Synthesis and unique catalytic performance of single-site Ti-containing hierarchical macroporous silica with mesoporous frameworks

Article abstract of DOI:10.1021/la1048634

Single-site Ti-containing hierarchical macroporous silica with mesoporous frameworks (Ti-MMS) was successfully prepared by a solvent evaporation method using organic surfactant and poly(methyl methacrylate) (PMMA) colloidal crystals as the template. The formation of a well-defined macroporous structure composed of mesoporous silica walls was characterized by SEM and TEM observations. The successful incorporation of tetrahedrally coordinated Ti oxide moieties within their frameworks was also confirmed by spectroscopic techniques such as UV-vis and XAFS measurements. Comparative studies revealed that Ti-MMS exhibited higher catalytic activities for the epoxidation of linear α-olefin compared to Ti-containing mesoporous silica without macropores (Ti-MS). The reaction rate was significantly enhanced on Ti-MMS depending on increases in the alkyl chain length of linear α-olefins. It was also found that Ti-MMS showed good catalytic performance in the selective epoxidation of methyl oleate, which is a kind of unsaturated fatty acid methyl ester (FAME), under acid-free reaction conditions with tert-butylhydroperoxide (TBHP) because of the advantages of the combination of hierarchical macroporous and mesoporous structures.

Full text of DOI:10.1021/la1048634

ARTICLE
pubs.acs.org/Langmuir
Synthesis and Unique Catalytic Performance of Single-Site Ti-
Containing Hierarchical Macroporous Silica with Mesoporous
Frameworks
Takashi Kamegawa,† Norihiko Suzuki,† Michel Che,‡ and Hiromi Yamashita*,†
†Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-
0871, Japan
‡Institut Universitaire de France and Laboratoire de Rꢀeactivitꢀe de Surface, Universitꢀe Pierre et Marie Curie, Paris 6, CNRS-UMR 7197,
Paris, France
S Supporting Information
b
ABSTRACT: Single-site Ti-containing hierarchical macroporous
silica with mesoporous frameworks (Ti-MMS) was successfully
prepared by a solvent evaporation method using organic surfactant
and poly(methyl methacrylate) (PMMA) colloidal crystals as the
template. The formation of a well-defined macroporous structure
composed of mesoporous silica walls was characterized by SEM and
TEM observations. The successful incorporation of tetrahedrally
coordinated Ti oxide moieties within their frameworks was also
confirmed by spectroscopic techniques such as UV-vis and XAFS measurements. Comparative studies revealed that Ti-MMS exhibited
higher catalytic activities for the epoxidation of linear R-olefin compared to Ti-containing mesoporous silica without macropores (Ti-
MS). The reaction rate was significantly enhanced on Ti-MMS depending on increases in the alkyl chain length of linear R-olefins. Itwas
also found that Ti-MMS showed good catalytic performance in the selective epoxidation of methyl oleate, which is a kind of unsaturated
fatty acid methyl ester (FAME), under acid-free reaction conditions with tert-butylhydroperoxide (TBHP) because of the advantages of
the combination of hierarchical macroporous and mesoporous structures.
frameworks and their catalytic performance have yet to be fully
investigated.
