Olefin metathesis over mesoporous alumina-supported rhenium oxide catalyst

Article abstract of DOI:10.1246/cl.2002.850

Rhenium oxide finely dispersed on mesoporous alumina with uniform pore size was found to be a more active and selective catalyst for liquid-phase metathesis reactions of terminal and inner olefins than rhenium oxide on normal γ-alumina with random pore shape.

Full text of DOI:10.1246/cl.2002.850

850
Chemistry Letters 2002
Olefin Metathesis over Mesoporous Alumina-supported Rhenium Oxide Catalyst
Makoto Onakaꢀ and Takashi Oikawa
Department of Chemistry, Graduate School of Arts and Sciences, The University of Tokyo, Meguro, Tokyo 153-8902
(Received June 3, 2002; CL-020480)
Rhenium oxide finely dispersed on mesoporous alumina with
surface area ¼ 166 m2/g; pore diameters ranging from 1to 20 nm;
pore volume ¼ 0:426 ml/g).
uniformpore size was found to be a more active and selective
catalyst for liquid-phase metathesis reactions of terminal and
inner olefins than rheniumoxide on normal ꢀ-alumina with
randompore shape.
Metathesis of alkenes (7-hexadecene (cis/trans ¼ 2:9) and 1-
octene) was performed in a batch reactor at 50 or À1 ꢁC.11
Figure 1 shows changes in the conversion of 7-hexadecene in
the metathesis at 50 ꢁC. On 7 wt% Re2O7/meso-Al2O3, the
conversion of 1a (cis=trans ¼ 2:9) smoothly reached the
statistical equilibriumvalue of 50% after 4 h to produce equal
amounts of 7-tetradecene (2a) and 9-octadecene (3a) with 95–
98% selectivity and cis/trans ratio of 0.23. In contrast, on a control
catalyst of 7 wt% Re2O7/ALO-7 the metathesis stopped at the
conversion of ꢂ30% (selectivity of 2a and 3a ¼ 93{95%; cis/
trans ratio ¼ 0:22) after 10 h due to the deactivation of the
catalyst. It is worth noting that 1) 7 wt% Re2O7/meso-Al2O3
revealed high metathesis activity without reductive pretreatment
on the catalyst; 2) a long inner olefin underwent metathesis on
7 wt% Re2O7/meso-Al2O3 under mild conditions (at 50 ꢁC) to
reach its chemical equilibrium without the formation of any side
products such as olefinic isomers and polymers of 7-hexadecene.
Olefin metathesis is an intriguing reaction in terms of not only
the reaction mechanism but also its practical application to
chemicals synthesis in chemical industry. Since the discovery of
olefin metathesis, a variety of homogeneous and heterogeneous
catalyst systems for metathesis have been developed.1 Especially
for the last seven years, rutheniumcarbene complexes have been
focused on as powerful homogeneous catalysts for elaborate
syntheses of pharmaceuticals and polymers with various func-
tional groups.2 By contrast to such marvelous development of
homogeneous catalysts, finding new efficient heterogeneous
catalysts for metathesis has been stagnant.
The discovery of FSM-163 and the M41S family4 of
mesoporous molecular sieves with uniform nanometer-sized
pores has stimulated interest in the potential use of these materials
as catalyst and catalyst support. In our previous study, we found
that MoO3 supported on mesoporous HMS silica5 with a narrow
pore-size distribution centered at 2 nmshowed much higher
catalytic activity for metathesis of 1-octene in a liquid phase than
MoO3 on commercial SiO2.6 In our continuous efforts to develop
more effective heterogeneous catalysts for liquid-phase olefin
metathesis than MoO3 on mesoporous silica, we next focused on
mesoporous alumina-supported rhenium oxide, because rhenium
oxide has been known as a more active species for metathesis than
molybdenum oxide, and mesoporous aluminas with homoge-
neous pores and high surface area have just been developed by
Davis7 and Pinnavaia.8 As compared with mesoporous silica,
mesoporous alumina has not been put to practical use in catalytic
organic reactions. In this communication we report how rhenium
oxide fixed on the surface of mesoporous alumina is different in
liquid-phase olefin metathesis from rhenium oxide on conven-
tional ꢀ-alumina.
Figure 1. Metathesis of 7-hexadecene to 7-tetradecene
and 9-octadecene catalyzed by rheniumoxide supported
on mesoporous alumina and ꢀ-alumina. (l): 7 wt%
Re2O7/meso-Al2O3, (s): 7 wt% Re2O7/ALO-7.
