Remarkable enhancement of catalytic activity of FSM-16 by modification with ammonium sulfate for acid-catalyzed reactions

Article abstract of DOI:10.1246/cl.2000.604

Impregnation of FSM-16 with ammonium sulfate followed by optimized thermal pretreatments, especially by evacuation, leads to a remarkable enhancement in the catalytic activity of FSM-16 for acid-catalyzed reactions.

Full text of DOI:10.1246/cl.2000.604

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Chemistry Letters 2000
Remarkable Enhancement of Catalytic Activity of FSM-16 by Modification with Ammonium
Sulfate for Acid-Catalyzed Reactions
†
John Kwaku Adu Dapaah, Yoshio Uemichi, Akimi Ayame, Hiromi Matsuhashi, and Masatoshi Sugioka*
Department of Applied Chemistry, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585.
†
Department of Science, Hokkaido University of Education, Hachiman-cho, Hakodate 040-8567.
(Received February 17, 2000; CL- 000165)
Impregnation of FSM-16 with ammonium sulfate followed
by optimized thermal pretreatments, especially by evacuation,
leads to a remarkable enhancement in the catalytic activity of
FSM-16 for acid-catalyzed reactions.
Recently, the synthesis of new materials such as MCM-
1, FSM-16, SBA-15, HMS, etc. has become the focus of
1
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considerable interest. In view of the fact that these mesoporous
materials exhibit relatively low acidity and as such insufficient
activity for acid-catalyzed reactions, it is highly desirable to
generate active acid sites. So far, the main mode for achieving
this aim has been the isomorphous substitution of framework
1
5
6
silicon with heteroatoms such as Al, Ga, Fe, and so on. In
addition, the method of grafting of various active moieties such
as metal alkoxides onto mesoporous silica surface has been
reported.7
In our previous work, a novel route for transforming
mesoporous silica FSM-16 into an active catalyst by sulfiding
8
with hydrogen sulfide after metal ion-exchange was reported.
We have also reported the remarkable enhancement of FSM-16
for 1-butene isomerization by the modification with iron (II)
sulfate.9 In this study, we report on the catalytic activity
enhancement of FSM-16 by modification with ammonium sul-
fate for acid-catalyzed reactions.
tion of cyclopropane.
The TG/DTA profiles recorded for the unsupported
[NH ] SO , FSM-16 and [NH ] SO /FSM-16 are presented in
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4 2
4
Figure 2. The TG profile for [NH ] SO reveals two steps of
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o
weight losses, one around 300 C and the other near 400 °C.
The first step, which is accompanied by an endothermic DTA
peak, can be attributed to the evolution of the ammonia from
[NH ] SO . The second step mainly involves the decomposi-
The [NH ] SO /FSM-16 catalyst was prepared by impreg-
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nating FSM-16 with a solution of ammonium sulfate to obtain a
wt% [NH ] SO loaded sample. The sample was then dried
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4 2
4
at 100 °C for 2 h followed by two pretreatment methods (viz: A
and B). Method A involved calcination at 100-500 °C for 3 h
in air, while in method B, the catalyst was evacuated at 200-500
tion of the sulfate anion. The TG profile for FSM-16 shows a
weight loss below 120 °C which is due to the desorption of
°
C for 2 h after calcination at 200 °C. Isomerization of 1-
butene and cyclopropane were conducted in a closed-circulation
reactor system made of Pyrex glass at 25 °C and 100 °C,
respectively. In both cases, the initial pressure of reactant was
4
0 Torr (5.33kPa) while the catalyst weight was 50 mg.
Product analysis system consisted of a gas chromatograph
equipped with a TCD and a 4 m propylene carbonate column
cooled at 0 °C. Thermogravimetric/differential thermal analy-
sis (TG/DTA) and infrared (IR) spectroscopy of adsorbed pyri-
dine were employed for characterization of the catalysts.
The catalytic activities of [NH ] SO /FSM-16 (A and B)
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for 1-butene isomerization are shown in Figure 1. It can be
observed that the catalysts prepared by method A exhibit maxi-
mum activity after calcination at 300 °C which is comparable to
those of FSM-16. On the other hand, a remarkable increase in
activity of catalysts prepared by method B was seen after
evacuation at 300 °C and it was quite close to the value
obtained for the FeSO /FSM-16 described in our previous
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paper.9 Almost similar results were obtained in the isomeriza-
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
605
adsorbed water. The supported sample exhibits an initial loss in
weight similar to that of FSM-16, but it shows further decrease
in weight as the temperature increases. It is evident that the rate
of weight loss above 300 °C is much more slower for
[NH ] SO /FSM-16. It was observed that in both cases (i.e., for A
and B) the Brønsted acid band was much more intense than the
Lewis acid band.
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Among the method B catalysts, the sample evacuated at 300
C exhibited the largest Brønsted acid peak. This sample also
o
[
NH ] SO /FSM-16 than the unsupported [NH ] SO . This
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4 2
4
indicates the relatively gradual decomposition of the salt in the
supported form.
showed a relatively larger peak than its counterpart prepared by
method A. These observations are partially in correlation with the
catalytic activity for the 1-butene isomerization reaction especially,
for the samples pretreated at 300 °C and above.
Figure 3 depicts the IR spectra of [NH ] SO /FSM-16 (A
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1
and B). Absorption bands in the 1400-1415 cm region were
observed for both A and B samples thermally pretreated at 200-
Calcination of [NH ] SO /FSM-16 at 200 °C followed by
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o
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00 °C. These bands are assignable to the asymmetric stretching
evacuation at 300 C markedly leads to enhanced catalytic activity
for 1-butene and cyclopropane isomerization. Similar to our previ-
10
vibration of S=O bond of the sulfate species. The sample cal-
9
cined at 100 °C shows a very broad band centred around 1443
ous report, it is assumed that the high activity is due to sulfate
-
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-1
cm , while a similar band is observed at 1437 cm . The bands
species so produced which interact with the SiOH group of FSM-
16 and transform them into Brønsted acid sites by their inductive
effect.
The authors wish to thank Toyota Central R&D Labs. Inc.,
Japan, for the kind provision of FSM-16.
+
11
may be attributed to the bending vibration band of NH . This
4
assignment is supported by the presence of broad bands in the
-1
3
000-3300 cm region (spectra not shown) associated with the
N-H stretching vibrations. It was noted that increasing calcina-
tion temperature caused the disappearance of the broad band
-1
while the 1400 cm region bands appeared. This can be related
to the gradual decomposition of the supported salt which pro-
ceeds by initial removal of ammonia. The S=O peak intensity
reached a maximum at 300 °C, after which it sharply decreased
in the case of the method A catalysts. As shown, after calcina-
tion at 500 °C, no visible peak ascribed to sulfate species is
observed.
References
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4
2
4
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4
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4
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2-
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Figure 4 shows the spectra of adsorbed pyridine on (method
A and B) catalysts after pyridine desorption by evacuation at 100
-
°
C for 30 min. Bands were observed at 1547, 1490 and 1446 cm
0
1
-1
in both cases. The 1547 cm peak is attributed to the pyridini-
-1
um ion associated with Brønsted acid site whilst 1446 cm corre-
sponds to coordinated pyridine at Lewis acid site. Thus both
Brønsted acid sites and Lewis acid sites are present on
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