Photometathesis activity and thermal stability of two types of mesoporous silica materials, FSM-16 and MCM-41

Article abstract of DOI:10.1039/b002501l

The metathesis reaction of propylene under photoirradiation was conducted over two types of mesoporous silica materials, FSM-16 and MCM-41, and amorphous silica evacuated at high temperature. In comparison between the types of mesoporous silica materials, FSM-16 showed higher activity than MCM-41 because the pore walls of FSM-16 with higher stability than MCM-41 would suppress the conversion of strained siloxane bridges into inactive unstrained bridges. The activity increased with increasing evacuation temperature, and influenced by the prehydration treatment before evacuation. FSM-16 and MCM-41 showed activity after evacuation at considerably lower temperature than amorphous silica. The stability of FSM-16 was higher than MCM-41 under pretreatment conditions.

Full text of DOI:10.1039/b002501l

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Photometathesis activity and thermal stability of two types of
mesoporous silica materials, FSM-16 and MCM-41
Yoshitaka Inaki,a Hisao Yoshida,*a Koichi Kimura,a Shinji Inagaki,b Yoshiaki Fukushimab and
Tadashi Hattoria
a Department of Applied Chemistry, Graduate School of Engineering, Nagoya University,
Nagoya 464-8603, Japan
b T oyota Central R & D L aboratories, Inc., 41-1, Y okomichi Nagakute, Aichi, 480-1192, Japan
Received 29th March 2000, Accepted 25th September 2000
First published as an Advance Article on the web 26th October 2000
The metathesis reaction of propene under photoirradiation was performed over two types of mesoporous silica
materials, FSM-16 and MCM-41, and amorphous silica evacuated at high temperature. The activity increased
with increasing evacuation temperature, and moreover, prehydration treatment before evacuation inÑuenced
the activity. The e†ect of these pretreatment conditions, however, di†ered from sample to sample. FSM-16 and
MCM-41, exhibited activity after evacuation at considerably lower temperature than amorphous silica.
Prehydration enhanced the activity of FSM-16 and amorphous silica, but suppressed that of MCM-41. It was
also observed that the stability of FSM-16 is higher than MCM-41 under pretreatment conditions. From these
results, the speciÐc features of mesoporous silica materials and the di†erence between FSM-16 and MCM-41
were discussed.
Introduction
Experimental
Two types of mesoporous silica materials, FSM-161,2 and
MCM-41,3,4 were Ðrst synthesized at almost the same time,
and attracted a great deal of attention as new materials. Both
have the same hexagonal arrangement of cylindrical nano-
pores and characteristic thin pore wall structure, although the
synthesis method and mechanism5 are clearly di†erent.
However, some reports have described the di†erences in their
properties such as thermal stability6 and adsorption behav-
ior.7
Utilization of mesoporous silica materials for catalysis has
been attempted through the introduction of heteroatoms.8
This was based on the knowledge that the silica materials are
catalytically inert, although silica actually catalyzes some reac-
tions.9 Recently, it was found that unmodiÐed mesoporous
silica has some advantages over amorphous silica for the
catalysis of some reactions. These are mild acidity10 and a
radical like function.11,12
Moreover, photocatalytic activities are reported on amor-
phous silica13v15 and mesoporous silica.16,17 We found that
unmodiÐed FSM-16 has a higher activity for photometathesis
of propene than amorphous silica.16 It was previously
believed that most of the catalysts involve transition metals
such as Mo, W, Re, etc. for the metathesis reaction.18 The
active sites on silica materials for photometathesis are
expected to be a new type of photocatalytic site. It was sug-
gested that the active sites for photometathesis on silica
materials are generated by desorption of surface hydroxy
groups.13,14,16
The aims of the present paper are to elucidate the advan-
tages of mesoporous silica materials over amorphous silica
through discussion of their thermal stability and photometa-
thesis active sites. Moreover, we will discuss the di†erences
between FSM-16 and MCM-41, which are recognized to have
the same pore structure at the nanometre level. Although
many improvements have been made in the synthesis methods
of mesoporous silica materials, the original methods for
FSM-161 and MCM-413 were employed here.
