A remarkable Mo catalyst for olefin metathesis: Hexagonal mesoporous silica-supported molybdenum oxide (MoO3/HMS)

Article abstract of DOI:10.1039/a806233a

Hexagonal mesoporous silica-supported molybdenum oxide exhibits much higher catalytic activity for the metathesis of oct-1-ene in the liquid phase, compared with MoO₃ on normal porous silica and MoO₃ on γ-alumina.

Full text of DOI:10.1039/a806233a

A remarkable Mo catalyst for olefin metathesis: hexagonal mesoporous
silica-supported molybdenum oxide (MoO3/HMS)
Tooru Ookoshi and Makoto Onaka*
Department of Chemistry, College of Arts and Sciences, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902,
Japan. E-mail: conaka@komaba.ecc.u-tokyo.ac.jp
Received (in Cambridge, UK) 6th August 1998, Accepted 21st September 1998
Hexagonal mesoporous silica-supported molybdenum oxide
exhibits much higher catalytic activity for the metathesis of
oct-1-ene in the liquid phase, compared with MoO3 on
normal porous silica and MoO3 on g-alumina.
MoO3/HMS samples exhibited a single diffraction peak corre-
sponding to a d100 spacing of > 3.0 nm,10 and high BET surface
areas of > 800 m2 g21, proving that the MoO3/HMSs were
mainly composed of mesopores. No diffraction peaks intrinsic
to MoO3 crystallites were observed, indicating that MoO3 was
finely dispersed on the interior surface of mesoporous HMS.
As a control, MoO3 was supported on commercially available
silica, CARIACT Q-3 (Fuji Silysia Chemical), which has a
narrow mesopore-size distribution centered at 3 nm, a specific
surface area of 619 m2 g21, a pore volume of 0.45 ml g21, and
75–500 mm particle sizes. The 3.5 and 7 wt% MoO3/SiO2 were
applied to the metathesis of oct-1-ene in a similar way to MoO3/
HMS.
By the use of 7 wt% MoO3/SiO2 (0.15 g) and 3.5 wt% MoO3/
SiO2 (0.3 g), the metathesis products were scarcely obtained at
323 K, as shown in Fig. 1. Surprisingly, MoO3-supporting HMS
catalysts could induce metathesis of oct-1-ene.§ The catalytic
activity is critically dependent on the kind of alkylamine which
functioned as templating agent in the formation of HMSs. In
particular, MoO3-supporting HMS(C8) prepared with the aid of
octylamine had the highest activity. At the early stage of the
metathesis, 7 wt% MoO3/HMS(C12) and 7 wt% MoO3/
HMS(C16) converted oct-1-ene more rapidly than 7 wt%
MoO3/HMS(C8). However, after this stage on 7 wt% MoO3/
HMS(C12) and 7 wt% MoO3/HMS(C16), the conversion
The application of mesoporous materials for various catalysts in
organic reactions has been intensively investigated since a
Japanese research group1 and researchers at Mobil Oil2
independently discovered mesoporous molecular sieves such as
FSM-16 and MCM-41 with uniform pore openings in the range
2.0–10.0 nm as well as a tunnel pore structure. For example,
acidic FSM-16 containing Al2O3 is an effective and recyclable
solid acid promoter for meso-tetraarylporphyrin synthesis from
the corresponding aromatic aldehydes and pyrrole.3 It has also
been shown that titanocene-derived MCM-41 shows high
efficiency in the epoxidation of cyclohexene and more bulky
cyclic olefins,4 while rac-ethenebis(indenyl)zirconium dichlo-
ride-grafted MCM-41 provides highly isotactic polypropenes
with a unique spherulite morphology.5
Supported molybdenum oxides have received much attention
as solid metathesis catalysts because they can be practically
used in industrial petrochemical processes such as the Shell
higher olefin process for producing detergent-range olefins.6
Their surface properties and catalytic activity are critically
influenced by the oxide support, the surface molybdenum oxide
content, the activation conditions, and the oxidation state of the
molybdenum species. Supported molybdenum catalysts have
generally been prepared in the following ways: (i) by impregna-
tion of the support with molybdate solution;7 (ii) by treatment of
the support with Mo(CO)6;8 and (iii) by reaction of the support
with p-allylmolybdenum compounds.9
Table 1 Structural properties of HMS, MoO3/HMS, and MoO3/SiO2
Surface
Mesoporous silica or
Mo-supported catalyst
d100
Spacing/nm
area/m2
g21
This paper focuses on hexagonal mesoporous silica (HMS) in
terms of developing a new silica support for molybdenum-based
olefin metathesis catalysts, and demonstrates that HMS impreg-
nated with molybdenum oxide (MoO3/HMS) is an efficient
catalyst for oct-1-ene metathesis [eqn. (1)].
