Synthesis of the nanosized MCM-22 zeolite and its catalytic performance in methane dehydro-aromatization reaction

Article abstract of DOI:10.1016/j.catcom.2013.10.007

A novel and facile synthesis method based on the combination of self-assembly and in-situ crystallization is developed for the preparation of nanosized MCM-22 zeolites (simplified as MCM-22-NZ hereafter) of about 40 nm, where the cationic polymer, PDDA, was added to play a role of protecting agent to avoid the synthesis colloids self-aggregation. MCM-22-NZ was characterized by XRD, TEM, DLS, NH₃-TPD, XRF, TG and N₂ adsorption analysis. The catalytic activity of MCM-22-NZ in methane dehydro-aromatization (MDA) reaction was also studied. Mo/HMCM-22-NZ showed better methane conversion, higher benzene yield and more considerable durability of the catalyst as compared to the conventional microsized catalyst.

Full text of DOI:10.1016/j.catcom.2013.10.007

Catalysis Communications 43 (2014) 218–222
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Synthesis of the nanosized MCM-22 zeolite and its catalytic performance
in methane dehydro-aromatization reaction
b
c
c
a
Xiaoyan Yin a, , Naibo Chu , Jianhua Yang , Jinqu Wang , Zhongfang Li
⁎
a
School of Chemical Engineering, Shandong University of Technology, Zibo 255049, PR China
The Central Research Institute of Yantai WH Polyurethane Co. Ltd., Yantai 264002, PR China
School of Chemical Engineering, Dalian University of Technology, Dalian 116012, PR China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 April 2013
Received in revised form 18 July 2013
Accepted 8 October 2013
Available online 16 October 2013
A novel and facile synthesis method based on the combination of self-assembly and in-situ crystallization is
developed for the preparation of nanosized MCM-22 zeolites (simplified as MCM-22-NZ hereafter) of about
40 nm, where the cationic polymer, PDDA, was added to play a role of protecting agent to avoid the synthesis
colloids self-aggregation. MCM-22-NZ was characterized by XRD, TEM, DLS, NH3-TPD, XRF, TG and N2 adsorption
analysis. The catalytic activity of MCM-22-NZ in methane dehydro-aromatization (MDA) reaction was also
studied. Mo/HMCM-22-NZ showed better methane conversion, higher benzene yield and more considerable
durability of the catalyst as compared to the conventional microsized catalyst.
Keywords:
MCM-22 zeolite
Nanocrystals
© 2013 Elsevier B.V. All rights reserved.
Methane dehydro-aromatization
Mo/HMCM-22-NZ
Durability of catalyst
1. Introduction
It is well known that the nanosized zeolites have substantial changes
in the catalytic properties, such as larger external surface areas, higher
Recently, methane dehydro-aromatization (MDA) reaction has
attracted increasing attention since it can directly convert methane
into high value-added chemicals like benzene, toluene and naphthalene.
It has been considered as one of the greatest potential technologies for
effective utilization of natural gas [1–6]. Up to now, Mo/HMCM-22
catalyst is one of the most promising catalysts in MDA reaction due to
its unusual channel structure and features with a higher yield of
benzene and a less yield of naphthalene in comparison with the Mo/
HZSM-5 catalyst under the same experimental conditions [1,6].
MCM-22 zeolite possesses two independent multidimensional
channel systems: two-dimensional 10-ring sinusoidal inter-layer
channel system and inter-layer channel system containing 12-ring
interlayer super-cages with inner free space of 0.71 × 0.71 × 1.82 nm,
both of which are accessible through 10-ring apertures [7]. Due to its
unique structure and physicochemical properties, MCM-22 has been
widely used in many hydrocarbon catalytic transforming processes
such as isomerization, alkylation, aromatization and cracking [1,6,8–10].
However, in MDA reaction, the methane conversion decreased drastically
with time-on-stream due to the heavy carbonaceous deposits on the
MCM-22 catalyst, which is a vital drawback for the reaction. Therefore,
many researchers have focused on how to improve the catalyst stability
or to develop unusual catalysts with high catalytic performance [11–13].
