One-pot synthesis of mesoporous ZrPW solid acid catalyst for liquid phase benzylation of anisole

Article abstract of DOI:10.1039/c3cy00918a

Mesoporous zirconium phosphotungstate (M-ZrPW), with large specific surface area (~170 m² g^-1), large pore volume (~0.25 cm ³ g^-1), uniform pore size distribution (~6.5 nm) and tunable W/Zr ratios (0-0.2), was successfully prepared via a facile one-pot evaporation-induced self-assembly (EISA) strategy. Small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) characterizations showed that these materials had a mesoporous structure even when the W/Zr ratio reached up to 0.2. The tungsten species introduced via this strategy highly were dispersed among the wall of mesoporous framework. More importantly, the tungsten species greatly improved the Bronsted acidic property and catalytic activity in the Friedel-Crafts benzylation reaction. The highest activity was obtained at a W/Zr ratio of 0.2 with the strongest Bronsted acidity. In addition, the influences of various reaction parameters such as reaction time, amount of catalyst and calcination temperature of the catalyst, systematically investigated in this paper. Furthermore, the M-ZrPW showed a higher catalytic activity than H-Beta, H-ZSM5 and ZrPW prepared by the sol-gel method. Meanwhile, M-ZrPW could be reused at least for five cycles in the benzylation reaction without any notable decrease of catalytic activity.

Full text of DOI:10.1039/c3cy00918a

Catalysis
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Technology
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PAPER
One-pot synthesis of mesoporous ZrPW solid acid
catalyst for liquid phase benzylation of anisole†
Cite this: Catal. Sci. Technol., 2014,
4, 838
Zhichao Miao, Huanling Song, Huahua Zhao, Leilei Xu and Lingjun Chou*ac
ab
ac
a
ab
2
−1
Mesoporous zirconium phosphotungstate (M-ZrPW), with large specific surface area (~170 m g ), large
3
−1
pore volume (~0.25 cm g ), uniform pore size distribution (~6.5 nm) and tunable W/Zr ratios (0–0.2),
was successfully prepared via a facile one-pot evaporation-induced self-assembly (EISA) strategy. Small-
angle X-ray diffraction (SXRD), transmission electron microscopy (TEM) and scanning electron micros-
copy (SEM) characterizations showed that these materials had a mesoporous structure even when the
W/Zr ratio reached up to 0.2. The tungsten species introduced via this strategy highly were dispersed
among the wall of mesoporous framework. More importantly, the tungsten species greatly improved the
Brønsted acidic property and catalytic activity in the Friedel–Crafts benzylation reaction. The highest
activity was obtained at a W/Zr ratio of 0.2 with the strongest Brønsted acidity. In addition, the influences
of various reaction parameters such as reaction time, amount of catalyst and calcination temperature of
the catalyst, systematically investigated in this paper. Furthermore, the M-ZrPW showed a higher catalytic
activity than H-Beta, H-ZSM5 and ZrPW prepared by the sol–gel method. Meanwhile, M-ZrPW could be
reused at least for five cycles in the benzylation reaction without any notable decrease of catalytic activity.
Received 12th November 2013,
Accepted 2nd December 2013
DOI: 10.1039/c3cy00918a
www.rsc.org/catalysis
9
–11
been attracting considerable attention in recent years.
1
. Introduction
Many kinds of solid acid catalysts were utilized in these
1
2,13
14,15
Friedel–Crafts (FC) benzylation is one of the fundamental
reactions in the field of organic synthesis for the preparation
of fine chemicals, dielectric fluids and pharmaceutical
chemicals. Conventionally, FC benzylation reaction is cata-
lyzed by strong homogeneous acids such as AlCl , FeCl ,
reactions, such as zeolites,
ion-exchanged resins,
1
6
17
sulfated metal oxide,
Ga-, Al-, GaAl-SBA-15,
niobium
1
8,19
20–22
phosphate,
heteropoly acids and their salts.
More-
1
–4
over, as for the benzylating agents, benzyl chloride and
benzyl alcohol are commonly employed in the FC benzylation
3
3
2
,5
23,24
ZnCl
2
and H
2
SO
4
.
Nevertheless, the complete separation of
reactions.
Compared with benzyl chloride, which pro-
the products from these reaction mixtures usually requires
an expensive and tedious purification process. Therefore,
from the viewpoint of green chemistry, the efficient solid
acid catalysts should be developed since these are reusable,
readily separable, environmentally friendly and can lead to
duces HCl, an environmental undesirable product, benzyl
alcohol only generates water as a side product in the reac-
tion, therefore, the use of benzyl alcohol instead of benzyl
2
5,26
chloride is an eco-friendly process.
Since the discovery of MCM-41,
porous materials have been fabricated and widely applied
2
7,28
a variety of meso-
6
–8
minimal pollution and waste.
In addition, the FC
2
9
30
benzylation reactions catalyzed by solid acid catalysts have
in many fields, such as the separation, sorption, con-
3
1
32
trolled release and heterogeneous catalysis. The solid
acid catalyst with mesostructure allows the reactant mole-
cules to access additional active acid sites in the pores,
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000,
People's Republic of China. E-mail: ljchou@licp.cas.cn; Fax: +86 0931 4968129;
Tel: +86 0931 4968066
3
3,34
resulting in improved catalytic activity.
Mesoporous
Nb , Ta–W, Nb–W and Nb–Mo oxides were successfully
2 5
O
b
University of Chinese Academy of Sciences, Beijing 100049,
synthesized and used as solid acid catalysts in FC
benzylation of anisole, and their activities were higher than
People's Republic of China
c
Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences,
3
5–38
Suzhou 215123, People's Republic of China
those of many conventional solid acid catalysts.
More-
†
Electronic supplementary information (ESI) available: The SXRD patterns,
over, the sulfated mesoporous Nb and Ta oxides with large
specific surface area were prepared and showed excellent
nitrogen adsorption and desorption isotherms and reaction results of M-ZrPW-25;
the WXRD patterns, Raman spectroscopy and nitrogen adsorption and desorption
isotherms of M-ZrPW-20 treated at 500–900 °C; XRD patterns, nitrogen adsorption
and desorption isotherms and TEM images of the recycled M-ZrPW-20 after five
cycles. See DOI: 10.1039/c3cy00918a
3
9–41
activity in the acid catalytic reactions.
