Mesoporous titanium-silica composite encapsulated γ-Fe 2O3: Novel magnetically recyclable heterogeneous catalysts for olefin epoxidation reactions

Article abstract of DOI:10.1007/s10562-011-0638-7

γ-Fe₂O₃ microparticles encapsulated with silica and an outer layer of ordered mesoporous titanium-silica (γ-Fe ₂O₃@nSiO₂@mTi-Si) were synthesized and used for the epoxidation of olefins. Characterizat

Full text of DOI:10.1007/s10562-011-0638-7

Catal Lett (2011) 141:1484–1490
DOI 10.1007/s10562-011-0638-7
Mesoporous Titanium–Silica Composite Encapsulated c-Fe O :
2
3
Novel Magnetically Recyclable Heterogeneous Catalysts for Olefin
Epoxidation Reactions
Chengyuan Yuan
•
Zhiwei Huang Jing Chen
•
Received: 26 February 2011 / Accepted: 30 May 2011 / Published online: 20 August 2011
Ó Springer Science+Business Media, LLC 2011
Abstract c-Fe O microparticles encapsulated with silica
catalysts greatly restrict their applications in practice.
2
3
and an outer layer of ordered mesoporous titanium–silica
Titanium-containing mesoporous molecular sieves have
been used as efficient heterogeneous catalysts in the
epoxidation of alkenes [11, 12]. Since the first synthesis
of Ti-MCM-41 by Corma et al. [13], various kinds of
titanium-containing mesoporous molecular sieves, such
as Ti-HMS [14–16], Ti-MCM-48 [17–19], Ti-MSU-1
[20] and Ti-SBA-15 [21, 22] have been synthesized and
employed as catalysts for epoxidation reactions. How-
ever, these conventional heterogeneous catalysts usually
need tedious procedures such as filtration and centrifu-
gation for recycling after reactions, which inevitably lead
to the leaching of catalyst. Magnetic separation provides
a convenient method for removing species by applying
an appropriate magnetic field. Magnetic nanoparticles
such as iron oxides particles have been paid growing
attention owing to their unique properties and potential
applications in various fields, such as magnetic resonance
imaging (MRI) contrast agents, magnetically assisted
drug delivery, hyperthermia, magnetic separation of
biomolecules and isolation and recycling of catalysts
(
c-Fe O @nSiO @mTi–Si) were synthesized and used for
2
3
2
the epoxidation of olefins. Characterization results showed
that this material exhibits a typical core–shell structure
with high surface area, narrow pore size distribution and
high magnetization. Catalytic activity tests showed that this
material presents high activity for the epoxidation of ole-
fins, and the catalyst could be easily recycled and reused
for several times.
Keywords Mesoporous Á Core shell Á Magnetic
separation Á Olefin epoxidation
1
Introduction
Epoxidation of alkenes is an important reaction because
epoxides are widely used as intermediates for the man-
ufacture of a wide range of important commercial
products [1, 2]. Transition metal titanium has been
widely taken as active species for epoxidation reactions
[
23–26]. However, as a result of anisotropic dipolar
attraction, pristine nanoparticles of iron oxides tend to
aggregate into large clusters and thus lose the specific
properties associated with single-domain, magnetic
nanostructures. Therefore, inert materials such as silica
were often coated on the surfaces of iron oxide nano-
particles to prevent their aggregation and improve their
chemical stability [27–31].
[
3]. Although many catalytic epoxidation reactions using
homogeneous catalysts have been successfully demon-
strated [4–10], the difficulties in separating of the
C. Yuan Á Z. Huang Á J. Chen (&)
State Key Laboratory for Oxo Synthesis and Selective
Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences, Lanzhou 730000, Gansu, China
e-mail: chenj@lzb.ac.cn
Presently, the integration of mesoporous silica with
magnetic iron oxides nanoparticles to compose core–shell
composites has attracted more and more interest [32–39].
These novel composites combine magnetic separability and
the advantages of mesoporous silica such as high surface
area, large pore volume, which make them widely applied
C. Yuan
Graduate University of Chinese Academy of Sciences, Beijing
1
00049, China
1
23

Mesoporous Titanium–Silica Composite
1485
in a variety of science and engineering disciplines, such as
drug delivery [36–39] and catalytic reactions [40].