HMS(C8)
7 wt% MoO3/HMS(C8)
HMS(C12)
7 wt% MoO3/HMS(C12)
HMS(C16)
3.0
3.0
3.5
3.4
4.0
3.5
—
1350
854
1450
1060
1230
844
619
514
563
7 wt% MoO3/HMS(C16)
Mo/HMS
a
SiO2
2 CH2=CH(CH2)5CH3
CH3(CH2)5CH=CH(CH2)5CH3
a
7 wt% MoO3/SiO2
3.5 wt% MoO3/SiO2
—
—
(1)
+
a
CH2=CH2
a CARIACT Q-3.
HMS was first prepared from tetraethylorthosilicate (TEOS)
and primary amine as a templating agent.10 The preparation of
HMS has several advantages over that of MCM-41: (i) the use
of more commercially available primary alkylamines as
templating agents in place of expensive alkyltrimethylammon-
ium halides; (ii) the applicability of shorter alkylamines as
templating agents; and (iii) easier procedures for sol–gel
processing than those for hydrothermal preparations for MCM-
41. In work, three HMSs were synthesized by the use of three
alkylamines with different alkyl chain lengths (C8, C12, C16).†
HMS(Cn) shall hereafter stand for the HMS obtained using Cn-
alkylamine.
MoO3-supporting catalysts were prepared by impregnation of
the HMSs with molybdate solution.‡ The HMS(Cn) supports
and MoO3/HMS catalysts were characterized using powder X-
ray diffraction and N2 adsorption. As shown in Table 1, all
Fig. 1 Metathesis of oct-1-ene on MoO3/mesoporous silica: - 7 wt%
MoO3/HMS(C8). 5 7 wt % MoO3/HMS(C12), / 7 wt% MoO3/
HMS(C16), ~ 7 wt% MoO3/SiO2 (CARIACT Q-3), ! 3.5 wt% MoO3/
SiO2 (CARIACT Q-3).
Chem. Commun., 1998, 2399–2400
2399

1-ene metathesis in the liquid phase under mild conditions. The
interior properties of hexagonal mesoporous silica are quite
different from those of normal porous silica and g-alumina,
hence HMSs can be expected to work as effective, new supports
for heterogeneous metal-catalyzed reactions.
Notes and references
† Under vigorous stirring, TEOS (100 mmol) was added to a mixture of
ethanol (650 mmol), deionized water (3000 mmol) and n-octylamine (25
mmol). The resulting mixture was aged by stirring for 48 h at room
temperature. Then, the resulting gel was filtered, washed with ethanol, dried
in vacuo at 393 K, and calcined at 873 K for 4 h in dry air. When n-
dodecylamine and n-hexadecylamine were used as templating agents, the
molar compositions of TEOS : amine : EtOH : H2O were 1.0 : 0.25 : 8.5 :
28.4 and 1.0 : 0.3 : 14 : 23, respectively.