In our previous
recent work, the mesoporous zirconium oxophosphate
(M-ZrPO) materials had been successfully synthesized and
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4
2
used as solid acid catalyst in the ketalization reaction. On
this basis, we suggest that the introduction of tungsten into
the M-ZrPO materials may enhance their acidic property
about M-ZrPW-25 are shown in the ESI.† For comparison, the
ZrPW synthesized from the sol–gel method was as reported
by Chudasama et al. and the molar ratios of Zr, P, W were
4
5
3
6,37
owing to the high oxidation states of tungsten.
Besides,
kept consistent with the M-ZrPW-20.
as far as we know, the reports related to the synthesis of
mesoporous zirconium phosphotungstate (M-ZrPW) mate-
rials through one-step strategy are very few and have poten-
tial to be investigated.
In this paper, the one-pot evaporation-induced self-
assembly (EISA) strategy was employed to synthesize a
series of M-ZrPW with different content of tungsten. The
characterization was carried out using small X-ray diffraction
2
.2 Characterization
Powder X-ray diffraction (XRD) measurements were
performed using an X'Pert Pro Multipurpose diffractometer
(PANalytical, Inc.) with Cu Kα radiation (0.15406 nm) at room
temperature from 0.6° to 5.0° (small angle) and 10.0° to 80.0°
(wide angle). Measurements were conducted using a voltage
of 40 kV, current setting of 20 mA for small angle XRD and
40 mA for wide angle XRD, step size of 0.02°, and count time
of 4 s.
The Raman spectra were recorded on a Laboram 010 con-
focal Raman system (Horiba JobinYvon, France) equipped
with a 632 nm He–Ne laser.
Transmission electron microscopy (TEM) images, fast
Fourier transform (FFT) patterns, selected area electron dif-
fraction (SAED) and energy-dispersive X-ray spectroscopy
(SXRD), transmission electron microscopy (TEM), scanning
electron microscopy (SEM) and N -physisorption to illustrate
2
the mesostructure of these materials. Moreover, UV-visible
diffuse reflectance spectra (UV-vis), Fourier transform infra-
red (FT-IR) and X-ray photoelectron spectroscopy (XPS) char-
acterizations were used to investigate the chemical bonds in
the materials. In addition, the influences of highly dispersed
tungsten species on the Brønsted acidic property and cata-
lytic activity of M-ZrPW in benzylation reaction were
discussed in detail. Finally, the solid acid catalyst was reused
for five cycles to investigate the reusability of M-ZrPW in the
FC benzylation reaction.
2
(EDX) measurements were performed on the TECNAI G F20
high-resolution transmission electron microscopy under a
working voltage of 200 kV.
The scanning electron microscopy (SEM) images were
obtained on a Hitachi Cold FE-SEM SU80X0 high-resolution
scanning electron microscope.
2
. Experimental section
2
.1 Synthesis of mesoporous zirconium phosphotungstate
The nitrogen adsorption and desorption isotherms at
−196 °C were recorded on an Autosorb-iQ analyzer
(Quantachrome Instruments U.S.). Prior to the tests, all the
samples were pretreated at 200 °C for 2 h. The specific sur-
face areas were calculated via the Brunauer–Emmett–Teller
(BET) method in the relative pressure range of 0.05–0.3; the
single-point pore volume was calculated from the adsorption
isotherm at a relative pressure of 0.990; the pore size distri-
butions were calculated using adsorption branches of
nitrogen adsorption–desorption isotherms by the Barrett–
Joyner–Halenda (BJH) method.
(
1
(
EO)106(PO) (EO) triblock copolymer (Pluronic F127, Mav
2 600, Sigma-Aldrich), zirconyl chloride octahydrate
=
70
106
ZrOCl ·8H O, ≥99.0%, Tianjin Fengyue Reagent Company),
2
2
trimethyl phosphate (PO(OCH ) , ≥99.0%, Sinopharm
Chemical Reagent Co. Ltd.), ammonium tungstate
3
3
(
(NH ) H [H (WO ) ]·H O, ≥99.0%, Sinopharm Chemical
4
5
5
2
4 6
2
Reagent Co. Ltd.), ethanol (≥99.7%, Sinopharm Chemical
Reagent Co. Ltd.). All the reagents were A.R. grade and used
as received without further purification.
Mesoporous zirconium phosphotungstate (M-ZrPW) was
synthesized via an improved one-pot evaporation-induced
self-assembly (EISA) strategy.
synthesizing M-ZrPW, 1.2 g of F127 was employed as
structure-directing agents (SDAs) and dissolved in 15 mL of
anhydrous ethanol. As the SDAs were completely dissolved,
Thermogravimetric-differential
scanning
calorimetry
4
3,44
In a typical procedure for
(TG-DSC) measurements were carried out on a NETZSCH
STA 449F3 thermogravimetric analyzer from room tempera-
−
1
ture to 1000 °C with the rate of 10 °C min under the air
atmosphere.
5
mmol of ZrOCl ·8H O, 3.75 mmol of PO(OCH ) (the molar
UV-visible diffuse reflectance spectra were recorded on a
PE Lambda 650S in the range of 190–700 nm.
Fourier transform infrared (FT-IR) spectra were recorded
on KBr pellets by a Nexus 870 infrared spectrometer with the
2
2
3 3
ratio of P/Zr was 0.75) and 0–1 mmol of tungsten species
were added into the above solution with vigorous stirring.
The solution was covered with a PE film and stirred for 6 h at
least. Finally, the solution mixture was transferred to a petri
dish (d = 9 cm) to undergo the slow EISA process at 60 °C for
−
1
wavenumber from 4000 to 400 cm .
X-ray photoelectron spectroscopy (XPS) analyses of the
samples were performed on a Thermon Scientific ESCALAB250xi
spectrometer. All binding energies were calibrated to the
C1s line (284.8 eV).
4
8 h, then 100 °C for 24 h in a drying oven. The obtained
xerogel was calcined by slowly increasing the temperature
−
1
(1 °C min ramping rate) to 500 °C and kept at the final tem-
perature for 6 h to remove the SDAs. The obtained template-
free self-assembled M-ZrPW was denoted as M-ZrPW-X, where
X (0, 5, 10, 15, 20, 25) stands for the molar percentage ratio
of W/Zr and the detailed characterization and discussion
X-Ray Fluorescence (XRF) spectra were recorded on a
Magix PW2403 (PANalytical, Inc.) analyzer.
Temperature programmed desorption of ammonia
(NH -TPD) was performed on a Tianjin Xianquan TP5000.