Herein, we report the synthesis of mesoporous micro-
particles with a silica-coated magnetic hematite core and
ordered mesoporous titanium–silica shell. The obtained
materials possess high surface area, uniform mesochanels
and high magnetization. These magnetic microparticles
could be employed as high active and reusable catalysts for
the epoxidation of many olefins. The materials could be
facilely recycled through magnetic separation and no sig-
nificant loss of activity and selectivity was found even after
recycling five times.
2.2 Catalysts Characterization
X-ray diffraction (XRD) was carried out on a PANalytical
X’pert Pro Diffractometer. X-ray photoelectron spectra
(XPS) was performed on a VG ESCALAB 210 spectrom-
eter, all binding energies were calibrated using the C2p
peak at 285.0 eV as a reference. Transmission electron
microscopy (TEM) micrographs were obtained with a
JEM-2010 electron microscope. The BET surface area
measurements were performed on a Micromeritics ASAP
2010 instrument at liquid nitrogen temperature. The Fou-
rier transform infrared spectroscopy (FT-IR) measurements
were carried out with a Bruker IFS 120HR FT-IR spec-
trometer, using KBr pellet technique. Magnetic properties
were characterized VSM by Lakeshore 7304.
2
Experimental
2
.1 Catalysts Preparation
2.3 Catalytic Tests
The synthesis procedure can be divided into three steps as
shown in Scheme 1. Uniform magnetite (Fe O ) particles
The activity of the c-Fe O @nSiO @mTi–Si catalyst was
2 3 2
tested for the epoxidation of olefin. In a typical experiment,
3
4
were prepared by a solvothermal method as described
previously [41]. In step I, a thin nonporous silica layer is
deposited on the surface of Fe O particles to protect the
a mixture of alkene (1.5 mmol), t-butyl hydroperoxide
O
2 3
(TBHP) (70 wt% in decane, 1.5 mmol) and c-Fe
@nSiO @mTi–Si (0.05 g) in 10 ml chloroform was
3
4
2
Fe O core from leaching into the mother system under
3
introduced into a closed 50 ml regular glass reactor with
vigorous stirring. The reaction was maintained at 70 °C for
12 h. Qualitative analysis was conducted with a HP
6890/5973 GCMS with chemstation containing a NIST
Mass Spectral Database. Quantitative analysis was con-
ducted with an Agilent 6820 GC equipped with a FID.
The reusability of the catalyst was as follows. After the
reaction, a bar magnet was externally applied with the aim
of separation of the catalyst from the reaction media. The
recycled catalyst was washed repeatedly with chloroform,
and alkene chloroform and TBHP were then added to start
the next run.
4
severe conditions. In detail, 0.10 g of Fe O particles
3
4
were treated with 50 ml of distilled water by ultrasoni-
cation for 10 min. After that, the magnetite particles were
separated and washed with distilled water, and then dis-
persed in the mixture of 80 ml of ethanol, 20 ml of water
and 1.0 ml of 25 wt% concentrated ammonia solution,
followed by the addition of 0.03 g tetraethyl orthosilicate
(
TEOS). After vigorous stirring at room temperature for
h, the product designated as Fe O @nSiO was sepa-
6
3
4
2
rated and washed with ethanol and distilled water. In
surfactant-templating process (step II), the Fe O @nSiO
2
3
4
microparticles prepared in step I were dispersed in a
mixed solution containing of 0.30 g of hexadecyl tri-
methyl ammonium bromide (CTAB), 80 ml of distilled
water, 60 ml ethanol and 1.20 ml of 25 wt% concentrated
ammonia solution. The mixed solution was vigorously
stirred for 30 min to form a uniform dispersion. Then a
solution of TEOS (0.40 g) and tetraisopropyl orthotitanate
3 Results and Discussion
3.1 Characterization
The nitrogen adsorption–desorption isotherms and pore
(
TIPOT, 0.02 g, Si/Ti = 30) was dropped very slowly.