Figure 2 shows the metathesis of more reactive terminal
olefin, 1-octene (1b) at a lower temperature of À1 ꢁC by use of
7 wt% Re2O7/meso-Al2O3 and two control catalysts of 2.1 and
7 wt% Re2O7/ALO-7. In the metathesis of 1-octene, 7 wt%
Re2O7/meso-Al2O3 revealed better performance in the reaction
rate and the selectivity to 7-tetradecene than the control
catalysts.12 It was reported that rheniumoxide supported on
À
alumina was present as monomeric surface ReO4 species,
13
Mesoporous alumina (designated as meso-Al2O3) was
prepared according to Davis’ procedure.9 The prepared meso-
Al2O3 had specific surface area of 564 m2/g, a narrow pore-size
distribution centered at 3 nm, and pore volume of 0.485 ml/g.
Re2O7-supporting meso-Al2O3 was prepared by impregnation of
the meso-Al2O3 with an ammonium perrhenate solution.10 As a
control catalyst, Re2O7 was also supported on typical ꢀ-alumina
provided by the Catalysis Society of Japan: JRC-ALO-7 (specific
independent of the rheniumloading. Interestingly, a compar-
ison of the metathesis activity among 3.5, 7, and 15 wt% Re2O7/
meso-Al2O3 disclosed that the highest activity was attained at
7 wt% Re loading, which was inconsistent with the previous
report in which the activity increased with the loading amount of
Re2O7 up to ꢂ18 wt%.14 2.1 wt% Re2O7/ALO-7, which has the
same rhenium oxide density on the alumina surface as 7 wt%
Re2O7/meso-Al2O3, showed almost the same catalytic activity as
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
851
References and Notes
1
K. J. Ivin and J. C. Mol, in ‘‘Olefin Metathesis and Metathesis
Polymerization,’’ Academic Press, San Diego (1997); J. C. Mol,
Catal. Today, 51, 289 (1999).
2
3
R. H. Grubbs, S. J. Miller, and G. C. Fu, Acc. Chem. Res., 28, 446
(1995).
T. Yanagisawa, T. Shimizu, K. Kuroda, and C. Kato, Bull. Chem.
Soc. Jpn., 63, 988 (1990); S. Inagaki, A. Koiwai, N. Suzuki, Y.
Fukushima, and K. Kuroda, Bull. Chem. Soc. Jpn., 69, 1449 (1996).
C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, and J. S.
Beck, Nature, 359, 710 (1992).
4
5
T. R. Pauly, Y. Liu, T. J. Pinnavaia, S. J. L. Billinge, and T. P.
Rieker, J. Am. Chem. Soc., 121, 8835 (1999).
Figure 2. Metathesis of 1-octene to 7-tetradecene and ethylene
catalyzed by rhenium oxide supported on mesoporous alumina and ꢀ-
alumina. (l): 7 wt% Re2O7/meso-Al2O3, (s): 7 wt% Re2O7/ALO-7,
(4): 2.1 wt% Re2O7/ALO-7. (a) Changes in the conversion of 1-octene,
(b) the selectivity to 7-tetradecene.
6
7
T. Ookoshi and M. Onaka, Chem. Commun., 1998, 2399.
F. Vaudry, S. Khodabandeh, and M. E. Davis, Chem. Mater., 8,
1451 (1996).
P. T. Tanev, M. Chibwe, and T. J. Pinnavaia, Nature, 368, 321
(1994).
A solution of dodecanoic acid (53.9 mmol) in 1-propanol (195 ml)
was added to a solution of Al(O-s-Bu)3 (178 mmol) in 1-propanol
(30 ml) and deionized water (10 ml), and the mixture was
vigorously stirred for 24 h at room temperature. Then, the mixture
was transferred into a 300 ml-autoclave, and aged at 110 ꢁC for 48 h.
The resulting gel was filtered, washed with EtOH (300 ml), and
dried in N2 for 12 h. The gel (2.0 g) was set in an electric furnace,
gradually heated to 600 ꢁC at a ramping rate of 9.6 ꢁC/min in N2,
and finally calcined at 600 ꢁC for 4 h in dry air to give mesoporous
alumina.
8
9
7 wt% Re2O7/ALO-7 with a little improvement in selectivity to 7-
tetradecene. The solvent also affected the rate of the metathesis of
1-octene catalyzed by Re2O7/meso-Al2O3: the reaction in
heptane was 1.5 times faster than that in benzene.
The scanning electron micrographs (SEM) indicated that the
meso-Al2O3 was made up of small alumina particles of 100–
300 nmin diameter, while ALO-7 showed the formof
agglomerates.