3
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A typical experiment for the TPD measurement was as follows:
the M-ZrPW (0.1 g) was pretreated at 400 °C for 2 h in the
flowing He to remove any moisture and absorbed impurities.
dimensional hexagonal structure. These diffraction peaks
indicated the existence of long-range ordered mesopores in
these three samples. However, when the W/Zr ratio was
increased further to 0.15 and 0.2, the SXRD pattern only
displayed a single broad peak at about 0.93° rather than the
conspicuous diffraction peaks. Compared with the above-
mentioned three samples, which had ordered mesostructure,
the orderliness of the pores became poorer in the M-ZrPW-15
and M-ZrPW-20. (For the M-ZrPW-25, there was no diffraction
peak in the SXRD patterns, indicating the completely disap-
pearance of the ordered mesostructure. The detailed discus-
sion about M-ZrPW-25 is shown in the ESI.†) In addition, the
small angle reflection peaks shifted to a lower 2θ region
(from 0.99° to 0.93°) from M-ZrPW-0 to M-ZrPW-5, corre-
sponding the d-spacing (100) changed to higher values (from
8.92 nm to 9.49 nm) (shown in Table 1). This indicated that
the pore size and unit cell parameter became larger with the
introduction of tungsten. The wide angle X-ray diffraction
(WXRD) patterns of these samples are shown in Fig. 1 (2).
All the patterns kept consistent with each other and
only exhibited two broad peaks in the 2θ range of 20–40° and
40–60°, indicating the existence of an amorphous pore wall
structure. No individual crystalline peak of zirconium phos-
phate or zirconia were observed. Meanwhile, there were no
peaks of tungsten oxide in the WXRD patterns, illustrating
After cooling to 100 °C, 10 mol% NH –He was introduced for
3
3
0 min. Physically absorbed NH3 was then removed by
desorbing in He at 100 °C for 60 min. The TPD experiment
was then carried out by raising the temperature of the sample
−
1
in a programmed manner (10 °C min ) to 900 °C. The same
sample without the introduction of NH was used as blank
3
control and no TCD singles were observed in the programmed
process from 100 to 900 °C.
The infrared spectra of adsorbed pyridine (pyridine-IR)
were recorded on a PE Frontier FT-IR spectrometer. The sam-
ple (~15 mg) was pressed into a pellet (~13 mm), evacuated
under vacuum at 400 °C for 1 h, then cooled to room temper-
ature and pyridine was introduced and adsorbed for 30 min.
The sample was raised to a desired temperature and evacu-
ated for 30 min, after which the spectrum was recorded. The
blank experiments were operated under the same conditions
and used as the background to ensure the accuracy of the
infrared spectra of the adsorbed pyridine. The Brønsted and
Lewis acidity was determined by the method proposed by
4
9
4
6
Emeis.
2
.3 Catalytic reaction
x
the high dispersion of WO among the mesoporous frame-
work even in M-ZrPW-20, which had a W/Zr ratio up to 0.2.
The same conclusion could also be derived from the Raman
Benzylation of anisole. Liquid phase Friedel–Crafts (FC)
benzylation of anisole was performed in a three-neck round
bottom flask coupled with a reflux condenser in a tempera-
3
9
3
spectra. As shown in Fig. 2, the bulk WO exhibited five
ture controlled oil bath as reported by Antonelli et al. In a
typical run, 0.2 g of M-ZrPW was added to a mixture of
anisole and benzyl alcohol (20 mL anisole + 2 mL benzyl alco-
hol) with dodecane (0.4 ml) used as an internal standard for
gas chromatography (GC) analysis. Nitrogen was introduced
into the flask through one of the gas inlets. The reaction was
carried out at 170 °C under reflux condition with vigorous
stirring for 2 h. The conversion of benzyl alcohol and selectiv-
ity of the products were monitored by a gas chromatography
−1
bands in the Raman spectra at 815, 725, 332, 280 and 140 cm ,
which belonged to the crystalline WO . However, there were
3
no obvious band in these regions in the Raman spectra of
M-ZrPW, implying that no crystalline WO existed among the
3
wall of mesostructure. As confirmed by the WXRD and Raman
spectra characterizations, the tungsten species were highly
dispersed among the wall of the mesostructure, this might be
on account that the W atoms in the materials were segregated
by the Zr and P atoms owing to the peculiar traits of the one-
(
GC) instrument (Agilent-7890A; equipped with a flame ioni-
zation detector (FID) and HP-5 column (30 m × 0.32 mm ×
.25 μm)). Gas chromatography-mass spectroscopy (GC-MS)
instrument (5975c vl MSD with triple-axis detector, GC
Agilent-7890A) was employed to identify the reaction prod-
ucts. After completion of the reaction, the catalyst was sepa-
rated by centrifugation and activated at 400 °C for 3 h for
regeneration.
5
0
pot preparation strategy. Therefore, the thermal agglomera-
tion of the WO nanoparticles during the progress of calcina-
x
0
tion was avoided to some extent, resulting in high dispersion
of the tungsten species in the mesostructure.
In order to further confirm the presence of mesopores in
M-ZrPW, TEM (Fig. 3) and SEM (Fig. 4) images of the sam-
ples were taken. The TEM images and corresponding FFT
patterns revealed the existence of long-range ordered pores
along the [110] direction (Fig. 3a and c) and [001] direction
3
3
. Results and discussion
.1. Mesoporous structure
(
Fig. 3b) in M-ZrPW-0, M-ZrPW-5 and M-ZrPW-10. By further
increasing the W/Zr ratios to 0.15 and 0.2, M-ZrPW-15
(Fig. 3d) and M-ZrPW-20 (Fig. 3e) showed wormlike meso-
porous channels rather than the long-range ordered pores of
the TEM images. Although no ordered mesostructure existed
in M-ZrPW-15 and M-ZrPW-20, the abundant wormlike meso-
pores could be clearly observed in the two samples. The simi-
lar feature could also be obtained in the SEM images, which
showed ordered mesopores from the [110] and [001]
Small angle X-ray diffraction (SXRD) is an important tech-
4
7,48
nique for the characterization of mesoporous materials.
The SXRD patterns of M-ZrPW with different W/Zr ratios are
shown in Fig. 1(1). The M-ZrPW-0, M-ZrPW-5 and M-ZrPW-10
presented a distinct diffraction peak in the range of 0.9–1°
and one weak diffraction peak around 1.9°, which could be
indexed as (100) and (110) reflections of P6mm two-
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Fig. 1 Small-angle X-ray diffraction (1) and wide-angle X-ray diffraction (2) patterns of the M-ZrPW-X samples: (a) M-ZrPW-0, (b) M-ZrPW-5,
c) M-ZrPW-10, (d) M-ZrPW-15, (e) M-ZrPW-20.