Preparation of samples
FSM-16, was prepared as described in ref. 1 except that hexa-
decyltrimethylammonium bromide [C
was used as a template. Kanemite (50 g) was synthesized by
calcination of water glass (SiO /Na O ratio was adjusted to
H
(CH ) N`Br~]
1
6 33
3 3
2
2
2.0 by addition of NaOH aqueous solution) at 973 K for 6 h,
followed by dispersion in 500 cm3 water with stirring for 3 h.
The wet kanemite was Ðltered o†, dispersed in 1.0 dm3 of a 0.1
mol dm~3 hexadecyltrimethylammonium bromide aqueous
solution, and heated at 343 K for 3 h with stirring. The pH of
the suspension was adjusted to 8.5 by addition of 2 mol dm~3
HCl aqueous solution and the suspension was left at 343 K
for a further 3 h with stirring. The resulting product was Ðl-
tered, washed thoroughly with water repeatedly and dried at
333 K to yield the precursor of FSM-16. The precursor was
calcined at 523 K in a Ñow of N for 1 h and subsequently at
873 K in Ñowing air for 5 h to remove the organic fraction.
MCM-41 was prepared by using the same template as
2
FSM-16, referring to the literature.3 120 g of water, 56.9 g of
water glass (ca. 29 wt.% SiO ) and 1.96 cm3 of sulfuric acid
2
were mixed with stirring (solution A). 50.4 g of surfactant
[C
H
(CH ) N`Br~] template was dissolved in 150 g of
1
6 33
3 3
water with stirring at 323 K (solution B). Solution A was
added to B slowly, followed by addition of 60 g of water. The
pH of the resulting gel was adjusted to 10.0 by addition of 1
mol dm~3 sulfuric acid solution. The gel was heated at 373 K
for 168 h in a sealed TeÑon bottle. The resulting product was
Ðltered, washed thoroughly with hot water (323 K) repeatedly
and dried at 373 K overnight to yield the precursor of
MCM-41. Calcination of the precursor was carried out as
described above for FSM-16.
Amorphous silica (referred to as AMS) was prepared by the
solÈgel method as described in ref. 19. A wet silica gel was
obtained by hydrolysis of ethyl orthosilicate in a waterÈ
ethanol mixture at its boiling point, followed by Ðltration.
Then the wet silica gel was dried at 393 K, and ground and
DOI: 10.1039/b002501l
Phys. Chem. Chem. Phys., 2000, 2, 5293È5297
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5293

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calcined at 773 K for 5 h in a dry stream of air to yield the
amorphous silica.
To prepare a more hydrated sample, prehydration treat-
ment was carried out as follows. The sample was impregnated
with distilled water at 343 K, evaporated to dryness, and then
stored under ca. 80% humidity at room temperature. Prehy-
drated samples were referred to as FSM-16-H, MCM-41-H
and AMS-H.
Characterization
Powder X-ray di†raction (XRD) patterns were recorded on a
Rigaku di†ractometer RINT 1200 using radiation of Ni-
Ðltered Cu-Ka (40 kV, 20 mA).
N adsorption isotherms were recorded on a Coulter Omni-
2
sorp Series 100 CX at 77 K. Before measurement of the iso-
therm, the catalyst was evacuated for 3 h at 673 or 1073 K.
Pore size distributions were calculated by the BJH method
(
adsorption branch).
The amount of dehydroxylation, which occurred under
evacuation at various temperatures, was estimated by ther-
mogravimetry (TG) in a He stream. After the sample was
placed in a He stream at 373 K for 4 h, the temperature was
raised at the rate of 3 K min~1 to 473 K, held for 2 h, and
then raised stepwise to 673, 873, 1073 and 1473 K. At each
step, the temperature was held for 2 h.
The amount of hydroxy groups was obtained by subtrac-
ting the weight at 1473 K from the weight at each tem-
perature. At 1473 K, all hydroxy groups are expected to be
desorbed. The validity of this method was conÐrmed by n-
butyllithium (Bu-Li) titration20 using FSM-16-H as an
example. After the sample evacuated at each temperature was
soaked in hexane, a hexane solution of Bu-Li was added
under a N2 atmosphere. The amout of butane evolved was
evaluated from the increment in the pressure, and the amount
of OH groups was estimated on the assumption that Bu-Li
reacts with SiÈOH to produce n-butane stoichiometrically.
