Synthesis of mesoporous Beta and Sn-Beta zeolites and their catalytic performances

Article abstract of DOI:10.1039/c4dt00567h

Mesoporous Beta zeolite has been successfully prepared through hydrothermal synthesis in the presence of cationic ammonium-modified chitosan as the meso-template. Through a subsequent solid-gas reaction between highly dealuminated mesoporous Beta zeolite and SnCl₄ steam at an elevated temperature, mesoporous Sn-Beta has been facilely obtained. It was revealed that the addition of cationic chitosan induced the nanocrystal aggregation to particle sizes of ～300 nm, giving rise to the intercrystalline/interparticle mesoporosity. In the Sn-implanting procedure, Sn species were demonstrated to be doped into the framework of the resulting mesoporous Beta zeolite in a tetrahedral environment without structural collapse. Due to the micro/mesoporous structures, both mesoporous Beta and Sn-Beta exhibited superior performances in α-pinene isomerization, Baeyer-Villiger oxidation of 2-adamantanone by hydrogen peroxide and the isomerization of glucose in water, respectively. the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt00567h

Volume 43 Number 22 14 June 2014 Pages 8111–8550
Dalton
Transactions
An international journal of inorganic chemistry
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ISSN 1477-9226
PAPER
Yongsheng Li, Jianlin Shi et al.
Synthesis of mesoporous Beta and Sn-Beta zeolites and their catalytic
performances

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PAPER
Synthesis of mesoporous Beta and Sn-Beta
zeolites and their catalytic performances†
Cite this: Dalton Trans., 2014, 43,
8196
a
b
a
b
a
a
Junjiang Jin, Xinxin Ye, Yongsheng Li,* Yanqin Wang, Liang Li, Jinlou Gu,
a
c
Wenru Zhao and Jianlin Shi*
Mesoporous Beta zeolite has been successfully prepared through hydrothermal synthesis in the presence
of cationic ammonium-modified chitosan as the meso-template. Through a subsequent solid–gas reac-
4
tion between highly dealuminated mesoporous Beta zeolite and SnCl steam at an elevated temperature,
mesoporous Sn-Beta has been facilely obtained. It was revealed that the addition of cationic chitosan
induced the nanocrystal aggregation to particle sizes of ∼300 nm, giving rise to the intercrystalline/inter-
particle mesoporosity. In the Sn-implanting procedure, Sn species were demonstrated to be doped into
the framework of the resulting mesoporous Beta zeolite in a tetrahedral environment without structural
collapse. Due to the micro/mesoporous structures, both mesoporous Beta and Sn-Beta exhibited
superior performances in α-pinene isomerization, Baeyer–Villiger oxidation of 2-adamantanone by
hydrogen peroxide and the isomerization of glucose in water, respectively.
Received 23rd February 2014,
Accepted 28th March 2014
DOI: 10.1039/c4dt00567h
www.rsc.org/dalton
internal surface ratio. However, the synthesized zeolites with
particle size smaller than 100 nm would cause a decrease in
1
. Introduction
3
b,8
Aluminosilicate zeolites and zeolitic metallosilicate containing micropore volume.
Moreover, nanozeolite powders are gen-
isolated transition metal ions have been extensively used as erally produced at low yields and their isolation is time-con-
2
a,7e
solid Brønsted acid catalysts in petrochemical processing and suming and costly.
The success in synthesizing ultra-large
solid Lewis acid catalysts for redox reactions, due to their pore zeolites provides an alternative choice. However, the
uniform, small pore size, flexible frameworks, and controlled increases in pore size were modest even though specific
1
9
chemistry. However, their applications are limited to small organic structure directing agents were employed. Further-
molecules that can diffuse through the narrow channels more, the lack of chemical and thermal stability, as well as the
1
a,b,2
(<0.8 nm) and small cavities (<1.5 nm typically).