(
Table 1 Textural properties of the M-ZrPW-X samples derived from SXRD and nitrogen adsorption and desorption data
SXRD
Nitrogen adsorption and desorption data
W/Zr
ratios
2
−1
3
−1
Samples
2θ (°)
d-Spacing (100) (nm)
Specific surface area (m g
)
Pore size (nm)
Pore volume (cm g
)
M-ZrPW-0
M-ZrPW-5
M-ZrPW-10
M-ZrPW-15
M-ZrPW-20
0
0.99
0.93
0.94
0.91
0.94
8.92
9.49
9.39
9.70
9.39
160.0
161.4
181.5
171.0
168.3
5.62
6.54
6.57
6.56
6.26
0.22
0.25
0.26
0.24
0.23
0.05
0.10
0.15
0.20
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characterization, which predicted the presence of ordered
mesopores in the samples with W/Zr from 0 to 0.1 and worm-
like mesopores for M-ZrPW-15 and M-ZrPW-20. Furthermore,
the corresponding SAED pattern of M-ZrPW-20 was also pro-
vided in the inset of Fig. 3e. There were no apparent electron
diffraction rings, implying that the wall of the mesoporous
framework was amorphous in structure, which could also
be seen from the WXRD patterns. In the EDX measurement
of M-ZrPW-20 (Fig. 3f), the exclusive peaks of Zr, P and W
elements were notably observed in the pattern, showing
that all the elements were successfully introduced into the
framework of the mesostructure. In addition, the values of
the W/Zr atomic ratios derived from EDX were very close to
the theoretical values (shown in Table 2). This might be due
to the fact that the tungsten species are highly dispersed in
the wall of the mesopores.
Fig. 2 Raman spectra of the M-ZrPW-X and bulk WO
3
samples:
(
(
a) M-ZrPW-0, (b) M-ZrPW-5, (c) M-ZrPW-10, (d) M-ZrPW-15,
e) M-ZrPW-20, (f) WO
The textural properties of the M-ZrPW with different W/Zr
3
.
ratios were characterized by
2
N -physisorption. Nitrogen
adsorption and desorption isotherms and the pore size distri-
butions (PSD) of the samples are shown in Fig. 5. For all the
samples, the isotherms could be classified as type IV with H1
shaped hysteresis loops, which are the typical characteristic
directions for M-ZrPW-10 (Fig. 4a and b) and wormlike meso-
pores for M-ZrPW-20 (Fig. 4c and d). The TEM and SEM
images agreed quite well with the results of the SXRD
Fig. 3 TEM and SAED images of (a) M-ZrPW-0, (b) M-ZrPW-5, (c) M-ZrPW-10, (d) M-ZrPW-15, (e) M-ZrPW-20, (f) EDX measurement of M-ZrPW-20.
The scale in images a–e: 50 nm.)
(
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Fig. 4 SEM images of M-ZrPW-X: (a), (b) M-ZrPW-10 and (c), (d) M-ZrPW-20.
Table 2 Analysis of the molar ratios of W/Zr in the M-ZrPW-X samples
Samples
Theoretical values
Calculated from XRF
Calculated from XPS
Calculated from EDX
M-ZrPW-0
M-ZrPW-5
M-ZrPW-10
M-ZrPW-15
M-ZrPW-20
0
0
0
0
0.05
0.10
0.15
0.20
0.04
0.09
0.14
0.18
0.04
0.08
0.13
0.17
0.05
0.09
0.15
0.21
5
1,52
of mesoporous materials.
In addition, all the capillary
profiles of the as-synthesized M-ZrPW-20 in air atmosphere
were given in Fig. 6. The TG curve mainly comprised three
obvious stages of weight loss during the temperature increase
from room temperature to 1000 °C. The first weight loss
stage occurred around 150 °C and was designated to the loss
of physically absorbed water and other volatile species (like
HCl), which were generated in the EISA process. The follow-
ing sharp weight loss (ca. 45 wt%), along with a drastic exo-
thermic peak in the DSC profile, occurred between 200 °C
and 350 °C, indicating the combustion of the SDAs. The last
weight loss observed between 350 °C and 500 °C was from
the further development of the inorganic framework. Besides,
no noticeable weight loss was observed over 500 °C, indicat-
ing the complete removal of the SDAs. In the DSC profile,
there was an exothermic peak at about 800–950 °C and this
peak was attributed to the phase transformation of the
pore wall. This conclusion could also be further confirmed
by the WXRD patterns and Raman spectra of the M-ZrPW-20
calcined at 500–900 °C (shown in Fig. S3†).
condensation steps of the hysteresis loops were very steep,
indicating the existence of a uniform pore size in the frame-
work of M-ZrPW. Meanwhile, as shown in Fig. 5 (2), all the
PSD were extremely narrow and the position located around
6
nm, once again reflecting the presence of a uniform pore
size in the mesoporous materials. Besides, the textural
parameters, such as specific surface area, pore size and
volume of all the samples were shown in Table 1. With
the increasing of the W/Zr ratio, the specific surface area
2
−1
3
−1
(
~170 m g ) and pore volume (~0.25 cm g ) changed little
and the pore size increased slightly from 5.6 nm to 6.5 nm.
Although the degree of order of mesostructure in M-ZrPW
suffered some damage when the W/Zr ratios increased to
0
.15 and 0.2, the excellent textural properties were success-
fully preserved. The introduction of tungsten species had
little influence on the textural properties of materials.
To investigate the calcination process and evaluate the
thermal stability of the obtained M-ZrPW, TG-DSC analysis
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Fig. 6 TG-DSC curves of the as-synthesized M-ZrPW-20.
Fig. 7 UV-vis diffuse reflectance spectra of the M-ZrPW-X samples:
(
(
a) M-ZrPW-0, (b) M-ZrPW-5, (c) M-ZrPW-10, (d) M-ZrPW-15,
e) M-ZrPW-20.
a new broad peak could be observed at about 260 nm. Mean-
while, this peak became more noticeable with the tungsten
content increasing from 0.05 to 0.2 and this broad peak
should be assigned to the isolated tungsten species or low-
condensed oligomeric tungsten oxide species in the wall of
5
6,57
mesostructure.
at about 400 nm, which was attributed to tungsten trioxide
and could be observed in bulk WO , might reflect the fact that
In addition, the absence of the broad peak
Fig. 5 Isotherms (1) and pore size distributions (2) of the M-ZrPW-X
samples: (a) M-ZrPW-0, (b) M-ZrPW-5, (c) M-ZrPW-10, (d) M-ZrPW-15,
3
(
e) M-ZrPW-20.
the tungsten species were highly dispersed in the mesoporous
framework and no crystalline WO3 was formed in M-ZrPW
3
.2. Chemical bonds and composition analysis
57–59
even when the tungsten content reached up to 0.2.