1. INTRODUCTION
For the past several decades, microporous and mesoporous
materials have attracted considerable attention because of their
fascinating characteristics such as unique pore structure, unusual
surface topology, large surface area, and catalytic performance.1-6 In
addition, recently, three-dimensionally ordered macroporous
(3DOM) materials, which typically have submicrometer ranges
of pores, were also intensively investigated and mainly prepared by
using colloidal crystals of close-packed uniform microspheres such
as polystyrene and poly(methyl methacrylate) (PMMA).7-26
These macroporous materials were of importance in the research
fields of photonic crystals,9-11 sensor devices,12,13 and cataly-
sts.14-17 The preparation methods based on colloidal crystals were
widely employed because of the possibility of designing various
fascinating macroporous materials by changing the size of the
colloidal crystals and the nature of the precursor. The interstices of
colloidal crystals used as a template were filled with material
precursors, resulting in the formation of intermediate composite
structured materials through the solidification of precursors. The
structured materials were then recovered after the complete re-
moval of colloidal crystals by calcination or extraction. Although the
preparation of various macroporous materials such as oxides,14-20
bioceramics,21,22 and another unique materials23-26 has already been
achieved, the preparation of tetrahedrally coordinated transition-
metal-containing hierarchical macroporous silica with mesoporous
The incorporation of metal ions (e.g., titanium, vanadium,
chromium, and molybdenum ions) within the framework struc-
ture of microporous and mesoporous materials and the anchor-
ing of organometallic moieties on their surface have attracted a
great deal of attention because of their prominent catalytic
activity and selectivity for specific catalytic and photocatalytic
reactions.27-37 Among them, Ti-containing porous materials are
the most interesting candidates for practical applications, allow-
ing the replacement of conventional stoichiometric reaction
processes. Ti-containing porous materials show remarkable cat-
alytic activity in the production of various organic chemicals
through oxidation reactions in the presence of aqueous H2O2 or
TBHP.3,27-31 However, in some cases, the catalytic performance
is affected by the hydrophilic/hydrophobic properties of the
catalyst surface as well as the accessibility of the active sites.5,6,38
The relatively small aperture diameter of micro/mesoporous
materials and the large, dense powder shapes lead to diffusion
limitations of molecular species.5,6,38
Received: September 3, 2010
Revised:
January 12, 2011
Published: February 04, 2011
r
2011 American Chemical Society
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With this in mind, we deal in the present study with the design
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of Ti-containing hierarchical macroporous silica with mesopor-
ous frameworks (Ti-MMS) by using an organic surfactant and
colloidal crystals of PMMA as a template. The materials were
characterized by various spectroscopic methods, and special
attention was given to the relationship between the presence of
hierarchical macroporous structure and catalytic performance.
The epoxidation of linear R-olefins of different lengths and that
of methyl oleate were investigated as model reactions.
2. EXPERIMENTAL SECTION
2.1. Materials. Tetramethoxysilane (abbreviated as TMOS), vi-
nyltrimethoxysilane (VTMOS), octadecyltrimethylammonium chloride
(C18TAC), and R-olefins (1-octene, 1-hexadecene, 1-hexadecene, and
1-eicosene) were purchased from Tokyo Kasei Kogyo Co., Ltd. Tita-
nium isopropoxide (TIP), 2,20-azobis(2-methylpropion amidine)dihy-
drochloride, and dichloromethane were obtained from Wako Pure Che-
mical Ind., Ltd. Methyl methacrylate monomer (MMA), HCl (37%),
methanol, and ethyl acetate were purchased from Nacalai Tesque Inc.
tert-Butyl hydroperoxide (TBHP, 5.0 M in decane) and methyl oleate
were also obtained from Aldrich. All chemicals were used without further
purification.
Figure 1. Schematic diagram of the procedures for the preparation of
Ti-MMS.
2.2. Preparation of the Catalyst. Monodisperse PMMA
spheres were synthesized by a method reported earlier.39,40 MMA (80
mL) was added to 320 mL of H2O with stirring (350 rpm) at 343 K
under an argon atmosphere. Then, 0.3 g of 2,20-azobis(2-methylpropion
amidine)dihydrochloride was added to the above mixture at the same
temperature. After continuous stirring for 2 h, the mixture was first
filtered with glass wool. The product was separated by centrifugation of
the thus-obtained opalescent solution, washed with water, and then
dried at 298 K for 24 h. The precursor solution of Ti-containing porous
silica was prepared using TMOS, VTMOS, C18TAC, and TIP as
discussed earlier by Ogawa et al.41 TMOS (27.4 g), VTMOS (8.9 g),
and TIP (0.34 g) were dissolved in methanol (3.1 g) with stirring at 343
K. Then, C18TAC (10.4 g), an HCl aqueous solution (3 mL, 1 mol/L)
and H2O (1.4 mL) were added to the above mixture. After stirring for 20
min, the solution was used for the preparation of Ti-MS and Ti-MMS.
The molar ratios were as follows: (TMOS þ VTMOS)/TIP/C18TAC/
CH3OH/H2O = 1:1/200:1/8:1/2.5:1/3 and TMOS/VTMOS = 3:1.
For the preparation of Ti-MMS, 20 mL of the precursor solution was
slowly loaded with 5.0 g of colloidal crystals of PMMA as the template of
macropores by a vacuum filtration methods using a Buchner funnel and a
process similar to that reported by Holland et al.7 The schematic
illustration of the synthesis procedure is shown in Figure 1. For the
preparation of Ti-containing mesoporous silica without macropores (Ti-
MS), the same precursor solution was spread on a poly(vinylidene
chloride) sheet and dried at 298 K. All samples were calcined in air at 823
were recorded at 298 K in fluorescence mode at the BL-7C facility of the
Photon Factory at the High-Energy Acceleration Research Organization
(KEK) in Tsukuba, Japan. The synchrotron radiation from a 2.5 GeV
electron storage ring was monochromatized by a Si(111) double crystal.