It has high cost, often hinders their wide application in industry.
been widely demonstrated that the mass transfer limitations With respect to supported zeolite crystals, hydrothermally
are an important issue in industrial applications involving zeo- stable and alkali-tolerable porous supports are highly required,
3
10
litic materials. To circumvent the diffusional limitations which can preserve their initial porous structures. Hierarchi-
imposed by zeolitic structures, several strategies have been cal zeolites, where mesoporosity and/or macroporosity are
3
d,4
pursued, such as the synthesis of zeolite nanocrystals,
introduced into the microporous framework of zeolites, are
regarded as the most promising materials. Nevertheless, the
term mostly refers to mesoporous zeolites, i.e. hierarchical zeo-
1
a,b,5
6
ultra-large pore zeolites,
supported zeolite nanocrystals
3
b,c,7
and inserting larger pores into the zeolite particles.
Zeolite nanocrystals can expose more active sites than con- lites featuring additional porosity in the mesopore size region
ventional zeolite crystals due to their higher external to (pore diameters in the range 2–50 nm) because the major
impact of auxiliary porosity on catalysis stems from porosity in
7
d,11
this size region.
a
Lab of Low-Dimensional Materials Chemistry, School of Materials Science and
In the last decade, various strategies have been developed
to synthesize zeolites with additional mesoporosity. Briefly,
these strategies can be classified into four categories: (a) direct
synthesis using different dual templating strategies, including
the common zeolite structure directing agents and additional
Engineering, East China University of Science and Technology, No. 130 Mei-long
Road, Shanghai 200237, P.R. China. E-mail: ysli@ecust.edu.cn;
Fax: (+86) 21-64250740
b
Shanghai Key Laboratory of Functional Materials Chemistry, East China University
of Science and Technology, No. 130 Mei-long Road, Shanghai 200237, P.R. China
c
12
State Key Laboratory of High Performance Ceramics and Superfine Microstructures,
secondary templates for mesostructuring the zeolite crystals;
Shanghai Institute of Ceramics, Chinese Academy of Science, No. 1295 Ding-xi Road,
Shanghai 200050, P.R. China. E-mail: jlshi@mail.sic.ac.cn
(
b) direct synthesis using only single but multi-functional tem-
plate, containing structure directing fragments for the micro-
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
1
3
c4dt00567h
and mesoscale in the same molecule; (c) generation of meso-
8196 | Dalton Trans., 2014, 43, 8196–8204
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1
4
pores in zeolite single crystals by post-synthesis treatment;
(
d) a synthetic route relying on specific reaction conditions
1
5
that make secondary templates unnecessary. Particularly,
some strategies have shown good versatility in the synthesis of
different-structured zeolites.
7
,16
However, little attention has
been devoted to fabrication of mesoporous zeolitic metallosili-
cates with high crystallinity by a simple templating route, prob-
ably due to their special synthetic conditions involved, such as
the introduction of the fluoride anion as the mineralizing
1
7
agent. Alternatively, to insert heteroatoms into the frame-
work of zeolites, several post-synthetic strategies have been
developed, such as solid–gas implanting, solid-state ion-
1
8
exchange and impregnation.
Thus, the combination of
hydrothermal synthesis of mesoporous zeolites using second-
ary templates and a subsequent post-synthetic route may open
the door to obtain mesoporous zeolitic metallosilicate.
Sn-Beta, a tin-containing molecular sieve with the zeolite Beta
topology, has received great attention in biocatalysis because Fig. 1 XRD patterns of Meso-Beta and Con-Beta.
1
7c,d,19
of its superiority in activating carbonyl groups.
However,
to the best of our knowledge, very few research studies about
1
8c
mesoporous Sn-Beta have been published.
In this work, mesoporous Beta zeolite was first synthesized
through a hydrothermal method in the presence of a cationic
derivative of chitosan, though chitosan has been widely used
20
in the preparation of organic/inorganic composites. Follow-
ing a dealumination process, post-synthesis was carried out to
obtain mesoporous Sn-Beta through the solid–gas reaction of
4
highly dealuminated Beta zeolite and SnCl vapor at an elevated
temperature. The physicochemical properties of the obtained
products were characterized by several techniques, including
2
XRD, N adsorption, SEM, TEM, NMR spectroscopy, TGA, UV-Vis
spectroscopy and temperature-programmed desorption (NH3-
TPD). Their catalytic behaviours were evaluated in α-pinene iso-
merization, selective oxidation of 2-adamantanone by hydrogen
peroxide and the isomerization of glucose in water, respectively.