surface activity, shorter diffusion path lengths, and lower tendencies
to carbon deposition in comparison to the ordinary micro-sized zeolite
crystals [14–17]. Two main different methods of zeolite nanocrystals
synthesis have been well summarized in the excellent review articles
[14,15]. One is to synthesize the nanosized zeolites from clear solutions
and gels by careful controlling of the exact synthesis parameters such as
the synthesis solution composition or crystallization temperature and
time [18,19]. The other method is to crystallize nanosized zeolites
within an inert matrix (carbon black particles or colloid-imprinted
carbons) which provides a steric hindered space for zeolite crystal
growth [20,21]. With the later method, nano-zeolite with size-
tailoring and uniform crystal size distributions can be prepared
easily. However, there is still a high requirement for the precursor
solution with clear and a low viscosity to make sure the entrance
for zeolite gel into the mesopores of the matrix [20], which limits
the application of the confined space synthesis method. For example,
it is not suitable for the colloidal MCM-22 zeolite synthesis system. So
far, the preparation and catalytic property of MCM-22 nanosized
zeolites (MCM-22-NZ) have not been reported.
Taking into account the colloidal synthesis system of MCM-22, a novel
and facile strategy for the nanocrystalline MCM-22 zeolite synthesis
which combines self-assembly with in-situ crystallization techniques is
proposed in this paper. In this route, polydiallydimethylammonium
chloride (PDDA) was used as a protecting or stabilizing agent during
the self-assemble of the cationic polymer and the negatively charged
inorganic silica species. With the assistant of in-situ crystallization, the
⁎
Corresponding author at: 12# Zhangzhou Road, Zibo City, Shandong Province,
255049, PR China. Tel./fax: +86 533 2786290.
E-mail addresses: yinxiaoyan731027@yahoo.cn, yinxiaoyan731027@163.com (X. Yin).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.10.007

X. Yin et al. / Catalysis Communications 43 (2014) 218–222
219
nanosized precursors turned into MCM-22 nanosized zeolite. The per-
formances of the MCM-22-NZ catalysts in the methane dehydro-
aromatization (MDA) reaction have also been studied. The results have
shown that the synthesized MCM-22-NZ displays superior catalytic
properties in comparison with the conventional micro-sized MCM-22
zeolites in MDA reaction.
2. Experimental method
2.1. MCM-22-NZ preparation
All reagents were used as received without further purification.
Cationic polymer, PDDA (molecular weight lies in the range of
2 × 105–3.5 × 105, 20 wt.%, purchased from Aldrich) was used for the
protecting or stabilizing agent in the synthesis. The MCM-22-NZ was
synthesized using hexamethyleneimine (HMI, N99%, purchased from
Aldrich) as a structure direction agent (SDA). 0.496g sodium hydroxide
(NaOH, N96%), 0.798 g sodium metaaluminate (NaAlO2, Al2O3: N45%),
and about 3 g PDDA were mixed in 85 mL deionized water and
vigorously agitated for more than 60 min. Then, 15.886 g ludox (AS-40,
SiO2: 40 wt.%, Aldrich) was added carefully into the above mixture by
dropping under vigorously agitated condition. After agitating for over
12 h, 5.35 g HMI was added to obtain the final mixture. The resultant
mixture was introduced into a stainless-steel autoclave, followed by
heating at 343K for 1day and then 423K for 7days under the condition
of rotating crystallization. After quenching the autoclave to room
temperature, the solid sample was separated from the mixture by
centrifugation, washed by deionized water and then dried at 393 K
over night. The SDA and the cationic polymers were removed by
calcination in air in a muffle at 823 K for 10 h. For comparison, the
synthesis experiment was carried out with the same composition
except for the presence of cationic polymers so as to obtain conventional
MCM-22 zeolites. The procedure of preparation of Mo/HMCM-22-NZ
and Mo/HMCM-22 catalysts was similar with that described in the
references [1,22].
Fig. 1. XRD patterns of the nanosized and conventional microsized MCM-22 zeolites.
3. Results and discussion
3.1. Characterization
Fig. 1 shows the X-ray diffraction (XRD) patterns of the calcined
nanosized and conventional micro-sized MCM-22 zeolites. Well-
resolved peaks in the 4–40° range are characteristic features of the
MCM-22 structure [24,25] without other crystalline phases and
2.2. Characterization and catalytic evaluation
The synthesized product was characterized by X-ray powder
diffraction (XRD) on a Rigaku-Dmax 2400 diffractometer equipped
with graphite monochromatized CuKα radiation in the 2θ angle ranging
from 5 to 50° and scanning electron micrograph (SEM, KYKY-2800B).
Transmission electron microscopy (TEM) was carried out on a Philips
Tecnai G2 20 instrument, operating at 200 kV. The crystal size
distribution was determined by dynamic light scattering (DLS)
with a ZETASIZER1000 instrument (DTS 5101, Malvern Ltd. Company).