size distribution of the synthesized c-Fe O @nSiO @mTi–
2 3 2
The mixture was vigorously stirred for 2 h at room
Si are shown in Fig. 1. The sample exhibits the typical IV
isotherms as defined by Brunauer et al. [43], indicating a
mesoporous structure of the sample. The isotherms exhibit
temperature firstly, and then heated to 70 °C for another
4
h to ensure that the TEOS and TIPOT hydrolyze
completely [42]. The product designated as Fe O
3
a sharp inflection in the P/P range of 0.2–0.4, which is
0
4
@
nSiO @CTAB/Ti–Si was collected with a magnet and
2
characteristic of capillary condensation within the mesop-
ores. The pore size distribution (Fig. 1, inset) shows a
sharp peak centered at a mean value of 2.4 nm, indicating a
uniform mesopores of the sample. The BET surface area
washed with ethanol and distilled repeatedly. Finally, to
remove the template of CTAB, the Fe O @nSiO @C-
3
4
2
TAB/Ti–Si was calcined in air at 500 °C for 4 h, giving a
reddish-brown final product designated as c-Fe O @n-
SiO @mTi–Si was obtained (step III).
2
and pore volume are calculated to be 848 m /g and
3
0.55 cm /g, respectively.
2
3
2
123

1
486
C. Yuan et al.
Scheme 1 Synthetic procedure
of c-Fe
Fe3O4@nSiO2
@CTAB/Ti-Si
r-Fe O @nSiO
2
@mTi-Si
2
3
Fe3O4@nSiO2
2 3
O
@nSiO
2
@mTi–Si
CTAB
TEOS
Calcination
Fe O
Fe O
Fe O
3
4
550 o
3
4
3
4
2 3
r -Fe O
TEOS, TIPOT
C
I
II
III
Ti-Si mesopores
3
2
2
1
1
00
50
00
50
00
0
0
0
0
0
0
0
.7
.6
.5
.4
.3
.2
.1
0.0
0
1
2
3
4
5
6
7
8
9
10
Pore Diameter (nm)
50
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
2
3
4
5
6
7
8
9
10
Fig. 1 N
the inset) of the synthesized c-Fe
2
adsorption–desorption isotherms and pore size distribution
@nSiO @mTi–Si
2
Theta (degree)
(
O
2 3
2
Fig. 2 The low-angle XRD pattern of the c-Fe
2
O
@nSiO @mTi–Si
3 2
The low-angle XRD pattern of the c-Fe O @n-
2
3
SiO @mTi–Si sample is shown in Fig. 2. One main peak at
2
•
∗
amorphous silica
γ-Fe O
about 2.5° is observed, which is the characteristic diffrac-
tion of MCM-41 [11], illuminating a hexagonal meso-
porous symmetry of the sample. Figure 3 shows the
wide-angle XRD pattern of the c-Fe O @nSiO @mTi–Si
Silica
2
3
•
2
3
2
b
sample and c-Fe O crystallites. Clear peaks due to the
2
3
∗
hematite c-Fe O phase at around 30.2, 35.7, 43.6, 53.6,
2
3
5
7.3 and 63.0°, were seen for the c-Fe O @nSiO @mTi–
2
3
2
Si sample, which are corresponding to the (220), (311),
(
400), (422), (511) and (440) reflections of c-Fe O ,
2
3
∗
respectively [44]. Other iron oxides phases such as a-Fe O
are not detected. In addition, the broad band at around 22°
is attributed to amorphous silica.
∗
2
3
∗
∗
∗
a
The morphological and structural features of the
c-Fe O @nSiO @mTi–Si sample are further examined by
2
3
2
20
30
40
50
60
70
80
HRTEM (Fig. 4). The sample shows a typical core–shell
structure (Fig. 4a). The magnetic cores are black spheres
with an average size of about 55 nm, while the mesoporous
titanium–silica shell shows gray color with an average
thickness of around 50 nm. Moreover, the obvious lattice
fringes in the HRTEM image (Fig. 4b) further confirm the
ordered pores structure of the mesoporous titanium–silica
shell, which is in good agreement with the low-angle XRD
results.