Fig. 1 XRD pattern of FSM-16 (A) and MCM-41 (B); as prepared
(a), after evacuation of (a) at 673 (b) and 1073 K (c); prehydrated
sample (d), after evacuation of (d) at 673 (e) and 1073 K (f).
were type IV isotherms of the IUPAC classiÐcation, indicating
that both samples were mesoporous materials. In the pore size
distributions of these samples evacuated at 673 K, a sharp
peak at ca. 3.1 nm was observed (Fig. 3Aa and Ba), indicating
that both samples have uniform nanopores. As listed in Table
Photometathesis of propene
Before photocatalytic metathesis reaction, the catalyst was
pretreated at various temperatures in the presence of 100 Torr
1, the BET surface areas of both samples evacuated at 673 K
O for 1 h, followed by evacuation for 1 h at the same tem-
2
were ca. 900 m2 g~1, and d
was 35.6 A and 38.1 A, respec-
Ž
Ž
perature. The photocatalytic reaction of propene was carried
100
tively. These results conÐrmed that both FSM-16 and
MCM-41 have essentially the same structures as described in
the original reports.1,3
out under photoirradiation using a 250 W ultrahigh-pressure
Hg lamp in a closed static system (dead volume 115 cm3,
propene 100 lmol) at ambient temperature. The powdered
catalyst (200 mg) was spread onto the Ñat bottom (12 cm2) of
a quartz reactor, and photoirradiated from the outside of the
reactor. The temperature of the catalyst bed was elevated by
ca. 10 K from room temperature by the photoirradiation.
After each photoirradiation period, the products were
analyzed by gas chromatography.
In the photocatalytic reaction, one ethene molecule and one
but-2-ene molecule were obtained from two propene mol-
ecules, reaction (1). The conversion of the photometathesis
reaction was deÐned as the sum of the yields of ethene and
but-2-ene.
However, there is a di†erence in the thermal stability
between FSM-16 and MCM-41 synthesized by each original
preparation method.1,3 After evacuation of FSM-16 and
MCM-41 at 673 K, four di†raction lines in the XRD pattern
were slightly weakened (Fig. 1Ab and Bb), but remained clear.
After evacuation at 1073 K, almost no further change
was observed in the di†raction lines of FSM-16 (Fig. 1Ac), but
the lines of MCM-41 were further weakened and three di†rac-
tion lines above 3¡ became unclear (Fig. 1Bc). The amount of
adsorbed N on FSM-16 did not decrease much after evac-
2
uation at 1073 K (Fig. 2A), while on MCM-41, the amount
adsorbed decreased markedly (Fig. 2B). The pore size distribu-
tion of MCM-41 (Fig. 3Bb) was shifted to a shorter region
and broadened after evacuation at 1073 K, and these changes
were greater than those for FSM-16 (Fig. 3Ab). The BET
2
C H ] C H ] C H
2 4 4 8
(1)
3
6
Results and discussion
surface area and d
of FSM-16 after evacuation at 1073 K
1
00
did not change much, but those of MCM-41 decreased notice-
ably (Table 1). These results indicate that the fundamental
regular hexagonal structure was deformed after thermal evac-
uation, and that MCM-41 is much easier to deform than
FSM-16.
Thermal stability of FSM-16 and MCM-41
Fig. 1 shows the XRD patterns of FSM-16 and MCM-41.
After calcination of the precursors (Fig. 1Aa and Ba), both
samples exhibited four di†raction lines in the low 2h region,
indicating that both have a regular hexagonal structure. The
di†raction intensity of FSM-16 was obviously higher than
When prehydration and subsequent thermal evacuation
was carried out on the samples, the pore structures of both
were further deformed. On FSM-16, however, the di†raction
lines remained clear (Fig. 1AdÈf), changes in the N2 adsorp-
that of MCM-41. The N adsorption isotherms of FSM-16
2
(
Fig. 2A) and MCM-41 (Fig. 2B) after evacuation at 673 K
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Table 1 BET surface area and d
of mesoporous silica samples
1
00
Evacuation
temperature/K
BET surface
area/m2 g~1
Sample
d/AŽ
FSM-16
673
073
673
073
673
073
673
073
924
998
971
920
900
786
902
786
35.6
35.0
36.8
33.2
38.1
36.5
37.1
33.4
1
1
1
1
FSM-16-H
MCM-41
MCM-41-H
tion isotherm were small (Fig. 2A), the pore size distribution
still sharp (Fig. 3Ac and d) and the BET surface area did not
change (Table 1). In contrast, for MCM-41-H, the di†raction
lines became unclear (Fig. 1BdÈf), the N adsorption isotherm
2
was close to a type I isotherm (Fig. 2B), the pore size distribu-
tion shifted and broadened remarkably and the BET surface
area decreased (Table 1). These results indicate that the pore
structure of MCM-41 was signiÐcantly deformed but that of
FSM-16-H was maintained after prehydration and thermal
evacuation.