The extended X-ray absorption fine structure (EXAFS) data were
examined using the analysis program (Rigaku REX2000). The pre-edge
peaks in the X-ray absorption near-edge structure (XANES) regions
were normalized for atomic absorption on the basis of the average
absorption coefficient of the spectral region. Fourier transformations
were performed on k3-weighted EXAFS oscillations in the range of 3-
10 Å-1 to obtain the radial structure function. Prior to UV-vis and
XAFS measurements, samples were calcined in O2 (>2.66 kPa) at 723 K
for 1 h and then degassed at 473 K for 1 h. Scanning electron microscope
(SEM) investigations were carried out using a JSM-6500 field-emission
microscope (JEOL). Prior to SEM analyses, sample surfaces were coated
with gold/palladium using an ion-sputtering device (JEOL JFC-1100) to
improve the electrical conductivity. The transmission electron micro-
scopy (TEM) image was obtained with a Hitachi Hf-2000 FE-TEM
equipped with a Kevex energy-dispersive X-ray detector operated at 200
kV. Nitrogen adsorption-desorption isotherms were recorded by using
a BEL-SORP max (BEL Japan, Inc.) at 77 K after degassing samples
under vacuum at 473 K for 2 h. The specific surface area was determined
according to the Brunauer-Emmett-Teller (BET) method at a relative
pressure of 0.05-0.3. Inductively coupled plasma (ICP) measurements
for the analysis of Ti content were performed using a Nippon Jarrell-Ash
ICAP-575 Mark II instrument.
2.4. Epoxidation of Linear r-Olefins. The epoxidation of linear
R-olefins (1-octene, 1-dodecene, 1-hexadecene, and 1-eicosene) with
TBHP was used as a test reaction. The reaction vessel, which was equipped
with a reflux condenser, was charged with catalyst (Ti-MMS and Ti-MS, 50
mg), linear R-olefin (10 mmol), CH2Cl2 (10 mL), and TBHP (2 mL) and
then heated to 323 K with magnetic stirring. The molar ratio of TBHP/R-
olefin was adjusted to 1.0. The analysis of the product in both reactions was
performed on a gas chromatograph (Shimadzu GC-14B with a flame
ionization detector) equipped with a TC-1 capillary column. The turnover
number (TON) of each reaction was determined by the ratio of the formed
amount of epoxide and the contents of Ti oxide moieties in 50 mg of Ti-MS
and Ti-MMS, respectively.
K for 5 h (heating rate 1 K min-1), which was long enough for the
3
complete removal of C18TAC and PMMA microspheres. C18TAC and
PMMA microspheres within the silica matrix were decomposed at
around 493 and 633 K, respectively. After calcination, Ti-MMS showed
opalescence depending on the angle under fluorescent light, although
the Ti-MS powder was simply white.
2.3. Characterization Techniques. Powder X-ray diffraction
(XRD) patterns were recorded using a Rigaku RINT 2500 diffract-
ometer with Cu KR radiation (λ = 1.5406 Å). Ultra-small-angle X-ray
scattering (USAXS) measurements were carried out on a Rigaku
SmartLab diffractometer with a Cu rotating anode X-ray source. The
d spacing was calculated from the first diffraction peak observed in the
USAXS profile by using Bragg’s equation: 2d sin θ = λ. Diffuse
reflectance UV-vis spectra were recorded at 298 K with a Shimadzu
UV-2450A double-beam digital spectrophotometer. Ti K-edge X-ray
absorption fine structure (XAFS) spectra of Ti-containing porous silica
2.5. Epoxidation of Methyl Oleate. The epoxidation of methyl
oleate was also performed using the same equipment. The reaction
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Figure 2. SEM images of (a) PMMA particles, (b) Ti-MS, and (c, d) Ti-MMS.
vessel was charged with catalyst (50 mg), methyl oleate (3 mmol), ethyl
acetate (3 mL), and TBHP as the oxidant (0.9 mL, TBHP/methyl oleate
molar ratio = 1.5). The resulting mixture was reacted at 363 K with
magnetic stirring under an argon atmosphere. The analysis of the
product was performed on a gas chromatograph (Shimadzu GC-2014
with a flame ionization detector)-equipped TC-1 capillary column.
