NO decomposition on ruddlesden-popper-type oxide, Sr3Fe 2O7, doped with Ba and Zr

Article abstract of DOI:10.1246/cl.2008.318

Study of the NO decomposition activity of the Ruddlesden-Popper-type oxide Sr₃Fe₂O₇ doped with Ba and Zr revealed that Sr₃Fe₂O₇ exhibits a high NO decomposition activity. Doping Ba and Zr for the Sr and Fe sites, respectively, is highly effective for improving NO decomposition activity. A high N₂ yield of 72% is achieved at 1123 K and a N₂ yield of 32% is sustained under a 2.5% oxygen cofeeding condition. Copyright

Full text of DOI:10.1246/cl.2008.318

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Chemistry Letters Vol.37, No.3 (2008)
NO Decomposition on Ruddlesden–Popper-Type Oxide, Sr Fe O , Doped with Ba and Zr
3
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ꢀ
1;2
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1
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1;2
Tatsumi Ishihara,
1
Yusuke Shinmyo, Kazuya Goto, Noriko Nishiyama, Hideharu Iwakuni, and Hiroshige Matsumoto
Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395
2
Center for Future Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395
(Received December 20, 2007; CL-071410; E-mail: ishihara@cstf.kyushu-u.ac.jp)
Study of the NO decomposition activity of the Ruddlesden–
is discussed mainly in terms of N2 yield. It is noted that no
N2O formation was observed in this study.
Popper-type oxide Sr3Fe2O7 doped with Ba and Zr revealed that
Sr3Fe2O7 exhibits a high NO decomposition activity. Doping Ba
and Zr for the Sr and Fe sites, respectively, is highly effective for
improving NO decomposition activity. A high N2 yield of 72%
is achieved at 1123 K and a N2 yield of 32% is sustained under a
Table 1 summarizes the NO decompositions in the presence
of Sr3Fe2O7 doped with various cations for the Fe site. As in the
1
3
case of SrFeO3 perovskite oxide, NO decomposition activity
of Sr3Fe2O7 was markedly improved by the use of a dopant.
In particular, a high N2 yield was generally obtained by doping
tetravalent cations, i.e., Zr, Ti, Ce, and Sn, for the Fe site. The
highest N2 yield is obtained by doping Zr for the Fe site. For
SrFeO3, the most pronounced effect was obtained by doping
Mg, which has a lower valence number than Fe resulting
in the formation of oxygen vacancies. However, despite their
similar structures, the optimum dopant is different between
them, which may be explained by the difference in the number
of oxygen vacancies. The crystal structure of Sr3Fe2O7 consists
of two blocks: a dual perovskite layer (SrFeO3) and a single rock
salt (SrO). Since a large number of oxygen vacancies originally
exist in the rock salt, the introduction of oxygen vacancies
into the perovskite layer by doping with a low-valence cation
is not effective, but the introduction of excess oxygen by doping
with a high-valence cation is effective for increasing NO
decomposition activity in the case of Sr3Fe2O7. Since the most
pronounced effects on NO decomposition were obtained using
Zr as a dopant, the effects of Zr were further studied.
2
.5% oxygen cofeeding condition.
The diesel engine is an ideal lean combustion engine that
exhibits high fuel efficiency. However, it produces a high con-
centration of nitrogen oxides (NOX), which are extremely toxic
to the human body and are also harmful to the environment being
principal causes of both acid rain and photochemical smog. At
present, because of the increase in the number of diesel engine
cars, the amount of NO emission in urban areas has been mark-
edly increasing. Several methods of NOX removal have been
proposed.1 Among them, the selective reduction of NOX by hy-
drocarbons has been studied extensively, and various catalysts,
–7
8
particularly Cu-ZSM-5, have been proposed for this reaction.
In contrast to NOX removal by selective reduction, the direct de-
composition of NO into N2 and O2 (2NO = N2 + O2) is the ide-
9
,10
al reaction owing to its simplicity.
However, because of
strong oxygen adsorption, the NO decomposition activity of con-
ventional catalysts decreases significantly under an oxygen co-
feeding condition.11 We have found that the perovskite oxide
Figure 1 shows the NO conversion and N2 and O2 yields
at 1123 K as functions of the Zr content (X) of the Sr3Fe2O7
VI
Ba0:8La0:2Mn0:8Mg0:2O3 (BLMMg), containing Mn , is highly
1
2
active for direct NO decomposition. In the presence of this
compound as a catalyst, the NO decomposition activity of
non-La- and non-Mg-doped BaMnO3 is low; however, it mark-
edly increases in BaMnO3 doped with a low-valence cation.
