Methodology for synthesizing crystalline metallosilicates with expanded pore windows through molecular alkoxysilylation of zeolitic lamellar precursors

Article abstract of DOI:10.1021/ja0758739

Postalkoxysilylation with diethoxydimethylsilane has been carried out on the zeolitic lamellar precursors of various topologies such as MWW, FER, CDO and MCM-47 aiming to construct new crystalline structures with expanded pore apertures between the layers. The silylation process and the crystalline and pore structures of the resulting materials have been investigated with the techniques of XRD, IR, ¹³C and ²⁹Si MAS NMR, ICP, SEM, HRTEM, elemental analyses, and N₂ adsorption. In contrast to forming known three-dimensional zeolite structures after direct calcination of the lamellar precursors, the silylation led to new crystalline structures with opener pores, as evidenced by the shift of layer-related diffractions to the lower-angle region in XRD patterns and the enlarged interlayer pores found by HRTEM images. After optimizing the treatment conditions, particularly the amount of silane agent, a maximum and homogeneous silylation was realized, which guaranteed the phase purity in interlayer expanded zeolites. The expanded structures were well preserved after calcination at 823 K or reflux in water for 1 to 2 weeks, indicating a high thermal stability and also a hydrothermal stability. The interlayer expanded zeolites prepared from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and solid acid-catalyzed reactions of bulky molecules than that of their counterparts with conventional MWW topology.

Full text of DOI:10.1021/ja0758739

Published on Web 06/04/2008
Methodology for Synthesizing Crystalline Metallosilicates with
Expanded Pore Windows Through Molecular Alkoxysilylation
of Zeolitic Lamellar Precursors
Peng Wu,*,† Juanfang Ruan,‡ Lingling Wang,† LeiLei Wu,† Yong Wang,
Yueming Liu,† Weibin Fan,§ Mingyuan He,† Osamu Terasaki,‡ and
Takashi Tatsumi§
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of
Chemistry, East China Normal UniVersity, North Zhongshan Rd 3663, Shanghai 200062, China,
Structural Chemistry, Arrhenius Laboratory, Stockholm UniVersity, 10691 Stockholm, Sweden,
and Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuda-chu,
Midori-ku, Yokohama 226-8503, Japan
Received August 9, 2007; E-mail: pwu@chem.ecnu.edu.cn
Abstract: Postalkoxysilylation with diethoxydimethylsilane has been carried out on the zeolitic lamellar
precursors of various topologies such as MWW, FER, CDO and MCM-47 aiming to construct new crystalline
structures with expanded pore apertures between the layers. The silylation process and the crystalline
and pore structures of the resulting materials have been investigated with the techniques of XRD, IR, 13
C
and 29Si MAS NMR, ICP, SEM, HRTEM, elemental analyses, and N2 adsorption. In contrast to forming
known three-dimensional zeolite structures after direct calcination of the lamellar precursors, the silylation
led to new crystalline structures with opener pores, as evidenced by the shift of layer-related diffractions
to the lower-angle region in XRD patterns and the enlarged interlayer pores found by HRTEM images.
After optimizing the treatment conditions, particularly the amount of silane agent, a maximum and
homogeneous silylation was realized, which guaranteed the phase purity in interlayer expanded zeolites.
The expanded structures were well preserved after calcination at 823 K or reflux in water for 1 to 2 weeks,
indicating a high thermal stability and also a hydrothermal stability. The interlayer expanded zeolites prepared
from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and
solid acid-catalyzed reactions of bulky molecules than that of their counterparts with conventional MWW
topology.
1. Introduction
dimensional (3D) crystalline zeolite structures by postmodifi-
cation. However, this kind of conversion is limited mostly
because of their relatively “rigid and hard” frameworks, with
the exception of zeolites that have lamellar sheets as their
structural unit. The zeolites, originating from lamellar precursors,
e.g., MCM-22 (MWW),4 ferrierite (FER),5 Nu-6(2) (NSI),6
CDS-1 (CDO),7 MCM-47,8 ERS-12,9 MCM-65,10 RUB-41
(RRO),11 and layered aluminofluorophosphate (AFO)12 are
already known, and they are possibly subject to structural
Zeolites are a class of important microporous crystalline
materials which serve as promising adsorbents, ion-exchangers,
catalyst supports, and especially active and selective catalysts.1
It has been and will continue to be a great challenge to develop
new zeolite structures with unique porosity, if possible with
micropores larger than a 10-membered ring (MR), for the
purpose of processing bulky reactant molecules as solid acid
and redox catalysts as well as providing selective adsorbents
for separation. Through designing organic structure-directing
agents (SDAs) and/or with the combination of crystallization-
supporting metal ions, for example Ge is capable of constructing
readily double 4 MR units hardly formed by Si alone, the direct
hydrothermal synthesis has been established as the most
effective, widely adopted method.1–3 It may be possible to
modify the known zeolites or to convert them to new three-
(4) Leonowicz, M. E.; Lawton, J. A.; Lawton, S. L.; Rubin, M. K. Science
1994, 264, 1910–1913.
(5) Schreyeck, L.; Caullet, P. H.; Mougenel, J. C.; Guth, J. L.; Marler, B.
Microporous Mater. 1996, 6, 259–271.
(6) Zanarrdi, S.; Alberti, A.; Cruciani, G.; Corma, A.; Forne´s, V.; Brunelli,
M. Angew. Chem., Int. Ed. 2004, 43, 4933–4937.
(7) Ikeda, T.; Akiyama, Y.; Oumi, Y.; Kawai, A.; Mizukami, F. Angew.
Chem., Int. Ed. 2004, 43, 4892–4896.
(8) Burton, A.; Accardi, R. J.; Lobo, R. F. Chem. Mater. 2002, 12, 2936–
2942.
† Department of Chemistry, East China Normal University, China.
‡ Structural Chemistry, Stockholm University, Sweden.
§ Chemical Resources Laboratory, Tokyo Institute of Technology, Japan.
(1) Davis, M. E. Nature 2002, 417, 813–821.