Fig. 2
N
2
adsorption–desorption isotherms and pore-size distribution
curve (inset) of Con-Beta and Meso-Beta.
2
. Results and discussion
2
.1. Mesoporous Beta zeolite
mesoporosity with large pore sizes. From the corresponding
Fig. 1 shows the XRD patterns of the synthesized mesoporous pore size distribution derived from the desorption branch of
Beta zeolite (Meso-Beta) and conventional beta (Con-Beta). As the isotherm using the Barrett–Joyner–Halenda (BJH) method,
can be seen, both Meso-Beta and Con-Beta exhibit a series of the mesopore size is estimated to be 20–50 nm. As listed in
diffraction peaks located at 7.8°, 13.4°, 14.5°, 21.5° and 22.5°, Table 1, significant increases in the total and external specific
2
1
respectively, characteristic of the BEA structure. This indi- surface area and the total and external pore volume are clearly
cates that the addition of cationic chitosan has not affected observed. These can be attributed to the generation of meso-
the crystallization of Beta zeolite. By taking the Con-Beta porosity in the sample of Meso-Beta. Meanwhile, it is worth
zeolite as a reference, the crystallinity of Meso-Beta is esti- noting that the decrease in the micropore volume and micro-
mated to be about 89%.
pore surface area is almost negligible.
The N2 adsorption–desorption isotherms and the corres-
Transmission electron microscopy (TEM) images, as shown
ponding BJH pore size distributions of Meso-Beta and in Fig. 3a and b, confirm the co-existence of micropores and
Con-Beta are shown in Fig. 2 and the corresponding structural mesopores in the Meso-Beta sample. Notably, Meso-Beta par-
properties are presented in Table 1. In addition to the repre- ticles contain plenty of stacked zeolite nanocrystals, which are
sentative type
I
isotherm characteristic of microporous believed to contribute to the mesoporosity. In the enlarged
materials, Meso-Beta presents a steep leap and a hysteresis TEM image (Fig. 3b and inset), randomly oriented micro-
loop at the P/P region of 0.88–0.97, indicating the presence of porous channels in the Meso-Beta particle can be observed,
0
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a
Table 1 Textural properties of the samples
Sn
(wt%)
S
BET
S
micro
S
external
V
total
V
micro
V
external
Pore diameter
(nm)
(m g−1)
2
(m g−1)
2
(m g )
2
−1
(cm g−1)
3
(cm g−1)
3
(cm g−1)
3
Sample
Si/Al
Meso-Beta
Con-Beta
H-Al-Meso-Beta
De-Al-Meso-Beta
Meso-Sn-Beta
Con-Sn-Beta
9.0
8.7
9.1
>1500
>1500
>2000
—
—
—
—
1.1
1.2
660
629
643
595
623
589
477
503
429
380
405
544
183
126
214
215
218
45
0.69
0.39
0.61
0.63
0.51
0.27
0.20
0.21
0.18
0.15
0.17
0.21
0.49
0.18
0.43
0.48
0.34
0.06
20–50
—
20–50
20–50
20–50
—
a
Si/Al ratio and Sn content were measured by inductively coupled plasma (ICP) analysis; BET surface area (SBET) is calculated from the Brunauer–
Emmett–Teller method; the micropore surface area (Smicro), external specific surface area (Sexternal) and the micropore volume (Vmicro) are
0
calculated from the t-plot method; the total pore volume (Vtotal) is evaluated at P/P = 0.98; the external pore volume (Vexternal) is calculated
according to Vtotal − Vmicro; the diameter of mesopore is estimated from the BJH method using the desorption branch of the isotherm curves.
bulky particles (about 2 μm in diameter) with rough surface
but without a visible porous structure. These results demon-
strate that the addition of cationic chitosan not only acts as a
meso-template by aggregating nanocrystals, but also decreases
the dimension of zeolite particles by hindering their further
2
2
growth.
