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Conversion of propane into butanes catalyzed by sulfated zirconia mixed with
Pt/ZrO2
Makoto Hinoa and Kazushi Arata*b
a Hakodate Technical College, Tokura-cho, Hakodate 042-8501, Japan
b Department of Science, Hokkaido University of Education, Hachiman-cho, Hakodate 040-8567, Japan.
E-mail: karata@hak.hokkyodai.ac.jp
Received (in Cambridge, UK) 21st September 1998, Accepted 17th November 1998
An active catalyst for the conversion of propane into butanes
is obtained by mechanically mixing sulfated ZrO2 and Pt/
ZrO2.
The reaction of propane (C3) was carried out at 200 °C and 20
ml min21 of He carrier over 0.3 g of SO4/ZrO2, but the
conversion was only 0.1%. The addition of platinum (0.5 or 2
wt%), Pt-SO4/ZrO2 (0.3 g), was ineffective even at 250 °C as
shown in Table 1. The addition of Pt was, however, effective
when Pt/ZrO2 was mechanically mixed with SO4/ZrO2. A
mixture of 0.3 g of SO4/ZrO2 and 0.3 g of 0.5 wt% Pt/ZrO2,
where the Pt quantity was equivalent to that in 0.3 g of 0.5 wt%
Pt-SO4/ZrO2, gave 3.2% conversion. The major product was
butanes (C4); trace amounts of pentanes (C5) were observed in
addition to ethane (C2) and methane (C1). Dehydrogenated
materials were not observed, though ethylene and propylene
were formed over Fe–Mn-sulfated ZrO2.5,6
Among conversion of light alkanes by cracking, coupling, or
isomerization in heterogeneous catalytic sytems much attention
has been focused on the coupling of methane, but the catalytic
systems still require high temperatures to obtain satisfactory
activity and selectivity.1 Sulfated zirconia and related catalysts
have received attention because of their high activities for
butane isomerization.2,3 Cheung and Gates tested Fe–Mn-
promoted sulfated ZrO2 for conversions of ethane and propane,
but conversions were low, being only 0.6% for the highest
propane conversion observed at 300 °C.4–6 We have demon-
strated that impregnation of sulfated ZrO2 with noble metals
such as Pt and Ir leads to pronounced activity for butane
conversion, the Pt concentration being 7–8 wt%; the catalyst
with Pt showed highest activity for the reaction.7,8 These noble
metal-added sulfated zirconias were applied to propane, but the
conversions were still low. However, the conversion was found
to be promoted by simply mechanically mixing Pt-supported
zirconia (Pt/ZrO2) with sulfated zirconia (SO4/ZrO2).
SO4/ZrO2 and 0.5 wt% Pt/ZrO2 catalysts were prepared as
described elsewhere.3,8,9 The thus-prepared catalysts, 0.3 g
SO4/ZrO2 and 0.3 g Pt/ZrO2, were mixed well by kneading with
a mortar and pestle. Other catalysts of sulfated Al2O3, TiO2, and
Fe2O3, together with WO3/ZrO2, were prepared as described
elsewhere.9
Reactions of propane were carried out in a microcatalytic
pulse reactor as described elsewhere.8 The catalyst was heated
at 300 °C for 1 h in an He flow before reaction. A slightly
continual gain of conversion was observed with pulse number,
and thus conversions were calculated on the basis of mol
fraction as the average of the 6th–10th pulse values.
The catalysts were then examined in butane; the Pt co-
c
impregnated catalyst, Pt–SO4/ZrO2 in Table 1, gave 48%
conversion for the first pulse at 80 °C (catalyst amount: 0.1 g),
while the mixture of SO4/ZrO2 and Pt/ZrO2 only gave 8%
conversion. Thus, the catalyst which is effective for butane is
not efficient for propane and vice versa.