(9) Millini, R.; Carluccio, L. C.; Carati, A.; Bellussi, G.; Perego, C.;
Cruciani, G.; Zanardi, S. Microporous Mesoporous Mater. 2004, 74,
59–71.
(10) Dorset, D. L.; Kennedy, G. J. J. Phys. Chem. B 2004, 108, 15216–
15222.
(2) (a) Corma, A.; Diaz-Caban˜as, M. J.; Mart´ınez-Triguero, J.; Rey, F.;
Rius, J. Nature 2002, 418, 514–517. (b) Corma, A.; Rey, F.; Valencia,
S.; Jorda´, J.; Rius, J. Nat. Mater. 2003, 2, 493–497.
(11) Wang, Y. X.; Gies, H.; Marler, B.; Mu¨ller, U. Chem. Mater. 2005,
17, 43–49.
(3) Burton, A. Nat. Mater. 2003, 2, 438–440.
(12) Wheatley, P. S.; Morris, R. E. J. Mater. Chem. 2006, 16, 1035–1037.
9
8178 J. AM. CHEM. SOC. 2008, 130, 8178–8187
10.1021/ja0758739 CCC: $40.75
2008 American Chemical Society

Synthesizing Crystalline Metallosilicates
A R T I C L E S
modifications. With the increase in number, these kinds of
zeolites are gradually forming an important family of mi-
croporous materials. As a representative among them, the
MWW-type aluminosilicate, well-known as MCM-22, has
already found important industrial applications to the selective
production of bulk petrochemicals such as cumene and ethyl-
benzene.13 However, the recently developed MWW-type ti-
tanosilicate, Ti-MWW, has been demonstrated to be an effective
catalyst for the epoxidation of various alkenes and ammoxi-
mation of ketones using hydrogen peroxide as a clean oxidant.14
The 3D structures of the above zeolites are invariably
constructed via topotactic dehyoxylation between the layers in
2D lamellar precursors. The interlayer pore entrance, originally
wide and open, then tends to be narrowed as a result of the
condensation of hydroxyl groups and the removal of SDA
molecules intercalated into the layers. More attractive applica-
tions are expected if new crystalline structures could be
constructed by postsynthesis with expanded pore systems but
still composed of the same framework units as the lamellar
zeolites. Two useful techniques, that is, the phase delamination15
and the interlayer pillaring with amorphous silica,16 have then
been developed to make full use of their potentially open
porosity, together with the frameworks of zeolitic nature. Both
delamination and pillaring are based on the swelling of the
lamellar precursor with surfactant in advance, a procedure
commonly used for the layered silicates. To cause structural
swelling, the zeolitic lamellar precursors with more stable and
stronger interlayer cross-linkages generally require much more
severe conditions of the basic media. This then inevitably leads
to a partial dissolution of the silicalite framework and also to a
structural degradation.17,18 Recently, it was reported that the
swelling with surfactant and then the expansion of the interlayer
spaces could be realized effectively at room temperature. This
weak treatment at low temperature is considered to be advanta-
geous to the preservation of the intralayer structure of the MCM-
22 precursor.18 Nevertheless, the swollen MCM-22 thus pre-
pared is only useful for interlayer pillaring with silica, but is
not suitable for delamination. Other new methods, which are
capable of opening the porosity and constructing new crystalline
structures but without destroying the basic building units,
are urgently expected to widen the range of applications of these
zeolites having lamellar precursors.
cationic surfactant, silylation, alcoholysis, and subsequent
condensation, which are usually required for the nonzeolitic
layered silicates.19 The resulting materials with expanded pore
windows, high crystallinity, and outstanding hydrothermal
stability are proven to be active solid acid and redox catalysts
for processing bulky molecules.
2. Experimental Section
2.1. Syntheses of Lamellar Precursors of Various Zeolites.
Ti- or B-containing MWW lamellar precursor was hydrother-
mally synthesized using hexamethyleneimine (HMI) as an SDA
from the gels with the molar compositions of 1.0 SiO2:
(0-0.033) TiO2: 0.67 B2O3: 1.4 HMI: 19 H2O following
previously reported procedures.14a Using the same method
described for the MWW-type ferrisilicate,20 the MWW lamellar
precursors containing Al, Ga, or Fe were synthesized from the
gels of 1.0 SiO2: 0.033 M2O3: 0.9 HMI: 0.15 Na2O: 40 H2O,
where M represents Al, Ga, or Fe. The crystallization was
carried out in Teflon-lined steel autoclaves under rotation (100
rpm) at 413 K for 7-10 days. The FER lamellar precursor,
so-called PREFER, was hydrothermally synthesized using
4-amino-2,2,6,6-tetramethylpiperidine as an SDA following
previously reported method.5 The gel with the compositions of
1.0 SiO2: 1.0 SDA: 1.5 NH4F: 1.0 HF: 15 H2O was crystallized
in autoclave at 443 K for 7 days. The precursor of CDO
topology, generally denoted PLS-1, was synthesized using
tetramethylammonium hydroxide (TMAOH) as an SDA ac-
cording to the literature method.7 The gel with a composition
of 1.0 SiO2: 0.2 TMAOH: 18K2O: 9 H2O: 3.4 Dioxane was
crystallized in autoclave under rotation at 423 K for 10 days.
A pure silicalite precursor with the MCM-47 structure was
synthesized using tetramethylene bis(N-methylpyrrolidinium)
dibromide as an SDA, which was synthesized through the
reaction of 1-methylpyrrolidine with 1,4-dibromobutane.8 The
product of lamellar precursor was crystallized from the gel with
a composition of 1 SiO2: 0.12 TMAOH: 0.30 NaOH: 40 H2O
at 443 K for 6 days.
All crystalline products were collected by filteration, washed
repeatedly with deionized water, and then dried at 473 K
overnight to obtain the lamellar precursors. A portion of
precursor was calcined in air at 823 K for 10 h to burn off the
occluded organic species to obtain corresponding zeolites with
3D structures.