2
Theta (degree)
Fig. 3 The wide-angle XRD patterns of (a) c-Fe
Fe @nSiO @mTi–Si
2 3
O and (b) c-
2
O
3
2
Figure 5 shows Ti2p XPS spectra of anatase TiO2
(Fig. 5a) and c-Fe O @nSiO @mTi–Si (Fig. 5b). Anatase
TiO shows a Ti2p line at 458.7 eV. Differently, the Ti2p3/2
2
3
2
2
3/2
line for c-Fe O @nSiO @mTi–Si is observed at 459.7 eV,
2
3
2
1
23

Mesoporous Titanium–Silica Composite
1487
Fig. 4 HRTEM images
of c-Fe O @nSiO @mTi–Si
2 3 2
which is about 1 eV higher than that of TiO anatase. This
2
which can be assigned as vibrations mode of Si–OH and
difference can be explained in terms of the effective positive
charge on the Ti atoms due to the Ti–O–Si linkage [45]. The
large shift of the binding energy of Ti2p3/2 spectra is usually
considered to be associated with isolated tetrahedrally
coordinated titanium sites that possess maximum number of
Ti–O–Si bonds per titanium atom. Therefore, the above
results suggest that titanium atoms in the c-Fe O @n-
Si–O–Si, respectively, indicating that the c-Fe O is suc-
cessfully covered by silica and/or titanium–silica shell.
2
3
The magnetic properties of the c-Fe O @nSiO @mTi–Si
2
3
2
were investigated using a superconducting quantum inter-
face device magnetometer. As shown in Fig. 7, the isother-
mal magnetization cure of the c-Fe O @nSiO @mTi–Si
2
3
2
increased rapidly with increasing applied magnetic field,
2
3
SiO @mTi–Si sample occupy a site-isolated position and
2
which exhibits a saturation magnetization (M ) value of 23
s
tetrahedrally coordinated structure.
emu/g. Taken the normalized c-Fe O content in the sample
2
3
FT-IR spectra of the c-Fe O and c-Fe O @n-
(45 wt%) into consideration, a M of 51 emu/g for c-Fe O
2
3
2
3
s
2 3
SiO @mTi–Si are illustrated in Fig. 6. The bands at about
2
encapsulated in the mesoporous titanium–silica shell is cal-
-
1
3
430 and 1630 cm for both c-Fe O and c-Fe O @n-
culated, which is much smaller than the theoretical M of 76
s
2
3
2
3
SiO @mTi–Si are attributable to the vibrations of adsorbed
2
emu/g for bulk c-Fe O [46]. The above difference can be
2 3
-
1
water molecules, while the band at around 580 cm is
associated with the Fe–O bonds. Compared to pure c-
Fe O , the c-Fe O @nSiO @mTi–Si sample shows two
explained by the defined size effects responsible for the
degradation of magnetic properties in iron oxide nanocrys-
tallites [47]. In the low magnetic field region, the magneti-
zation curve of the c-Fe O @nSiO @mTi–Si exhibits a
2
3
2
3
2
-
1
strong adsorption bands at around 960 and 1090 cm
,
2
3
2
Fig. 5 Ti2p XPS spectra of
(
A)
(B)
4
58.7
459.7
TiO
Fe
2
anatase (a) and c-
@nSiO @mTi–Si (b)
2
O
3
2
Ti2p3/2
Ti2p3/2
Ti2p1/2
Ti2p1/2
4
56 457 458 459 460 461 462 463 464 465 466 467 468
456 457 458 459 460 461 462 463 464 465 466 467 468
Binding Energy (eV)
Binding Energy (eV)
123