Nitrogen adsorption analysis was carried out with a Micromeritics
ASAP 2020 adsorption analyzer at 77 K. The X-ray fluorescence (XRF)
spectrometry analysis was carried on Bruker SRS-3400 instrument. TG
profiles were recorded on a NETZSCH STA 449 C instrument. NH3
temperature-programmed desorption (NH3-TPD) was performed on a
conventional set-up equipped with a thermal conductivity detector.
0.2 g of the sample was first flushed with He (30 ml/min) at 873 K for
30 min, then cooled to 423 K and saturated with NH3 until equilibrium.
It was then flushed with He again until the baseline of the integrator
was stable. NH3-TPD was then promptly started from 423 to 900 K at
15 K/min.
The MDA reaction was carried out in a continuous flow quartz
tubular fixed-bed reactor (8 mm i.d.) at atmospheric pressure and
973 K, a space velocity of 1500 mL/(g·h). The effluents were
analyzed by an on-line gas chromatograph equipped with ten-
way sampling valve (Valco) for auto-sampling every time per
30 min and the detailed procedures were described in the previous
studies [23].
Fig. 2. Particle size distribution determined by DLS (a) and the corresponding TEM image
of the MCM-22-NZ (inset figure in a), and SEM image of the conventional microsized
MCM-22 zeolites (b).

220
X. Yin et al. / Catalysis Communications 43 (2014) 218–222
amorphous phase, confirming the formation of MCM-22 zeolites
with the high crystallinity. Obviously, the XRD peaks for the nano-
zeolites are considerably broader than the conventional micro-
sized MCM-22 as the crystal size decrease according to Scherrer
equation, indicating the formation of the MCM-22-NZ.
TEM and DLS have been adopted to determine the crystal size
distribution, and the results are shown in Fig. 2a. It is estimated that
the MCM-22-NZ obtained in this work possesses an average size of
40–50 nm with a narrow particle size distribution as determined by
DLS. The TEM image presents very uniform crystal particle with crystal
sizes of about 40nm, which matches the result of DLS.
3.2. Growth mechanism
Different from the nanosized MCM-22 shown in Fig. 2a, the
conventional MCM-22 zeolite synthesized in the control experiment
shows uniform platelet-like crystals of about 2 μm in size (Fig. 2b).
This indicates cationic polymer, PDDA, plays the crucial role in the
synthesis process of the MCM-22-NZ. It has been reported that
Ludox (SiO2 particles) can be used as the coating nanoparticles by
electrostatically self-assembly with PDDA to achieve the desired
topology and structure. Additionally, the cationic polymer is often
used to modify substrate surface by exploiting the electrostatic
attraction for their deposition [26–28]. Because of the electrostatic
stabilization effect, polyelectrolytes can also be used as stabilizing
agents for colloids to avoid the self-aggregation [29,30].
In this work, PDDA really plays the vital role of protection agent to
avoid the synthesis colloids self-aggregation. Fig. 3 shows the TEM
images of the synthesis colloids with and without the presence of
PDDA. Clearly, compared with the synthesis colloids without PDDA
(Fig. 3a), dispersive nano-silica species can be identified in the image
with the presence of PDDA (Fig. 3b). This is attributed to the existence
of the cationic polymer PDDA, which can effectively interact with
negatively charged inorganic silica species in the synthesis system due
to the electrostatically self-assembly. Moreover, during the rotating
crystallization process, PDDA prevents the inorganic silica species
Fig. 3. TEM images of the synthesis colloids without PDDA (a) and with the presence of
PDDA (b).
Fig. 4. Schematic diagram for the synthesis of MCM-22-NZ by the facile strategy combined self-assembly with in-situ crystallization.

X. Yin et al. / Catalysis Communications 43 (2014) 218–222
221
from self-aggregation and intergrowth. It is well known that the
architecture of silica precursor impacts the morphology of the result
zeolite crystals considerably after nucleation and crystallization.
From the results of our experiment, the amount of PDDA can
effectively impact the interaction between PDDA and Ludox. So, the
size of the colloids can be controlled by varying the amount of
PDDA. The intensive research work is carrying out in our laboratory
now and the results were not shown in this paper.
major steps: i) formation of the isolated small precursor particles
using PDDA as protecting or stabilizing agent by self-assembly of the
cationic polymer and the negatively charged inorganic silica species;
ii) in-situ crystallization of the nanosized precursors into nano-zeolite;
iii) removal of the cationic polymers.