2.2. Alkoxysilylation of Lamellar Precursors. The zeolite
precursors were alkoxysilylated with Me2Si(OEt)2 under low
pH conditions. Typically, 1 g of precursor was mixed with 50 g
of aqueous solution of 2M HNO3 and a desirable amount of
Me2Si(OEt)2 (TCI). The mixture was then refluxed at 373 K
for 20 h to induce the silylation. The solid-to-liquid weight ratio
was always fixed at 1:50, while the amount of alkoxysilane was
varied in the range of 0-0.3 g per gram of lamellar precursor.
The silylated sample was filtered and washed with deionized
water repeatedly and dried at 393 K for 10 h. The samples were
further calcined in air at 823 K for 10 h to remove any organic
species. The resulting interlayer expanded zeolites are denoted
IEZ-ABC, where ABC represents the three letter code of the
zeolite structure.
We report here a versatile method of converting 2D lamellar
precursors into novel 3D crystalline metallosilicates according
to a strategy of inserting a monomeric Si source into the
interlayer spaces through one-step dialkoxysilylation followed
by removal of the organic moieties. Such a simple soft-chemical
methodology for expanding the pore structure avoids stepwise
modifications such as interlayer expanding by ion-exchange with
(13) Cheng, J. C.; Degnan, T. F.; Beck, J. S.; Huang, Y. Y.; Kalyanaraman,
M.; Kowalski, J. A.; Loehr, C. A.; Mazzone, D. N. Stud. Surf. Sci.
Catal. 1998, 121, 53–58.
(14) (a) Wu, P.; Tatsumi, T.; Komatsu, T.; Yashima, T. J. Phys. Chem. B
2001, 105, 2897–2905. (b) Wu, P.; Tatsumi, T.; Komatsu, T.; Yashima,
T. J. Catal. 2001, 202, 245–255. (c) Song, F.; Liu, Y.; Wu, H.; He,
M.; Wu, P.; Tatsumi, T. J. Catal. 2006, 237, 359–367. (d) Wang, L.;
Liu, Y.; Xie, W.; Zhang, H.; Wu, H.; Jiang, Y.; He, M.; Wu, P. J.
Catal. 2007, 246, 205–214.
(15) Roth, Q. J.; Kresge, C. T.; Vartuli, J. C.; Leonowicz, M. E.; Fung,
A. S.; McCullen, S. B. Stud. Surf. Sci. Catal. 1995, 94, 301–308.
(16) Corma, A.; Forne´s, V.; Pergher, S. B.; Maesen, Th; L. M.; Buglass,
G. Nature 1998, 396, 353–440.
(19) (a) Mochizuki, D.; Shimojima, A.; Imagawa, T.; Kuroda, K. J. Am.
Chem. Soc. 2005, 127, 7183–7191. (b) Mochizuki, D.; Kuroda, K.
New J. Chem. 2006, 30, 277–285.
(17) Wu, P.; Nuntasri, D.; Ruan, J.; Liu, Y.; He, M.; Fan, W.; Terasaki,
O.; Tatsumi, T. J. Phys. Chem. B 2004, 108, 19126–19131.
(18) Maheswari, S.; Jordan, E.; Kumar, S.; Bates, F. S.; Penn, R. L.; Shantz,
D. F.; Tsapatsis, M. J. Am. Chem. Soc. 2008, 130, 1507–1516.
(20) Wu, P.; Ling, H.; Komatsu, T.; Yashima, T. Chem. Commun. 1997,
663–664.
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A R T I C L E S
Wu et al.
2.3. Characterization and Analysis Methods. Powder X-ray
diffraction (XRD) patterns were collected on a MAC Science
MX-Labo diffractiometer (Cu KR radiation). The morphology
was monitored by scanning electron microscopy (SEM) on a
Hitachi S-5200 or S-4800 microscope. High resolution transmis-
sion electron microscopy (HRTEM) measurements were carried
out with a 300 kV TEM (JEOL-3010, Cs ) 0.6 mm, resolution
1.7Å). The 13C and 29Si MAS NMR spectra were recorded on
a JEOL JNM ECA-400 multinuclear solid-state magnetic
resonance spectrometer. IR spectra were collected on a Perkin-
Elmer 1600 FTIR spectrometer at room temperature. The IR
spectra in the hydroxyl stretching vibration region were
measured after evacuating the self-supported wafers (30 mg of
Ø 2 cm) at 557 K for 3 h, whereas the spectra in the framework
vibration region were recorded using conventional KBr tech-
nique without evacuation. Elemental analyses of CHN were
carried out on a Perkins-Elmer 2400 series II CHNS/O analyzer,
while the amount of metals was quantified using inductive
couple plasma mass spectroscopy on a Shimadzu ICPS-8000E-
ICP instrument. UV-visible spectra were recorded on a JASCO
V-550 spectrometer with a mode of diffusion reflectance using
BaSO4 as a reference.
2.4. Catalytic Reactions. The liquid-phase catalytic reactions
were carried out in a 50 mL reactor equipped with a condenser
and a magnetic stirrer. The epoxidation of cyclohexene with
H2O2 was carried out using 0.05 g of catalyst, 10 mmol of
substrate, 10 mmol of H2O2 (30 wt%),10 mL of MeCN at 333
K for 2 h. The Beckmann rearrangement of cyclohexanone
oxime was carried out using 0.1 g of catalyst, 0.1 g of oxime,
20 g of PhCN solvent at 403 K for 2 h. The Baeyer-Villiger
oxidation of cyclohexanone with H2O2 was carried out using
0.1 g of catalyst, 5 mmol of cyclohexanone, 2.5 mmol of H2O2
(30 wt%), and 4 mL of MeCN at 358 K for 3 h. The reaction
products were analyzed on a Shimadzu GC-14B gas chromato-
graph equipped with an OV-1 capillary column and an FID
detector. The amount of unconverted H2O2 was determined by
the standard titration method with 0.1 M Ce(SO4)2 solution.
