One-step synthesis of hierarchical aluminosilicates using alkoxy-functionalized ionic liquid as a novel template

Article abstract of DOI:10.1039/c5nj02927a

Hierarchical zeolites have bridged the gap between conventional zeolite and mesoporous materials, which not only maintain the excellent advantages of microporous sieves, but also effectively resolve the diffusion limitations. Herein, a novel alkoxy-functionalized ionic liquid was employed as a mesoporous structure-directing agent to synthesize hierarchical aluminosilicates with dual micro-mesoporous channels. X-ray diffraction (XRD), N₂ adsorption-desorption isotherms (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed desorption (TPD), thermogravimetric analysis (TGA) and ²⁷Al magic-angle spinning nuclear magnetic resonance (²⁷Al MAS NMR) were used to characterize the structural and textural features of the hierarchical aluminosilicates. The results showed that the ionic liquid (MTPI) employed played the role of a mesoporous structure-directing agent which was trapped within the pores of a faujasite structure through -Si-O-Al- and -Si-O-Si- linkages. The mesoporous diameters and structures of the final hierarchical materials could be uniformly tailored by tuning the added amount of template. Hierarchical aluminosilicates with the combined advantages of both mesoporous properties and the microporous crystalline structure of zeolites exhibited high catalytic activity and resistance to deactivation in the alkylation of o-xylene with styrene, as compared to the conventional zeolite with the sole presence of micropores. The distinct catalytic performance of hierarchical aluminosilicates could be attributed to the short diffusion routes and abundant exposed acidic sites on the external surface.

Full text of DOI:10.1039/c5nj02927a

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Page 1 of 36
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One-step synthesis of hierarchical aluminosilicates using
alkoxy-functionalized ionic liquid as a novel template
a
a
a,
b
Xiaoqin Fu , Xiaoli Sheng , Yuming Zhou *, Zhiwei Fu ,
a
a
a
Shuo Zhao , Zewu Zhang , Yiwei Zhang
a
School of Chemistry and Chemical Engineering, Southeast University, Jiangsu Optoelectronic
Functional Materials and Engineering Laboratory, Nanjing 211189, P. R. China.
b
Nuclear and radiation safety center, MEP, Beijing 100082, P. R. China
Eꢀmail: ymzhou@seu.edu.cn (Y. Zhou); Tel: +86 25 52090617; Fax: +86 25 52090617.
Abstract
Hierarchical zeolites have bridged the gap between conventional zeolite and
mesoporous materials, which not only maintain excellent advantages of microporous
sieve, but also effectively resolve the diffusion limitations. Herein, novel
alkoxyꢀfunctionalized ionic liquid was employed as a mesoporous structureꢀdirecting
agent to synthesize hierarchical aluminosilicates with dual microꢀmesoporous
2
channels. Xꢀray diffraction (XRD), N adsorptionꢀdesorption isotherms (BET),
scanning electron microscopy (SEM), transmission electron microscopy (TEM),
temperatureꢀprogrammed desorption (TPD), Thermogravimetric Analysis (TGA) and
2
7
27
Al magicꢀangle spinning nuclear magnetic resonance ( Al MAS NMR) were used
to characterize the structural and textural features of the hierarchical aluminosilicates.
The results reflected that the present ionic liquid (MTPI) played the role of
mesoporous structureꢀdirecting agent which was trapped within the pores of faujasite
structure through ꢀSiꢀOꢀAlꢀ and –SiꢀOꢀSiꢀ linkages. The mesoporous diameters and
structure of the final hierarchical materials could be uniformly tailored by tuning the

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added amount of template. Hierarchical aluminosilicates with the combined
advantages of both mesoporous properties and the microporous crystalline structure of
zeolites exhibited high catalytic activity and resistance to deactivation in the
alkylation of oꢀxylene with styrene, as compared with the conventional zeolite with
sole presence of micropores. The distinct catalytic performance of hierarchical
aluminosilicates could be attributed to the short diffusion routes and abundant
exposed acid sites on the external surface.
Keywords: hierarchical aluminosilicates; ionic liquid MTPI; template; alkylation;
catalytic activity