The structural configuration and local environment of
Si and Al atoms in Meso-Beta and Con-Beta were investigated
2
9
27
by Si and Al MAS NMR spectroscopy, as given in Fig. S1.† It
2
9
is found that Meso-Beta displays a similar Si NMR spectrum
as Con-Beta. Two major peaks at δ = −116 ppm and −108 ppm
corresponding to Si(4Si) species and the peak at −104 ppm
resulting from both Si(3Si, 1Al) or Si(3Si, 1OH) are clearly pre-
2
3
sented. Additionally, the weak peak centered at δ = −99 ppm
shows the existence of Si(2Si, 2Al) or Si(2Si, 1Al, 1OH) sites
8
a,24
27
due to the low Si/Al ratio.
In terms of Al NMR, both
Meso-Beta and Con-Beta exhibit a pronounced peak centered
at around δ = 55 ppm and a weak peak centered at around δ =
0
ppm, which are attributed to framework tetrahedral and
octahedral aluminium species, respectively. Assuming that the
concentrations of the tetrahedral and octahedral aluminium
are proportional to the respective intensities of the resonances
at δ = 55 ppm and δ = 0 ppm, the AlTd/AlOh ratio can be quanti-
fied to be 4.42 and 4.10 for Con-Beta and Meso-Beta, respect-
2
5
ively. It is well known that calcination in air would induce a
partial dealumination process from octahedral aluminum
2
6
species to tetrahedral aluminum species. Thus the lower
AlTd/AlOh ratio in Meso-Beta implies its more extensive dealu-
mination process due to the more locally developed heat
(
Fig. 3 TEM images (a, b) of Meso-Beta; SEM images of Meso-Beta (c, d) (nanocrystallinity).
and Con-Beta (e, f) at different magnifications.
more entrapped organics) and lower thermal stability
8
a
Thermogravimetric analyses (TGA) were performed to inves-
tigate whether cationic polymer N-(2-hydroxy)-propyl-trimethyl
indicating that mesoporosity was formed by the aggregation of ammonium chitosan chloride (HTCC) participated in the syn-
nanocrystals. Scanning electron microscopy (SEM) images thesis of Meso-Beta. Fig. S2† shows thermogravimetric analysis
provide more detailed insights into the morphology and struc- curves of as-synthesized Con-Beta, as-synthesized Meso-Beta
ture of the samples. As presented in Fig. 3c and d, Meso-Beta and HTCC. As-synthesized Con-Beta shows a weight loss of
particles possess irregular morphology of about 300 nm diam- 20.9% due to the loss of water and TEA template, while as-syn-
eters and are composed of closely stacked zeolite nanocrystals thesized Meso-Beta displays a weight loss of 21.3%, slightly
(
30–40 nm in size). In addition to the intercrystal mesoporos- higher than that of Con-Beta. For both samples, the weight
ity, the interparticle voids are proposed to contribute to the losses below 170 °C can be ascribed to the removal of
mesoporosity to some extent. In contrast, Con-Beta contains adsorbed water. Remarkably, a specific weight loss in the
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Scheme 1 Reaction
pathway
for
acid-catalyzed
α-pinene
isomerization.
3
Fig. 4 NH -TPD profiles of H-type Con-Beta and Meso-Beta.
isomerization is a typical weak acid-catalyzed reaction, which
3
0a
can occur on both weak and strong acid sites, as illustrated
in Scheme 1. Table 2 represents the conversion of α-pinene
and selectivity to some main products (camphene, limonene,
terpinolene, α- and γ-terpinene) over H-type Con-Beta and
H-type Meso-Beta, respectively. It is observed that Con-Beta
shows a conversion of 21.3%, probably due to the hindrance
effect of its intrinsic microporosity. In contrast, Meso-Beta
gives an enhanced conversion of 32.2% under the same con-
ditions, without significant changes in selectivity towards the
main products. Considering the higher concentration/strength
of acid sites in H-Type Con-Beta, the enhanced catalytic activity
may be mainly attributed to the favoured mass transfer in
Meso-Beta for both reactants and products, due to the pres-
ence of a mesopore network.
region of 170–330 °C is observed for as-synthesized Meso-Beta,
which can be ascribed to the initial decomposition of HTCC
2
7
(
Fig. S2b†). These results indicate that HTCC participated
in the synthesis of Meso-Beta as the meso-template via
the flocculating effect, giving birth to the intercrystalline
3
1
2
2a,28
mesoporosity.