Figure 1. XRD patterns of various lamellar precursors (a), 3D zeolites
formed by direct calcination of precursors (b), and interlayer expanded
crystalline zeolites prepared by alkoxysilylation of precursors and further
calcination (c). The structure code indicates the type of layer sheets.
common feature was observed in which the layer-related
diffractions shifted to a higher 2θ region (Figure 1b). The
structural changes essentially involved the burning off of the
occluded organic SDA species, the condensation of the interlayer
silanol groups, and the formation of cross-linkage between the
layers. The direct calcination resulted in ordered 3D crystalline
zeolite structures but a decrease in layer spacing, for example,
from 26.93 to 25.09 Å for MWW. Thus, the calcined samples
had a narrower pore entrance between the layers than that of
the original lamellar precursors.
Nevertheless, when the precursors were silylated with DEDMS
[(EtO)2SiMe2], crystalline and stable materials were obtained
even after removing all organic species by calcination in air. In
contrast to normal 3D zeolites obtained by direct calcination of
the precursors, the silylated samples showed different but well-
resolved XRD patterns in which the layer-related diffractions
appeared in lower angles (Figure 1c). This indicates that an
expansion of pore structure occurred at least between the layers.
The structures changed mainly along the direction of layer
stacking. These materials are nominated interlayer expanded
zeolites (IEZ). The layer-related diffraction observed for both
the precursor and the directly calcined sample was absent at
the same 2θ position in the XRD pattern of silylated one
(particularly obvious for FER, CDO, and MCM-47). This
suggests that a homogeneous interlayer silylation occurred
throughout the crystals and the IEZ sample was of phase purity
rather than a composite structure of conventional 3D zeolite
and interlayer-expanded material. Moreover, when the adjacent
layers of the precursors were condensed upon direct calcination,
the 3D structures formed had a relatively lower crystallinity
(Figure 1b), probably due to a great strain of Si-O-Si bonds.7,8
The phenomenon was paricularly observed for CDO and MCM-
47. This was, however, not the case or less noticeable for
corresponding IEZ samples, as they showed a higher crystallinity
and well-defined diffractions. It seems that the stressing of the
interlayer cross-linkages may be effectively relaxed by inserting
3. Results and Discussion
3.1. Interlayer Alkoxylation of Various Zeolite Lamellar
Precursors. Various zeolitic lamellar precursors have been
silylated with organic silanes in acidic media into highly ordered
crystalline materials. Diethoxydimethylsilane (DEDMS) with
two ethoxy groups was intentionally chosen to connect two up-
and-down layers, possibly via the reaction with surface silanol
groups; meanwhile, the two methyl groups would avoid
intermolecular condensation. In the case of triethoxymethylsilane
and tetraethoxysilane (TEOS), a serious condensation of silanes
occurred, which may lead to the deposition of amorphous silica
on the zeolite crystals. However, when dichlorodimethylsilane
was employed as a silylating agent, very similar results to
DEDMS were obtained. Figure 1 reports the XRD patterns of
the lamellar precursors before and after direct calcinations, as
well as after the silylation with DEDMS and further calcination.
The precursors used were the titanosilicate for MWW structure
and pure silicalites for the other zeolite structures. The XRD
patterns of the precursors exhibited characteristic diffractions
due to layered structures at lower angles (Figure 1a), which are
in agreement with those reported in the literature.4,5,7,8 The
precursors were converted to corresponding 3D crystalline
structures with so-called MWW, FER, CDO, and MCM-47
topologies, following a direct calcination in air, during which a
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Synthesizing Crystalline Metallosilicates
A R T I C L E S
Table 1. Physicochemical Properties of Lamellar Precursors,
Directly Calcined Samples and Interlayer Expanded Zeolites
d-spacing /Å
precursor
3Db
surface area /m2 g-1
original zeolites
hkla
IEZc
3Db
IEZc
MWW
FER
CDO
001
200
020
020
26.93
13.07
10.20
11.25
25.09 27.58
9.36 11.75
9.12 11.47
9.16 11.51
620
403
300
312
625
410
438
410
MCM-47
a Representative layered structure-related plane. b Three-dimensional
zeolites obtained by direct calcination of the precursors. c Interlayer
expanded zeolites prepared by silylation of precursor with DEDMS and
further calcination.
Figure 3. IR spectra of Ti-containing MWW lamellar precursor, after
silylated with (a) 0 g, (b) 0.05 g, (c) 0.10 g, (d) 0.15 g, and (e) 0.30 g
Me2Si(OEt)2 per gram of the precursor in 2 M HNO3 without calcination.
showed a similar band at 220 nm to the conventional Ti-MWW
in the UV-visible spectra, which is attributed to the charge
transfer from oxygen atoms to Ti4+, characteristic of tetrahe-
drally coordinated Ti in the framework.21,22 However, the IR
spectra in the region of hydroxyl stretching vibration showed
the bands at 3620, 3630, and 3638 cm-1 for IEZ-MWW
aluminosilicate, gallosilicate, and ferrisilicate, respectively (Sup-
porting Information Figure S1). These bands are assigned to
the structural Si(OH)M (M ) Al, Ga, or Fe) groups,20,23
indicating the presence of metal ions still in the framework.
These silylated materials with opener pores may serve as
potential solid acid with tunable Brønsted acidity for catalyzing
the substrates with large molecular dimensions. Nevertheless,
a demetalation took place to certain degree during the silylation,
which is reasonably due to the treatment performed in an acidic
media, in most cases 2M HNO3. For example, the Si/Al ratio
of 15 in the precursor of MCM-22 aluminosilicate changed to
35 in Al-IEZ-MWW after the silylation.
Figure 2. XRD patterns of various interlayer expanded metallosilicalites
of IEZ-MWW. (a) borosilicate, (b) titanosilicate, (c) aluminosilicate, (d)
gallosilicate, and (e) ferrisilicate. The samples were prepared by the silylation
of corresponding MWW precursors with Me2Si(OEt)2 and then calcined.
the silicon species between the layers. This then contributed to
a slight increase in specific surface area as shown next.
Table 1 summarizes the physicochemical properties of
lamellar precursor, directly calcined samples, as well as silylated
and subsequently calcined samples. The interlayer spacings were
expanded by silylation by 2.3-2.5 Å in the IEZ samples.