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1
. Introduction
Zeolites are the most important microporous materials with wellꢀordered
1
2ꢀ5
channels and cavities. They account for massive use in industry
thanks to their
advantages of strong acid strength, good shape selectivity characters and excellent
6
, 7
thermal/hydrothermal stability. Among those zeolites used in the modern industrial
processes, zeolite Y has been the most extensively employed material of fluid
8
catalytic cracking (FCC) catalysts for more than 50 years. However, the molecular
dimension of the micropore is only about 7.4 Å. Reactants and products with sizes
beyond the microporous dimensions will slow transport to/from the active sites
located inside the zeolite crystals, leading to an unacceptably slow intracrystalline
9
diffusion rate. This has been a major drawback for the industrial applications of
10
zeolites Y. Mesoporous silicate (2 < pore diameter < 50 nm) have gained increasing
11
interest ever since the first synthesis of MCMꢀ41, because the large pore diameter
allows grafting of bulky organic moieties. However, purely siliceous materials lack
reactive sites, leading to its functionalization relies entirely on incorporation of
12
13
heteroatoms. In particular, Al is capable of producing acid sites in porous silica.
Thus, it is possible to integrate hierarchically microꢀmesoporous aluminosilicates
1
4ꢀ16
materials to tackle the conflict between pore accessibility and catalytic activity.
Hierarchical aluminosilicates with zeolite Y frameworks contain both micropores
and mesopores, preserving the intrinsic zeolite properties and displaying the potential
17
of diffusion via mesoporous channels. Thus, various methods have been utilized to
18
synthesize these hierarchical materials. Zhu et al. reported a method that using

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cetyltrimethylammonium bromide (CTAB) micelle as the soft template, meanwhile
tertbutyl alcohol (TBA) and the 1, 3, 5ꢀtrimethylbenzene (TMB) were as coꢀsolvents,
by which obtained hierarchical aluminosilicates with zeolite Y frameworks. Javier
1
9
PérezꢀRamírez and coꢀworkers had fabricated a broad family of hierarchical Y and
the ultraꢀstable derivative (zeolite USY) by postꢀprocessing method. Dealumination of
zeolites Y was carried out by the treatment of acid and base for the introduction of
8
mesopores. Tao’s group prepared zeolite Y with mesoporous channels using the hard
template method by employing carbon aerogel as a mesoporous template. After
removal of the carbon aerogel template by calcination, the products possessed
relatively uniform mesoporous channels and contained the FAU framework. Even
though these preparation methods have introduced substantial mesoporosity in zeolite
crystals, considering the complexity of these synthetic procedures, the limitation of
pore tunability and the energy consuming, these methods are still unsuitable for
industrial applications. Lately, Liu’s group had designed a supermolecular
(softꢀtemplate) approach to prepare mesoporous zeolite Y with an bifunctional
2
0
3 3 3 6 3 2
ammonium salt [(CH O) SiC H N(CH ) −C18H37]Cl as structure directing agent.
Depending on the synthesis conditions, soft templates have developed as a remarkably
effective alternative for inducing tunable mesopores into zeolites. Unfortunately, soft
templates usually have disadvantages of expensive, infrequent or the synthetic
processes are complex and lowꢀyield, which are not benefit for industrial applications.
Thus, it is crucial to develop a series of appropriate templates.
Nowadays, roomꢀtemperature ionic liquids have attracted overwhelming

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attentions as environmental benign “green solvents” due to their remarkable
21, 22
properties.
Ionic liquid has polarity, but the low interface tension makes it formed
micelles easily. Most importantly, ionic liquid can form extended hydrogenꢀbonds
between molecules in the liquid state, which is the basis of molecular recognition and
2
3
selfꢀassembly process. Hence, ionic liquids are able to aggregate and produce
micelles, and they can be used as templates for preparation of the nanoporous
2
4
materials. Gao et al. successfully synthesized a series of micro/mesoporous silicate
materials using P123 and longꢀchain 1ꢀalkylꢀ3ꢀmethylimidazoliumꢀbased (Cnmim)
−
−
−
ionic liquids [C mim]X (X = Cl , Br and BF ) as the coꢀtemplates. It was
n
4
investigated that the structure of the materials changed along with the differences of
2
5
the alkyl chain length and anion. Wang et al. had obtained a twoꢀdimensional
hexagonal p6mm mesopore structure (MCMꢀ41) as well as with a cubic gyroid
mesoporous silica Ia3d (MCMꢀ48) framework using the ionic liquid
1
ꢀhexadecylꢀ3ꢀmethylimidazolium bromide as the template under basic condition.
Therefore, imidazolium based ionic liquids owing to their distinctive properties are
appropriate to synthesize micro/mesoporous materials. However, the synthesis of
highly ordered micro/mesoporous materials has rarely been reported using
alkoxyꢀfunctionalized
ꢀmethylꢀ3ꢀ[3'ꢀ(trimethoxysilyl) propyl] imidazolium chloride (MTPI) was chosen to
serve as a mesoporous template. The presence of the alkoxyꢀfunctionalized group
CH O) ꢀSiꢀ can quickly hydrolyze to HOꢀSiꢀ, yield firm ꢀSiꢀOꢀSiꢀ, ꢀSiꢀOꢀAlꢀ bonds
that anchor the MTPI into the microporous framework, which substantially enhance
ionic
liquid.
Thus,
the
ionic
liquid
1
(
3
3

