Direct Decomposition of NO on Cu-Doped La(Ba)Mn(In)O3 Perovskite Oxide under Coexistence of O2, H2O, and SO 2

Article abstract of DOI:10.1246/cl.2003.1176

It was found that the substitution of Mn with Cu in La_0.7Ba _0.3Mn_0.8In_0.2O₃ is effective for increasing activity to NO direct decomposition. NO direct decomposition proceeds on the perovskite oxide of

Full text of DOI:10.1246/cl.2003.1176

1176
Chemistry Letters Vol.32, No.12 (2003)
Direct Decomposition of NO on Cu-Doped La(Ba)Mn(In)O3 Perovskite Oxide
under Coexistence of O2, H2O, and SO2
Tatsumi Ishihara,y Kazuhiro Anami, Keiko Takiishi, Hiroshi Yamada,yy Hiroyasu Nishiguchi, and Yusaku Takita
Department of Applied Chemistry, Faculty of Engineering, Oita University, Dannoharu 700, Oita 870-1192
yDepartment of Applied Chemistry, Faculty of Engineering, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka, 812-8581
yyGraduate School of Engineering, Oita University, Dannoharu 700, Oita 870-1192
(Received September 9, 2003; CL-030838)
It was found that the substitution of Mn with Cu in
La0:7Ba0:3Mn0:8In0:2O3 is effective for increasing activity to
NO direct decomposition. NO direct decomposition proceeds
on the perovskite oxide of La0:7Ba0:3Mn0:6In0:2Cu0:2O3 under
coexistence of O2, H2O, and SO2 at high temperature.
evaporated at the ahead of reactor.
Table 1 summarized the NO decomposition activity on
La0:7Ba0:3Mn0:8In0:1M0:1O3 (M = Ti,Cr,V,Ni,Co,Fe, or Cu) at
1073 K. Since no additional phase was observed on XRD pat-
terns in all doped LBMI oxides and shift in diffraction angle
of peaks was also observed, doped metal cation is considered
to substitute the lattice position of Mn in LaMnO3 oxide. It is
seen that N2 or O2 yield was strongly affected by the dopant
for Mn. Activity to NO decomposition on LBMI greatly decreas-
ed by doping Ti, Cr, and V. On the other hand, it is seen that N2
yield greatly improved by doping Fe, Co, Ni, and Cu. In partic-
ular, N2 yield becomes 1.5 times higher than that of nondoped
one by doping Cu. Therefore, it is clear that the partial substitu-
tion of Mn with Cu is effective for increasing NO decomposition
activity. In this study, we investigated the NO decomposition ac-
tivity on Cu added LBMI.
Figure 1 shows the N2, O2, NO2, N2O yields on Cu-added
LBMI at 1223 K as a function of Cu amount. It is seen that for-
mation of N2O was hardly observed over all compositions exam-
ined. N2 yield increased with increasing Cu amount and the larg-
est N2 yield was achieved at the composition from x ¼ 0:2 to 0.3
in La0:7Ba0:3Mn0:8ꢁxIn0:2CuxO3. Considering the O2 yield, it can
be said that the optimum amount for Cu addition seems to exist
at La0:7Ba0:3Mn0:6In0:2Cu0:2O3 (denoted as LBMICu). It is also
noted that NO2 may be formed in a cool zone after the reactor.
It is reported that coexistence of O2 and H2O shows signifi-
cant interference for NO decomposition6,10 and so, NO direct de-
composition under coexistence of O2 and H2O is highly difficult
subject. This is because H2O and O2 strongly adsorb on the ac-
tive site resulting in deactivation of the catalyst. Figure 2 shows
the term stability of N2 and N2O yield on LBMICu catalyst un-
der coexistence of 5% H2O and 1% O2. It is seen that under co-
existence of H2O and O2, N2 yield of ca. 50% was stably sus-
Nitrogen oxides (NOx), which are mainly formed by an in-
ternal combustion engine, are extremely toxic for human body
and harmful for environment as a main source of acid rain. At
present, several methods have been proposed for NOx remov-
al.1–4 Among them, direct decomposition of NO to N2 and O2
(2NO = N2 + O2) is the most ideal method for the NO removal,