Fig. 4 illustrates the temperature-programmed desorption
of ammonia (NH -TPD) profiles on H-type Con-Beta and Meso-
3
Beta with a similar Si/Al ratio. For H-type Con-Beta, the TPD
curve shows a gradual rise in the low temperature region, a
maximum at 205 °C, and thereafter a decline with a smaller
peak appearing at 380 °C. The existence of two TPD peaks
means that the H-type Con-Beta has weak as well as strong
acid sites. Apparently, H-type Meso-Beta shows a similar TPD
profile with lower desorption temperatures (180 °C and 330 °C,
respectively) and lower amounts of desorbed ammonia, indi-
2.2. Mesoporous Sn-Beta
cating the lower concentration/strength of acid sites in Meso- Fig. 5 shows the XRD patterns of H-Al-Meso-Beta, De-Al-Meso-
Beta. Such acidic properties can probably be ascribed to the Beta, Meso-Sn-Beta and Con-Sn-Beta. It can be seen that all
lower aluminium content, lower crystallinity and lower frame- the samples display the characteristic diffraction peaks associ-
8
a,29
work aluminium species in the sample of Meso-Beta.
ated with BEA topology. The highest diffraction intensity on
The catalytic performances of H-type Meso-Beta and H-type Con-Sn-Beta suggests its high crystallinity, probably due to the
Con-Beta were tested on the isomerization of α-pinene, which addition of a fluoride anion as a mineralizing agent. Mean-
is the main ingredient of turpentine. To make the best of this while, the comparable diffraction intensities and microporos-
widespread bicyclic monoterpene, the value added products of ity (shown in Table 1) among H-Al-Meso-Beta, De-Al-Meso-Beta
α-pinene isomerization have been widely used in the pharma- and Meso-Sn-Beta indicate the absence of crystalline structure
3
0
ceutical and perfume industries. The acid catalysed α-pinene damage during the dealumination and SnCl vapor treatment.
4
a
Table 2 The catalytic performance of the samples
Selectivity (%)
Sample
Conversion (%)
Camphene
α-Terpinene
Limonene
γ-Terpinene
Terpinolene
Others
Con-Beta
Meso-Beta
21.3
32.2
18.6
19.7
7.6
7.2
29.3
30.7
4.7
4.4
9.4
8.7
30.4
29.2
a
Reaction conditions: 70 °C, 30 min, 0.1 g of catalyst, 2.0 mL of α-pinene.
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Fig. 5 XRD patterns of H-Al-Meso-Beta (A), De-Al-Meso-Beta (B),
Meso-Sn-Beta (C) and Con-Sn-Beta (D).
Fig. 7
N
2
adsorption–desorption isotherms and pore-size distribution
curve (inset) of Con-Sn-Beta and Meso-Sn-Beta.
UV-Vis spectroscopic technique provides a conventional
tool to detect the coordination state of Sn species in Sn-con-
taining metallosilicates. UV-Vis spectra of Meso-Sn-Beta and
Con-Sn-Beta are given in Fig. 6. One main absorption band in
the region of 210–220 nm relevant to isolated Sn atoms is
observed for both Meso-Sn-Beta and Con-Sn-Beta, indicating
derived from the desorption branch of Meso-Sn-Beta, the
mesopore size is estimated to be about 20–50 nm, in accord-
ance with that of Meso-Beta indicated above. From the struc-
tural parameters of the samples listed in Table 1, after a
dealumination process and a subsequent solid–gas reaction,
Meso-Sn-Beta maintained similar structural features as the
parent H-Al-Meso-Beta. It is noteworthy that Meso-Sn-Beta
IV
the presence of isolated, tetrahedrally coordinated Sn species
1
8e
within their zeolite frameworks.
These results confirm the
2
−1
shows higher external specific surface area (218 m g ), total
applicability of gas–solid reaction to introduce tetrahedrally co-
3
−1
3
−1
pore volume (0.51 cm g ) and external volume (0.34 cm g
than those of Con-Beta, due to the preserved hierarchy.
)
18c
ordinated Sn species.