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the stability of mesopores. Like the case of zeolite synthesis, the organic tail of MTPI
constructs the mesoporous channels while the silica moiety is incorporated in the
resultant microporous frameworks. Therefore, mesoporous channels are formed with
crystalline microporous zeolite Y by calcination to eliminate the template MTPI.
In the present work, a facile route to synthesize hierarchical aluminosilicates
with zeolites Y frameworks possessing both micropores and mesopores has been
reported. Firstly, the alkoxyꢀfunctionalized ionic liquid MTPI was synthesized from
cheap raw materials by ultrasonic/ microwave synergistic method within 2 min. Then
hierarchical zeolites were obtained using the aforementioned MTPI as a template. A
series of hierarchical zeolite Y with tunable mesoporous structure and various
morphologies could be synthesized by changing the added amount of MTPI during
synthesis. Combining the above two aspects together, the formation mechanisms for
the synthesis of mesoporous zeolite Y using MTPI as the template were tentatively
elucidated. Moreover, the microꢀmesoporous zeolite Y, combining the advantages of
mesoporous materials with microporous zeolite crystals, is expected to be more
suitable for catalytic reactions involving large molecules as a catalyst. Thus its
catalytic activity in the alkylation of oꢀxylene with styrene was investigated.
2
. Experimental Section
2
.1 Materials
ꢀmethylimidazole (99%), 3ꢀchloropropyl trimethoxysilan (98%), sodium
metasilicate (Na SiO , SiO 44ꢀ47%), sodium aluminate (NaAlO ), aluminum sulfate
1
2
3
2
2

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2 4 3 2
octadecahydrate (Al (SO ) ·18H O, 99%), sodium hydroxide (NaOH, AR, 96%) were
of analytical grade, and all of them were purchased from Aladdin. Deionized water
was used in all experiments. All chemicals were used as received without further
purification.
2
.2 Synthesis of MTPI
Ionic liquid MTPI had been synthesized by ultrasonic/microwave synergistic
method using 21.75 g (0.265 mol) of 1ꢀmethylimidazole and 52.66 g (0.265 mol) of
ꢀchloropropyl trimethoxysilane in a solventꢀfree process. The two hybrid materials
3
were poured into a reaction vessel, and then placed into a microwave oven equipped
with ultrasonic. The ultrasonic power was set at 300 W with a cycle of working 1.1 S
and intermitting 1.1 S. The mixture was irradiated at 320 W, reaction temperature was
o
1
20 C and irradiation continued for a total of 2 min. Then the product was directly
dried under continuous evacuation (1 mm Hg) at 100 °C for 12 h without any
purification. After cooling to room temperature, the product was obtained as yellowish
1
viscous liquid, which was stored under dry conditions. MTPI was characterized by H,
2
9
1
Si spectroscopy (Fig. 1). H NMR (CDCl
H, ꢀNꢀCH=CHꢀNꢀ), 7.366 (s, 1H, ꢀNꢀCH=CHꢀNꢀ), 4.252 (t, 2H, ꢀNꢀCH
H, ꢀNꢀCH ), 3.488 (t, 9H, ꢀSiꢀOCH ), 1.934 (quint, ꢀCH ꢀCH ꢀCH ꢀ), 0.558 (t, 2H,
3
): δ = 10.411 (s, 1H, ꢀNꢀCHꢀNꢀ), 7.592 (s,
1
3
2
ꢀ), 4.052 (s,
3
3
2
2
2
2
9
ꢀ
SiꢀCH ꢀ). Si NMR (DMSOꢀd6): δ = ꢀ68.357. In addition, the NMR spectroscopy
2
was used to characterize the trace amounts of remaining 1ꢀmethylimidazol and
3
1
ꢀchloropropyl trimethoxysilane, respectively. The maximum content of remaining
ꢀmethylimidazol is 1.95%. And the content of remaining 1ꢀmethylimidazol is 2.70%.

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1
29
Fig. 1 (a) H NMR spectrum of MTPI, (b) Si spectrum of MTPI.