This
UV-vis spectroscopy was employed to characterize the coordi-
nation modes and distinguish the tungsten species between
incorporated metal and extra-framework metal oxides in
conclusion agreed quite well with the results of the WXRD
and Raman spectra characterization.
The FT-IR spectra of M-ZrPW with different W/Zr ratios
were shown in Fig. 8. The M-ZrPW-0 exhibited a broad peak
5
3,54
M-ZrPW.
tion of tungsten (M-ZrPW-0) showed an absorption peak at
05 nm, which was attributed to the Zr–O–P coordination.
The weak band at about 300 nm could be due to the interac-
As shown in Fig. 7, the sample without introduc-
−
1
centred at 1070 cm , arising from the Zr–O–P bonds in
−
1
2
the mesostructure. Meanwhile, the peaks at 1630 cm and
−
1
3450 cm were assigned to the surface hydroxyl groups.
Furthermore, with the increasing of the tungsten content,
4
+
tion of Zr cations with the phosphate counteranions in the
5
5
−1
mesoporous framework. With the introduction of tungsten,
a weak peak at 830 cm could be observed and this peak was
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tungsten introduced in the preparation process. Moreover,
the W/Zr ratios on the sample surfaces showed only slight
differences with the bulk compositions, calculated from the
characterization of XRF. In addition, all the W/Zr ratios
derived from XPS, XRF and EDX characterizations were con-
sistent with the theoretical values. This indicated that the
tungsten species was successfully introduced into the wall
and dispersed homogeneously in the wall of the meso-
structure even when the W/Zr ratio reached 0.2.
3.3. Acidic property
The acidic property of calcined M-ZrPW was evaluated by
NH -TPD. All the TPD profiles of M-ZrPW-X (shown in
3
Fig. 8 FT-IR spectra of M-ZrPW-X samples: (a) M-ZrPW-0, (b) M-ZrPW-5,
Fig. 10 (1)) were similar to each other in shape and the
characteristic TPD profile showed an obvious broad peak at
(c) M-ZrPW-10, (d) M-ZrPW-15, (e) M-ZrPW-20.
150–400 °C and a weak peak at about 600 °C. This indicated
that all the samples had abundant acid sites. In addition,
the peak strength at 150–400 °C increased from M-ZrPW-0 to
M-ZrPW-20, implying that the acidity of M-ZrPW increased
with the introduction of the tungsten species. This could be
further confirmed from the infrared spectra of the adsorbed
attributed to the W–O –W vibration in the framework indicat-
c
ing that the tungsten species was successfully introduced into
6
0,61
the wall of the mesostructure.
The high-resolution XPS spectra were employed to investi-
gate the surface chemical composition as well as the oxida-
tion state of the tungsten species in M-ZrPW. The W 4f XPS
spectra of the M-ZrPW with different W/Zr ratios were shown
in Fig. 9. All XPS spectra in the W 4f region were similar to
each other in shape. The core level spectrum displayed two
peaks corresponding to W 4f7/2 and W 4f5/2 with binding
energies of 36.2 and 38.3 eV, respectively. Therefore, it could
be inferred that the tungsten species mainly existed as high
6
+
62
oxidation state W in the wall of the mesoporous structure.
6
+
The high oxidation state W might account for the improve-
ment of the Brønsted acidic property with the increasing of
the tungsten content in M-ZrPW.
In addition, the surface W/Zr ratios of M-ZrPW were
shown in Table 2. These values were determined by the XPS
line areas of Zr 3d and W 4f. The W/Zr ratios on the sample
surface increased linearly in agreement with the increase of
3
Fig. 10 (1) NH -TPD profiles of M-ZrPW-X samples, (2) IR spectra for
Fig. 9 High-resolution XPS spectra of M-ZrPW-X samples: (a) M-ZrPW-5,
pyridine adsorbed on M-ZrPW-X samples recorded at 150 °C: (a) M-
(b) M-ZrPW-10, (c) M-ZrPW-15, (d) M-ZrPW-20.
ZrPW-0, (b) M-ZrPW-5, (c) M-ZrPW-10, (d) M-ZrPW-15, (e) M-ZrPW-20.
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pyridine. The pyridine-IR spectra were employed to evaluate
the types and strength of Brønsted and Lewis acid sites in
M-ZrPW with different W/Zr ratios. The pyridine-IR spectra
with benzyl alcohol. All the reaction schemes are presented
9
,16,63
in Scheme 1.
In this reaction system, benzylanisoles are
4
6
the products of benzylation of anisole with benzyl alcohol
and dibenzyl ether is a product of the auto-etherification of
benzyl alcohol. Meanwhile, the dibenzyl ether is also a good
benzylating agent, and it can react with anisole to produce
benzylanisole.
of M-ZrPW-X (shown in Fig. 10 (2)) exhibited bands at 1450,
−
1
1
575 and 1610 cm , demonstrating the existence of Lewis
acid sites in the materials. Moreover, the bands at 1540 and
−
1
1
640 cm were the characteristic bands of pyridinium ion,
showing the presence of Brønsted acid sites. In addition, the
In the first set of experiments, the benzylation reaction
was carried out by using M-ZrPW with different ratios of
W/Zr as solid acid catalysts. After reacting at 170 °C for 2 h,
o-benzylanisole, p-benzylanisole and dibenzyl ether were
detected as products, whereas m-benzylanisole was not
detected in the GC instrument. As shown in Fig. 11 (1), the
variety of tungsten content resulted in a remarkably different
reaction activity toward the benzylation reaction. The
M-ZrPW-0, without the introduction of tungsten, only showed
17.8% conversion of benzyl alcohol. However, with the
increase of the tungsten content, the conversion increased
gradually and reached the maximum conversion 100% for
M-ZrPW-20. At the same time, the selectivity of benzylanisole
(o-benzylanisole and p-benzylanisole) for FC benzylation also
followed a similar pattern. The selectivity observed for
M-ZrPW-X gradually increased with the introduction of tung-
sten species (53.6%, 66.0%, 75.2%, 77.7%, 87.2% for
M-ZrPW-X, respectively). It is well known that the benzylation
of anisole with benzyl alcohol is promoted by the Brønsted
−
1
band at 1490 cm was a combination between two separate
−
1
bands at 1540 and 1450 cm , corresponding to Brønsted and
Lewis acid sites, respectively. These indicated that both
Brønsted and Lewis acid sites existed in M-ZrPW. Moreover, it
−
1
is noteworthy that the bands at 1540 and 1640 cm , which
belonged to the Brønsted acid sites, were enhanced stepwise
with the increase of the tungsten content, indicating that the
introduction of tungsten species improved the Brønsted acid-
ity of M-ZrPW. In addition, the Brønsted and Lewis acidity
derived from the pyridine-IR spectra were shown in Table 3.