Considering the fact that the zeolites had relatively rigid
structures inside the layers, the spacing expansion is presumed
to mainly contribute to an enlargement of the pore windows
between the layers. The N2 adsorption at 77 K indicated that
the IEZ samples had comparable or slightly higher specific
surface areas in comparison to corresponding 3D zeolites
obtained by directly calcining the precursors. This was in
agreement with the above XRD patterns to verify that the IEZ
samples were highly crystalline materials.
The synthesis strategy was also applicable to a variety of
metallosilicalite precursors. Figure 2 shows the XRD patterns
of the samples prepared by silylating the MWW precursors
containing Ti, B, Al, Ga, or Fe after further calcination. After
calcinations, all of the samples still showed clearly in the low
angle region the resolved 001 and 002 diffractions due to an
expanded layer structure, and also showed well-defined diffrac-
tions in the high angle region. In contrast, their precursors
generally gave relatively broad diffractions in the high angle
region (not shown) as reported previously.14a,18 Different from
interrupted interlayer connection in the precursors, these materi-
als are thus considered to have a 3D crystalline structure rather
than a 2D lamellar structure. Various metallosilicates having
interlayer expanded pores were then prepared readily by
inserting the silicon atoms between the layers.
3.2. Investigation into Interlayer Alkoxysilylation with IR
and Solid-State NMR. Concerning the degree of silylation, we
have investigated the effect of silylation conditions such as
treatment temperature, acid concentration, and particularly silane
amount for all kinds of zeolite precursors mentioned in this
work. Generally, a successful interlayer silylation preferred a
refluxing treatment in 2M HNO3. To reach a maximum
silylation, the silylation was carried out under these conditions
by varying the amount of DEDMS. IR spectroscopy was
employed to monitor the silylation processes of lamellar
precursors. Figure 3 shows the IR spectra of MWW precursor
and silylated but uncalcined samples using a different amount
of DEDMS. The precursor showed the bands at 2926 and 2850
cm-1 (Figure 3a), which are due to the stretching vibration of
CH2 groups originated from hexamethyleneimine (HMI), the
SDA used for the crystallization of the precursor. The HMI
molecules are reported to occupy both the interlayer space and
the intralayer 10-MR channels.24 The HMI molecules confined
in the intralayer sinusoidal channels were hardly extracted by
the acid treatment in silylation. Thus, the 2926 and 2850 cm-1
-
bands were still observed after the silylation but decreased
slightly in intensity. The silylation, however, developed new
(21) Vayssilov, G. N. Catal. ReV. Sci. Eng. 1997, 39, 209–216.
(22) Bellussi, G.; Rigguto, M. S. Stud. Surf. Sci. Catal. 2001, 137, 911–
932.
(23) Corma, A.; Corell, C.; Pe´rez-Pariente, J. Zeolites 1995, 15, 2–8.
(24) Lawton, S. L.; Fung, A. S.; Kennedy, G. J.; Alemany, L. B.; Chang,
C. D.; Hatzikos, G. H.; Lissy, D. N.; Rubin, M. K.; Timken, H.-K. C.;
Steuernagel, S.; Woessner, D. E. J. Phys. Chem. 1996, 100, 3788–
3798.
The interlayer silylation did not change the coordination states
of the framework metal ions. The IEZ-MWW titanosilicate
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A R T I C L E S
Wu et al.
Figure 4. Dependence of the intensity of 850 cm-1-band on the amount
of Me2Si(OEt)2 used in the slilylation of MWW precursor.
bands at 2970 and 850 cm-1, which are assigned as CH3
asymmetric, stretching the rocking of CH3 groups attached to
Si.25,26 This confirmed the incorporation of (CH3)2Si moiety
into the zeolite. The intensity of the 850 cm-1-band increased
with an increasing Me2Si(OEt)2 amount, but finally it leveled
off at a silane to precursor weight ratio of 0.15 g g-1 (Figure
4), indicating a saturated incorporation of silane groups.
CHN elemental analyses indicated that the MWW precursor
contained 10.23 wt% carbon and 2.03 wt% nitrogen species,
corresponding to a C/N atomic ratio of 5.8. The value was very
similar to the C/N ratio of HMI (6). The silylated sample
prepared using 0.15 g silane relative to 1.0 g precursor contained
8.95 wt% carbon and 1.46 wt% nitrogen, showing a C/N atomic
ratio of 7.2. The decrease in the total amount of organic species
should be due to the removal of a part of the HMI, especially
those located in interlayer spaces by acid extraction, while the
increase in C/N ratio was gained by the incorporation of
(CH3)2Si groups. On the basis of a reduced amount of nitrogen,
we could calculate the amount of carbon related to the HMI
molecules removed by acid washing, and then the amount of
carbon incorporated through the silylation. The maximum
amount of (CH3)2Si groups was 2.5 molecules per unit cell for
MWW structure. According to the structure of MWW topology,4
there are 2 pillaring sites per unit cell in the MWW precursor.
It is thus deduced that the amount of (CH3)2Si groups incor-
porated is enough to realize a complete and homogeneous
interlayer silylation and then construct the cross-linkages
between the layers. The extra (CH3)2Si groups, corresponding
to 0.5 molecules per unit cell, may be incorporated through
reaction with the terminal silanols on the crystal surface or the
internal silanols on the defect sites.
The treatment conditions optimized in the silylation of MWW
precursor were also applicable to other precursors. Similarly,
the silylation with DEDMS of the precursors of FER, CDO,
and MCM-47 developed the silane group-related band at 850
cm-1 which was absent in the IR spectra of precursors (Figure
5).This confirmed the incorporation of (CH3)2Si groups between
the layers of these precursors.
The incorporation of (CH3)2Si groups by the silylation of
lamellar precursors has been further investigated by 13C MAS
NMR and 29Si MAS NMR techniques. Figure 6A, trace a,
reveals a typical 13C MAS NMR spectrum of MWW precursor
which showed three resonances at 57.0, 48.5, and 26.5 ppm.