3.3. Catalytic evaluation
By using our proposed method, the separated nanosized crystals can
be obtained successfully after in-situ crystallization. The rationale of this
method can be illustrated by the schematic diagram in Fig. 4. The
demonstrated procedure of MCM-22-NZ synthesis involves three
The catalytic activity of MCM-22-NZ in methane dehydro-
aromatization (MDA) reaction was also studied in this paper. Fig. 5(a)
presents the properties of MCM-22-NZ and conventional micro-sized
MCM-22 zeolites synthesized in this study over Mo-based catalyst in
MDA reaction. It was reported that the optimized Mo content was
6 wt.% for Mo/HMCM-22 catalysts [1,6]. Therefore, Mo content 6 wt.%
was chosen for both nanosized Mo/HMCM-22 and conventional
microsized Mo/HMCM-22 catalysts. Under the same employed reaction
conditions, significant improvement in the catalytic performance of the
MDA reaction has been observed for the nanosized Mo/HMCM-22. The
MCM-22-NZ catalyst exhibited much higher CH4 conversion and much
higher yield of benzene (increased about 30%) than those of the
conventional Mo/HMCM-22 catalysts synthesized in the present work.
The Mo/HMCM-22-NZ catalyst still displays good catalyst stability
with the benzene yield of over 6% until the reaction runs for 24 h. On
the contrary, for the conventional microsized Mo/HMCM-22 catalyst,
a heavier coke deposit leads to a rapid decrease of the methane con-
version with time-on-stream.
The XRF analysis of the conventional Mo/HMCM-22 and Mo/HMCM-
22-NZ catalysts is listed in Table 1, which results show that the Mo/
HMCM-22-NZ possesses the similarity to the conventional Mo/
HMCM-22 catalyst in terms of SiO2/Al2O3 ratio and Mo content. The
NH3-TPD results of the conventional HMCM-22, HMCM-22-NZ, the
conventional Mo/HMCM-22 and Mo/HMCM-22-NZ (Fig. 5b) in our
work show the similarity of both types and areas of peaks. Besides,
the results are reasonably consistent with that reported by Bao [1],
and the peak at about 518K (peak L) was attributed to the desorption
of the physisorbed NH3 species and/or NH3 adspecies residing on
non-exchangeable cationic sites, while the peak at 627 K (peak H)
was assigned to the desorption of NH3 adspecies adsorbed on
exchangeable protonic sites, i.e., Brönsted acid sites. Compared to
HMCM-22 and HMCM-22-NZ, Mo/HMCM-22 and Mo/HMCM-22-NZ
showed a decreased high-temperature peak. The shape of high-
temperature peaks of Mo/HMCM-22 and Mo/HMCM-22-NZ are
similar and the intensity of the latter was slightly weaker than that
of the former.
Taking into account that there is no post-treatment or post-
synthesis adopted to improve the catalytic performance, and the Mo/
HMCM-22-NZ catalyst possesses the similarity to the conventional
catalyst in terms of SiO2/Al2O3 ratio, Mo content and the acidity, the
high activity and exceptional stability of Mo/HMCM-22-NZ catalyst
are reasonably attributed to the nanosized effect of the catalyst
particle. The BET surface areas and pore volumes of traditional
MCM-22 and MCM-22-NZ are listed in Table 2. For the traditional
MCM-22 synthesized in this work, the data are similar with those
reported in literatures 1 and 31. While, the BET surface area of
MCM-22-NZ (491 m2/g) is higher than that of the traditional MCM-
22 (448 m2/g). The nanocrystal MCM-22-NZ with morphology of
polycrystalline grains also generates the secondary pores from inter-
crystal gap of nanoscale MCM-22-NZ. So, the nanosized MCM-22-NZ
Table 1
Results of XRF analysis of the conventional Mo/HMCM-22 catalyst and the Mo/HMCM-22-
NZ catalyst.
Catalysts
Mo (wt.%)
SiO2 (wt.%)
Al2O3 (wt.%)
[SiO2/Al2O3]
Fig. 5. The catalytic performance comparison for Mo/HMCM-22-NZ catalyst and
conventional Mo/HMCM-22 catalyst in MDA reaction (a), NH3-TPD spectra of the different
catalysts (b), and TG profiles of the coked catalysts (c).
Mo/HMCM-22
Mo/HMCM-22-NZ
5.9
6.0
85.3
84.7
5.1
5.04
28.4
28.6

222
X. Yin et al. / Catalysis Communications 43 (2014) 218–222
Table 2
4. Conclusions
BET surface areas and pore volumes of the conventional MCM-22 and MCM-22-NZ.