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2
.3 Synthesis of mesoporous zeolite Y
The mesoporous zeolite Y was hydrothermally synthesized by addition of ionic
liquid (MTPI) into the conventional synthesis compositions for microporous zeolite Y.
In a typical synthesis experiment: the blended solution involved 15.379 g of
Na
precursor was obtained by mixing 0.07 g of NaOH, 2.20 g of Na
NaAlO and 7.2 mL of deionized water, then the mixture stirred at 50 °C for 1 h and
2
SiO
3
, 52 mL of deionized water, followed by the addition of precursor (the
2
SiO , 0.16 g of
3
2
aged at 50 °C for 5 h) was added dropwise to the solution, after which the mixture
o
was stirred at 50 C for 1.5 h, during which 1ꢀmethylꢀ3ꢀ[3'ꢀ(trimethoxysilyl) propyl]
imidazolium chloride was slowly added dropwise. After the mixture was further
stirred for another 1.5 h, 0.18 g of NaOH, 3.49 g of Al
2 4 3 2
(SO ) ·18H O and 1.17 g of
NaAlO were added under vigorous magnetic stirring. The resulting synthesis mixture
2
was further vigorously stirred for another 12 h, a homogeneous milk white solution
was observed. The resultant aluminosilicates gel had a molar composition of 1.0
Na
2
O/0.93 SiO
2
/0.088 Al
2
O
3
/21.86 H
2
O/ x MTPI (x = 0.05, 0.1, 0.15, 0.2 and 0.25),
O. Then the resultant
wherein x represents the molar ratio of MTPI/Na
2
aluminosilicates gel was transferred into a Teflonꢀlined autoclave and heated in an
o
oven at 100 C for one day (referred to as the crystallization time). The crystallization
o
products were collected by filtration with deionized water, dried at 100 C in an air.
o
ꢀ1
Then calcination was carried out with a heating rate of 3 C·min , and kept at the
o
target temperature 600 C for 6 h to remove the template. The final hierarchical
zeolites NaY with x = 0.05, 0.1, 0.15, 0.2 and 0.25 were denoted as NaYꢀxMTPI. For

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comparison, the conventional NaY was obtained by the same procedure as the above
except for the addition of MTPI and was denoted as “NaY”.
2
.4 Catalytic reaction
The alkylation reactions of styrene with oꢀxylene have been chosen as a model
reaction of large molecules to investigate the catalytic ability of the hierarchical
zeolite Y. Before the catalytic tests, all the samples were ionꢀexchanged by repeated
o
+
4
procedure with 1 M NH Cl solution at 90 C and then converted to the H form via
o
calcination in air at 550 C for 6 h. Catalysts were denoted as HYꢀxMTPI or HY. In a
typical reaction, the alkylation reactions were carried out in a continuously stirred oil
batch reactor under reflux conditions. 45 g (0.4239 mol) of oꢀxylene, 5.89 g (0.0566
mol) of styrene (molar ratio of oꢀxylene to styrene is 7.5 : 1) and 1.00 g of catalyst
o
were mixed and the reaction was conducted at 120 C for 3 h under stirring in a
threeꢀnecked roundꢀbottom flask with a reflux condenser. Firstly, the mixture of the
small amount of oꢀxylene were added to the roundꢀbottom flask, followed by the
desired amount of catalyst, then the mixture of a certain amount of styrene and the
remaining oꢀxylene was dropwise added into the flask for 2 h. The final reaction
mixture remained for another 1 h. After the reaction, unreacted oꢀxylene was distilled
out under atmospheric pressure and the obtained liquid was denoted as crude product.
The crude product was analyzed with GCꢀ9890A gas chromatograph equipped with
OVꢀ1 capillary column and a flame ionization detector (FID). The yield of
1
ꢀphenylꢀ1ꢀxylylethane (PXE) was defined as follows:
actual product weight
Yield of PXE (%) =
× 100%
theoretical product weight