1
488
C. Yuan et al.
Table 1 The recycling of the c-Fe
the epoxidation of cyclohexene
2 3
O @nSiO
2
@mTi–Si catalyst in
a
a
Epoxide selectivity (%)
b
Entry
Conversion (%)
b
c
1
39
No
90
89
86
86
85
2
3
4
5
6
(1st)
(2nd)
(3rd)
(4th)
(5th)
88
86
84
82
81
1
630
9
60
5
80
Reaction conditions: 1.5 mmol cyclohexene, 1.5 mmol TBHP, 0.05 g
catalyst, 10 ml CHCl
, 70 °C, 12 h. Conversion and selectivity for
cyclohexene were determined by GC using an internal standard
3
430
3
(
n-dodecane) technique
a
Side products were 2-cyclohexene-ol and 2-cyclohexene-one
1
090
b
c
The catalyst was bare c-Fe
2 3
O
The product was 2-cyclohexene-one
500
1000
1500
2000
2500
3000
3500
-1
Wavenumber (cm )
Fig. 6 The FT-IR spectra of a c-Fe
Si
O
2 3
and b c-Fe
2 3
O @nSiO
2
@mTi–
catalysts. As can be seen from Table 1 (entries 2–6), the c-
Fe O @nSiO @mTi–Si catalyst could be reused five times
2
3
2
without significant loss of activity and selectivity, indi-
cating the high stability of the catalyst. The slight decrease
of activity for the catalyst may be resulted by either the
incomplete magnetic separation of the catalyst [35] or the
loss of the active Ti sites by coke deposition [48]. More-
over, ICP analysis of the filtrate confirmed that the metal Ti
content was determined to be negligible (Ti \ 5 ppb).
Therefore, it can be said that the present reaction proceeds
on the mesoporous titanium–silica shell of the catalyst.
Furthermore, Koner et al. [49] reported that c-Fe O
2
2
1
5
0
5
0
5
0
5
2
1
1
0
5
0
5
0
-
700 -600 -500 -400 -300 -200 -100
0
100 200 300 400 500 600 700
-5
1
-
-
-
10
15
20
Field (Oe)
-
12000
-8000
-4000
0
4000
8000
12000
-
-
-
-
-
10
15
20
25
2
3
nanoparticles in NaY-zeolite matrix exhibited high activity
in the epoxidation of olefins. In our condition, however, no
epoxide was detected when bare c-Fe O was solely used
2
3
as catalyst (entry 1).
Field (Oe)
It should be noted here that our catalyst provides a
simple way for the separation of the catalyst from the
reaction mixture due to the heterogeneous nature and
magnetic properties of the catalyst. As shown in Fig. 8, the
catalyst could be easily separated form the reaction
mixture.
Fig. 7 The magnetic hysteresis loops of c-Fe
Inset shows low field region of the hysteresis loop
2 3 2
O @nSiO @mTi–Si.
symmetric hysteresis loop (Inset), indicating the ferromag-
netic behavior of the c-Fe O @nSiO @mTi–Si.
2
3
2
In addition, the c-Fe O @nSiO @mTi–Si catalyst can
2
3
2
3
.2 Catalytic Activity
be used for the epoxidation of a wide range of cyclic and
linear alkenes (Table 2). It seems that the epoxidation of
cyclic alkenes is much easier than the epoxidation of linear
alkenes, as a high conversion of 98% was obtained for
cyclooctene, and the epoxidation of other cyclic alkenes
are all above 67%. In contrast, the conversion of the
epoxidation of both 1-heptene and 1-dodecene are below
50%. Taken the selectivity to epoxide into consideration,
almost 100% selectivity to the desired product was
achieved for the epoxidation of cyclooctene, indene,
1-heptene and 1-dodecene. Due to the formation of other
The activity of the c-Fe O @nSiO @mTi–Si catalyst was
tested for the epoxidation of cyclohexene with TBHP as
2
3
2
oxidant (Table 1). The c-Fe O @nSiO @mTi–Si catalyst
2
3
2
exhibited high activity and selectivity for the epoxidation
of cyclohexene. At a mild reaction temperature of 70 °C, a
high conversion of 88% of cyclohexene was achieved at
9
0% epoxide selectivity. We also investigated the recy-
cling of the catalyst in respect that stability is a very
important factor for the application of heterogeneous
1
23

Mesoporous Titanium–Silica Composite
1489
Fig. 8 Magnetic separation and
recycling of c-
Fe O @nSiO @mTi–Si catalyst
2 3 2
a
2 3 2
Table 2 Epoxidation of various olefins catalyzed by the c-Fe O @nSiO @mTi–Si catalyst
Entry
1
Alkene
Conversion (%)
70
Epoxide selectivity (%)
O
b
(
87)
O
2
3
4
98
68
67
(
100)
O
c
(
54)
O
(
100)
o
5
6
48
37
(
100)
O
(
100)
a
Reaction conditions: 1.5 mmol olefin, 1.5 mmol TBHP, 0.05 g catalyst, 10 mL CHCl
hexene were determined by GC using an internal standard (n-dodecane) technique
3
, 70 °C, 12 h. Conversion and selectivity for cyclo-
b
Side product was cyclopentone
c
Side products were benzaldehyde and phenylacetaldehyde
oxidation products, the epoxide selectivity for cyclopen-
tene and styrene were lower, which are 87 and 54%,
respectively.