Thus, the mesoporous structure was deformed after prehy-
dration and thermal evacuation, but the degree of thermal
deformation was noticeably larger for MCM-41 than for
FSM-16. It is noteworthy that, for MCM-41 and MCM-41-H,
the BET surface area decreased on evacuation at 1073 K. This
indicates that not only deformation but also surface recon-
struction occurred signiÐcantly on the pore walls of MCM-41
compared with FSM-16. The lower thermal stability of the
pore wall of MCM-41 than that of FSM-16, as mentioned
above, is in agreement with the result reported in ref. 6. It has
been suggested that the high heat resistivity of FSM-16 would
be attributable to the regular atomic arrangement in the silica
wall.21
Fig. 2
N adsorption isotherm of FSM-16 (A) and MCM-41 (B). As
prepared samples evacuated at 673 (…) and 1073 K (>), and prehy-
drated samples evacuated at 673 (L) and 1073 K (|).
2
Active sites for photometathesis over silica materials
Fig. 4 shows the conversions of photometathesis of propene
over silica materials after evacuation at various temperatures.
All silica samples exhibited activity for photometathesis with
the activity of FSM-16 being clearly the highest. The activity
of FSM-16 increased with increasing evacuation temperature
(Fig. 4a). On the other hand, amorphous silica exhibited no
activity at evacuation temperatures below 873 K, and
exhibited activity only after evacuation at 1073 K (Fig. 4e).
The activity of MCM-41 increased (Fig. 4c) in a similar way to
FSM-16. It is noteworthy that this behavior was observed in
both mesoporous silica materials. Prehydration increased the
activity of FSM-16, especially after evacuation at 873 K (Fig.
4
b). Similarly, the activity of prehydrated amorphous silica
was larger than that of unhydrated sample after evacuation at
073 K (Fig. 4f), although after evacuation below 873 K it
1
exhibited no activity, even after prehydration. The activity of
prehydrated MCM-41 (Fig. 4d) was lower than that of
unhydrated MCM-41 (Fig. 4c).
Fig. 5 shows the amount of surface hydroxy groups on
FSM-16 and FSM-16-H after evacuation at various tem-
peratures, as measured by TG. The amount of surface OH
groups on FSM-16 evacuated at 473 K was 3.2 mmol g~1 (2.1
OH nm~2), which is similar to the value of 2.5 OH nm~2 on
MCM-41 evacuated at 383 K.22 With a rise in the evacuation
temperature, the amount of OH groups decreased on both
FSM-16 and FSM-16-H. The amount of OH groups on
FSM-16-H evacuated below 673 K was larger than that on
FSM-16. However, the amount on FSM-16-H became less
than on FSM-16 after evacuation above 873 K. These results
indicate that prehydration increased not only the amount of
OH groups, but also the amount of dehydroxylation. Closely
Fig. 3 Pore size distribution of FSM-16 (A) and MCM-41 (B). As
prepared samples evacuated at 673 (a) and 1073 K (b), and prehydrat-
ed samples evacuated at 673 (c) and 1073 K (d).
Phys. Chem. Chem. Phys., 2000, 2, 5293È5297
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groups measured here are in accessible locations for molecules
such as propene, which are smaller than the Bu-Li molecule.
Fig. 6 shows the relation between the photometathesis
activity and the amount of desorbed hydroxy groups over
silica materials as evaluated by TG. The amount of dehy-
droxylation was indicated as that desorbed above 473 K. The
activity of all samples increased as the amount of dehydroxy-
lation increased. On the prehydrated samples, the amount of
dehydroxylation was larger than that on unhydrated samples,
at the same time, the activity was higher on prehydrated
samples, except for MCM-41-H. These results suggest that the
active sites for photometathesis are generated by the dehy-
droxylation of hydroxy groups as previously proposed.13,14,16
However, the activity depended on the thermal evacuation
temperature di†erently from the sample to the sample.
