Sulfated zirconia-supported palladium as a highly active and highly selective catalyst for the oxidation of ethylene in the vapor phase

Article abstract of DOI:10.1246/cl.2009.222

Pd supported on sulfated zirconia with a S/Zr ratio of 0.077 exhibited high activity and high selectivity for the oxidation of ethylene to partially oxidized products, including acetaldehyde and acetic acid, in the vapor phase. Copyright

Full text of DOI:10.1246/cl.2009.222

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Chemistry Letters Vol.38, No.3 (2009)
Sulfated Zirconia-supported Palladium as a Highly Active and Highly Selective Catalyst
for the Oxidation of Ethylene in the Vapor Phase
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Tomoaki Hamada, Yoshinori Sakamoto, Yasunobu Ooka, Toshio Okuhara, and Yuichi Kamiya
1
Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810
Research Faculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810
2
(Received December 19, 2008; CL-081196; E-mail: Kamiya@ees.hokudai.ac.jp)
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1
Pd supported on sulfated zirconia with a S/Zr ratio of 0.077
solid was calcined at 673 K for 5 h at a heating rate of 2 K min
Other catalysts (Table 1) were prepared according to previously
.
exhibited high activity and high selectivity for the oxidation of
ethylene to partially oxidized products, including acetaldehyde
and acetic acid, in the vapor phase.
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reported methods.
The oxidation of ethylene was performed in a fixed-bed flow
reactor (stainless steel SUS 317, inner diameter = 10 mm). The
catalyst (2 cm , 60–80 mesh) was pretreated in the reactor at
573 K for 1 h in a 1:1 mixture of H2 and He at a flow rate of
60 cm min . After cooling in a He flow to the reaction temper-
ature of 423 K, the reactant gas (C2H4:O2:H2O:He = 50:7:30:13
in vol %) was fed into the reactor at a total flow rate of 100 cm
3
Catalysts combining a solid acid with a precious metal, such
as Pt and Pd, are often called bifunctional catalysts and show an
3
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1
excellent performance for the skeletal isomerization of alkanes.
3
Over this type of catalyst, the metal sites promote dehydrogen-
ation and hydrogenation, and the skeletal isomerization of the
corresponding carbenium ion occurs at the acid sites. That is,
the precious metal and solid acid separately catalyze the respec-
tive reactions. In fact, a catalyst composed of a physical mixture
of a solid acid and a precious metal shows a catalytic perform-
ance similar to or higher than that of the corresponding solid
ꢁ1
ꢁ1
min (SV = 3000 h ) and a total pressure of 0.6 MPa. The
effluent gas was introduced into a trap kept at 200 K in order
to liquefy and collect the products. The liquefied products were
analyzed by using a gas chromatograph with a flame ionization
detector (GC-FID, Simadzu 8A) and a Porapak QS column. The
gaseous products that passed through the trap were analyzed by
using an on-line gas chromatograph (Aera, Micro GC M200).
The results for the different catalysts are summarized in
Table 1, in which STY represents the space time yield of the
sum of the partially oxidized products (POxP), including acetic
acid and acetaldehyde. Pd/Cs2:5H0:5PW12O40, Pd/MoO3–ZrO2,
Pd/Nb2O5, Pd/SiO2–Al2O3, Pd/H-ꢀ, and Pd/H-mordenite gave
only low STYs and/or low selectivities for the reaction. Pd–
H4SiW12O40/SiO2 showed decent selectivity for POxP (70%),
but the STY was moderate. On the other hand, Pd/SO4–ZrO2
gave a significantly high STY per unit volume as well as unit
weight of the catalyst. In addition, the formation of COx was
remarkably suppressed over Pd/SO4–ZrO2 (selectivity for COx
was only 6%), meaning that Pd/SO4–ZrO2 exhibited the highest
selectivity for POxP (94%) among the catalysts examined. Al-
though we have shown that Pd/WO3–ZrO2 shows high activity
2
acid-supported precious metal catalyst.