Therefore, the use of dopants is highly effective for achieving
high NO decomposition activity, which may be the result of
the introduction of oxygen vacancies into lattice. Although
BaMnO3 has a high NO decomposition activity, its Mn compo-
nent makes it not preferable from the viewpoint of toxicity. We
have also found that SrFeO3 perovskite oxide shows a rather
a
Table 1. NO decomposition on doped Sr3Fe2O7 catalysts
Conversion/%
Yield/%
NO
N2
O2 N2O NO2
No dopant
Sr3Fe1:8A0:2O7
70.2
38.2 14.3 0.0 28.0
þꢀ
A = Zr
Ni
Ce
70.5
70.3
69.0
66.5
71.2
71.2
65.7
62.2
58.9
44.9
26.3
49.6 31.2 0.0 19.7
48.8 31.3 0.0 19.5
48.1 30.0 0.0 19.5
47.9 29.6 0.0 18.5
47.0 27.9 0.0 21.7
46.2 26.2 0.0 22.5
43.8 24.9 0.0 20.4
43.2 25.1 0.0 18.6
38.3 21.0 0.0 18.9
28.8 14.1 0.0 15.4
Mn
Ti
Sn
Mg
Co
Ru
Hf
1
3
high NO decomposition activity. In this study, the NO decom-
position activity of Sr3Fe2O7 oxide with a Ruddlesden–Popper
structure, a perovskite-related structure that contains a much
higher number of oxygen vacancies, was investigated.
Doped Sr3Fe2O7 was prepared by conventional solid-
.
state reaction. Sr(CH3COO)2 0.5H2O (Wako Pure Chem.),
.
Fe(NO3)3 3H2O (Kishida Chem.), and nitrie acid were used as
Mo
Sr2:7B0:3Fe1:8Zr0:2O7
15.7 6.9 0.0
9.7
starting materials. The formation of single-phase Sr3Fe2O7 was
confirmed by XRD analysis. The direct decomposition of NO
was performed with a conventional fixed-bed gas-flow reactor
with a quartz glass tube of 12-mm diameter. NO2 formation
was observed by the reaction of NO and O2 produced by NO
decomposition; thus, the yield of N2 was always higher than
that of O2. The activity of each catalyst for NO decomposition
þꢀ
B = Ba
Pr
La
79.2
73.1
73.5
71.7
62.2 38.6 0.0 20.3
53.2 31.6 0.0 20.8
52.7 29.3 0.0 22.1
51.0 28.9 0.0 21.4
Ce
aTemperature: 1123 K, NO: 1%, W=F ¼ 3:0 g s cmꢁ3
.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.3 (2008)
319
100
100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Ba0.8La0.2Mn0.8Mg0.2O3-δ
Sr2.7Ba0.3Fe1.6Zr0.4O7-δ
9
8
7
6
0
0
0
0
NO conv.
N yield
2
N yield
2
50
4
3
2
1
0
0
0
0
0
O yield
2
O yield
2
0
.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
X in Sr Fe Zr O
7−δ
3
2−X
X
7
73
873
973
1083
1173
Figure 1. NO conversion and N2 and O2 yields at 1123 K as
functions of Zr content of Sr3Fe2O7 catalyst (NO: 1%, W=F ¼
Temperature/K
ꢁ
3
3
:0 g s cm ).
Figure 2. Temperature dependences of N2 and O2 yields with
the use of Sr2:7Ba0:3Fe1:6Zr0:4O3 and Ba0:8La0:2Mn0:8Mg0:2O3.
catalyst. The NO conversion and N2 yield monotonically in-
creased with increasing X up to 0.4. For the catalyst with
X ¼ 0:4, the N2 yield is almost 1.5 times higher than that for
the nondoped one. Therefore, the optimized Zr amount for dop-
ing is approximately X ¼ 0:4. Since XRD analysis suggested
that the secondary phases of SrO and SrZrO3 start to form at
approximately X ¼ 0:3, the solubility limit of Zr seems to be
between X ¼ 0:3 and 0.4. As a result, an excess of Zr dopant
forms the secondary phase of SrZrO3 resulting in decreased
NO decomposition activity. Thus, the optimum amount for
Zr doping is X ¼ 0:4, which is slightly higher than the solubility
limit.