Amorphous silica exhibited activity when the evacuation
temperature was increased from 873 to 1073 K (Fig. 4e).
Prehydration increased the activity of amorphous silica, but
the activity was also observed only after evacuation at 1073 K
(Fig. 4f). Apparently, the curves of the activity against the
amount of dehydroxylation were not linear for amorphous
silica (Fig. 6), indicating that dehydroxylation does not always
produce the active sites and some speciÐc sites generated by
dehydroxylation would be active sites.
It is widely known that evacuation temperature has an
e†ect on the kind of sites generated by the dehydroxylation of
surface hydroxy groups.23 When the evacuation temperature
is lower than 923 K, only adjacent hydroxy groups hydrogen-
bonded to each other are dehydroxylated and unstrained
siloxane bridges (3 SiÈOÈSi3 ) are formed. Above 923 K, on the
other hand, most of the surface hydroxy groups are isolated,
i.e., they are not hydrogen-bonded to each other. These iso-
lated hydroxy groups begin to be dehydroxylated in this tem-
perature range ([923 K), resulting in the generation of
strained siloxane bridges (3 SiÈOÉ É ÉSi3 ). In this severe tem-
perature condition, deformation of the silica framework due to
thermal vibrations is large enough to allow interaction of iso-
lated hydroxy groups, yielding strained siloxane bridges.23
Since amorphous silica did not exhibit any activity after evac-
uation at 873 K (Fig. 4C) in the present study, unstrained
siloxane bridges and adjacent hydroxy groups, which are
found in abundance under this condition, are not the active
sites. On the other hand, amorphous silica exhibited activity
only after evacuation at 1073 K (Fig. 4C). Since the amount of
isolated hydroxy groups decreases above 923 K, this result
indicates that the isolated hydroxy groups are not the active
sites, but their dehydroxylation is required to generate active
Fig. 4 Photometathesis conversion of propene over silica materials
evacuated at various temperature; FSM-16 (a), FSM-16-H (b),
MCM-41 (c), MCM-41-H (d), AMS (e) and AMS-H (f).
similar results were observed on MCM-41 and amorphous
silica. The validity of the amount of surface OH groups
obtained by TG was conÐrmed by using Bu-Li titration,
which gave almost the same results as TG (Fig. 5). At the
same time, this result conÐrmed that almost all hydroxy
Fig. 5 Amount of surface OH groups on FSM-16 evacuated at
various temperatures, estimated by TG for FSM-16 (…)and FSM-16-
H (L). The results by Bu-Li titration for FSM-16-H (|) are also
shown.
Fig. 6 Relation between the photometathesis conversion and the
amount of desorbed OH groups on FSM-16 (…), FSM-16-H (L),
MCM-41 (>), MCM-41-H (|), AMS (=) and AMS-H (K).
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sites. Tanaka et al.13 also suggested that the photometathesis
active sites on amorphous silica would be generated by dehy-
droxylation of isolated hydroxy groups. Thus, it may be con-
cluded that the active sites are the strained siloxane bridges
generated by the dehydroxylation of isolated hydroxy groups,
or, at least, relate to the strained siloxane bridges, which are
would suppress the conversion of strained siloxane bridges
into inactive unstrained bridges.
Acknowledgements
This work was partly supported by Nippon Sheet Glass
Foundation for Materials Science and Engineering.
known to be reactive: they dissociatively adsorb NH ,
3
CH OH and BH .24
References
3
3
In the case of FSM-16, both the activity and the amount of
dehydroxylation also increased with a rise in the evacuation
temperature (Fig. 4 and 5). Prehydration drastically increased
the activity of FSM-16 (Fig. 4b). The relation between activity
and the amount of desorbed hydroxy groups on both FSM-16
and FSM-16-H was not linear (Fig. 6). These results were in
good agreement with those on amorphous silica, indicating
that the active sites for photometathesis over FSM-16 are also
the strained siloxane bridges or related sites. Similar results
were found for MCM-41.
1
2
3
S. Inagaki, Y. Fukushima and K. Kuroda, J. Chem. Soc., Chem.
Commun., 1993, 680.