The former two resonances are attributed to the C1 in HMI,
while the latter one is attributed to the C2 and C3 in HMI.24
Figure 5. IR spectra of (a) lamellar precursors and (b) after silylated with
Me2Si(OEt)2 in 2M HNO3without calcination.
The presence of two resonances for C1 of HMI is presumably
associated with the residence of HMI in two distinct void spaces,
that is, interlayer channels and intralayer channels. What is more
attractive is that the silylation developed a new resonance at
-2.0 ppm in13C MAS NMR spectrum (Figure 6A, trace b),
which is due to the configuration of (CH3)2Si groups.25
In the case of the precursor of FER, multiple resonances were
observed in the region of 20-60 ppm (Figure 6B, trace a). They
are very similar to those reported previously and are attributed
to the carbon atoms having different positions in the molecule
of 4-amino-2,2,6,6-tetramethylpiperidine, the SDA used for the
synthesis PREFER.5 After the silylation, these resonances
disappeared almost, while the resonance due to (CH3)2Si
appeared at -2.0 ppm (Figure 6B, trace b). Since the intralayer
channels of PREFER, having only 8-MR pore windows, are
not open enough to accommodate bulky molecules, the SDA
with a relatively large molecular size is considered to be
predominantly occluded inside the void spaces between the FER
layers. Thus, in comparison to above HMI in the MWW
precursor, the SDA molecules in PREFER were more easily
removed by the acid refluxing during silylation. However, the
precursor of CDO, so-called PLS-1, showed a single resonance
at 56.9 ppm assigned to the SDA of tetramethylammonium
(Figure 6C, trace a). This small cation wherever located was
extracted readily and completely during the silylation and
resulted in a spectrum in which the signal at 56.9 ppm was
almost absent (Figure 6B, trace b). Meanwhile, the resonance
due to (CH3)2Si was again visible at -2.0 ppm, confirming the
interlayer silylation. Interestingly, the silylated PREFER also
(25) Joo, J.; Hyeon, T.; Hyeon-Lee, J. Chem. Commun. 2000, 1487–1488.
(26) Yamamoto, K.; Nohara, Y.; Domon, Y.; Takahashi, Y.; Sakata, Y.;
Ple´vert, J.; Tatsumi, T. Chem. Mater. 2005, 17, 3913–3920.
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Figure 7. 29Si MAS NMR spectra. (a) lamellar precursor, and (b) after
silylated with Me2Si(OEt)2 in 2M HNO3without calcination, and (c) silylated
sample after calcination.
Figure 6. 13C MAS NMR spectra of (a) lamellar precursors and (b) after
silylated with Me2Si(OEt)2 in 2M HNO3without calcination.
showed a signal at -5.4 ppm in the 13C MAS NMR spectrum.
This resonance could be due to (i) the (CH3)2Si groups located
in different places other than interlayer spaces, and /or (ii) the
CH3Si groups formed by losing a methyl group in (CH3)2Si as
a result of decomposition under refluxing conditions. When we
carried out the silylation of PLS-1 at a higher temperature, such
as 443 K in a sealed autoclave, the resonance at -5.4 ppm
became more intense, while the resonance at -2.0 ppm became
weaker (Supporting Information Figure S2). This result allows
us to tentatively assign the resonance at -5.4 ppm to the silane
groups losing a CH3 group, that is, CH3Si unit.
Figure 7 shows the 29Si MAS NMR spectra of various
lamlellar precursors before and after alkoxysilylation with
DEDMS. For all precursors, the main resonances at -110 and
-120 ppm were from silicon atoms coordinated with four silicon
atoms (Q4). A distinguished resonance at -103 ppm was also
particularly observed for the precursors of FER and CDO. This
resonance is attributable to the silicon-bearing OH groups,
(OH)Si(SiO)3 (Q3),5 indicating the precursors contained abun-
dant silanol groups on the layer surface. After the silylation,
the Q3 resonance decreased greatly in intensity, while the
samples exhibited a new resonance at -15 ppm at the expense
of Q3 groups (Figure 7A-C, trace b). This signal is attributed
to the silicon atom from Si(CH3)2(OSi)2 groups (D2).27 The
results clearly indicate that the silylation occurred through the
Figure 8. IR spectra in hydroxyl stretching region of (a) Al-MCM-22 (Si/
Al ) 15), (b) Al-IEZ-MWW, (c) FER silicalite, and (d) IEZ-FER after
evacuation at 773 K for 2 h.
reaction of silane groups with the silanols on the layer surface
to form pillaring silicon species between the layers.
Using silylated PREFER as an example, we have investigated
the effect of calcination on the structural change. After burning
off the organic species by calcination in air, the D2 resonance
disappeared instead of forming a more intensive signal at -92
ppm (Figure 7B, trace c).This resonance could be assigned to
Si(OH)2(OSi)2 groups (Q2)28 or 3MR Q3 units possibly formed
through the polymerization of Me2Si(OEt)2 to cyclic silane
species.27 It is very difficult for us to directly differentiate two
kinds of signals having very similar chemical shifts. To clarify
(27) Engelhardt, G.; Michel, D. High-Resolution Solid-State NMR of
Silicates and Zeolites; John Wiley & Sons Ltd.:New York, 1987.
(28) Woolery, G. L.; Alemany, L. B.; Dessau, R. M.; Chester, A. W.
Zeolites 1986, 6, 14–16.
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Wu et al.