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Actual product weight = crude product weight × PXE (chromatography) %
.5 Characterizations
2
Powder Xꢀray diffraction (XRD) patterns of the synthesized zeolites were
recorded on a Bruker D8 Advance diffractometer (Germany) system. Transmission
electron microscopy (TEM) experiments were conducted on a JEMꢀ1230 with an
acceleration voltage of 100 kV. Scanning electron microscope (SEM) images was
used to reveal the morphologies and microstructures of synthesized zeolites on
Hitachi Sꢀ3400N with an acceleration voltage of 20 kV. Fourier transform infrared
spectra (FTꢀIR) of these samples were recorded on a Bruker Tensor 27 (German)
ꢀ1
ꢀ1
using DRIFT techniques, scanned from 4000 cm to 500 cm . The Si/Al molar ratios
of the samples were obtained by Xꢀray fluorescence (XRF) measurements on a
2
7
Switzerland’s ARL 9800 XRF apparatus. The solidꢀstate Al magicꢀangle spinning
2
7
nuclear magnetic resonance ( Al MAS NMR) spectra were collected by a Bruker
1
DSXꢀ400 spectrometer. H NMR spectra were performed on an AvanceII 200
2
9
spectrometer (Bruker), using CDCl
3
as a solvent. Si NMR spectra were collected by
a Bruker DSXꢀ500 spectrometer, using DMSOꢀd6 as a solvent. Surface acidity was
measured by NH
3
ꢀTPD in a TPꢀ5000 apparatus (made in China) at atmospheric
o
pressure. The sample (150 mg) was preheated at 500 C for 1 h, and then cooled down
to room temperature under a flowing He stream. At this temperature, sufficient pulses
3
of NH were injected until adsorption saturation. The textural properties of the
asꢀsynthesized samples were determined by the nitrogen adsorption and desorption
isotherms on an ASAPꢀ2020 (Micromertics USA) at 77 K. The samples were out

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o
gassed for 6 h at 350 C before the measurements. The specific surface area (SBET
was determined from the linear part of the BrunauerꢀEmmettꢀTeller (BET) equation
P/P = 0.05ꢀ0.25). The pore size distribution was calculated using the
)
(
0
BarrettꢀJoynerꢀHalenda (BJH) method from the desorption branch of the N isotherm.
2
The total pore volume (Vtotal) was estimated from the amount of nitrogen adsorbed at
0
a relative pressure (P/P ) of ca.0.995. The thermal behavior of a washed,
asꢀsynthesized sample was followed on a Perkin Elmer Pyris 6 TGA analyzer with a
o
ꢀ1
heating rate of 20 C/min under an air flow of 30 mL·min .
3
. Results and discussion
In this study, hierarchical zeolites Y were synthesized via a oneꢀstep method
using an ionic liquid MTPI as the single template, where no secondary template and
additives were added. The characterization of the samples was done by XRD, BET,
27
SEM, TEM, NH ꢀTPD, TGA and Al NMR. The catalytic activity of hierarchically
3
microꢀmesoporous zeolite Y was assessed by using the alkylation of oꢀxylene with
styrene. In addition, a postulate mechanism for the synthesis of hierarchically
microꢀmesoporous zeolite Y was proposed.
3
.1 Characterization
3
.1.1 Crystallinity and structural studies

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Fig. 2 XRD patterns of these samples, synthesized in the absence (conventional) or in the presence
of MTPI (a), and smallꢀangle XRD patterns for NaYꢀ0.15MTPI (b).

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Fig. 2a provides the XRD patterns of the synthesized samples in the absence or
in the presence of MTPI with various molar ratios of MTPI/Na O. The XRD patterns
2
2
6
of all the samples show that the typical topological structure of zeolite Y, the only
change is the intensity of characteristic peaks. Initially, only some broad diffraction
peaks with much lower intensity are preserved for conventional NaY, indicating its
2
lower crystallinity. While continuing raising the molar ratio of MTPI/Na O amount up
to 0.15, relative crystallinities of zeolites Y are increased continuously. It suggests that
a higher amount of MTPI favored better crystallinity. Further increasing the molar
ratio of MTPI/Na O to 0.25, the synthesized zeolite Y shows a relative low
2
crystallinity. The phenomena indicate that the large amount of MTPI in the initial gel
is not beneficial to the crystallization process. In addition, the sample NaYꢀ0.15MTPI
exhibits a broad peak in the low 2θ region of 0.5ꢀ5° (Fig. 2b), indicating the formation
27
of a wormꢀlike mesoporous channels. It is reasonably concluded that the positive
contributions of template MTPI to the crystal growth and mesoporous channels in the
crystallization process.
3
.1.2 Study of textural properties

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Fig. 3 N
2
adsorption−desorption isotherms of the samples induced by different molar ratio of
MTPI/Na O (A), the corresponding pore size distribution calculated by BJH model based on the
2
desorption curves (B).