S. Inagaki, A. Koiwai, N. Suzuki, Y. Fukushima and K. Kuroda,
Bull. Chem. Soc., Jpn., 1996, 69, 1449.
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, E. W. Shep-
pard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am.
Chem. Soc., 1992, 114, 10834.
4
5
C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S.
Beck, Nature, 1992, 359, 710.
S. OÏBrien, R. J. Francis, S. J. Price, D. OÏHare, S. M. Clarck, N.
Okazaki and K. Kuroda, J. Chem. Soc., Chem. Commun., 1995,
However, a remarkable di†erence was observed between the
mesoporous silica materials and amorphous silica. The meso-
porous silica materials exhibited activity even after evacuation
at 673 K (Fig. 4A, B), i.e., the required temperature to generate
active sites was much lower than for amorphous silica (Fig.
2
423.
6
7
8
9
C.-Y. Chen, S.-Q. Xiao and M. E. Davis, Microporous Mater.,
1
995, 4, 1.
S. Inagaki, Y. Fukushima, K. Kuroda and K. Kuroda, J. Colloid
Interface Sci., 1996, 180, 623.
A. Corma, Chem. Rev., 1997, 97, 2373; J. Y. Ying, C. P. Mehnert
and M. S. Wong, Angew. Chem. Int. Ed. Engl., 1999, 38, 56.
J. N. Armor, J. Catal., 1981, 70, 72; J. N. Armor and P. M.
Zambri, J. Catal., 1982, 73, 57; M. Lacroix, G. M. Pajonk and S.
J. Teichner, J. Catal., 1986, 101, 314; Y. Matsumura, K. Hash-
imoto and S. Yoshida, J. Chem. Soc., Chem. Commun., 1987, 1599;
G. N. Kastanas, G. A. Tsigdinos and J. Schwank, J. Appl. Catal.,
4C). The dehydroxylation of isolated hydroxy groups far apart
from each other is said to require thermal deformation of the
silica framework,23 and thermal deformation of the pore wall
structure occurred on both FSM-16 and MCM-41 under
evacuation at high temperature (Fig. 1È3 and Table 1). Thus,
the higher activity of mesoporous silica materials may be
attributed to the easy deformation of the pore cell, leading to
the dehydroxylation of isolated hydroxy groups to generate
the active sites, the strained siloxane bridges or related sites.
Although common behavior was observed for both meso-
porous silica materials, there was a marked di†erence between
them. The activity of MCM-41 per amount of desorbed
hydroxy groups was considerably lower than that of FSM-16
1
988, 44, 33; Y. Matsumura, K. Hashimoto and S. Yoshida, J.
Catal., 1989, 117, 135; E. W. Bittner, B. C. Bockrath and J. M.
Solar, J. Catal., 1994, 149, 206.
1
0
T. Yamamoto, T. Tanaka, T. Funabiki and S. Yoshida, J. Phys.
Chem. B, 1998, 102, 5830; Y. Tanaka, N. Sawamura and M.
Iwamoto, T etrahedron L ett., 1998, 39, 9457.
11 Y. Sakata, M. A. Uddin, A. Muto, K. Koizumi, Y. Kanada and
K. Murata, J. Anal. Appl. Pyrolysis, 1997, 43, 15.
1
2
3
T. Hattori, T. Ebigase, Y. Inaki, H. Yoshida and A. Satsuma,
Stud. Surf. Sci. Catal., 2000, 129, 837.
(
Fig. 6), and the activity increased rather slowly with a rise in
evacuation temperature from 873 to 1073 K (Fig. 4B). In the
case of FSM-16, both unhydrated and prehydrated samples
exhibited a quite similar relationship between the photometa-
thesis activity and the amount of dehydroxylation (Fig. 6).
This could be due to the thermal stability of FSM-16. In con-
trast, the activity of MCM-41 decreased after prehydration
1
T. Tanaka, S. Matsuo, T. Maeda, H. Yoshida, T. Funabiki and S.
Yoshida, Appl. Surf. Sci., 1997, 121/122, 296.13.
14 H. Yoshida, T. Tanaka, S. Matsuo, T. Funabiki and S. Yoshida,
J. Chem. Soc., Chem. Commun., 1995, 761.
1
5
A. Morikawa, M. Hattori, K. Yagi and K. Otsuka, Z. Phys.
Chem., N. F., 1977, 140, 309; M. Anpo, C. Yun and K. Kubo-
kawa, J. Catal., 1980, 61, 267; Y. Kubokawa, M. Anpo and C.