epoxidation of olefins. Characterization results revealed
that the highly dispersed magnetic hematite (c-Fe O )
2
3
nanoparticles cores were successfully encapsulated by
mesoporous titanium–silica shell. The core–shell structured
material exhibits ordered hexagonal mesopores, high sur-
face area and high magnetization. Catalytic testing results
showed that the c-Fe O @nSiO @mTi–Si is an efficient
4
Conclusions
2
3
2
In this work, c-Fe O3 microparticles encapsulated with
silica and an outer layer of ordered mesoporous titanium–
heterogeneous catalyst system for the epoxidation of ole-
fins. Recovery of the catalyst was facilely accomplished by
external application of a permanent magnet, and the spent
2
silica were developed as a new efficient catalyst for the
123

1
490
C. Yuan et al.
catalyst could be recycled five times without significant
loss in catalytic activity and selectivity. The features of the
present catalyst, such as facile preparation, easy recovery
and simple recycling are particular desirable for practical
applications. This novel magnetic recyclable catalyst is
expected to be utilized in many other important catalytic
processes.
20. Bagshaw SA, Pouzet E, Pinnavaia TJ (1995) Science 269:1242
2
1. Luan ZH, Maes EM, Zhao DY, Czernuszewicz RS, Kevan L
1999) Chem Mater 11:3680
(
2
2. Zhang WH, Lu JQ, Han B, Li MJ, Xiu JH, Ying PL, Li C (2002)
Chem Mater 14:3413
23. Mornet S, Vasseur S, Grasset F, Duguet E (2004) J Mater Chem
4:2161
1
2
2
2
4. Astruc D, Lu F, Aranzaes JR (2005) Angew Chem Int Ed 44:7852
5. Melero JA, Grieken RV, Morales G (2006) Chem Rev 106:3790
6. Gijs MAM, Lacharme F, Lehmann U (2010) Chem Rev 110:1518
Acknowledgments The authors express their gratitude for the
financial support of this work provided by National Science Fund for
Distinguished Young Scholars of China (No. 20625308).
27. Butterworth MD, Illum L, Davis SS (2001) Colloids Surf A
179:93
28. Szab o´ DV, Vollath D (1999) Adv Mater 11:1313
2
3
3
9. Donselaar LN, Philipse AP, Suurmond J (1997) Langmuir
3:6018
0. Liu QX, Xu ZH, Finch JA, Egerton R (1998) Chem Mater
0:3936
1. Correa-Duarte MA, Giersig M, Kotov NA, Liz-Marz a´ n LM
1998) Langmuir 14:6430
1
References
1
1
2
. Xia QH, Ge HQ, Ye CP, Liu ZM, Su KX (2005) Chem Rev
05:1603
. Chen LY, Chuah GK, Jaenicke S (1998) J Mol Catal A: Chem
32:281
(
1
3
3
2. Wu PG, Zhu JH, Xu ZH (2004) Adv Funct Mater 14:345
3. Zhang L, Qiao SZ, Jin YG, Chen ZG, Gu HC, Lu GQ (2008) Adv
Mater 20:805
1
3
4
. Joergensen KA (1989) Chem Rev 89:431
3
3
3
3
3
3
4
4
4
4
4
4. Yi DK, Lee SS, Papaefthymiou GC, Ying JY (2006) Chem Mater
