Preparation of an MCM-41/Nafion® composite material; a selective catalyst for
-methylstyrene dimerization
Masahiro Fujiwara,* Koji Kuraoka, Tetsuo Yazawa, Qiang Xu, Mutsuo Tanaka and Yoshie Souma
Osaka National Research Institute (AIST-MITI), 1-Midorigaoka, Ikeda, Osaka 563-8577, Japan.
E-mail: fujiwara@onri.go.jp
Received (in Cambridge, UK) 16th June 2000, Accepted 29th June 2000
Published on the Web 21st July 2000
A MCM-41/Nafion® composite prepared from tetraethoxy-
silane and Nafion gel solution with cetyltrimethylammon-
ium surfactant, is a highly selective catalyst for -methyl-
styrene dimerization to form the corresponding acyclic
dimer.
2.8 nm in accord with an organically modified MCM-41.2 The
minor pore type had a diameter of 3.8 nm and corresponded to
MCM-41.1 From the IR spectrum, it was confirmed that the
template was removed because of the absence of alkyl
adsorptions of the template around 2900 cm21. All these results
indicate that the preparation of the MCM-41/Nafion composite
was successful.
The synthesis of mesoporous materials is one of the most
important subjects in modern chemistry. MCM-41 obtained by
the utilization of surfactant micelles1 is actively studied for
applications to catalysts. Recently organically modified MCM-
41 materials using alkyl-substituted silane compounds have
been prepared for use as catalysts and other applications.2 On
the other hand, DuPont has recently reported amorphous silica/
Nafion composites which were effective solid acid catalysts.3 It
is thought that the combination of the new technology for
fabricating mesoporous materials and Nafion resin creates a
novel class of functional solid acid materials.4 Here, we report
the first preparation (to our knowledge) of a MCM-41/Nafion
composite material and its applications as a solid acid
catalyst.
The MCM-41/Nafion composite was obtained by the follow-
ing procedure; 0.1 g of Nafion gel obtained from a 5% Nafion
solution (Aldrich) in ethanol was dissolved in 1.5 mL of
ethanol. This solution was added slowly to a mixture of
tetramethylammonium hydroxide (8 mmol) and cetyltrimethyl-
ammonium bromide (4.5 mmol) in distilled water (15 mL) with
vigorous stirring. Then, tetraethoxysilane (30 mmol) was added
dropwise with stirring to the resulting mixture. Finally, the
mixture was transferred to a Teflon beaker and crystallized in a
stainless steel autoclave at 130 °C under autogeneous pressure
for 24 h. The white solid obtained was washed twice with 200
mL of distilled water and dried at 60 °C. The removal of the
template and acidification of the Nafion resin were performed
by refluxing in concentrated sulfuric acid (3 mL) in ethanol (300
mL) for 18 h. After two further refluxes in ethanol (300 mL), the
recovered solid was dried at 150 °C for 20 h.
This novel composite material was applied to the dimeriza-
tion of a-methylstyrene (AMS) to produce the corresponding
acyclic dimer, 4-methyl-2,4-diphenylpent-1-ene 1, which is a
chain transfer agent amongst other uses.5 Although this reaction
using solid sulfuric acid has been actively studied,5 the
significant side reaction to form the cyclic dimer, 1,1,3-trime-
thyl-3-phenylindan 3, often results in low production of 1
(Scheme 1). The yields of the desired dimer 1 [Fig. 2(a)] and of
the undesired dimer 3 [Fig. 2(b)] as a function of time are shown
using the MCM-41/Nafion composite, as well as for Nafion
NR-50, Nafion SAC-13 (silica/Nafion composite),3 Amber-
lyst® 15 (all obtained from Aldrich) and Al-MCM-41.6†
Although SAC-13 and Amberlyst 15 had high activity, the
yields of 1 drastically decreased with time and substantial
increases of the bicyclic dimer 3 were observed. For NR-50, the
reaction rate was quite slow as reported3 and 3 was formed in
considerable yield even at a low conversion of AMS. On the
other hand, when the MCM-41/Nafion composite was used, the
yield of 1 was about 70% and scarcely decreased with reaction
time. Furthermore, the formation of 3 was low even after 1000
min. This high selectivity shown by the MCM-41/Nafion
composite is not simply derived from the mesoporous channel
structure since 3 was obtained in high yield using Al-MCM-41
which was reported as an acid catalyst.6 Furthermore, other
types of MCM-41/Nafion composite obtained from impregnat-
ing Nafion solution to MCM-417 also afforded 3 in 30% yield
with a lower yield of 1 (25%) after 300 min. As expected,
MCM-41 itself (silica material without Nafion resin or other
metals) showed no activity for this dimerization under our
conditions (no conversion of AMS even after 1500 min). Thus,
the MCM-41/Nafion composite prepared in this work was an
excellent catalyst to produce 1 via the dimerization of AMS.
Fig. 1 shows the XRD pattern of the MCM-41/Nafion
composite obtained.† A clear peak at 2q = 2.15° was observed
which was assigned to the (100) reflection of MCM-41 type
materials.1 The (110) and (200) reflections from MCM-41
appeared as broad peaks at 2q ≈ 4.1°. The BET surface area and
pore volume were estimated at 619 m2 g21 or 0.64 cm3 g21
,
respectively. The diameter of the main pore type (ca. 90%) was
Scheme 1
The low yield of 3 for our MCM-41/Nafion composite
suggests poor catalytic activity for Friedel–Crafts reactions.8
The conversion of 1 to 3 at 60 °C scarcely proceeded with the
MCM-41/Nafion composite (3% after 24 h), whereas SAC-13
considerably catalyzed this reaction (17% after 6 h and 56%
Fig. 1 X-Ray diffraction pattern of the MCM-41/Nafion composite.
DOI: 10.1039/b004842i
Chem. Commun., 2000, 1523–1524
This journal is © The Royal Society of Chemistry 2000
1523