‡ A representative preparation procedure for the 7 wt% MoO3/HMS catalyst
is given: HMS (1.0 g) was kept in contact with saturated steam in a
desiccator for 12 h. To the wet HMS was added an aqueous solution (5 ml)
of (NH4)6Mo7O24·4H2O (0.0923 g). The mixture was stirred gently for 10
min, and dried to almost complete dryness at room temperature under a
stream of dry N2. Five ml of deionized water was added to the supported
HMS. The mixture was stirred for 10 min, and exposed again to a N2 stream
reaching almost complete dryness. Then, the catalyst was dried further at
393 K for 2 h under reduced pressure of 1 mmHg.
§ A representative metathesis reaction was performed as follows: the MoO3/
HMS catalyst (0.15 g), which had been predried at 873 K for 2 h in dry air,
was weighed and placed in a 20 ml round-bottomed Pyrex flask. The Mo
catalyst contained in the flask was again treated at 773 K under reduced
pressure of 0.6 mmHg in a tubular electric furnace. After cooling, to the
catalyst was added oct-1-ene (3.5 mmol) in dry n-heptane (5 ml), and the
mixture was stirred at 323 K under a dry N2 stream. After a specified time,
the solid catalyst was filtered off, and the organic products were collected
and analyzed by GC using an internal standard of n-decane. Tetradec-7-ene
was isolated from the organic products through distillation on a Kugelrohr
apparatus at 373 K bath temperature under 3 mmHg.
¶ When the distilled products from the metathesis of oct-1-ene on 7 wt%
MoO3/HMS(C8) were oxidatively cleaved upon treatment with RuCl3 and
NaIO4, no aldehydes other than heptanal were detected. This result indicates
that during the metathesis, no isomerization of the CNC bonds in the olefinic
substrates or products took place.
Fig. 2 SEM micrographs of (a) HMS(C8) and (b) HMS(C12) (scale: 30 mm
= 1.5 mm).
reached the highest limit owing to the deactivation of the
catalysts, and the yield of tetradec-7-ene and the selectivity to
tetradec-7-ene decreased [7 wt% MoO3/HMS(C12), yield: 23%
(at 4 h), 17% (at 16 h), selectivity: 75% (at 4 h), 55% (at 16 h);
7 wt% MoO3/HMS(C16), yield: 29% (at 4 h), 19% (at 16 h),
selectivity: 81% (at 4 h), 52% (at 16 h)] due to the fact that the
olefinic products gradually decomposed when in contact with
the catalysts. In contrast, on 7 wt% MoO3/HMS(C8), the yield
of tetradec-7-ene steadily increased from 14% (at 4 h) to 44%
(at 16 h) while maintaining high tetradec-7-ene selectivity [74%
(4 h), 77% (at 16 h)], indicating that the metathesis product,
tetradec-7-ene,¶ did not undergo further metathesis, polymeri-
zation, isomerization, or degradation on the catalyst. In this
case, the products other than tetradec-7-ene are mainly highly
polymerized products from oct-1-ene.
The SEMs in Fig. 2 of HMS(C8) and HMS(C12) indicate that
HMS(C8) is made up of small silica particles of < 50 nm in
diameter, while HMS(C12) is spherical silica of 200–700 nm.
The shape and size of HMS(C16) (not shown in Fig. 2) are
almost the same as those of HMS(C12). Based on the powder X-
ray and SEM analysis, HMS(8) has not only smaller pore
diameter, but also shorter pore length than HMS(12) and
HMS(16). Therefore, it is supposed that at the initial stage of the
metathesis (in Fig. 1), MoO3/HMS(12) and MoO3/HMS(16)
showed higher conversions of oct-1-ene owing to easier passage
of the olefin in the wider pores, but MoO3/HMS(8) was
suffering from less deactivation of the Mo sites or less blockage
of the pores by polymeric side-products owing to the shorter
channel structure, leading to retention of the high yield and high
selectivity of the metathesis product.
1 T. Yanagisawa, T. Shimizu, K. Kuroda and C. Sato, Bull. Chem. Soc.
Jpn., 1990, 63, 988; S. Inagaki, Y. Fukushima and K. Kuroda, J. Chem.
Soc., Chem. Commun., 1993, 680.