ꢁ3
(
NO: 1%, W=F ¼ 3:0 g s cm ).
and Zr is desirable as a NO decomposition catalyst in terms of
environmental impact. The high NO decomposition activity of
Sr2:7Ba0:3Fe1:6Zr0:4O is sustained in the presence of O , result-
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2
ing in a N yield of 32% under a 2.5% O cofeeding condition
2
2
1
5
(See Figure S.I.1). Thus, it is clear that the Ruddlesden–
Popper-type oxide Sr Fe O doped with Ba and Zr is a highly
active catalyst for direct NO decomposition.
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References and Notes
1
2
M. Iwamoto, Shokubai 1995, 37, 614.
H. Hamada, Y. Kintaichi, M. Sasaki, T. Ito, T. Yoshinari,
Appl. Catal., A 1992, 88, L1.
In our previous study of BaMnO3, additives into the Ba
site of BaMnO3 were found to be also useful for increasing
1
2
NO decomposition activity. In Table 1, the effects of dopants
for the Sr site of Sr3Fe1:8Zr0:2O7 are also shown. Clearly,
3
4
Y. Teraoka, H. Fukuda, S. Kagawa, Chem. Lett. 1990, 1.
H. Imagawa, T. Tanaka, N. Takahashi, S. Matsunaga, A.
Suda, H. Shinjoh, J. Catal. 2007, 251, 315.
S. C. Shen, S. Kawi, J. Catal. 2003, 213, 241.
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T. Nanba, A. Obuchi, Y. Sugiura, C. Kouno, J. Uchisawa,
S. Kushiyama, J. Catal. 2002, 211, 53.
ꢁꢀ
a dopant for the Sr site is highly effective for increasing NO
decomposition activity. Among the examined dopants, it was
found that Ba shows the most pronounced effects of increasing
NO decomposition activity. The pronounced effects of Ba
doping could be explained by the enhanced NO adsorption. In
the NO decomposition catalyst, NO adsorption and activation
are two of the most important steps in NOX removal, and Ba is
5
6
7
8
9
M. Iwamoto, H. Yahiro, Y. Mine, S. Kagawa, Chem. Lett.
1989, 213.
Y. Teraoka, T. Harada, S. Kagawa, J. Chem. Soc., Faraday
Trans. 1998, 94, 1887.
1
3,14
generally effective for enhancing NO adsorption.
As a result,
the optimum dopants are Ba for the Sr site and Zr for the Fe site
in Sr3Fe2O7 oxides.
10 T. Imanaka, T. Masui, H. Masaki, Adv. Mater. 2007, 19,
3660.
11 M. Iwamoto, H. Yahiro, K. Tanda, N. Mizuno, Y. Minem,
S. Kagawa, J. Phys. Chem. 1991, 95, 3727.
12 H. Iwakuni, Y. Shinmyou, H. Yano, H. Matsumoto, T.
Ishihara, Appl. Catal., B 2007, 74, 299.
Figure 2 shows the temperature dependences of N2 and O2
yields on Sr2:7Ba0:3Fe1:6Zr0:4O3. In Figure 2, the NO decompo-
sition activity of the BLMMg catalyst, which was identified as
one of the most active NO decomposition catalysts in our previ-
1
2
ous study, is also shown. It is seen that NO decomposition pro-
ceeds on doped Sr3Fe2O7 at approximately 873 K. With increas-
ing temperature, N2 yield monotonically increased, and at
13 H. Iwakuni, Y. Shimmyou, H. Matsumoto, T. Ishihara, Bull.
Chem. Soc. Jpn. 2007, 80, 2039.
1
123 K, N2 yield of 75% is obtained, which is similar to the yield
14 S. Iwamoto, R. Takahashi, M. Inoue, Appl. Catal., B 2007,
70, 146.
15 Supporting Information is available electronically at the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index.html.
obtained with the BLMMg catalyst but much higher than that
obtained with SrFe0:7Mg0:3O3 (N2 yield: 43% at 1073 K).
Since the Sr3Fe2O7 catalyst contains Fe, which is more
environmentally friendly than Mn, Sr3Fe2O7 doped with Ba
Published on the web (Advance View) February 16, 2008; doi:10.1246/cl.2008.318