TON was defined as epoxide/Ti atoms in a catalyst. The selectivity of
the epoxide was calculated by the ratio of the formed amount of methyl
9,10-epoxy stearate to the consumed amount of methyl oleate.
The thickness of these walls was estimated to be about 70-80 nm,
which is much smaller than the particle size of Ti-MS (Figure 2b).
Thus, Ti-MMS has many mesopore entrances with short meso-
porous channels. The macropore diameter (ca. 300 nm) was also
slightly smaller than the original PMMA particles size because of
the shrinkage of the silica network during calcination.
TEM images providing more detailed information about the
overview of hierarchical macroporous and mesoporous struc-
tures of Ti-MMS are shown in Figure 3. These images show the
uniformity and direct evidence of the existence of interconnected
hierarchical macropores. Moreover, it was confirmed that the
silica walls, which divide the neighboring macropores, consist
mainly of mesoporous structure.
The USAXS profiles of Ti-MS and Ti-MMS were measured to
investigate the structural differences between Ti-MS and Ti-
MMS. USAXS is quite effective at characterizing density fluctua-
tions on the submicrometer scale. As shown in Figure 4, Ti-MMS
showed periodic peaks in the region of 2θ < 0.07°, but no peak
was observed in the case of Ti-MS. The d spacing calculated from
the peak (2θ = 0.025°) was determined to be ca. 353 nm, which
was quite similar to the interval of the hierarchical macroporous
layer. These results clearly indicated the structural differences
between Ti-MS and Ti-MMS due to the existence of hierarchical
macroporous structure.
XRD patterns of Ti-MS and Ti-MMS were also measured to
confirm the formation of mesoporous structure (Figure 5). The
diffraction peak assigned to the mesoporous structure was clearly
observed in the region of 2θ < 5°. Although the position of the
most intense peak was almost the same in both samples, Ti-MMS
exhibits a broad, relatively weak diffraction peak because of the
destruction of ordered mesoporous structure to some degree by
the construction of macropores.
3. RESULTS AND DISCUSSION
3.1. Characterization of Ti-MS and Ti-MMS. The SEM
image of PMMA particles used to prepare the colloidal crystals
(Figure 2a) shows that they are approximately spherical with a
narrow size distribution (diameter ca. 400 nm). Colloidal crystals
of these PMMA particles were used as templates to form the
macroporous structure. The precursor solutions used to synthe-
size mesoporous silica thin films and powders through the
evaporation of solvents followed by calcination to remove the
organic surfactant were taken as appropriate reaction liquids for
the preparation of hierarchical macroporous silica with mesopor-
ous frameworks because there is no need for vigorous stirring, a
long aging time, or conventional hydrothermal processes. These
types of precursor solutions were consequently selected for the
preparation of Ti-MS and Ti-MMS. SEM images of the prepared
samples are shown in Figure 2b-d. Ti-MS has a dense powder
form with an ill-defined morphology compared to Ti-MMS. In
line with the structure of aligned PMMA colloidal crystals, a
uniform macroporous structure of Ti-MMS was successfully ob-
tained by using the same precursor solution of Ti-MS, as shown in
Figure 2c. The magnified SEM image (Figure 2d) of Ti-MMS
clearly suggests the formation of interconnecting macroporous
networks. The silica walls separating two neighboring macropores
were formed by regularly aligned and interconnected small particles.
In the nitrogen adsorption/desorption measurements, Ti-MS
and Ti-MMS exhibit a typical type-IV isotherm (Figure 6). The
inflections of the isotherms attributed to the capillary condensation
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Figure 5. XRD patterns of (a) Ti-MS and (b) Ti-MMS.
Figure 3. (a) TEM image of Ti-MMS. (b) Enlargement of image a.
Figure 6. Nitrogen adsorption/desorption isotherms and pore size
distribution curve (inset) of (a) Ti-MS and (b) Ti-MMS.
transition from the 1s core level of the Ti atom to three different
kinds of molecular orbitals (1t1g, 2t2g, and 3eg) of anatase TiO2
with octahedral geometry.42-44 Meanwhile, in the case of TIP, a
sharp, single pre-edge peak was observed at around 4970 eV,
which was due to the 1s to 3d transition of isolated titanium
atoms surrounded by four oxygen atoms. Ti-MMS and Ti-MS
also exhibited a characteristic, intense single pre-edge peak. This
peak was quite similar to that of TIP, showing the existence of Ti
oxide moieties with tetrahedral coordination in Ti-MS and Ti-
MMS.42-44 The Fourier transforms of EXAFS spectra of Ti-
MMS and Ti-MS show an intense peak assigned to the existence
of oxygen neighbors (Ti-O) at ca. 1.8 Å (without a phase-shift
correction), but other peaks due to the Ti neighbors (Ti-O-
Ti) were hardly observed between 2.0 and 3.0 Å.42-44 These
results clearly indicate the successful incorporation of isolated
tetrahedral Ti oxide moieties within the mesopores without the
formation of aggregated Ti oxide species.