2 C. T. Kresge, M. E. Leonowicz, R. J. Roth, J. C. Vartuli and J. B. Beck,
Nature, 1992, 359, 710; 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. Sheppard, J. B. Higgins and L. Schlenker, J. Am. Chem. Soc.,
1992, 114, 10 834.
3 T. Shinoda, Y. Izumi and M. Onaka, J. Chem. Soc., Chem. Commun.,
1995, 1801.
4 T. Maschmeyer, F. Rey, G. Sankar and J. M. Thomas, Nature, 1995,
378, 159.
There are also distinct differences in the catalytic activities on
olefin metathesis between MoO3-supporting HMS and normal
silica. Although the reasons why the MoO3/HMS shows much
higher catalytic performance have yet to be elucidated, it is
likely that silica with hexagonal channel-type pores is adequate
for fixing finely dispersed molybdenum oxides and for
stabilizing the molybdenum species in the oxidation state which
is essential to the metathesis catalysis. Disordered normal silica
could not play such a role.
5 J. Tudor and D. O’Hare, Chem. Commun., 1997, 603.
6 K. Weissermel and H-J. Arpe, Industrielle Organische Chemie, VCH,
Weinheim, 4th edn., 1994.
Silica-supported molybdenum catalysts are normally acti-
vated by cocatalysts such as tetraalkyltin11 or by photoreduc-
tion.12 Neither the presence of such volatile and poisonous
cocatalysts nor the photoactivation process is necessary for the
MoO3/HMS system to show high catalytic performance.
MoO3/HMS(C8) was also compared not only with traditional
Al2O3-supported13 molybdenum catalyst (MoO3/Al2O3)14 but
also with MoO3/Al2O3 modified with CoO14 or K2O15 in the
metathesis of oct-1-ene at 323 K.16 In the light of the yield of
tetradec-7-ene as well as the selectivity to tetradec-7-ene, 7 wt%
MoO3/HMS(C8) is much superior to 7 wt% MoO3/Al2O3
[yield: 3.8% (at 4 h), 12.5% (at 16 h), selectivity: 35% (at 4 h),
35% (at 16 h)], 7 wt% MoO3/2 wt% CoO/Al2O3 [yield: 4.9% (at
3 h), 3.4% (at 16 h), selectivity: 52% (at 3 h), 27% (at 16 h)], and
7 wt% MoO3/0.3 wt% K2O/Al2O3 [yield: 3.6% (at 3 h), 4.5% (at
16 h), selectivity: 51% (at 3 h), 51% (at 16 h)].
7 T. Sodesawa, E. Ogata and Y. Kamiya, Bull. Chem. Soc. Jpn., 1979, 52,
1661.
8 R. F. Howe and C. Kemball, J. Chem. Soc., Faraday Trans. 1, 1974, 70,
1153.
9 Y. I. Yermakov, B. N. Kuznetsov and A. N. Startsev, Kinet. Katal.,
1974, 15, 539.
10 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 865.
11 V. I. Bykov, T. A. Butenko, E. S. Finkel’shtein, P. V. Petrovskii and
V. M. Vdovin, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 37, 1580.
12 B. N. Shelimov, I. V. Elev and V. B. Kazansky, J. Mol. Catal., 1988, 46,
187.
13 g-Alumina [N611(N) from Nikki Chemical Co.; specific surface area
181 m2 g21, pore volume 0.36 ml g21] was used.
14 A. Ismayel-Milanovic, J. M. Basset, H. Praliaud, M. Dufaux and L. de
Mourgues, J. Catal., 1973, 31, 408.
15 R. Nakamura, H. Iida and E. Echigoya, Chem. Lett., 1972, 273.
16 Al2O3-supported MoO3 catalysts (0.15 g) were used in the meta-
thesis.
In conclusion, MoO3-supporting hexagonal mesoporous
silica which was prepared in the sol–gel reaction directed by
relatively short alkylamine shows remarkable catalysis in oct-
Communication 8/06233A
2400
Chem Commun., 1998