On the other hand, we have recently proposed a novel cata-
lytic function of the bifunctional catalysts including Pd/WO3–
ZrO2 and Pd–H4SiW12O40/SiO2 that the acid sites promote
the reoxidation of metallic Pd sites into the corresponding oxi-
3
dized Pd sites. In fact, Pd/WO3–ZrO2 and Pd–H4SiW12O40/
SiO2 exhibit high catalytic activities for a Wacker-type reaction
involving the transformation of ethylene to acetic acid via an
3
–5
acetaldehyde intermediate in the gas-phase. Showa Denko
K.K. developed the world’s first commercial process employing
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,7
a highly active and selective Pd–H4SiW12O40/SiO2 catalyst.
This process is considered to be environmentally benign because
8
it uses a heterogeneous catalysis. However, in order to improve
the yield of the process, a better catalyst is needed. In the present
publication, we report that Pd supported on sulfated zirconia
9
3,4
(
SO4–ZrO2), which is known as a solid superacid, is an excel-
and high selectivity for the gas-phase oxidation of ethylene,
lent catalyst for the Wacker-type reaction involving the gas-
phase oxidation of ethylene to partially oxidized products, in-
cluding acetaldehyde and acetic acid.
Pd/SO4–ZrO2 was superior in both activity and selectivity to
Pd/WO3–ZrO2. In addition, even after 9 h, the activity and
selectivity of Pd/SO4–ZrO2 barely changed (Table 1) and the
color change in the catalyst after the reaction was subtle,
suggesting that the coke formation was little. Xie et al. have
reported that a styrene divinylbenzene copolymer-supported Pd
catalyst shows high selectivity for partially oxidized products
(85%) in the gas-phase oxidation of ethylene at 393 K.10 Li
and Iglesia have found that a multicomponent catalyst
(0.0025 wt % Pd/Mo0:16V0:31Nb0:08Ox/TiO2) suppresses the for-
mation of COx (selectivity = 11%) and consequently exhibits
Sulfated zirconia (SO4–ZrO2) samples with different S/Zr
ratios were prepared by using an incipient wetness method with
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dilute sulfuric acid (0.5 mol dm , Wako Pure Chem. Co.) and
Zr(OH)4 (Dai-ichi Kigenso Kagaku Kogyo Ltd), which was
dried overnight at 373 K before use. The resulting solid was
dried at 373 K and calcined at 973 K for 3 h at a heating rate
ꢁ1
of 2 K min . The S/Zr ratio of SO4–ZrO2 was changed by
changing the amount of dilute sulfuric acid added. The amount
of sulfur in the calcined SO4–ZrO2 was estimated from the
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high selectivity for the partially oxidized products. The results
in Table 1 demonstrate that Pd/SO4–ZrO2 is superior in selec-
tivity to the previously reported catalysts.
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amount of SO4 formed by the combustion of the sample in
O2 by using ion chromatography. Pd/SO4–ZrO2 was prepared
by impregnating SO4–ZrO2 with an aqueous solution
The chemical and physical properties of SO4–ZrO2 change
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(80 mmol dm ) of PdCl2 (Wako Pure Chem. Co.). The Pd load-
ing was adjusted to 1.0 wt %. After drying at 373 K, the resulting
depending on the sulfur content. Thus, we investigated the
effect of the S/Zr atomic ratio on the STY and selectivity. We
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.3 (2009)
223
Table 1. Catalytic data for gas-phase oxidation of ethylene over various catalystsa
c
d
STY
Selectivity /%
Conversion
b
Catalyst
/
mol h 1 dm (mol h kg
ꢁ
ꢁ3
ꢁ1
ꢁ1
)
POxP
AcOH
AcH
EtOH
COx
of O2/%
e
e
Pd/SO4–ZrO2
Pd/SO4–ZrO2 (at 9 h)
2.81 (3.02)
2.61 (2.81)
1.34 (0.76)
0.88 (1.15)
0.62 (0.30)
0.64 (0.40)
0.10 (0.10)
0.07 (0.15)
0.03 (0.06)
0.02 (0.02)
94
92
82
70
24
55
76
72
48
40
53
73
74
55
17
36
24
29
38
22
41
19
8
15
7
19
52
43
10
18
0
0
0
10
15
0
1
0
4
4
6
8
27
37
32
21
68
25
4
5
6
4
f
g
Pd/WO3–ZrO2
18
20
61
45
23
28
48
56
Pd–H4SiW12O40/SiO2h
Pd/Cs2:5H0:5PW12O40
Pd/MoO3–ZrO2i
Pd/Nb2O5
j
Pd/SiO2–Al2O3
Pd/H-ꢀ
Pd/H-mordenite
k
l
a
ꢁ1
Reaction conditions: C2H4:O2:H2O:He = 50:7:30:13, GHSV = 3000 h , temperature 423 K, and pressure 0.6 MPa. The data was
b
c
collected at 3 h. Loading amount of Pd was 1.0 wt % except for 1.5 wt % Pd–40 wt % H4SiW12O40/SiO2. Space time yield of sum
of acetic acid (AcOH) and acetaldehyde (AcH). POxP: AcOH + AcH, EtOH: ethanol. S/Zr = 0.077. The data was collected at
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tion was performed at 1073 K. Si/Al = 5.3. Si/Al = 12.5. Si/Al = 10.