The N2 adsorption–desorption isotherms and the corres-
ponding pore-size distributions of Meso-Sn-Beta and Con-Sn-
Beta are presented in Fig. 7. A high uptake caused by micro-
pore filling is observed at low relative pressure (<0.01) for both
samples. Unlike the representative Type I (Langmuir) isotherm
for Con-Sn-Beta, Meso-Sn-Beta exhibits a mixture of type I and
IV, with a larger adsorption amount and a hysteresis loop
above the relative pressure of 0.8, suggesting the presence of
mesoporosity. According to the BJH pore-size distribution
SEM and TEM images of Con-Sn-Beta and Meso-Sn-Beta
are given in Fig. 8. Notably, unlike the bulky particles of
Fig. 8 SEM images of Con-Sn-Beta (a) and Meso-Sn-Beta (b); TEM
images (c, d) of Meso-Sn-Beta at different magnifications.
Fig. 6 UV-Vis spectra of Meso-Sn-Beta and Con-Sn-Beta.
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route in the presence of cationic ammonium-modified chito-
san, with the latter further by a post-synthetic solid–gas reac-
tion of highly dealuminated mesoporous Beta zeolite with
SnCl
san induced the nanocrystal aggregation to particle sizes of
300 nm, giving rise to intercrystalline/interparticle meso-
4
vapor. It is revealed that the addition of cationic chito-
∼
porosity. In the Sn-implanting procedure, Sn species are
demonstrated to be doped into the framework of the resulting
mesoporous Beta zeolite in a tetrahedral environment without
structural collapse. Due to the generated meso-/microporous
structure, mesoporous Beta and Sn-Beta exhibited significantly
higher performances in α-pinene isomerization, selective oxi-
dation of 2-adamantanone by hydrogen peroxide and the iso-
Scheme 2 Baeyer–Villiger oxidation of 2-adamantanone by hydrogen merization of glucose in water than their counterparts without
peroxide (top); isomerization of glucose to fructose (bottom).
mesostructure. It is expected that this preparation strategy can
be applied to other structured and heteroatom-substituted zeo-
litic materials.
Table 3 Catalytic properties of different catalysts
Reactions
-Adamantanone + hydrogen peroxide
Con-Sn-Beta
Meso-Sn-Beta
a
2
64.7
69.1
82(40)
4. Experimental
b
Isomerization of glucose
53.1(35.1)
4.1. Chemicals and synthetic procedures
a
The data represent the reactant conversion [%]. The lactone
b
Chemicals. Chitosan (MW ∼ 100 000, degree of deacetylation
selectivity is higher than 99%. The first data represent the glucose
conversion [%]. The number in parentheses indicates the yield of was 95%) was purchased from Zhejiang Golden-Shell Pharma-
fructose.
ceutical Co., Ltd. Glycidyltrimethylammonium chloride
(
GTMAC, 90%), tin chloride (99%), α-pinene (98%) and 2-ada-
mantanone (99%) were obtained from Sigma-Aldrich. Tetra-
ethylammonium hydroxide (TEAOH, 35%) was purchased from
Tokyo Chemical Industry Co., Ltd. Fumed silica (Aerosil 200)
was obtained from Degussa Co., Ltd. The rest of the reagents,
Con-Sn-Beta (∼1 μm, Fig. 8a), Meso-Sn-Beta particles possess
similar morphology and structure as the parent material Meso-
Beta. Especially, the meso-/microporous structure was well pre-
served after the dealumination process and the SnCl vapor
4
treatment. Thus, Meso-Sn-Beta is expected to suffer from less
diffusion limitation to bulky substrate molecules.
including NaOH, NaAlO
2 4 3 3 3
, NH NO , HNO , AgNO , tin(IV) chlor-
ide pentahydrate (SnCl ·5H O), chlorobenzene, glucose and
4
2
tetraethyl orthosolicate (TEOS), were purchased from Sino-
pharm Chemical Reagent Co., Ltd and were of reagent grade.