The new route of combination self-assembly with in-situ crys-
tallization techniques was proposed to facilely prepare nano-sized
MCM-22 zeolite catalysts (MCM-22-NZ). In this route, PDDA prevents
the inorganic silica species from self-aggregation and intergrowth, and
finally very uniform MCM-22 crystal particles with crystal sizes of
about 40 nm could be obtained easily after rotating crystallization.
From the results of N2 adsorption and TG analysis, the nano-sized
MCM-22-NZ catalysts possess higher surface activity and lower
tendencies to carbon deposition compared to the conventional micro-
sized MCM-22 catalysts. Therefore, the MCM-22-NZ catalyst displayed
higher methane conversion, higher benzene yield and stronger catalyst
stability in methane dehydro-aromatization (MDA) reaction compared
to the conventional micron scale catalyst. This work revealed a new and
feasible way for the synthesis of nanosized zeolite catalysts. The
demonstrated route may be extended to synthesize other types of
zeolite catalysts with unusual structure and properties.
Sample
Si/Al
ratio
Surface area
(m2/g)
Micropore area
(m2/g)
Micropore
volume
Reference
(cm3/g)
MCM-22
MCM-22
MCM-22
30
15
15
458
453
448
352
335
356
0.16
0.15
0.16
[1]
[31]
This
paper
This
paper
MCM-22-NZ 15
491
359
0.17
catalyst can possess higher surface activity and lower tendencies to
carbon deposition, which lead to the remarkable increase in the
catalytic durability. Furthermore, the nanosized MCM-22, because of
its small size, has shorter diffusion path length and easier access for
the reactant, increases the diffusion rate of molecules and shortens
the residence time of molecules in channels of nanocrystal, resulting
in the higher CH4 conversion.
Acknowledgment
TG analysis of the coked catalysts also confirmed that the nano-
sized MCM-22 catalyst can favor strong coking-resistance and result
in strong catalyst stability. TG profiles of the coked Mo/HMCM-22
and Mo/HMCM-22-NZ catalysts were shown in Fig. 5c. The coked
Mo/HMCM-22 catalyst shows a weight loss of about 15% after 20 h
on stream. By contrast, the coked Mo/HMCM-22-NZ catalyst displays
about 16% weight loss after 50 h on stream. Therefore, the average
rate of coke formation on the Mo/HMCM-22-NZ catalyst (about
0.32% per hour) is lower than the 0.75% coke formation rate of
the Mo/HMCM-22 catalyst. These results demonstrate that the Mo/
HMCM-22-NZ catalyst possesses much better tolerance to carbonaceous
deposits, which is favorable to strong catalyst stability.
Mo/HMCM-22-NZ plays the important role of high quality bi-
functional catalysts in MDA reaction. It is well known that there is an
induction period in the early stage of the reaction in which the MoO3
species are reduced by CH4 into Mo2C species, accompanied by the
depositing of carbonaceous cokes (carbonaceous deposits associated
with molybdenum). The transformation of molybdenum oxide to
molybdenum carbide is dominant for this period. It is reasonable that
much carbonaceous deposits associated with molybdenum occur in
the early reaction stage. Moreover, the formed Mo2C species are active
species for CH4 activation and can continuously activate CH4 to produce
active intermediates. Subsequently, the active intermediates are
condensed on the acid site of catalysts and benzene is produced. At
the same time, the aromatic coke deposits form on the acid site,
which would lead to the deactivation of the catalyst.
Compared to the conventional Mo/HMCM-22 catalyst, the nano-
structure of the Mo/HMCM-22-NZ catalyst is beneficial to the well-
distribution of the Mo active species on the zeolite support. So, Mo active
species can have the efficient combination with the zeolite acidic sites.
Furthermore, Mo/HMCM-22-NZ provides easier access to the active
sites for both reactant and larger product molecules like benzene. The
fast transport of larger products is in favor for improving both
catalyst activity and durability of catalyst as reported by literature
works [32–35]. Therefore, high quality bifunctional catalyst (Mo/
HMCM-22-NZ) naturally gives rise to higher methane conversion,
higher benzene yield and stronger catalyst stability in comparison
with the conventional Mo/HMCM-22 catalyst.
The financial supports of the National Key Technology R&D Program
(2006BAE02B05) and National Natural Science Foundation of China
(21076119 and 21276148) are greatly acknowledged.
References
[1] Y. Shu, D. Ma, L. Xu, Y. Xu, X. Bao, Catal. Lett. 70 (2000) 67.