d
e
f
g
h
i
h. W/Zr = 0.2 and calcination was performed at 1073 K. 1.5 wt % Pd–40 wt % H4SiW12O40/SiO2. Mo/Zr = 0.2 and calcina-
j
k
l
þ
as accepting H released during the formation of acetaldehyde
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,4
by the conjugated base of the acid sites. The relationship be-
tween the STY of POxP and the number of acid sites of SO4–
ZrO2 (shown in Figure 1) strongly supports this idea. The acid
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amount of SO4–ZrO2 (S/Zr = 0.077) was 0.49 mmol g
,
which is much larger than those of WO3–ZrO2 (W/Zr = 0.2,
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1
ꢁ1
0
.23 mmol g ) and 40 wt % H4SiW12O40/SiO2 (0.07 mmol g ,
1
3
estimated by using benzonitrile-TPD ). The large number of
acid sites as well as the strong acidity may be one reason for
the high activity and high selectivity of Pd/SO4–ZrO2 toward
the oxidation of ethylene.
References and Notes
1
2
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A. Zhang, I. Nakamura, K. Aimoto, K. Fujimoto, Ind. Eng.
Chem. Res. 1995, 34, 1074; Z. Paal, Z. Zhan, I. Manninger,
Figure 1. Changes in STY and selectivity over Pd/SO4–ZrO2
as a function of the acid content of SO4–ZrO2. STY of ( )
POxP, ( ) acetaldehyde, and ( ) acetic acid, and ( ) selectivity
for POxP. POxP means partially oxidized products, which in-
cluded acetaldehyde and acetic acid. S/Zr atomic ratios were
´
W. M. H. Sachtler, J. Catal. 1995, 155, 43; M. C. Alvarez-
´
Galv a´ n, A. Brito, F. J. Garc ´ı a-Alvarez, V. A. de la Pe n˜ a
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3
8.
(
1) 0.035, (2) 0.077, (3) 0.154, and (4) 0.474.
3
4
5
6
7
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prepared four SO4–ZrO2 catalysts with S/Zr ratios in the range
of 0.035–0.474. The surface areas of the SO4–ZrO2 catalysts
2
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were determined to be 80, 106, 72, and 20 m g for S/Zr ratios
of 0.035, 0.077, 0.154, and 0.474, respectively. The acid amount
of SO4–ZrO2 estimated by using temperature-programmed de-
sorption (TPD) of NH3 also changed depending on the S/Zr
ratio (Figure 1). SO4–ZrO2 (S/Zr = 0.077) and SO4–ZrO2 (S/
Zr = 0.154) possessed large numbers of the acid sites and high
surface areas. In Figure 1, STYs of POxP ( ), acetaldehyde ( ),
and acetic acid ( ), and selectivity for POxP ( ) are plotted
against the acid amount. The catalytic activity changed depend-
ing on the S/Zr ratio, whereas the selectivity was independent
of the S/Zr ratio. The Pd/SO4–ZrO2 (S/Zr = 0.077) catalyst
with the highest STY of POxP possessed the largest number
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0
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Published on the web (Advance View) January 31, 2009; doi:10.1246/cl.2009.222