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The nitrogen adsorption and desorption isotherms show distinct differences in
their shapes for the materials obtained in the absence or in the presence of MTPI
during the synthesis process (Fig. 3A). The zeolite NaY presents a classical type I
20
isotherm, which is generally observed for microporous solids. The isotherms of
those samples in the presence of ionic liquid MTPI shows representative
characteristics of type IV. Each has an obvious wellꢀdefined hysteresis attributed to
27
the presence of predominant mesoporous structure. With increasing molar ratio of
MTPI/Na O, the pressure onset of the hysteresis gradually shifts to higher values,
2
from 0.4 (x ≤ 0.15) to 0.7 (x ≥ 0.2), indicating pore size shrinkage. Furthermore, the
size distributions in Fig. 3B give more clear evidence. When the molar ratio of
2
MTPI/Na O is less than or equal to 0.15, a narrow distribution with main mesopores
at 3.89 nm is observed. While in the case of x = 0.2 (or 0.25), a small pore size
distribution at 3.89 nm with another dominant peak at 9.5 nm (or 12.82 nm) is found.
With further increasing the molar ratio of MTPI/Na O, more ionic liquid molecules
2
are aggregated to forming bigger micelles, which results in the maximum peak value
of the pore size distribution shifting to larger scale. Meanwhile, its pore size
distribution becomes broader.
From the physicochemical properties summarized in Table 1, it is particularly
noteworthy that the surface area and tꢀplot external surface area of mesoporous Y
2
increased with the increase of the molar ratio of MTPI/Na O from 0.05 to 0.15. While
both the surface area and the external area of samples with x = 0.2 (or 0.25) are
decreased compared with NaYꢀ0.15MTPI. Moreover, the corresponding crystallinities

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of them are decreased (Fig. 2). It can be reasonable concluded that the addition of too
much and too little MTPI also influence the complete zeolite growth and the
2
introduction of mesopores. Therefore, suitable molar ratio of MTPI/Na O is important
for fabrication of highly crystallized and ordered hierarchical aluminosilicates.
Table 1 Characteristic data of samples synthesized in the absence (conventional) or in the
presence of MTPI
a
b
c
sample
S
BET
S
ext
V
micro
V
total
Pore size
(nm)
Si/Al
2
ꢀ1
2
ꢀ1
3
ꢀ1
3
ꢀ1
(
m ·g ) (m ·g ) (cm ·g ) (cm ·g )
NaYꢀ0.05MTPI
NaYꢀ0.10MTPI
NaYꢀ0.15MTPI
NaYꢀ0.20MTPI
NaYꢀ0.25MTPI
NaY
621
648
690
539
448
595
82
68
76
37
33
11
0.25
0.27
0.28
0.23
0.19
0.29
0.38
0.35
0.39
0.30
0.25
0.31
3.89
3.89
3.89
2.19
2.26
2.3
3.89; 9.35
3.88; 12.82
0.74
2.34
2.41
2.15
a
b
c
BET method
tꢀplot method
BJH model applied to the desorption branch of the isotherms

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3
.1.3 Morphological properties
Fig. 4 SEM images of asꢀsynthesized samples: NaY (a), NaYꢀ0.05MTPI (b), NaYꢀ0.1MTPI (c),
NaYꢀ0.15MTPI (d), NaYꢀ0.2MTPI (e), and NaYꢀ0.25MTPI (f).
In addition to elucidate the influence of templates’ amount on the formation of
hierarchical aluminosilicates, we carried out SEM images (Fig. 4) to show their
structure morphologies. SEM images display the stepwise product changes of those
samples. The typical octahedral structure is observed in the samples with a low

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amount of ionic liquid MTPI (Figs. 4b and c) or in absence of MTPI (Fig. 4a). The
intermediate phase (Fig. 4d) reveals the analogous cauliflowerꢀlike formed by primary
block particles. Along with the increase of templates’ concentration, the final products
show dense spherical morphology with smooth surface (Figs. 4e and f).
3
.1.4 Study of calcination
In order to investigate the pyrolysis behavior of sample NaYꢀ0.15MTPI and ionic
liquid template, thermogravimetric analysis (TGA) was employed to monitor the
degradation behavior in air atmosphere. As shown in Fig. 5A, a notable weight loss of
o
approximately 12.45% is observed below 120 C, which is corresponded to physically
2
0
absorbed water in the zeolite framework. The obvious weight loss of 7.07%
o
appearing in the temperature ranges 120ꢀ300 C is mainly attributed to the
28
decomposition of template. At the end, approximately 80 wt% aluminosilicates
residues are left. It is important to note that template MTPI can be removed after
o
calcination at 600 C, giving rise to a mesoporous structureꢀdirecting agent.
FTꢀIR was carried out to analysis the structure of sample NaYꢀ0.15MTPI before
and after calcination (Fig. 5B). Prior to calcination, those absorption peaks at 2976,
ꢀ1
2
901 and 1387 cm are observed, which are assigned to different CꢀH bond stretching
29
vibrations from the ionic liquid MTPI. However, these bands disappear after
calcination of the sample. These spectra prove that calcination of the composite
crystals removes the ionic liquid MTPI and forms hiearchical zeolite Y with
intercrystalline mesopores.