The effect of mixing was examined further at temperatures of
225 and 250 °C; the yields of C4 were ≈ 4% with higher
conversions of C3, but showing lower selectivity for the
formation of C4 (Table 1). In terms of preparation temperature
of the catalysts the highest activity was observed upon
calcination at 600 °C for SO4/ZrO2 and 750°C for Pt/ZrO2.
The effect of modifying the proportion of platinum in the
catalyst was studied. Catalysts with 0.6 and 1.2 g of Pt/ZrO2
showed 4.2 and 4.6% propane conversion at 200 °C, with 3.4
and 3.1% C4 yields, respectively. This indicates that the effect
of concentration of platinum is relatively small. In terms of
isomers of C4 the selectivity for isobutane was 60–65% in each
case.
The effect of mixing of Pt/ZrO2 for the reaction of propane
was examined for other sulfated metal oxides, Al2O3, TiO2, and
Fe2O3 in addition to WO3/ZrO2, the acidities of which are lower
relative to SO4/ZrO2.3 These materials showed a noticeable
effect upon mixing for the conversion reaction of butane to
isobutane.9,10 Remarkable conversions of C3 over these sub-
stances mixed with Pt/ZrO2 were obtained at 250 °C, but the
yield of C4 was low, at most 0.1%. Thus, high superacidity is
needed to form C4 products.
XPS experiments were carried out in order to elucidate the
surface properties of Pt/ZrO2. The binding energy of Pt 4f was
72.6 eV, which was far from that of the metallic state (71.7 eV),
but close to that of cationic Pt species.11
The formation of higher molecular weight alkanes is brought
about by catalysis of the cracking ability in addition to the
protonation of propane by a superacid to form a carbonium ion.5
This behavior was also shown by the formation of propane from
ethane in the present system, although the yield was low
(Table 1).
Table 1 Activities of the catalysts for the reaction of propane
Products (%)
Conversion
Catalyst
T/°C (%)
C1
C2
C4
C5
SO4/ZrO2
Pt–SO4/ZrO2
Pt–SO4/ZrO2
200
200
250
200
200
200
225
250
250
250
250
250
250
300
0.1
0.2
0.3
3.2
4.2
4.6
6.1
10.6
8.4
8.9
Tra
0
Tr
Tr
Tr
Tr
0.1
0.2
0
0
0
Tr
Tr
0
0.1
0.1
0
0
0
0
0
b
c
0.2 0.1
0.2 3.0
0.7 3.4
1.2 3.1
1.6 4.1
4.9 3.8
6.3 Tr
6.4 0.1
9.4
10.7
0.3g
0.1g
SO4/ZrO2–Pt/ZrO2
SO4/ZrO2–Pt/ZrO2
SO4/ZrO2–Pt/ZrO2
SO4/ZrO2–Pt/ZrO2
SO4/ZrO2–Pt/ZrO2
SO4/Al2O3–Pt/ZrO2
SO4/TiO2–Pt/ZrO2
SO4/Fe2O3–Pt/ZrO2
WO3/ZrO2–Pt/ZrO2
d
e
0.1
0.3
0.3
1.8
2.1
2.4
3.9
3.3
5.5
16.2
13.3
14.0
5.8
0
0
0
0
f
SO4/ZrO2–Pt/ZrO2
SO4/ZrO2-Pt/ZrO2
f
16.3
0
Notes and references
1 E. N. Voskresenskaya, V. G. Roguleva and A. G. Anshits, Catal. Rev.-
Sci. Eng., 1995, 37, 101.
a
b,c
Trace. Prepared by sulfation of zirconia gel followed by platinization
and calcination (b 0.5, c 2 wt% Pt). d,e Reaction with d 0.6 or e 1.2 g of 0.5%
Pt/ZrO2 and 0.3 g of SO4/ZrO2. f Reaction of ethane. g Yield of C3.
2 X. Song and A. Sayari, Catal. Rev.-Sci. Eng., 1996, 38, 329.
Chem. Commun., 1999, 53–54
53
Hino, Makoto