UV-vis absorption depends not only on the structure but also
on the dispersion of Ti oxide moieties. It has already been
reported that the absorption below 250 nm is attributed to
isolated tetrahedral Ti oxide monomers and the bands above 250
nm are assigned to tetrahedral Ti oxide dimers or small oligo-
mers.42-44 The absorption edge of Ti-MS and Ti-MMS is
located at around 250 nm (Figure 8). The distinct peak observed
at around 210 nm is assigned to the ligand-to-metal charge-
transfer (LMCT) transition of the isolated Ti oxide monomer
Figure 4. Ultra-small-angle X-ray scattering profiles of (a) Ti-MS and
(b) Ti-MMS.
of nitrogen in mesopores are observed in the same P/P0 region.
The increase in the amount of nitrogen adsorbed on Ti-MMS in
the high P/P0 region can be taken as an estimate of small interstices
between the connected mesoporous particles. The BET surface
areas of Ti-MS and Ti-MMS were measured to be 972 and 1053
m2/g, respectively. It was also confirmed that the pore size distri-
butions are scarcely changed by the presence of macroporous
structure, showing the formation of relatively uniform mesopores.
The concentrations of Ti oxide moieties within prepared Ti-MS
and Ti-MMS were determined to be 0.37 and 0.31 wt % as Ti
metal, respectively, by inductively coupled plasma (ICP) analysis.
Ti K-edge XAFS and UV-vis absorption spectra were used to
clarify the nature of Ti oxide moieties incorporated within the
mesoporous silica frameworks. The local structure of Ti oxide
moieties was investigated by Ti K-edge XAFS measurements. As
can be seen in Figure 7, Ti oxide moieties show a well-defined
pre-edge peak depending on the environment of titanium. TiO2
powder shows well-defined pre-edge peaks attributed to the
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Figure 7. (A-D) XANES and (a-d) Fourier transforms of EXAFS
spectra of (A, a) TiO2 (anatase), (B, b) tetrapropyl orthotitanate, (C, c)
Ti-MS, and (D, d) Ti-MMS.
Figure 9. Epoxidation of linear R-olefins ((A) 1-octene, (B) 1-dode-
cene, (C) 1-hexadecene, and (D) 1-eicosene) by TBHP on Ti-MS and
Ti-MMS (reaction time 24 h).
mesoporous materials has also been reported.5,6,38 The observed
order of catalytic activity could be explained by the increasing
diffusion limitation of linear R-olefins in both catalysts. However,
in each reaction system, Ti-MMS had a higher catalytic perfor-
mance in the production of the corresponding epoxide than did
Ti-MS, although both catalysts contain almost the same number
of Ti oxide moieties. The ratio of TON ((TON on Ti-
MMS)/(TON on Ti-MS)) in each reaction system increased
as epoxidation of 1-octene (ca. 1.6) < 1-dodecene (ca. 1.7) <
1-hexadecene (ca. 2.4) < 1-eicosene (ca. 2.6), indicating the
advantages of hierarchical macroporous and mesoporous struc-
tures. Compared with the molecular size of 1-octene, the
mesopores are enough large and do not inhibit the diffusion of
1-octene to the inside of the pores. However, with increases in
the alkyl chain length of R-olefin, the differences between the
alkyl chain length and the size of the mesopores become small,
leading to limitations of reactants diffusing to the inside of pores.
As a consequence, Ti-MMS having many mesopores apertures
and a short mesoporous channel is advantageous to each reaction
system, especially the epoxidation of R-olefin with a long alkyl
chain. The efficient catalytic performance is presumably accom-
plished by decreasing diffusion limitations and facilitating the
efficient transport of reactants to the catalytically active sites in
each reaction system.