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Fig. 5 Thermogravimetric (TGA) curve of hierarchical zeolite NaYꢀ0.15MTPI (A). FTꢀIR spectra
of sample NaYꢀ0.15MTPI before and after calcination (B).

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3
.1.5 Porosity characterization
Fig. 6 TEM images of samples NaY(A) and NaYꢀ0.15MTPI (B, C, D) (the mesoporosity in the
crystal is marked by red lines).
The TEM images of conventional NaY and hierarchical zeolite NaYꢀ0.15MTPI
are shown in Fig.
6. From the Fig.
6a, only the ordered microporous channels are
presented and no mesoporous channels are detected. Whereas, TEM images (Figs.
6
B,
C and D) give direct evidence for the presence of intracrystalline mesostructure in the
hierarchical zeolite NaYꢀ0.15MTPI. These results are consistent with those of other
2
6, 30
literature.
The observation of disordered wormlike mesostructure confirms the
presence of mesopores (the mesoporosity in the crystal is marked by red lines). The

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26
mesoporous structure are well present in the nearest neighboring frameworks,
2
combining with the corresponding N adsorptionꢀdesorption isotherms, indicating that
the formation of hierarchical zeolite Y framework. Moreover, the wormlike
mesoporous structure are quite curve and the width are differed. It may be attributed
to the disordered aggregation of MTPI, reflecting that the ionic liquid micelles are
mesoporous templates.
3
.1.6 NH
3
-TPD analysis
3
Fig. 7 NH ꢀTPD profiles of HY and hierarchical HYꢀxMTPI.
Acidic properties of classical HY and hierarchical HYꢀxMTPI are investigated by
3
ꢀTPD analysis, with the TPD profiles presented in Fig. 7. There is a desorption
NH
3
peak of NH at 200 °C–300 °C observed in the sample HY, which is attributed to the

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adsorption to NH
of MTPI, desorption peaks of NH
sample HYꢀ0.05MTPI exhibits two NH
corresponding to the weak acid site and the medium strong acid sites, respectively.
The curves of NH ꢀTPD from samples HYꢀ0.1MTPI and HYꢀ0.15MTPI show only
one peak, the higherꢀtemperature NH ꢀTPD peak being used to evaluate the
3
of the weak acid sites. While continuing raising the added amount
gradually shift to slightly higher temperature. The
desorption peaks at 250 °C and 350 °C,
3
3
3
3
concentration of strong acid sites in the hierarchical aluminosilicates. However, with
the further increasing amount of template MTPI, the peak for acid sites is not very
obvious for samples HYꢀ0.2MTPI and HYꢀ0.25MTPI. Moreover, the strength and the
amount of acid sites of the HYꢀ0.15MTPI zeolite are the highest among the
hierarchical aluminosilicates, which contributes to the highest catalytic activity (Table
2
). It may be ascribed to its largest BET surface area, highest mesoporous pore
volume, and highest crystallinities of NaYꢀ0.15MTPI resulting in a higher proportion
3
1
of framework Al species.

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27
3
.1.7 Al MAS NMR spectrometric analysis
27
Fig. 8 Al MAS NMR spectra of microporous HY and hierarchical HYꢀxMTPI.
27
27
Fig. 8 presents the Al NMR spectra of these aluminosilicates. The Al MAS
NMR spectrum for all asꢀsynthesized samples exhibit two distinct signals at around
7 ppm assigned to fourꢀcoordinated Al in the zeolite framework and around 0 ppm
5
11
attributed to the extraꢀframework octahedral coordination of Al, respectively. The
hierarchical zeolites HYꢀxMTPI possess more extraꢀframework aluminum species
than the sample HY, which is attributed to the formation of extraꢀframework
aluminum species during the crystallization process. This confirms the above
characterization results that the addition of MTPI leads to the formation of mesopores
in the external surface of zeolite, and the enhancement of peaks at around 0 ppm is
resulted from the exposure of extraꢀframework aluminums. In comparison with the

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27
classical HY, the Al NMR signals of all hierarchical zeolites HYꢀxMTPI at around
5
7 ppm are strengthen. Particularly, the HYꢀ0.15MTPI zeolite possesses the most
intense peak at 59 ppm, which is attributed to that most of the aluminium atoms are
located inside the aluminosilicates framework on tetrahedral sites with the Si or Al
atoms, establishing ꢀAlꢀOꢀSiꢀ, ꢀAlꢀOꢀAlꢀ linkages. It may be contributed to the
improvement of the acid amount and acid strength for the hierarchical HYꢀ0.15MTPI.
3
.2 Possible mechanism