[2] Y. Xu, X. Bao, L. Lin, J. Catal. 216 (2003) 386.
[3] Z. Sobalík, Z. Tvaruzková, B. Wichterlová, V. Fíla, Š. Špatenka, Appl. Catal. A Gen. 253
(2003) 271.
[4] H. Liu, W. Shen, X. Bao, Y. Xu, Appl. Catal. A Gen. 295 (2005) 79.
[5] A. Hassan, A. Sayari, Appl. Catal. A Gen. 297 (2006) 159.
[6] L. Liu, D. Ma, H. Chen, H. Zheng, M. Cheng, Y. Xu, X. Bao, Catal. Lett. 108 (2006)
25.
[7] C. Delitala, M.D. Alba, A.I. Becerro, Microporous Mesoporous Mater. 118 (2009) 1.
[8] S. Laforge, D. Martin, M. Guisnet, Microporous Mesoporous Mater. 67 (2004)
235.
[9] G. Xu, X. Zhu, X. Niu, Microporous Mesoporous Mater. 118 (2009) 44.
[10] I. Kolev, V. Mavrodinova, M.R. Mihályi, M. Kollár, Microporous Mesoporous Mater.
118 (2009) 258.
[11] X. Dong, Y. Song, W. Lin, Catal. Commun. 8 (2007) 539.
[12] Y. Li, L. Liu, X. Huang, X. Liu, W. Shen, Y. Xu, X. Bao, Catal. Commun. 8 (2007) 1567.
[13] A.C.C. Rodrigues, J.L.F. Monteiro, Catal. Commun. 9 (2008) 1060.
[14] L. Tosheva, V.P. Valtchev, Chem. Mater. 17 (2005) 2495.
[15] S.C. Larsen, J. Phys. Chem. C 111 (2007) 18464.
[16] M. Firoozi, M. Baghalha, M. Asadi, Catal. Commun. 10 (2009) 1582.
[17] L. Sun, X. Guo, G. Xiong, X. Wang, Catal. Commun. 25 (2012) 18.
[18] W. Song, R.E. Justice, C.A. Jones, V.H. Grassian, S.C. Larsen, Langmuir 20 (2004) 8301.
[19] W. Song, V.H. Grassian, S.C. Larsen, Chem. Commun. (2005) 2951.
[20] I. Schmidt, C. Madsen, C.J.H. Jacobsen, Inorg. Chem. 39 (2000) 2279.
[21] S. Kim, J. Shah, T.J. Pinnavaia, Chem. Mater. 15 (2003) 1664.
[22] H. Liu, L. Su, H. Wang, W. Shen, X. Bao, Y. Xu, Appl. Catal. A Gen. 236 (2002) 263.
[23] N. Chu, J. Yang, J. Wang, S. Yu, J. Lu, Y. Zhang, D. Yin, Catal. Commun. 11 (2010) 513.
[24] Y. Wu, X. Ren, Y. Lu, J. Wang, Microporous Mesoporous Mater. 112 (2008) 138.
[25] Y. Wu, X. Ren, J. Wang, Microporous Mesoporous Mater. 116 (2008) 386.
[26] F. Caruso, R.A. Caruso, H. Möhwald, Science 282 (1998) 1111.
[27] F. Caruso, H. Lichtenfeld, M. Giersig, H. Möhwald, J. Am. Chem. Soc. 120 (1998) 8523.
[28] G. Decher, Science 277 (1997) 1232.
[29] S. Chen, Langmuir 15 (1999) 7551.
[30] H. Chen, Y. Wang, Y. Wang, S. Dong, E. Wang, Polymer 47 (2006) 763.
[31] A. Corma, V. Martinez-Soria, E. Schnoeveld, J. Catal. 192 (2000) 163.
[32] W. Li, A. Lu, R. Palkovits, W. Schmidt, B. Spliethoff, F. Schüth, J. Am. Chem. Soc. 127
(2005) 12595–12600.
[33] F. Schüth, Annu. Rev. Mater. Res. 35 (2005) 209–238.
[34] F.S. Xiao, L. Wang, C. Yin, K. Lin, Y. Di, J. Li, R. Xu, D.S. Su, R. Schlgl, T. Yokoi, T. Tatsumi,
Angew. Chem. Int. Ed. 45 (2006) 3090–3093.
[35] K. Egeblad, C.H. Christensen, M. Kustova, C.H. Christensen, Chem. Mater. 20 (2008)
946–960.