The uses of renewable raw materials have recently attracted
much attention because of the natural resource savings as well as
the design of a sustainable system. Among them, the derivatives
of FAMEs were commercially used for plasticizers, additives in
lubricants, and so on.45,46 These chemicals are mainly produced
through acid-catalyzed reactions on the industrial level.45 The
selective epoxidation of FAMEs obtained from renewable raw
materials has also been investigated by using Ti-containing
catalysts in an environmentally friendly way with high efficie-
ncy,30,47 whereas the development of more efficient systems is
strongly desired. Considering the above experimental results for
the epoxidation of linear R-olefins, Ti-MMS could be expected to
show higher catalytic performance in the transformation of bulky
compounds such as FAMEs to the corresponding epoxides. The
Figure 8. Diffuse reflectance UV-vis spectra of (a) Ti-MS and (b) Ti-
MMS.
with tetrahedral coordination.42-44 These results clearly show
the existence of isolated Ti oxide monomers as dominant Ti
oxide moieties within Ti-MS and Ti-MMS, in good agreement
with the XAFS results. The above characterizations clearly
indicated the successful incorporation of tetrahedral Ti oxide
moieties with a single-site nature into silica-based material
possessing hierarchical macroporous and mesoporous structures.
3.2. Catalytic Reactions. The epoxidation of linear R-olefins
(1-octene (C8), 1-dodecene (C12), 1-hexadecene (C16), and
1-eicosene (C20)) with TBHP was used as a test reaction to
investigate the effect of the hierarchical macroporous structure
on the catalytic performances of Ti-containing porous silica.
Figure 9 shows the turnover number (TON) defined as the ratio
of produced epoxide to the number of Ti moieties included in Ti-
MS and Ti-MMS. The selectivity of corresponding epoxides was
almost the same on both catalysts. For example, the selectivity of
epoxide was as high as 98% in the case of the epoxidation of
1-octene. As shown in Figure 9A-D, decreases in catalytic
activity were observed with increasing chain length of linear R-
olefins from 1-octene (CH2dCH(CH2)5CH3) to 1-eicosene
(CH2dCH(CH2)17CH3) on Ti-MS and Ti-MMS, respectively.
The relatively small size of the pores and the long diffusion path
adversely affecting the catalytic performance of microporous and
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the higher catalytic performances of Ti-MMS are achieved by their
advantageous structure for the diffusion of substances during each
reaction. Moreover, Ti-MMS was effective at transforming methyl
oleate to the corresponding epoxide, showing the possibilities of
hierarchical macroporous and mesoporous structures in the design
of more efficient catalysts.
’ ASSOCIATED CONTENT
S
Supporting Information. XRD pattern of recovered Ti-
b
MMS after the epoxidation reaction of methyl oleate and the
reaction-time profiles of the epoxidation of methyl oleate with
the selectivity of epoxide over Ti-MS and Ti-MMS. This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax/Tel: þ81-6-6879-7457. E-mail: yamashita@mat.eng.osaka-
u.ac.jp.
Figure 10. Epoxidation of methyl oleate to methyl 9,10-epoxy stearate
by TBHP on Ti-MS and Ti-MMS (reaction time 4 h).
’ ACKNOWLEDGMENT
selective epoxidation of methyl oleate, which is a kind of FAME,
was thus performed on Ti-MS and Ti-MMS using TBHP as a
model reaction. As shown in Figure 10, Ti-MMS exhibited about
a 2.8 times higher catalytic performance for the epoxidation of
methyl oleate to methyl 9,10-epoxy stearate than did Ti-MS
without the formation of undesired byproducts. Even though the
structure of the catalysts was quite different, the selectivities of
methyl 9,10-epoxy stearate and TBHP were as high as 97 and
98% on each catalyst. The conversion of methyl oleate increased
in proportion to the reaction time and was reached at around
70% on Ti-MMS after 24 h (Figure S1). After the filtration of Ti-
MMS at a reaction temperature in the middle term of the
reaction, it was confirmed that further conversion of methyl
oleate to methyl 9,10-epoxy stearate was stopped. This result is
clear evidence of the absence of Ti leaching from Ti-MMS into
the liquid phase, which shows good correspondence with the
stability of a previously reported Ti-containing catalyst.47 Moreover,
it was found that the structure of Ti-MMS was maintained even
after the catalytic reaction (Figure S2). These results clearly shows
the advantages of hierarchical macroporous and mesoporous
structures in the transformation of bulky molecules obtained from
renewable raw materials to corresponding high-value-added pro-
ducts.