1
. Xiong DL, Wu M, Wang SF, Li FW, Xia CG, Sun W (2010)
Tetrahedron Asymmetr 21:374
. Matsumoto K, Oguma T, Katsuki T (2009) Angew Chem Int Ed
8:614
5. Shokouhimehr M, Piao Y, Kim J, Jang Y, Hyeon T (2007) An-
gew Chem Int Ed 46:7039
5
6
7
8
4
8:7432
6. Zhao WR, Gu JL, Zhang LX, Chen HR, Shi JL (2005) J Am
Chem Soc 127:8916
7. Kim J, Lee JE, Lee J, Yu JH, Kim BC, An K, Hwang Y, Shin CH,
Park JG, Kim J, Hyeon T (2006) J Am Chem Soc 128:688
8. Lin YS, Wu SH, Hung Y, Chou YH, Chang C, Lin ML, Tsai CP,
Mou CY (2006) Chem Mater 18:5170
9. Deng YH, Qi DW, Deng CH, Zhang XM, Zhao DY (2008) J Am
Chem Soc 130:28
0. Shylesh S, Sch u¨ nemann V, Thiel WR (2010) Angew Chem Int Ed
. Kondo S, Saruhashi K, Seki K, Matsubara K, Miyaji K, Kubo T,
Matsumoto K, Katsuki T (2008) Angew Chem Int Ed 47:10195
. Berkessel A, Brandenburg M, Leitterstorf E, Frey J, Lex J,
Schafer M (2007) Adv Synth Catal 349:2385
. Sawada Y, Matsumoto K, Kondo S, Watanabe H, Ozawa T,
Suzuki K, Saito B, Katsuki T (2006) Angew Chem Int Ed
4
5:3478
9
. Kato CN, Negishi S, Yoshida K, Hayashi K, Nomiya K (2005)
Appl Catal A: Gen 292:97
4
9:3428
1
1
0. Khare S, Shrivastava S (2004) J Mol Catal A: Chem 217:51
1. Beck JS, Vartuli JC, Roth WJ, Leonowica ME, Kresge T, Schmitt
KD, Chu CTW, Olson DH, Sheppard EW (1992) J Am Chem Soc
1. Xu XQ, Deng CH, Gao MX, Yu WJ, Yang PY, Zhang XM (2006)
Adv Mater 18:3289
2. Wr o´ blewska A, Fajdek A, Waijzberg J, Milchert E (2009) J
Hazard Mater 170:405
3. Brunauer S, Deming LS, Deming WE, Teller E (1940) J Am
Chem Soc 62:1723
4. Mori K, Kanai S, Hara T, Mizugaki T, Ebitani K, Jissukawa K,
Kaneda K (2007) Chem Mater 19:1249
1
14:10834
2. Blasco T, Corma A, Navarro MT, Pariente JP (1995) J Catal
56:65
3. Corma A, Navarro MT, Pariente JP (1994) J Chem Soc Chem
Commun 2:147
1
1
1
1
1
4. Tanev PT, Chibwe M, Pinnavaia TJ (1994) Nature 368:317
5. Corma A, Camblor MA, Esteve P, Martinez A, Perezpariente J
4
4
5. Gao XT, Wachs IE (1999) Catal Today 51:233
6. Cullity BD (1972) Introduction to magnetic materials. Addision-
Wesley, Reading
(1994) J Catal 145:151
1
6. Pinnavaia TJ, Tanev PT, Wang JL, Zhang WZ (1995) Mat Res
Soc Symp Proc 371:53
7. Gontier S, Tuel A (1995) Zeolites 15:601
8. Koyano KA, Tatsumi T (1996) Chem Commun 2:145
9. Zhang WZ, Pinnavaia TJ (1996) Catal Lett 38:261
4
4
4
7. Craik DJ (1975) Magnetic oxides. Wiley, New York
8. Butt JB (1974) Chemical reaction engineering. ASC, Washington
9. Dutta B, Jana S, Bhattacharjee A, G u¨ tilich P, Iijima SI, Koner S
1
1
1
(
2010) Inorg Chim Acta 363:696
1
23