Figure 9. SEM images of (a) 3D MWW, (b) IEZ-MWW, (c) FER, (d) IEZ-FER, (e) CDO, (f) IEZ-CDO, (g) MCM-47, and (h) IEZ-MCM-47.
this issue, we have compared the silylation between the FER
lamellar precursor (uncalcined) and the 3D FER silicalite
(directly calcined sample of precursor) under the same condi-
tions. If the polymerization and cyclization of Me2Si(OEt)2
actually occurred in the treatment, the silylated 3D FER silicalite
should gave similar signal at -92 ppm. Nevertheless, in contrast
to the silylation of precursor which developed new signals at
-12 ppm and -92 ppm after calcination, the silylation of the
calcined silicalite already with the 3D FER structure led to the
same 29SiMAS NMR spectra as the parent (Supporting Informa-
tion Figure S3). No additional resonances due to D2, Q2, and/
or 3MR Q3 signals were developed at -12 and -92 ppm. This
would rule out the possibility of the formation of 3MR Q3 units
and their contribution to the -92 ppm-resonance. In fact, the
elemental analyses indicated that the amount of silane incor-
porated by silylation was 2.15 mmol g-1 for the lamellar
precursor and 0.13 mmol g-1 for the 3D FER silicalite,
respectively. The content of the latter was much lower. The IR
spectra also revealed that the 850 cm-1 band was almost
invisible for the silylated 3D FER (Supporting Information
Figure S4). The precursor and 3D FER silicalite differed mainly
in the interlayer silanol groups. Above results suggest not only
that the silane molecules were hardly incorporated once the
interlayer silanols were condensed by calcination to construct
the 3D FER structure, but also that the silane was not
polymerized to deposit on the crystal surface or inside the pores.
Thus, we could exclude the formation of cyclic or other types
of siloxanes in silylation and then assign the -92 ppm-signal
to Q2 group rather than 3MR Q3 group. The Q2 group-groups
resulted from the incorporated Si(CH3)2(OSi)2 by losing two
methyl groups in calcination. These results clearly verified that
the alkoxysilyl groups actually condensed with the silanols on
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Synthesizing Crystalline Metallosilicates
A R T I C L E S
Figure 12. HRTEM images of calcined IEZ-MWW (a) and IEZ-FER (b)
taken along the direction of layer stacking.
samples. Figure 8 shows the IR spectra in the hydroxyl
stretching vibration region of pure silica 3D FER and IEZ-FER
as well as 3D MWW MCM-22 aluminosilicate and correspond-
ing Al-IEZ-MWW. The 3D FER showed a main band at 3745
cm-1 due to terminal silanols. In addition to the 3745 cm-1
-
band, the 3D MCM-22 showed an another band at 3620 cm-1
due to the framework Al(OH)Si groups.23 The interlayer
silylation of MWW and FER lamellar precursors with
Figure 10. Selected area electron diffraction patterns of 3D MWW (left
column) and IEZ-MWW (right column) along [001] and [100] directions.
Me2Si(OEt)2 developed, in both cases, a new band at 3730 cm-1
,
which was nearly invisible for corresponding 3D MWW and
FER counterparts, but made the bands at 3745 and 3620 cm-1
almost intact. The 3730 cm-1-band was ascribed to a kind of
internal silanols,29 probably corresponding to a kind of hydrogen-
bonded geminal dSi(OH)2 groups. These results were in
agreement with above Q2 signal observed in above 29Si MAS
NMR spectra, giving a strong evidence for the incorporation
of Si(CH3)2(OSi)2 groups introduced by silylation first and then
formation of silicon species bearing silanols in following
calcination.
3.3. Electron Microscopy Investigation. Figure 9 shows the
SEM images of various 3D zeolites and corresponding IEZ
materials. The crystals of these materials were all thin flakes,
which, however, were different in shape and size in terms of
their fundamental zeolite structures. A direct calcination of the
precursor, and silylation and subsequent calcination did not
result in any significant changes to the crystal morphology.
Although the XRD patterns clearly evidenced a structural
expansion along the direction of layer stacking after the
silylation (Figure 1), the SEM images gave no information
concerning the changes in crystal thickness. Thus, the formation
of new crystalline structure by silylation took place not through
destroying and reconstructing the macro crystals but at an atomic
or molecular level.
The structural changes as a result of silylation have been
investigated by HRTEM measurement on two IEZ structures.
Figure 10 and Figure 11 show the selected area diffraction
patterns of 3D MWW and IEZ-MWW, 3D FER and IEZ-FER
along two or three main directions, respectively. They revealed
that IEZ materials had very similar pore arrays and sizes within
the layers to the 3D structures obtained by direct calcination.
However, as evidenced by the d-spacing measured by HRTEM
(Supporting Information Table S1), the well-ordered pores were
expanded along the direction perpendicular to the layers in the
IEZ samples, that is, along the [001] direction for IEZ-MWW
and [200] for IEZ-FER. The values of pore expansion were in
agreement with the data obtained by XRD shown in Table 1.
Figure 11. Selected area electron diffraction patterns of 3D FER (left
column) and IEZ-FER (right column) along [001], [010], and [100]
directions.
the layer surface to create new Si-O-Si linkages, which
contributed to the interlayer expansion.
IR spectroscopy also gave us consistent evidence for the
(29) Fan, W.; Wu, P.; Namba, S.; Tatsumi, T. J. Catal. 2006, 243, 183–
formation of Q2 groups in the silylated and further calcined
191.
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A R T I C L E S
Wu et al.
depicts the sequence using MWW precursor as an example. In
silylation, the DEDMS molecules react with silanol groups
attached to the layer surface to realize incorporation of mono-
meric silane groups and formation of Si-O-Si linkages
between the layers (Figure 13, parts a and b). The subsequent
calcination burns off the methyl groups coordinated to the Si,
as well as SDA species occluded in the pores, leading to a new
pore structure pillared mainly by Si(OH)2 groups (Figure 13c).
The silylation thus makes the number of interlayer pore window
increase by two in comparison to directly calcined precursor
(Figure 13d). We cannot deny the possibility of forming partially
the Si-O-Si connection between the neighboring silane groups
in case of the zeolite structures making them close to each other.
To understand this complicated issue, a final structural resolution
is needed for particular case.
3.5. Hydrothermal Stability of IEZ Materials. The thermal
stability of IEZs should not be taken as an important issue, as
their structures survived the calcination at 823 K in air.