To evaluate the catalytic performance of Meso-Sn-Beta for
reactions involving bulky molecules, the selective oxidation of
Preparation
of
ammonium-modified
chitosan. The
2
-adamantanone by H O in the solvent chlorobenzene and
2 2
ammonium-modified chitosan, N-(2-hydroxy)-propyl-trimethyl
the isomerization of glucose in water were carried out, as illus-
trated in Scheme 2. The catalytic data of the samples are sum-
marized in Table 3. In the Baeyer–Villiger oxidation of
ammonium chitosan chloride (HTCC) was prepared by a modi-
2
0e,27
fied method proposed elsewhere.
Synthesis of mesoporous Beta zeolite. 0.12 g NaOH and
.56 g NaAlO were mixed with 11.25 g tetraethylammonium
2
-adamantanone, Meso-Sn-Beta gives a higher conversion
0
2
(69.1%) than that of Con-Sn-Beta (64.7%) at similar Sn
hydroxide (35%, TCI) and stirred for 1 h. Then, 3.6 g fumed
silica (Aerosil 200, Degussa) was added into this solution,
forming a thick sol after continuous stirring for about 3 h at
room temperature. Afterwards, an aqueous solution containing
content. Meanwhile, in the isomerization of glucose, a higher
fructose yield (40%) is also observed for Meso-Sn-Beta than
that of Con-Sn-Beta (35%). It has been reported that the hydro-
phobicity of the zeolite catalyst is favorable in both catalytic
2
1.5 g HTCC and 10 g H O was added dropwise into the result-
1
8c,32
reactions above.
Taking into account the more hydro-
ing mixture under stirring. After stirring overnight, the earth
yellow mixture was charged into Teflon-lined steel autoclaves
for hydrothermal treatment at 140 °C for 5 days. The product
was collected by centrifugation, washed with deionized water
until the pH was below 9, dried overnight at 100 °C and cal-
cined at 600 °C for 10 h. The sample is labeled as Meso-Beta.
For comparison, conventional Beta zeolite with a similar Si/Al
ratio was synthesized under similar procedures in the absence
of HTCC solution and labeled as Con-Beta.
phobic nature of micrometer sized Con-Sn-Beta and the bulky
molecular size of the ketone and glucose, the catalytic results
observed here suggest the more dominant role of diffusions of
reactants and/or products.
3
. Conclusions
In this work, mesostructured Beta and Sn-Beta zeolites have
For catalysis, H-form Con-Beta and Meso-Beta were
been successfully prepared through a hydrothermal synthetic obtained by ion exchanges with 1 M NH NO solution at 70 °C
4
3
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three times and the subsequent calcination in air at 550 °C for saturation was reached. The gaseous or physisorbed NH
h. removed by purging He flow at 100 °C for 1 h. Then the temp-
Synthesis of mesoporous Sn-Beta. Mesoporous Beta zeolite erature was raised from 100 to 550 °C with a heating rate of
3
was
5
H-type) obtained above was used as the parent material. Deal- 1 °C min− and the desorbed NH
umination of H-type mesoporous Beta zeolite (H-Al-Meso-Beta) chromatography. UV-vis spectra were recorded on the Shi-
was performed by treating the parent material with a concen- madzu UV-310PC spectrometer with BaSO as a reference.
1
(
3
was detected by gas
4
−
1
trated nitric acid solution (13 M, 20 mL g ) at 100 °C for 20 h.
In the subsequent post-incorporation of Sn species, 0.5 g of 4.3. Catalytic reactions
dealuminated mesoporous Beta zeolite (De-Al-Meso-Beta,
Si/Al > 1500) was first pretreated in a quartz tubular reactor at
The isomerization was carried out at atmospheric pressure in
a glass reactor equipped with a reflux condenser under mag-
netic stirring. In a typical run, 0.10 g catalyst and 2.0 mL of
α-pinene (98%, Sigma) were charged into a glass flask to react
at 70 °C for 30 min under magnetic stirring. After fast cooling
down to room temperature, the solid catalyst was filtered and
the remaining liquid was analyzed using an Agilent 7890 gas
chromatograph equipped with a HP-5MS capillary column and
interfaced to a 5975C mass-selective detector. The Chem-
station software was used to collect and analyze the data. The
content of each product was calculated using the area normali-
zation method. The Baeyer–Villiger oxidation of 2-adamanta-
none (99%, Sigma) by hydrogen peroxide was carried out in a
5
00 °C for 2 h under a flow of dry N . Then, the N flow was
2 2
4
diverted through an anhydrous SnCl (99%, Sigma) liquid in a
−1
glass bubbler with a flow rate of 0.05 L min . The flow con-
taining SnCl vapor was allowed to contact the zeolite powder
4
for about 10 min. Afterwards, the sample was purged with
pure N
from the zeolite powder. After cooling to the room temperature
under a N atmosphere, the resulting zeolite powder was
washed with deionized water extensively until chloride ions
2 4
at 500 °C for about 4 h to remove any residual SnCl
2
were not detected in the filtrate by AgNO solution (0.1 M) and
3
then dried in air at 100 °C overnight. The obtained product
was labeled as Meso-Sn-Beta.