There were no obvious changes in the Lewis acidity of
M-ZrPW, however, the Brønsted acidity increased gradually
−
1
−1
from 19.9 μmol g to 55.1 μmol g with the W/Zr ratios
increasing from 0 to 0.2. The improved Brønsted acidity
might be due to the highly dispersed tungsten species with
6
+
high oxidation state (W ) among the wall of the meso-
structure, which was introduced through the one-pot EISA
strategy. The improved Brønsted acidity might largely influ-
ence the catalytic performance of M-ZrPW in the following
benzylation reaction.
2
2,64–66
acid sites.
Therefore, the improvement of the catalytic
activity might be due to the increase of the Brønsted acidic
nature which was caused by the introduction of the tungsten
species in M-ZrPW (as shown in Table 3). In addition, a plau-
sible reaction mechanism was presented. As shown in
3
.4. Catalytic performance study
Due to the excellent acidic property, M-ZrPW was used as a
solid acid catalyst in the liquid phase benzylation of anisole
Scheme 2, the Brønsted acid sites functioned as the catalyst
+
for the formation of benzyl cation (C
6
H
5
CH
2
) from benzyl
+
alcohol and then C H CH attacked the anisole ring to pro-
6
5
2
9
,19
duce benzylanisole in the course of the FC benzylation.
Table 3 The acidity of M-ZrPW-X derived from pyridine-IR
In addition, the selectivity of dibenzyl ether, a byproduct of
benzyl alcohol, was 46.3%, 34.0%, 24.8%, 22.3%, 12.8% for
M-ZrPW-X, respectively. The gradual decrease of dibenzyl
ether selectivity kept consistent with the increase of Brønsted
acid strength, this might be due to the fact that the dibenzyl
ether was used as a benzylating agent and consumed in
the benzylation reaction under the existence of sufficient
Brønsted acidity
Lewis acidity
Total acidity
−1
−1
−1
Samples
(μmol g
)
(μmol g
)
(μmol g
)
M-ZrPW-0
M-ZrPW-5
M-ZrPW-10
M-ZrPW-15
M-ZrPW-20
19.9
33.2
35.4
38.4
55.1
83.0
75.3
81.7
85.8
88.5
102.9
108.5
117.1
124.2
143.6
Scheme 1 Friedel–Crafts benzylation reaction between anisole and benzyl alcohol.
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Brønsted acid sites. Due to the better performance of
M-ZrPW-20, this was chosen as the representative catalyst
for the further studies.
The progress of benzylation of anisole with benzyl alco-
hol over M-ZrPW-20 was studied by analyzing the reaction
product at different time interval (Fig. 11 (2)). Initially, the
conversion of benzyl alcohol and the yield of benzylanisole
were increased with the time and the maximum benzyl
alcohol conversion (100%) and benzylanisole yield (87.2%)
was achieved at 120 min for M-ZrPW-20. However, the yield
of dibenzyl ether increased to the maximum 17.2% only
after 60 min, and decreased slightly to 12.8% at 120 min.
This might be due to the fact that the dibenzyl ether was a
good benzylating agent, and it was consumed, along with
the benzyl alcohol, at the end of the benzylation reaction.
After 120 min, there were few changes in the curves. In
addition, the results of leaching test were shown in
Fig. 11 (2). After removing M-ZrPW-20 from the reaction sys-
tem at 60 min, there were few changes in the yield of
benzylanisole, indicating that the M-ZrPW-20 was truly a
heterogeneous catalyst.
Moreover, the effects of the catalyst amount on the activity
were examined and the results were shown in Fig. 12 (1). It
was found that the conversion and selectivity increased grad-
ually with the increase of the catalyst amount from 0.05 to
0.2 g. The maximum conversion was 100% with 87.2% selec-
tivity when the catalyst amount reached 0.2 g. The existence
of sufficient Brønsted acid sites was beneficial for the
improvement of conversion and selectivity. The catalytic
activity changed little after a further increase of the catalyst
amount to 0.3 g.
Fig. 11 Friedel–Crafts benzylation reaction: (1) catalyzed by M-ZrPW-X
with different W/Zr ratios; (2) catalyzed by M-ZrPW-20 at different
times (BA: benzylanisoles, DE: dibenzyl ether).
Scheme 2 A plausible reaction mechanism of Friedel–Crafts benzylation reaction catalyzed by M-ZrPW-X.
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Therefore, we deduced that both the high dispersion of the
tungsten species and the high specific surface area were in
favor to the improvement of catalytic activity.
In order to evaluate the recyclability of the catalyst, we
carried out a five run test over the M-ZrPW-20 sample under
the optimized reaction conditions (shown in Fig. 13 (1)).
Compared with the fresh catalyst, no significant decline in
conversion or selectivity was observed after five cycles, indi-
cating that the M-ZrPW-20 sample could be reused as a solid
acid catalyst. In addition, the catalyst regenerated after five
cycles was characterized by XRD, N -physisorption and TEM.
2
As shown in Fig. S5 and S6,† the mesostructure of the
M-ZrPW-20 sample is maintained after five cycles. Mean-
while, the specific surface area, pore size distribution and
pore volume changed little, indicating that the catalyst suf-
fered little damage in the acid-catalyzed reaction. Moreover,
Fig. 13 (2) showed the activity of M-ZrPW-20 and control
catalysts (H-Beta, H-ZSM5 and ZrPW synthesized from the
sol–gel method) in the benzylation reaction. Compared with
the control catalysts, the M-ZrPW-20 showed a remarkable
higher catalytic activity. Therefore, the M-ZrPW was a good
solid acid catalyst in the benzylation reaction.
