of the synthesized ITQ-37
(Fig. S2, ESI†) shows a total weight loss of ca. 20.2% in the
same region. With reference to the empirical formula given
by the structural analysis of ITQ-37,25 as well as TG and
compositional analyses, the formula of our as-synthesized
ITQ-37 can be given as [Ge96Si96O400H32](C24N6H33F3)8.81. Be-
cause of the high content of Ge, the calcined ITQ-37 gradu-
ally lost its crystallinity in a moisture containing atmo-
sphere upon removal of the organic templates (Fig. S3,
ESI†). However, the framework was stable in a dry atmo-
sphere. The N2 adsorption measurements showed that the
Brunauer–Emmett–Teller (BET) surface area of the calcined
ITQ-37 is 820 m2 g−1 with a t-plot micropore area of 603
Fig. 5 Solid state 19F MAS NMR spectra of (a) U1 and (b) ITQ-37.
* represent spinning sidebands.
Fig. 6 Solid-state 13C MAS NMR spectra of (a) U1, (b) ITQ-37 and (c)
13C NMR spectra in D2O solution of tmbiBr3.
−126.8 ppm for ITQ-37 and −122.4 ppm for U1 likely belongs
to the mobile fluoride ions in channels,35 which just act as
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m2 g−1 (Fig. S4, ESI†), which is comparable to values reported
by Corma et al.25 and Yu et al.29
Templating effect during the crystallization of ITQ-37
ITQ-37 is the first reported chiral germanosilicate zeolite and
has, to date, the largest 30-ring channel with a pore size
reaching the mesoporous scale.25 It crystallizes in a cubic chi-
ral space group, P4132, with a unit cell volume of 18 636 Å3.
Each unit cell of ITQ-37 contains 20 D4Rs, inside which the
F− ions are located. This requires at least 20 SDA cations in
the channels for charge balancing. In our as-synthesized ITQ-
37, there are approximately 8.8 tmbi cations estimated from
the analyses. The location and conformation of these SDA
cations in zeolites are very much desired, because they may
obtain information about the structure-directing mechanism.
Unfortunately, it is a significant challenge to accurately locate
the SDAs by X-ray diffraction analysis due to the disorder. Re-
cently, Corma et al. showed that photoluminescence spectro-
scopy is an useful method to investigate the possible aggrega-
tion state of aromatic-containing SDAs used for the synthesis
of zeolite ITQ-29.37
Solid-state photoluminescence spectra (λex = 272 nm) of
the as-synthesized ITQ-37 (Fig. 7) showed a strong broad blue
emission centered at 440 nm upon excitation at ∼270 nm,
which is almost the same as that of the tmbiBr3 salt. Both
spectra are quite different with that of the diluted tmbiIJOH)3
solution with a concentration of (OH−) of about 1 × 10−4
(Fig. 8). The latter exhibited a strong single emission band at
approximately 300 nm, which can be assigned to the π*–π
transition of the tmbi molecule.
M
Fig. 8 Photoluminescence spectra of the diluted tmbiIJOH)3 in water:
(a) c(OH−) = 1.0 × 10−4 M, λex = 272 nm and (b) c(OH−) = 0.3 M, λex
=
344 nm.
As shown in Fig. 9, single crystal X-ray diffraction analysis
of the tmbiBr3 crystals reveals that the organic cation tmbi
adopts a cis,cis,cis configuration and forms head-to-head di-
mers via the parallel benzene rings. The distance between
the benzene rings is approximately 3.79 Å, which indicates
strong π–π interactions.38 Therefore, the blue emission at 440
nm in both the synthesized ITQ-37 and the bromide salt of
tmbi can be attributed to the formation of tmbi excimers.
This implies that the tmbi cations formed dimers during the
synthesis, which then acted as SDAs and filled the channels
of ITQ-37. In comparison, there was only one strong emission
Fig. 9 Packing of tmbi in tmbiBr3 based on single crystal refinement.
The solvent molecules, bromine and hydrogen atoms are omitted for
clarity.
Fig. 7 Solid-state photoluminescence spectra (λex = 272 nm) of (a)
tmbiBr3, (b) ITQ-37 and (c) U1.
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at 310 nm in U1, which resembles that of the dilute tmbi so-
lution, indicating the presence of only tmbi monomer in U1.