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Scheme 1 (a) Schematic diagram represents the synthesis of hierarchical zeolite Y using MTPI
as a template. (b) Schematic representation of the stepwise product changes of those samples with
2
MTPI micelles aggregates at different molar ratio of MTPI/Na O.
Given our results, we propose a possible mechanism for the synthesis of
hierarchical zeolite Y with 1ꢀmethylꢀ3ꢀ[3'ꢀ(trimethoxysilyl) propyl] imidazolium
chloride ionic liquids (MTPI) as a novel template (Scheme 1). In aqueous solution,
alkoxyꢀfunctionalized (CH
3
O)ꢀSiꢀ bonds can quickly hydrolyze to HOꢀSiꢀ and form
firm ꢀSiꢀOꢀSiꢀ, ꢀSiꢀOꢀAlꢀ bonds anchoring in the zeolite framework, which
26
substantially enhance the stability of mesopores. On the one hand, the electrostatic
interaction between the positively charged imidazole head group and negatively
charged aluminosilicates gels lead to the formation of mesopores. On the other hand,
head group forming bulky hydrophobic barriers in the micelles also act as an effective
structureꢀdirecting agent for the zeolite, promoting the formation of mesoscale

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micelles. So the resultant zeolites exhibit mesoporous channels presenting between
the neighboring crystalline microporous frameworks. Moreover, the mesoporous
diameter can be tailored by changing the synthesis condition in the presence of MTPI.
The ionic liquid nucleation and growth follow the classic nucleation and growth
theory. Thus, samples display the stepwise product changes with the increase of
templates’ concentration which gradually from the blocky phases to spheres (Scheme
1
b). At the low amount of MTPI, the ionic liquid MTPIs are well dispersed in the
aluminosilicates gel to undertake the mesoporous structureꢀdirecting agent by
anchoring and templating. Especially, mesoporous zeolite Y introducing at the
appropriate amount (x = 0.15) has many good properties, such as good crystallinity,
high mesopore volume, large surface area and strong acid sites. With the continuing
increase of MTPIs, ionic liquids aggregate to be many large micelles and attract the
traditional composition of zeolite Y by the ꢀSiꢀOꢀSiꢀ, ꢀSiꢀOꢀAlꢀ bonds to the
formation of spherical mesoporous zeolite Y. Consequently, only a small portion of
MTPI undertakes the mesoporous structureꢀdirecting agent, resulting in the decrease
of the BET surface area, external surface and mesopore volumes. These phenomena
are certified by SEM images and BET.

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3
.3 Catalytic activity
Scheme 2 Reaction scheme of alkylation of oꢀxylene with styrene over a heterogeneous catalyst.
Alkylation reactions of oꢀxylene and styrene over the conventional HY and
hierarchical zeolites HYꢀxMTPI catalysts were carried out to discover their difference
in catalytic performance. And the catalytic activity of different catalysts is shown in
Table 2. The detailed reaction scheme is shown in Scheme 2: reaction (1) is the PXE
formation reaction whereas reaction (2) and (3) represent the formation of styrene
oligomers and more substitutes, respectively. From Table 2, it is noteworthy to
mention that classical zeolite HY has poor catalytic performance. While a significant
increase of yields of PXE are achieved with all the hierarchical zeolites HYꢀxMTPI.
Especially, the sample HYꢀ0.15 MTPI shows the best catalytic performance in terms
of yield and selectivity, which can be attributed to its largest mesoporous volume,

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abundant acid amount and structural properties which are favorable for fast diffusion
of products.
a
Table 2 Activity of various catalysts in alkylation of oꢀxylene with styrene
b
c
Catalyst
Styrene conversion PXE yield
PXE Selectivity
(%)
(%)
(%)
Classical HY
HYꢀ0.05MTPI
HYꢀ0.1 MTPI
HYꢀ0.15 MTPI
HYꢀ0.2 MTPI
HYꢀ0.25 MTPI
84.53
96.26
98.89
97.56
90.23
87.78
12.67
40.00
73.78
82.01
40.51
36.62
14.99
41.55
75.84
82.93
44.89
41.72
a
o
Reaction conditions: oꢀxylene: styrene = 7.5: 1, reaction temperature = 120 C, reaction time
=
3.0 h, catalyst loading = 20 % (w/w of styrene)
b
c
Isolated yield based on the amount of styrene
Including all products