Fig. 12 Friedel–Crafts benzylation reaction: (1) catalyzed by M-ZrPW-20
with different amount of catalyst; (2) catalyzed by M-ZrPW-20 treated at
500–900 °C.
The influence of calcination temperature on the activity
of M-ZrPW-20 was also investigated. The M-ZrPW-20 samples
treated at 500–900 °C were utilized as catalysts in the
benzylation reaction and the results were shown in
Fig. 12 (2). With the calcination temperature increased from
5
00 to 700 °C, the conversion and selectivity decreased
slightly. This might be due to the decrease of specific surface
area with the increase of the calcination temperature, just as
shown in Table S1.† In addition, due to the tungsten species
still highly dispersed among the wall of the mesostructure
(shown in Fig. S3†), there was no drastic decline in catalytic
activity. However, there was a drastic decrease of catalytic
activity and a conversion of only 50.9% and 13.7% for
M-ZrPW-20 samples treated at 800 °C and 900 °C, respectively.
As shown in the WXRD patterns and Raman spectra of the
M-ZrPW-20 samples treated at different temperatures (shown
in Fig. S3†), the tungsten species in the wall of the meso-
structure began to aggregate to form crystal WO
specific surface area decreased to 45.9 and 10.1 m
3
and the
2
−1
g
in
the M-ZrPW-20 samples treated at 800 °C and 900 °C, respec-
tively. The aggregation of tungsten species and the decrease
of specific surface area might account for the decrease of
the catalytic activity after treatment at 800 °C and 900 °C.
Fig. 13 Friedel–Crafts benzylation reaction: (1) the recyclability of
M-ZrPW-20; (2) catalyzed by different solid acid catalysts.
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1
5 M. A. Harmer, W. E. Farneth and Q. Sun, J. Am. Chem. Soc.,
4
. Conclusion
1
996, 118, 7708–7715.
A series of M-ZrPW were successfully synthesized through
one-pot EISA strategy. The W/Zr ratios of the samples could
be accurately controlled through dominating the precursors.
Meanwhile, the M-ZrPW obtained from this method had
obvious mesostructure, large specific surface area, large pore
volume and uniform pore size distribution. The tungsten spe-
cies, introduced through this one-pot strategy, was highly dis-
persed in the wall of the mesostructure. Due to the excellent
textural properties and highly dispersed tungsten species, the
Brønsted acidic property and reaction activity of M-ZrPW
were greatly improved with the introduction of the tungsten
species. Moreover, the M-ZrPW was successfully used as a
solid acid catalyst in the liquid phase benzylation of anisole
by benzyl alcohol and showed good catalytic performances.
Compared with the fresh catalyst, no obvious decrease in
catalytic activity was observed after five cycles. Furthermore,
the M-ZrPW showed higher catalytic activity than H-Beta,
H-ZSM5 and ZrPW synthesized from the sol–gel method.
Therefore, the M-ZrPW can be employed as a solid acid cat-
alyst in the benzylation reaction.
16 M. H. Al-Hazmi and A. W. Apblett, Catal. Sci. Technol.,
2011, 1, 621–630.
17 M. J. Gracia, E. Losada, R. Luque, J. M. Campelo, D. Luna,
J. M. Marinas and A. A. Romero, Appl. Catal., A, 2008, 349,
148–155.
18 M. H. C. de La Cruz, Â. S. Rocha, E. R. Lachter,
A. M. S. Forrester, M. C. Reis, R. A. S. San Gil, S. Caldarelli,
A. D. Farias and W. A. Gonzalez, Appl. Catal., A, 2010, 386,
60–64.
19 M. H. C. de la Cruz, J. F. C. da Silva and E. R. Lachter, Catal.
Today, 2006, 118, 379–384.
20 C. Ramesh Kumar, K. T. V. Rao, P. S. Sai Prasad and
N. Lingaiah, J. Mol. Catal. A: Chem., 2011, 337, 17–24.
21 K.-I. Shimizu, K. Niimi and A. Satsuma, Appl. Catal., A,
2008, 349, 1–5.
22 K. Okumura, K. Yamashita, M. Hirano and M. Niwa,
J. Catal., 2005, 234, 300–307.
23 S. K. Das, M. K. Bhunia, A. K. Sinha and A. Bhaumik, J. Phys.
Chem. C, 2009, 113, 8918–8923.
24 J. Dou and H. C. Zeng, J. Phys. Chem. C, 2012, 116,
7
767–7775.
2
2
2
5 N. Candu, S. Wuttke, E. Kemnitz, S. M. Coman and
V. I. Parvulescu, Pure Appl. Chem., 2012, 84, 427–437.
6 C. R. Kumar, P. S. S. Prasad and N. Lingaiah, Appl. Catal., A,
Acknowledgements
The authors sincerely acknowledge the financial support
from the National Basic Research Program of PR China
2
010, 384, 101–106.
7 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz,
C. T. Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson and
E. W. Sheppard, J. Am. Chem. Soc., 1992, 114, 10834–10843.
8 C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and
J. S. Beck, Nature, 1992, 359, 710–712.
(No. 2011CB201404) and the National Natural Science
Foundation of China (no. 21133011).
2
2
Notes and references
9 M. Grün, A. A. Kurganov, S. Schacht, F. Schüth and
K. K. Unger, J. Chromatogr., A, 1996, 740, 1–9.
1
G. A. Olah, Friedel-Crafts and Related Reaction, Wiley-
Interscience, New York, 1964.
30 L. Mercier and T. J. Pinnavaia, Adv. Mater., 1997, 9, 500–503.
31 N. K. Mal, M. Fujiwara and Y. Tanaka, Nature, 2003, 421,
350–353.
2
3
G. A. Olah, Friedel-Crafts Chemistry, Wiley, New York, 1973.
V. V. Bokade and G. D. Yadav, J. Nat. Gas Chem., 2007, 16,
1
86–192.
32 Q. Yuan, A. Yin, C. Luo, L. Sun, Y. Zhang, W. Duan, H. Liu
and C. Yan, J. Am. Chem. Soc., 2008, 130, 3465–3472.
33 A. Sinhamahapatra, N. Sutradhar, B. Roy, P. Pal, H. C. Bajaj
and A. B. Panda, Appl. Catal., B, 2011, 103, 378–387.