This work was supported by a grant-in-aid for scientific
research (KAKENHI) from the Ministry of Education, Culture,
Sports, Science and Technology (no. 21760630). The X-ray
absorption measurements were performed at the BL-7C facility
of the Photon Factory at the National Laboratory for High-
Energy Physics, Tsukuba, Japan (2009G169). We thank Dr. Eiji
Taguchi and Prof. Hirotaro Mori at the Research Center for
Ultra-High Voltage Electron Microscopy, Osaka University, for
assistance with TEM measurements. We thank Rigaku Corpora-
tion for measurements of ultra-small-angle X-ray scattering
profiles. H.Y. acknowledges his invited professorship at UPMC.
’ REFERENCES
(1) Cundy, C. S.; Cox, P. A. Chem. Rev. 2003, 103, 663.
(2) Wight, A. P.; Davis, M. E. Chem. Rev. 2002, 102, 3589.
(3) Notari, B. Adv. Catal. 1996, 41, 253.
(4) Corma, A. Chem. Rev. 1997, 97, 2373.
(5) Tao, Y.; Kanoh, H.; Abrams, L.; Kaneko, K. Chem. Rev. 2006,
106, 896.
(6) Egeblad, K.; Christensen, C. H.; Kustova, M.; Christensen, C. H.
Chem. Mater. 2008, 20, 946.
(7) Velev, O. D.; Jede, T. A.; Lobo, R. F.; Lenhoff, A. M. Nature
1997, 389, 447.
(8) Holland, B. T.; Blanford, C. F.; Stein, A. Science 1998, 281, 538.
(9) Wijnhoven, J. E. G.J.; Vos, W. L. Science 1998, 281, 802.
(10) Blanco, A.; Chomski, E.; Grabtchak, S.; Ibisate, M.; John, S.;
Leonard, S. W.; Lopez, C.; Meseguer, F.; Miguez, H.; Mondia, J. P.;
Ozin, G. A.; Toader, O.; van Driel, H. M. Nature 2000, 405, 437.
(11) Vlasov, Y. A.; Bo, X. Z.; Sturm, J. C.; Norris, D. J. Nature 2001,
414, 289.
(12) Lee, Y. J.; Heitzman, C. E.; Frei, W. R.; Johnson, H. T.; Braun,
P. V. J. Phys. Chem. B 2006, 110, 19300.
(13) Barry, R. A.; Wiltzius, P. Langmuir 2006, 22, 1369.
(14) Sadakane, M.; Sasaki, K.; Kunioku, H.; Ohtani, B.; Ueda, W.;
Abe, R. Chem. Commun. 2008, 6552.
4. CONCLUSIONS
Isolated tetrahedral Ti oxide moieties containing hierarchical
macroporous silica with mesoporous structure (Ti-MMS) were
successfully prepared by applying a solvent evaporation method
using two kinds of templates: an organic surfactant and PMMA
colloidal crystals. The formation of hierarchical macroporous and
mesoporous structures and nature of Ti oxide moieties were
investigated in detail by SEM, TEM, and other spectroscopic
measurements. It was found that Ti-MMS led to a significant
enhancement of the reaction rate in the epoxidation of long-
chain R-olefins compared to Ti-MS because of the advantageous
structure for the efficient diffusion of reactants to the catalytically
active sites. The most important point in the construction of
hierarchical macroporous structure is reducing the particle size of
mesoporous silica accompanying the formation of many apertures
and the shortening of the mesoporous channels. We estimate that
(15) Kamegawa, T.; Suzuki, N.; Yamashita, H. Chem. Lett. 2009, 38,
610.
(16) Chen, X.; Li, Z.; Ye., J.; Zou, Z. Chem. Mater. 2010, 22, 3583.
(17) Dhainaut, J.; Dacquin, J. P.; Lee, A. F.; Wilson, K. Green Chem.
2010, 12, 296.
(18) Li, F.; Wang, Z.; Ergang, N. S.; Fyfe, C. A.; Stein, A. Langmuir
2007, 23, 3996.
2878
dx.doi.org/10.1021/la1048634 |Langmuir 2011, 27, 2873–2879

Langmuir
ARTICLE
(19) Loiola, A. R.; da Silva, L. R. D.; Cubillas, P.; Anderson, M. W. J.
Mater. Chem. 2008, 18, 4985.
(20) Xue, C.; Wang, J.; Tu, Bo.; Zhao, D. Chem. Mater. 2010, 22,
494.
