Table 2 Catalytic properties of catalysts
DIPN selectivity (mol%)
Catalyst
Conv.a (mol%) DIPN yield (mol%)
2,6
2,6+2,7
Otherb
Other productsc (mol%)
AlClx/MCM-41
AlClx/MCM-41(ESM)
AlCl3
H/MCM-41
H/Mordenite
88.5
85.2
96.4
60.4
84.8
65.5
72.3
56.3
38.4
44.5
41.0
60.9
36.7
38.6
44.3
2.20
2.82
0.986
1.64
2.00
40.4
17.5
26.1
37.9
33.6
34.3
27.7
43.7
61.6
55.4
a Conversion of naphthalene. b Other DIPN isomers. c Other products except DIPNs including MIPN, tri-, and tetra-IPNs, etc.
mm). Product identification was carried out using a GC/MS
system. Comparisons of the catalytic performance of the
catalysts are summarized in Table 2.
ride species had hardly changed. It was also observed that both
the activity and selectivity towards 2,6-DIPN remained un-
changed.
Table 1 shows that both the pure-silica and the aluminosili-
cate MCM-41 materials are of high quality with a pore diameter
of 3.0 nm. As expected, immobilization of aluminium chloride
on MCM-41 silica resulted in a reduction of surface area, pore
volume, and pore diameter. The chemical analysis data further
prove the attachment of aluminium chloride on the surface of
the MCM-41 silica. The Al contents analyzed using ICP-AES
are consistent with that analyzed using XPS.
Overall, the results discussed above demonstrate that im-
mobilization of aluminium chloride on mesoporous MCM-41
silica can create substantial density of acidic sites, which are
catalytically responsible for the liquid-phase isopropylation of
naphthalene. Most remarkably, a significant increase in se-
lectivity towards 2,6-DIPN can be achieved through the use of
external surface-silylated MCM-41 support. The immobilized
catalyst system is recyclable and reusable without observable
loss in activity and selectivity, demonstrating its promise as an
environmentally friendly alternative catalyst for the isopropyla-
tion of naphthalene.
We thank the University of Queensland for partial financial
support and the Australian Academy of Science for traveling
support (via the program Scientific Visit to North America for
Young Australian Scientists). X. S. Z. wishes to acknowledge
Ms Lim Hwee Ling for her help during manuscript revision.
It can be seen from Table 2 that the highest activity was
observed on AlCl3 while the lowest activity was observed on H/
MCM-41. The two immobilized catalysts exhibit a reasonable
catalytic activity, similar to that of H/Mordenite. Despite a
slightly lower activity for catalysts AlClx/MCM-41 and AlClx/
MCM-41(ESM) compared to AlCl3, there are significant
differences in the yield and selectivity of products. With AlClx/
MCM-41 and AlClx/MCM-41(ESM) as the catalysts, DIPNs
were the major products, whereas the other catalysts produced
a large amount of other products. Very remarkably, AlClx/
MCM-41(ESM) catalyzed the formation of 72.3% DIPNs with
a selectivity of 2,6-DIPN of 60.9% while AlClx/MCM-41
produced 65.5% DIPNs with a selectivity of 2,6-DIPN of
41.0%. The significant enhancement of selectivity towards
2,6-DIPN after modification of the external surface of the
MCM-41 support is explicable only in terms of the differences
in the pore-opening size and the nature of the external surfaces
of the two catalysts. The selective modification of the external
surface of the MCM-41 support resulted in a reduction of the
pore-opening size (see Table 1) and the poisoning of the
external catalytically active sites. The former probably enabled
shape-selectivity while the latter led to the avoidance of the
catalytic reaction taking place on the external surface of the
AlClx/MCM-41(ESM) catalyst.
Notes and references
† The IUPAC name for cetyl is hexadecyl.
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After the 4 h reaction, catalyst AlClx/MCM-41(ESM)† was
filtered off, washed with hot benzene and calcined at 450 °C for
2 h. Subsequent characterization using 27Al NMR and catalytic
tests were carried out. The chemical shifts of 27Al before and
after the 4 h reaction were found to be about 53.0 and 52.2 ppm,
respectively, indicating that the immobilized aluminium chlo-
Chem. Commun., 2001, 2306–2307
2307