2
5 mL round-bottomed flask equipped with a reflux conden-
ser. The vessel was charged with 2 mmol of 2-adamantanone,
mmol of H (30 wt%), 50 mg of catalyst and 10 mL of
chlorobenzene. The mixture was stirred vigorously at 90 °C for
h. After the reaction, the mixture was cooled, centrifuged,
For comparison, conventional bulky Sn-Beta with a similar
Sn content was synthesized directly according to the litera-
4
2 2
O
19c
ture. The procedures involved dealuminated BEA seed fabri-
cation and Sn-Beta synthesis. The Sn-Beta crystallization was
carried out in a Teflon-lined stainless steel autoclave under
static conditions at 140 °C for 22 days. And the obtained
product was labeled as Con-Sn-Beta.
4
and the upper solution was collected by a micro-syringe. The
samples were analyzed by GC-MS (Agilent, 7890/5975C). Iso-
merization experiments were carried out in a stainless steel
autoclave (10 mL) heated in a temperature-controlled oil bath.
In a typical experiment, 4.1 g of an aqueous solution com-
posed of 10% (wt/wt) glucose and the corresponding catalyst
amount to achieve a metal : glucose molar ratio of 1 : 50 were
added into the sealed reactor equipped with a magnetic stir-
ring bar. The reactor was placed in a 110 °C oil bath and
removed after 30 min. The reaction was stopped by cooling the
reactor in an ice bath and the samples were analyzed by
means of high performance liquid chromatography (HPLC)
using an Agilent 1200 system.
4
.2. Characterization
Powder XRD patterns were collected on a Bruker D8 Focus
diffractometer with graphite-monochromatized Cu Kα radi-
ation (λ = 0.15405 nm), typically run at a voltage of 40 kV and
current of 40 mA. The contents of Al and Sn in different
samples were determined from the results of inductively
coupled plasma analysis (Varian 710-ES). The N
isotherms were measured at 77 K using Quantachrome NOVA
200e after outgassing at 200 °C for 10 h. The specific surface
2
adsorption
4
area and pore size distribution were calculated using the Bru-
nauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH)
methods, respectively. The micropore surface area and volume
were calculated by the t-plot method, and the total pore
Acknowledgements
volume was evaluated at P/P = 0.98. Field emission scanning This work was financially supported by the National Basic
0
electron microscopy (FE-SEM) images were obtained using a Research Program of China (973 Program, 2013CB933200);
FEI Magellan 400 scanning electron microscope. Transmission Program for New Century Excellent Talents in University
electron microscopy (TEM) observations were performed on a (NCET-10-0379); NSFC (grant no. 51172070, 51132009,
2
9
JEOL-2010F electron microscope operated at 200 kV. Si and 51202068); Shuguang Project (11SG30); and The Fundamental
2
7
Al MAS NMR spectra were recorded on a Bruker AVANCE 600 Research Funds for the Central Universities.
spectrometer. The TG analysis was carried out under the air
−
1
atmosphere at a heating rate of 10 °C min using a NETZSCH
STA 409 PG/PC instrument. Temperature-programmed deso-
rption of ammonia (NH -TPD) was conducted on a homemade
Notes and references
3
apparatus loaded with 150 mg of samples. The catalyst was
pretreated at 550 °C for 1 h and then cooled down to 100 °C
under He flow. Pure NH3 was introduced until adsorption
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