10 The preparation of 7 wt% Re2O7 supporting meso-Al2O3 (desig-
nated as 7 wt% Re2O7/meso-Al2O3) was as follows: The meso-
Al2O3 (1.0 g) was immersed in a solution of NH4ReO4 (0.31 mmol)
in deionized water (5 ml), and the suspension was gradually dried
up at roomtemperature for 12 h in N 2. After complete evaporation
of the water, deionized water (5 ml) was added to the solid sample,
and the drying procedure was repeated. The supported sample was
then set in an electric furnace and heated in dry air to 600 ꢁC at a
ramping rate of 6.9 ꢁC/min, and finally calcined at 600 ꢁC for 4 h to
give 7 wt% Re2O7/meso-Al2O3.
On both the transmission electron micrographs (TEM) of
7 wt% Re2O7/meso-Al2O3 and 7 wt% Re2O7/ALO-7 we could
not observe any rheniumoxide particles on the surface of the
alumina supports. In addition, no diffraction patterns specific to
Re2O7 crystals were found in both the catalysts by powder X-ray
diffractometry. Combined, these analytical results imply that the
rheniumoxide was finely dispersed on the surface of meso-Al O3
2
and ALO-7.
Then, the structures of dispersed rheniumoxide on meso-
Al2O3 and ꢀ-alumina (ALO-7) were compared by extended X-
ray absorption fine structure (EXAFS) and X-ray absorption near-
edge structure (XANES) spectroscopy.15 Unfortunately, no
difference in Re–O distances between the two catalysts was
observed fromthe data of EXAFS. Both the rheniumions on
meso-Al2O3 and ALO-7 were identified as tetra-coordinated
11 As activation of the Re catalyst, Re2O7/meso-Al2O3 (0.6 g
(C16H32), 0.3 g (C8H16)) put in a 30 ml flask was heated to 500 ꢁC
at a ramping rate of 7.9 ꢁC/min, and finally at 500 ꢁC under 0.6 Torr
(1 Torr ꢃ 133:322 Pa) for 2 h. After cooling to roomtemperature
under evacuation, the flask was filled with N2. After the addition of
n-heptane solvent (5 ml) to the catalyst, the metathesis was run at
50 ꢁC (C16H32) or À1 ꢁC (C8H16) by introducing alkene (5.0 mmol
(C16H32), 7.9 mmol (C8H16)) into the flask in N2. After a specified
time, the solid catalyst was filtered and washed with hexane (15 ml).
The combined filtrate was analyzed with a gas chromatograph using
an internal standard (n-decane). The geometrical isomer ratios of
olefin products isolated through fractional distillation were
determined by NMR.
À
ReO4 ions based on XANES.
Although the structural uniqueness of Re2O7/meso-Al2O3
has not been fully elucidated, we speculate that the intermediate
oxidation state of rheniumspecies, which is necessary for the
propagation of the metathesis reaction,1 could be more stabilized
and maintained by the framework of mesoporous alumina than
that of ꢀ-alumina, and so that the rate and selectivity of the
metathesis reactions could be enhanced.16
12 The amount of rhenium oxide included in each catalyst was
adjusted to be the same. Cis/trans ratios of 7-tetradecene produced
were 0.22 on 7 wt% Re2O7/meso-Al2O3, 0.23 on 7 wt% Re2O7/
ALO-7, and 0.23 on 2.1 wt% Re2O7/ALO-7.
13 F. P. J. M. Kerkhof, J. A. Moulijn, and R. Thomas, J. Catal., 56, 279
(1979).
14 F. Kapteijn, L. H. G. Bredt, and J. C. Mol, Recl. Trav. Chim. Pays-
Bas, 96, 139 (1977).
15 A. S. Fung, P. A. Tooley, M. J. Kelley, D. C. Koningsberger, and B.
C. Gates, J. Phys. Chem., 95, 225 (1991).
16 When Re2O7 was supported on mesoporous silica, the catalyst
showed no metathesis of 1-octene. This is due to the sublimation of
Re2O7 fromSiO 2 during the calcination at 600 ꢁC in preparation of
the catalyst. With mesoporous aluminosilicate (Al-HMS)-doped
Re2O7 the metathesis of 1-octene took place. However, the
isomerization of olefin competed against the metathesis owing to
the acidic character of Al-HMS, and the selectivity to 7-
teteradecene drastically fell to 3.5%.
In summary, rhenium oxide finely dispersed on mesoporous
alumina with uniform pore size of 3 nm was a more active and
selective catalyst for metathesis of terminal and inner olefins in a
liquid phase than rheniumoxide on normal ꢀ-alumina. Rhenium
oxide on meso-Al2O3 was found more efficient in metathesis than
that on ꢀ-alumina when ReO4À was fixed on the alumina surface
with the same Re ion density.
We thank Prof. Seitaro Namba of Teikyo University of
Science and Technology for SEM and TEM measurements, and
Prof. Tsunehiro Tanaka and Dr. Takashi Yamamoto of Kyoto
University for the EXAFS experiments and helpful discussions.