Chemistry of Materials
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example that the hierarchical lamellar zeolite is prepared by
organic pillars to generate secondary pore architecture in
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the self-assembly of the commercially available monoquater-
nary ammonium surfactant and inorganic zeolite layers has
been realized.
mesoscale. The mixture of fumed silica (AEROSIL 200) and
the calcined ITQ-1 silicate (its detailed synthesis procedure
was shown in Supporting Information) was used as the start-
ing silica source, in which the molar percentage of fumed
silica was varied as 0, 25, 50, 75 and 100 %. In a typical syn-
thesis, the silica source (fumed silica and ITQ-1 seed) was
In traditional syntheses, the simple surfactant CTAB was
highly expected to cooperate with the organic structure-
directing agent (OSDA) in hydrothermal synthesis, leading
to the direct crystallization of hierarchical zeolites. However,
these two types of organic templates with different proper-
ties hardly act in a synergistic manner, but in fact, they usu-
ally compete to direct independently the formation of meso-
pores and micropores, leading to phase separation. Generally,
the self-assembly of surfactant molecules and the growth of
microporous crystalline framework are incompatible with
each other from both thermodynamic and kinetic viewpoints.
Consequently, it is difficult to achieve highly-ordered zeolite
phases and mesostructures simultaneously, even when a
complex multiammonium surfactant is adopted. Thus, it is
regarded as a well-known challenge in the field of hierar-
chical zeolite to discover controllable systems in which the
simple surfactant and inorganic crystalline zeolite phase can
self-assemble cooperatively to generate micro- and mesopo-
rous materials with simplicity and potential industrial viabil-
ity.
+
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added to an aqueous solution of IM OH under stirring at
room temperature for 1 h, resulting in the gel A with a molar
+
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2 2
composition of 1.0 SiO : 0.5 IM OH : 25 H O. The gel A was
transferred into an autoclave and reacted at 443 K for 1 h un-
der rotation, and then cooled to room temperature quickly to
obtain the gel B. Subsequently, the aluminum source NaAlO2
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(44.3 % Al
2 3 2
O , 37.5 % Na O) and CTAB surfactant were intro-
duced into the gel B, giving a mixture with final molar com-
+
-
1
2 2 2 3
position of 1.0 SiO : 0.5 IM OH : 25 H O : (0 ~ /30) Al O : 1.0
CTAB. The resulting gel was sealed in an autoclave and fur-
ther treated at 423 K under rotation condition. After crystalli-
zation for a period of time, the product ECNU-7P (Si/Al = 15 ~
∞
) was obtained after filtration and dried at 353 K. The
OSDAs and surfactants were removed by calcination in air at
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73 K for 6 h, giving rise to a hierarchical zeolite ECNU-7.
Besides, the pillaring of the multilamellar Al-ECNU-7P was
33
performed according to the method reported previously.
For control experiment, the conventional MCM-22 alumino-
silicate was synthesized according to that reported in the
In this contribution, we approached for the first time
the hydrothermal preparation of a mesostructured multila-
mellar MWW zeolite ECNU-7P by controllable self-
assembling of simple surfactant CTAB and lamellar zeolite
precursors through a zeolite seed and CTAB-assisted disso-
lution-recrystallization route. The small quaternary ammo-
nium hydroxide, 1,3-bis(cyclohexyl)imidazolium hydroxide,
was used as the small OSDA to direct the crystallization of
MWW sheets, whereas the bulky CTAB surfactants pillared
the layers thus constructed. The combination of the charac-
literature,34 while the MCM-56 analogue was post-
synthesized from the as-made MCM-22 precursor by a mild
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acid treatment.
RESULTS AND DISCUSSION
Synthesis and characterization of multilamellar zeolite
ECNU-7P. The syntheses of the swelling-type multilamellar
MWW zeolite were tried under various hydrothermal condi-
+
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+
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tions using CTAB and IM OH as soft templates. IM OH has
been demonstrated to possess the ability for directing the
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terizations, such as 2D H- Si solid-state NMR, X-ray, elec-
tron microscopy and rotation electron diffraction (RED)
analyses, provided molecular-level insights into the interac-
tions between CTAB molecules with respect to crystalline
zeolite layers. The cationic hydrophilic head group of CTAB
had a strong interaction with the inorganic zeolite layer and
was embedded in the hemi-cavities on the MWW layer sur-
face, while its hydrophobic long-chain alkyl group (C16) sup-
ported the neighboring MWW nanosheets, resulting in al-
ternative self-assembly of inorganic zeolite layers and organ-
ic CTAB layers in the multilamellar zeolite ECNU-7P. With
the assistance of MWW zeolite seed, the Al-containing
ECNU-7P could be synthesized in a wide range of Si/Al rati-
os (15 ~ ∞). The calcined Al-ECNU-7 with hierarchical struc-
ture exhibited excellent activity, selectivity and stability in
the catalytic reactions involving bulky molecules.
MWW topology. The syntheses were carried out using the
pre-prepared MWW-type silicate (well known as ITQ-1) or
the mixture of ITQ-1 and amorphous silica as the starting
material. A very successful result was obtained in the case of
Al-ECNU-7P (Si/Al = 50) with 3D MWW ITQ-1 as the sole
starting material, in which the MWW sheets were stacked in
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an ordered manner (Figure 1Ea). Taking this as the repre-
sentative, the crystallization process could be divided into
two stages. At Stage I, the starting silica source (the calcined
+
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ITQ-1 silicate in this case) was mixed with the IM OH solu-
tion to give the gel A, which was hydrothermally treated at
443 K for 1 h to degrade the crystalline structure of original
MWW zeolite to obtain the gel B. Then, the aluminum
source together with the simple surfactant CTAB were intro-
duced into the resulting gel B, and then the synthesis con-
tinued at 423 K in Stage II. The Stage I was the same as the
early procedure that we reported in the synthesis of novel
32
EXPERIMENTAL SECTION
layered zeolite ECNU-5P, during which the crystals of
Synthesis of organic structure-directing agent (OSDA).
MWW silicate were dissolved significantly in the basic medi-
um as the MWW framework greatly collapsed within 1 h,
giving a solid yield of only 17.8 wt.% (Figure 1Cb). The re-
maining solid exhibited somewhat broadened PXRD peaks
with reduced intensity, which was attributed to the residual
crystalline MWW phase (Figure 1Ab and 1Bb). Thus, the dis-
solved silicate fragments in liquid phase as well as the re-
maining solid phase, both still containing or consisting of the
basic building units of the MWW structure, may act as nutri-
ent species for crystallization in the next synthesis stage.
+
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1,3-bis(cyclohexyl)imidazolium hydroxide (IM OH ) was em-
ployed as the OSDA for the crystallization of MWW zeolite.
The synthesis procedure and characterization of the organic
compound are represented in Supporting Information, which
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are the same as those reported previously.
Synthesis of multilamellar precursor ECNU-7P and hier-
archical zeolite ECNU-7. Multilamellar precursor ECNU-7P
was synthesized using dual organic templates, those were,
+
-
IM OH as the OSDA for crystallizing microporous MWW
topology and commercially available CTAB surfactant as the
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