34 A. Dutta, A. K. Patra, S. Dutta, B. Saha and A. Bhaumik,
J. Mater. Chem., 2012, 22, 14094–14100.
4
5
6
7
8
A. Sipos and S. Berényi, Tetrahedron, 2008, 64, 5851–5860.
A. Corma and H. García, Chem. Rev., 2003, 103, 4307–4366.
N. Mizuno and M. Misono, Chem. Rev., 1998, 98, 199–218.
J. H. Clark, Green Chem., 1999, 1, 1–8.
K. Tanabe and W. F. Hølderich, Appl. Catal., A, 1999, 181,
3
99–434.
35 K. Nakajima, T. Fukui, H. Kato, M. Kitano, J. N. Kondo,
S. Hayashi and M. Hara, Chem. Mater., 2010, 22, 3332–3339.
36 C. Tagusagawa, A. Takagaki, A. Iguchi, K. Takanabe,
J. N. Kondo, K. Ebitani, T. Tatsumi and K. Domen, Chem.
Mater., 2010, 22, 3072–3078.
9
J. J. Chiu, D. J. Pine, S. T. Bishop and B. F. Chmelka,
J. Catal., 2004, 221, 400–412.
1
1
0 C. Tagusagawa, A. Takagaki, S. Hayashi and K. Domen,
J. Am. Chem. Soc., 2008, 130, 7230–7231.
1 K. Okumura, T. Tomiyama, S. Shirakawa, S. Ishida,
T. Sanada, M. Arao and M. Niwa, J. Mater. Chem., 2011, 21,
37 C. Tagusagawa, A. Takagaki, A. Iguchi, K. Takanabe,
J. N. Kondo, K. Ebitani, S. Hayashi, T. Tatsumi and
K. Domen, Angew. Chem., Int. Ed., 2010, 49, 1128–1132.
38 C. Tagusagawa, A. Takagaki, A. Iguchi, K. Takanabe,
J. N. Kondo, K. Ebitani, T. Tatsumi and K. Domen, Catal.
Today, 2011, 164, 358–363.
2
29–235.
1
1
1
2 A. M. F. Bidart, A. P. S. Borges, L. Nogueira, E. R. Lachter
and C. J. A. Mota, Catal. Lett., 2001, 75, 155–157.
3 N. Narender, K. V. V. K. Mohan, S. J. Kulkarni and
I. A. K. Reddy, Catal. Commun., 2006, 7, 583–588.
39 Y. Rao, M. Trudeau and D. Antonelli, J. Am. Chem. Soc.,
2006, 128, 13996–13997.
4 M. A. Harmer and Q. Sun, Appl. Catal., A, 2001, 221, 45–62.
This journal is © The Royal Society of Chemistry 2014
Catal. Sci. Technol., 2014, 4, 838–850 | 849

View Article Online
Paper
Catalysis Science & Technology
4
4
4
4
4
4
0 Y. Rao, J. Kang and D. Antonelli, J. Am. Chem. Soc.,
54 M. S. Morey, J. D. Bryan, S. Schwarz and G. D. Stucky, Chem.
Mater., 2000, 12, 3435–3444.
55 S. K. Das, M. K. Bhunia, A. K. Sinha and A. Bhaumik, ACS
Catal., 2011, 493–501.
56 O. Klepel, W. Bøhlmann, E. B. Ivanov, V. Riede and H. Papp,
Microporous Mesoporous Mater., 2004, 76, 105–112.
57 X. L. Yang, W. L. Dai, R. Gao and K. Fan, J. Catal., 2007, 249,
278–288.
58 A. Stein, M. Fendorf, T. P. Jarvie, K. T. Mueller, A. J. Benesi
and T. E. Mallouk, Chem. Mater., 1995, 7, 304–313.
59 E. Briot, J.-Y. Piquemal, M. Vennat, J.-M. Bregeault,
G. Chottard and J.-M. Manoli, J. Mater. Chem., 2000, 10,
953–958.
2
007, 130, 394–395.
1 J. Kang, Y. Rao, M. Trudeau and D. Antonelli, Angew. Chem.,
Int. Ed., 2008, 47, 4896–4899.
2 Z. Miao, L. Xu, H. Song, H. Zhao and L. Chou, Catal. Sci.
Technol., 2013, 3, 1942–1954.
3 J. Fan, S. W. Boettcher and G. D. Stucky, Chem. Mater.,
2
006, 18, 6391–6396.
4 Q. Yuan, L. Li, S. Lu, H. Duan, Z. Li, Y. Zhu and C. Yan,
J. Phys. Chem. C, 2009, 113, 4117–4124.
5 S. Ghodke and U. Chudasama, Appl. Catal., A, 2013, 453,
2
19–226.
4
6 C. A. Emeis, J. Catal., 1993, 141, 347–354.
4
7 P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and
G. D. Stucky, Nature, 1998, 396, 152–155.
60 B. Orel, U. O. Krašovec, N. Grošelj, M. Kosec, G. Dražič and
R. Reisfeld, J. Sol-Gel Sci. Technol., 1999, 14, 291–308.
61 K. N. Rao, A. Sridhar, A. F. Lee, S. J. Tavener, N. A. Young
and K. Wilson, Green Chem., 2006, 8, 790–797.
62 F. Di Gregorio and V. Keller, J. Catal., 2004, 225, 45–55.
63 A. B. Deshpande, A. R. Bajpai and S. D. Samant, Appl. Catal.,
A, 2001, 209, 229–235.
64 M. H. C. de la Cruz, M. A. Abdel-Rehim, A. S. Rocha,
J. F. C. da Silva, A. da Costa Faro Jr and E. R. Lachter, Catal.
Commun., 2007, 8, 1650–1654.
4
4
5
5
8 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson,
B. F. Chmelka and G. D. Stucky, Science, 1998, 279, 548–552.
9 W. Cai, J. Yu, C. Anand, A. Vinu and M. Jaroniec, Chem.
Mater., 2011, 23, 1147–1157.
0 L. Xu, H. Song and L. Chou, Appl. Catal., B, 2011, 108–109,
1
77–190.
1 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou,
R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl.
Chem., 1985, 57, 603–619.
65 T. Kitano, T. Shishido, K. Teramura and T. Tanaka, J. Phys.
Chem. C, 2012, 116, 11615–11625.
5
2 M. Kruk and M. Jaroniec, Chem. Mater., 2001, 13,
3
169–3183.
66 K. Yamashita, M. Hirano, K. Okumura and M. Niwa, Catal.
Today, 2006, 118, 385–391.
5
3 R. S. Weber, J. Catal., 1995, 151, 470–474.
850 | Catal. Sci. Technol., 2014, 4, 838–850
This journal is © The Royal Society of Chemistry 2014