Yun, Proceedings of the 7th International Congress on Catalysis
(
Fig. 4B). Brinker et al. reported that reconstruction of the
silica surface led to conversion of the strained siloxane to the
unstrained one at high temperature above 873 K.25 As men-
tioned above, signiÐcant thermal deformation, and moreover,
surface reconstruction occurred on the pore walls of MCM-41
in comparison with FSM-16. And, further, we previously
observed in an FTIR study that the strained siloxane bridges
were generated on FSM-16 and MCM-41 evacuated above
(B), ed. T. Seiyama and K. Tanabe, Kodansha, Tokyo, 1981, p.
1171; A. Ogata, A. Kazukawa and M. Enyo, J. Phys. Chem.,
1986, 90, 5201; H. Yoshida, T. Tanaka, M. Yamamoto, T. Fun-
abiki and S. Yoshida, Chem. Commun., 1996, 2125; H. Yoshida, T.
Tanaka, M. Yamamoto, T. Yoshida, T. Funabiki and S. Yoshida,
J. Catal., 1997, 171, 351.
1
6
H. Yoshida, K. Kimura, Y. Inaki and T. Hattori, Chem. Commun.,
1
997, 129.
873 K, and that they were more abundant on FSM-16 than
17 H. Yoshida, C. Murata, Y. Inaki and T. Hattori, Chem. L ett.,
on MCM-41.12 From these results, it is proposed that the
lower stability of the pore wall of MCM-41 would cause con-
version of the strained siloxane bridges once formed into
unstrained ones at high temperature and hence MCM-41
would have lower activity than the more stable FSM-16.
1998, 1121.
1
1
2
2
2
8
9
0
1
2
K. J. Ivin and J. C. Mol, in OleÐn Metathesis and Metathesis
Polymerization, Academic Press, London, 1997.
S. Yoshida, T. Matsuzaki, T. Kashiwazaki, K. Mori and K.
Tarama, Bull. Chem. Soc. Jpn., 1974, 47, 1564.
H. Yoshida, T. Tanaka, T. Funabika and S. Yoshida, J. Chem.
Soc., Faraday T rans., 1994, 90, 2107.
Conclusion
S. Inagaki, Y. Fukushima and K. Kuroda, Stud. Surf. Sci. Catal.,
1998, 84, 125.
The active sites for photometathesis of propene over silica
materials were proposed to be strained siloxane bridges, or
related sites, generated by dehydroxylation of isolated
hydroxy groups at high temperature. Mesoporous silica
materials, FSM-16 and MCM-41, with thin pore walls
exhibited activity after evacuation at considerably lower tem-
perature than amorphous silica, because thermal deformation
of their pore walls occurs easily to generate the active sites. In
comparison between the types of mesoporous silica materials,
FSM-16 exhibited higher activity than MCM-41 because the
pore walls of FSM-16 with higher stability than MCM-41
X. S. Zhao, G. Q. Lu, A. K. Whittaker, G. J. Millar and H. Y.
Zhu, J. Phys. Chem. B, 1997, 101, 6525.
2
2
3
4
I.-S. Chuang and G. E. Maciel, J. Phys. Chem. B, 1997, 101, 3052.
J. B. Peri, J. Phys. Chem., 1966, 70, 2937; M. J. D. Low, N.
Ramasubramanian and V. V. Subba Rao, J. Phys. Chem., 1967,
71, 1726; B. A. Morrow, I. A. Cody and L. S. M. Lee, J. Phys
Chem., 1975, 79, 2405; B. A. Morrow and I. A. Cody, J. Phys
Chem., 1976, 80, 1995; B. A. Morrow, I. A. Cody and L. S. M.
Lee, J. Phys Chem., 1976, 80, 1998; B. A. Morrow, I. A. Cody and
L. S. M. Lee, J. Phys Chem., 1976, 80, 2761.
2
5
C. J. Brinker, R. J. Kirkpatrick, D. R. Tallant, B. C. Bunker and
B. Montez, J. Non-Cryst Solids, 1988, 99, 418.
Phys. Chem. Chem. Phys., 2000, 2, 5293È5297
5297