(21) Yan, H. W.; Zhang, K.; Blanford, C. F.; Francis, L. F.; Stein, A.
Chem. Mater. 2001, 13, 1374.
(22) Melde, B. J.; Stein, A. Chem. Mater. 2002, 14, 3326.
(23) Wijnhoven, J. E. G. J.; Zevenhuizen, S. J. M.; Hendriks, M. A.;
Vanmaekelbergh, D.; Kelly, J. J.; Vos, W. L. Adv. Mater. 2000, 12, 888.
(24) Stein, A. Microporous Mesoporous Mater. 2001, 44-45, 227.
(25) Stein, A.; Schroden, R. C. Curr. Opin. Solid State Mater. Sci.
2001, 5, 553.
(26) Sadakane, M.; Takahashi, C.; Kato, N.; Ogihara, H.; Nodasaka,
Y.; Doi, Y.; Hinatsu, Y.; Ueda, Y. Bull. Chem. Soc. Jpn. 2007, 80, 677.
(27) Sheldon, R. A.; Wallau, M.; Arends, I. W. C. E.; Schuchardt, U.
Acc. Chem. Res. 1998, 31, 485.
(28) Thomas, J. M.; Raja, R.; Lewis, D. W. Angew. Chem., Int. Ed.
2005, 44, 6456.
(29) Corma, A.; Garcia, H. Adv. Synth. Catal. 2006, 348, 1391.
(30) Guidotti, M.; Ravasio, N.; Psaro, R.; Gianotti, E.; Marchese, L.;
Coluccia, S. Green Chem. 2003, 5, 421.
(31) Wu, P.; Tatsumi, T. Catal. Surv. Asia 2004, 8, 137.
(32) Kamegawa, T.; Takeuchi, R.; Matsuoka, M.; Anpo, M. Catal.
Today 2006, 111, 248.
(33) Yamashita, H.; Yoshizawa, K.; Ariyuki, M.; Higashimoto, S.;
Che, M.; Anpo, M. Chem. Commun. 2001, 435.
(34) Kamegawa, T.; Morishima, J.; Matsuoka, M.; Thomas, J. M.;
Anpo, M. J. Phys. Chem. C 2007, 111, 1076.
(35) Mori, K.; Miura, Y.; Shironita, S.; Yamashita, H. Langmuir 2009,
25, 11180.
(36) Lin, W. Y.; Frei, H. J. Am. Chem. Soc. 2005, 127, 1610.
(37) Kamegawa, T.; Sakai, T.; Matsuoka, M.; Anpo, M. J. Am. Chem.
Soc. 2005, 127, 16784.
(38) Choi, M.; Na, K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R.
Nature 2009, 461, 246.
(39) Zou, D.; Ma, S.; Guan, R.; Park, M.; Sun, L.; Aklonis, J. J.;
Salovey, R. J. Polym. Sci., Part A: Polym. Chem. 1992, 30, 137.
(40) Schroden, R. C.; Al-Daous, M.; Blanford, C. F.; Stein, A. Chem.
Mater. 2002, 14, 3305.
(41) Ogawa, M.; Ikeue, K.; Anpo, M. Chem. Mater. 2001, 13, 2900.
(42) Thomas, J. M.; Sankar, G. Acc. Chem. Res. 2001, 34, 571.
(43) Yamashita, H.; Kawasaki, S.; Ichihashi, Y.; Harada, M.; Takeu-
chi, M.; Anpo, M.; Stewart, G.; Fox, M. A.; Louis, C.; Che, M. J. Phys.
Chem. B 1998, 102, 5870.
(44) Marchese, L.; Maschmeyer, T.; Gianotti, E.; Coluccia, S.;
Thomas, J. M. J. Phys. Chem. B 1997, 101, 8836.
(45) Biermann, U.; Friedt, W.; Lang, S.; L€uhs, W.; Machm€uller, G.;
Metzger, J. O.; R€usch gen. Klaas, M.; Schfer, H. J.; Schneider, M. P.
Angew. Chem., Int. Ed. 2000, 39, 2206.
(46) Meier, M. A. R.; Metzger, J. O.; Schubert, U. S. Chem. Soc. Rev.
2007, 36, 1788.
(47) Rios, L. A.; Weckes, P.; Schuster, H.; Hoelderich, W. F. J. Catal.
2005, 232, 19.
2879
dx.doi.org/10.1021/la1048634 |Langmuir 2011, 27, 2873–2879