Further studies showed that upon increasing the concen-
imidazolium tmbi as an SDA confirms that SAT strategy is a
general, facile approach to synthesize extra-large pore zeolites.
tration of the tmbiIJOH)3 solution to 0.1 M, the emission band Conclusions
at 300 nm due to the tmbi monomer disappears (Fig. 8), re-
In this study, we successfully utilized a readily-prepared,
placed by a new emission band at ca. 450 nm similar to those
of the solid tmbiBr3 and the synthesized ITQ-37 (Fig. 7). This
new emission could be attributed to the formation of
excimers, similar to other polyaromatics.39–42 These results
indicate that there exist tmbi dimers or similar aggregates in
the concentrated tmbi(OH)3 solution because of the
π-stacking interactions between adjacent aromatic rings. It is
noted that the gels that yield ITQ-37 (e.g. y = 0.5 and z = 5)
have a tmbi concentration much higher than the tmbi(OH)3
solution used in the photoluminescence spectroscopic studies.
Based on the above-mentioned results, we postulated that
the tmbi molecules self-assembled into the supramolecular
aggregates via π–π interactions between the benzene rings at
high concentrations of tmbi in the gels (Si : OH− = 1), which
then acted as SDAs for the formation of ITQ-37. This is
supported by the photoluminescence studies of the synthe-
sized ITQ-37 and the concentrated tmbi solution, both of
which showed the presence of tmbi excimers. A high tmbi
concentration and a low temperature would favor the forma-
tion of supramolecular interactions between SDA molecules.
Consistently, extra-large pore ITQ-37 crystallizes under these
conditions. On the other hand, a low concentration of tmbi
or higher crystallization temperature disfavors the formation
of self-assembled dimers. As a result, only a lamellar phase
U1 was crystallized, in which tmbi monomers are present, as
shown by NMR (Fig. 6) and photoluminescence studies
(Fig. 7).
semi-rigid imidazolium tmbi as an SDA in synthesizing a chi-
ral, extra-large pore germanosilicate zeolite, ITQ-37. The for-
mation of ITQ-37 showed a strong dependence on tmbi con-
centration and crystallization temperature. XRD, elemental
analysis, TGA, and NMR and photoluminescence spectro-
scopic studies showed that the formation of supramolecular
assemblies via π–π interactions between the aromatic rings of
tmbi occurred in the tmbi concentrated gels at low crystalli-
zation temperatures, and the supramolecular assemblies thus
formed acted as SDAs for the crystallization of ITQ-37. This
study demonstrates that the supramolecular assembly
templating approach is a general, applicable strategy, which
has great potential in synthesizing new, large and extra-large
pore zeolites.
Acknowledgements
We are grateful for financial support from the National Natu-
ral Science Foundation of China (grant number 21071075),
the Open Project of State Key Laboratory of Coordination
Chemistry (SKLCC201507), and the Science Foundation of
Bengbu Medical College (BYKY1404ZD) of China.
Notes and references
1 J. Sterte and J. E. Otterstedt, Appl. Catal., 1988, 38, 131–142.
2 H. Du, C. Fairbridge, H. Yang and Z. Ring, Appl. Catal., A,
2005, 294, 1–21.
It is noted that the extra-large pore germanosilicate zeolite
ITQ-37 was first synthesized by Corma et al. using a bulky,
rigid pentacyclic diquaternary ammonium molecule (Fig. 1)
as SDA.25 Furthermore, Yu et al.29 reported the synthesis of
ITQ-37 using another bulky and rigid tetracyclic quaternary
ammonium SDA (Fig. 1). Interestingly, the tmbi is a readily-
prepared, semi-rigid cation that can efficiently direct the for-
mation of extra-large pore ITQ-37 through the supramolecu-
lar assembly templating (SAT) approach. The concept of SAT
was introduced by Corma et al. during the synthesis of high-
silica zeolite ITQ-29 (framework code LTA), which is based on
a supramolecular self-assembly of two small identical aro-
matic anilinium-derived molecules through π–π interactions.
The resulting bulky “dimer” succeeded in directing the for-
mation of ITQ-29, with large spherical cavities of 1.14 nm di-
ameter.37 Similar effects were observed during the synthesis
of large-cage AlPO4-LTA molecular sieve43 and large-pore
AlPO4-5,40–42 wherein supramolecular assemblies of aromatic
SDA molecules were found in the as-prepared AlPO4 molecu-
lar sieves. Recently, by using the SAT approach, we have suc-
cessfully synthesized a new extra-large pore zeolite NUD-1
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