Nevertheless, although the Si species incorporated effectively
pillar the layers and cross-link the layers to enlarge the interlayer
pores, both 29SiMAS NMR and IR investigation showed that
those Si species are not tetrahedrally coordinated to four Si
atoms, but contain a part of OH groups, mostly existing in
Si(OH)2 configuration. This would increase the hydrophilicity
of resulting materials and bring about hydrothermal stability
problem. We thus have investigated the hydrothermal stability
of IEZ by refluxing the samples in water. As shown by XRD
patterns (Figure 14), there were no obvious decrease in intensity
and changes in diffraction position when IEZ-MWW and IEZ-
FER were boiled at 373 K in water for 1-2 weeks. The
diffractions due to expanded layer structures were still observed
in the low angle region, indicating that the structures were totally
preserved. The high hydrothermal stability of IEZ is presumably
contributed by the pillaring Si species firmly connected to the
layers.
Figure 13. Sequence of postsynthesizing interlayer expanded zeolites
through dialkoxysilylation of lamellar precursor (using MWW precursor
as a representative). (a) MWW lamellar precursor, (b) the interlayer structure
expanded via the reaction of silane with silanols on the layer surface, (c)
formation of a novel ordered 3D crystalline structure with enlarged pore
window in comparison to normal 3D MWW structure, and (d) common
3D MWW structure obtained by a direct interlayer dehydroxylation.
Figure 14. XRD patterns of IEZ-MWW (aluminosilicate) before (a) and
after (b) refluxed in boiling water for 6 days IEZ-FER (pure silicalite); (c)
and after (d) refluxed in boiling water for 15 days .
3.6. Catalytic Properties of IEZ Materials. The IEZ materials,
having larger pores than the 3D structure obtained by direct
calcination, are expected to show higher catalytic activities for
bulky molecules. Using MWW metallosilicates as representa-
tives, the catalytic properties of IEZ thus have been investigated
in processing bulky molecules as both redox and solid acid
catalysts. In comparison to their counterparts with conventional
3D MWW topology, Ti-containing IEZ-MWW catalysts showed
much higher conversion and specific activity (turnover number
per Ti active site) in cyclohexene oxidation with H2O2 (Sup-
porting Information Table S2). This reaction is reported to
require large-pore zeolites as effective catalysts.14b Additionally,
Al and Ga-containing IEZ-MWW catalysts were superior to their
3D MWW counterparts in Beckmann rearrangement of cyclo-
hexanone oxime and Baeyer-Villiger oxidation of cyclohex-
anone with H2O2, respectively (Supporting Information Table
S2). Both reactions involving cyclic substrates and products are
considered to require open reaction spaces.31–33 The activity
improvement should be contributed by the silylation which
created opener pores between the layers. The IEZ catalysts,
The TEM images have been examined carefully and randomly
in the regions of crystals, which evidenced that the pores were
enlarged along the layer stacking direction uniformly. The XRD
patterns noted earlier evidenced already that the IEZ materials
were almost free of the phases owing to the precursors and the
3D structures obtained by direct calcination. This should be
ascribed to a maximum degree of interlayer silylation was
realized after optimizing the silylation conditions, particularly
the amount of alkoxysilane (Figures 2 and 4).
The number of tetrahedral atoms of the aperture of interlayer
pores increased by two, e.g. forming 12-MR pores in both IEZ-
MWW and IEZ-FER (vis-a-vis 10-MR pores of 3D MWW and
FER) as showed by the enlarged HRTEM images along the layer
stacking direction (Figure 12). In the case of IEZ-MWW, XRD,
and HRTEM verified that it was very similar to previously
reported Ti-YNU-1, which has been obtained only by chance
when a postsynthesized Ti-containing MWW precursor with an
extremely low Ti content (generally Si/Ti >70) was acid-
treated.30a The present method, however, is proved to be more
general, neither depending on the precursor types nor the metal
content.
(30) (a) Fan, W.; Wu, P.; Namba, S.; Tatsumi, T. Angew. Chem., Int. Ed.
2004, 43, 236–240. (b) Ruan, J.; Wu, P.; Slater, B.; Terasaki, O.
Angew. Chem., Int. Ed. 2005, 44, 6719–6723.
(31) Camblor, M. A.; Corma, A.; Garc´ıa, Semmer-Herle´dan, V.; Valencia,
S. J. Catal. 1998, 177, 267–272.
3.4. Possible Mechanism for Interlayer Silylation and
Pore Expansion. The above results allow us to propose a
possible mechanism for constructing new zeolite structures
through interlayer silylation of lamellar precursors. Figure 13
(32) Ngamcharussrivichai, C.; Wu, P.; Tatsumi, T. J. Catal. 2004, 227,
448–458.
(33) Corma, A.; Nemeth, L. T.; Renz, M.; Valencia, S. Nature 2001, 412,
423–425.
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Synthesizing Crystalline Metallosilicates
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possessing much open reaction spaces, were thus easily acces-
sible to the substrates with large molecular dimensions and also
advantageous to product desorption.
porosity, not only serve as effective heterogeneous catalysts for
large molecules, but also are expected to provide promising
selective adsorbents for adsorption and separation.
Acknowledgment. National Natural Science Foundation of
China (20673038), NCET-04-0423 Science and Technology Com-
mission of Shanghai Municipality (STCSM) (06SR0710 and
06dj14006), 973 Program (2006CB202508), and Shanghai Leading
Academic Discipline Project (B409) are thanked for funding (PW).
Supports from Swedish Research Council, VR, and Japanese
Science and Technology Agency, JST, are acknowledged (OT and
TT).
4. Conclusions
A methodology has been demonstrated for postsynthesizing
new crystalline zeolites with enlarged pores through alkoxysi-
lylating various zeolitic lamellar precursors. The interlayer
structures of MWW, FER, CDO, and MCM-47 topologies are
expanded successfully by the silylation of corresponding precur-
sors. The structural transformation is independent of the
metallosilicate types and the metal contents. The resulting
materials evolve to ordered crystalline structures having opener
pore windows and a high thermal/hydrothermal stability. The
construction of structures is realized as a result of inserting
monomeric silane source forming Si-O-Si linkages between
the layers. These materials, composed of the building units
identical to directly calcined precursors but exhibit larger
Supporting Information Available: IR, 13C and 29Si MAS
NMR spectra, d-spacing values obtained by HRTEM and the
results of catalytic reactions. This material is available free of
charge via the Internet at http://pubs.acs.org.
JA0758739
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