since the process is simple and of high efficiency. However, it is
well-known that the formed oxygen adsorbs strongly on the cat-
alyst resulting in a deactivation of catalyst. It was reported that
Cu–ZSM-5,5 LaNiO3,6 and Sr/La2O3-based perovskite oxide7
are active for the direct decomposition of NO. In particular,
Teraoka et al. reported that La0:8Sr0:2CoO3 is highly active for
the NO decomposition.8 The high activity for NO decomposition
under a practical exhaust gas condition is expected on perovskite
oxide catalyst. In our previous study, it was found that
La0:7Ba0:3Mn0:8In0:2O3 (LBMI) perovskite oxide exhibits the
high activity to NO direct decomposition.9 In the present study,
effects of transition cation substitution for Mn in LBMI were
studied for further increasing the NO decomposition activity.
In particular, effects of coexistence of H2O, O2, and SO2, which
are generally contained in exhaust gas from internal combustion
engines, on NO decomposition were also studied.
Doped LaMnO3 was prepared by a conventional solid solu-
tion method. The precursor of LaMnO3-based perovskite oxide
was obtained by using the aqueous suspension of a calculated
amount of La(NO3)3, Ba(NO3)2, Mn(CH3COO)2, In2O3, and
metal nitrate. Obtained mixtures were calcined in air at 1273 K
for 3 h. From X-ray diffraction measurement, it was confirmed
that the obtained sample was consisted of a single phase of
LaMnO3-based perovskite oxide. Direct decomposition of NO
was performed with a conventional fixed bed gas flow reactor
and a gaseous mixture of 1% NO diluted with He was fed to
the catalyst bed at W=F ¼ 3:0 gꢀmin/cm3, where W and F mean
the catalyst weight and the gas flow rate. Here, for the accelerat-
ed deactivation by oxygen formed in NO decomposition, we
generally used the concentration of NO at 1%, which is much
higher than that in the actual exhaust gas. Produced N2, O2,
and fed NO were analyzed with an on-lined gas chromatography
with thermal conductivity detector (TCD). Formation rate of
NO2 was estimated by N2 and O2 material balance. Addition
of H2O was performed by using micro pump and fed H2O was
Table 1. Effects of M cation in La0:7Ba0:3Mn0:2In0:2M0:1O3 on
NO decomposition at 1073 K
Yield%
Dopant
N2
O2
NO2
N2O
none
Ti
46.8
2.2
19.1
0.6
27.7
1.6
10.7
23.4
0
0
0
0
Cr
V
Ni
Co
Fe
Cu
10.7
25.7
58.0
59.0
64.5
69.4
0.0
2.3
34.923.1
38.0
44.2
42.3
0
21.0
20.4
27.1
0
0
0
PNO = 1%, W=F ¼ 3 g-cat. min cmꢁ3
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.12 (2003)
1177
existence of SOx.11 Figure 3 shows the N2 yield at 1123 K as a
function of time under coexistence of H2O, O2, and SO2.
Although the period for term stability test is not long, it is evi-
dent that the catalyst is tolerant against SOx and the stable N2
yield was sustained over 10 h, while the further decrease in N2
yield was observed by coexistence of SO2. N2 yield decreased
from 55 to 33% in the initial 5 h. SOx is strongly adsorbed on
the active site on LBMICu resulting in the decreased N2 yield.
However, after stopping SOx co-feed, the N2 yield was recov-
ered to almost the original level. Therefore, deactivation of cat-
alyst is not permanent and it is considered that SOx adsorption is
not strong at 1123 K on this catalyst. This is also supported by no
compound containing sulfur formed during reaction by XRD
measurement.
100
1123K
N2
80
60
40
20
0
O2
NO2
N2O
0.4
Consequently, this study revealed that Cu-added
La(Ba)Mn(In)O3 is highly attractive as NO decomposition
catalyst under the actual exhaust gas atmosphere.
0.0
0.1
0.2
0.3
0.5
X in La0.7Ba0.3Mn0.8-XCuXIn0.2O3
Figure 1. N2, O2, N2O yield on Cu added LBMI at 1123 K as a
function of Cu amount. (PNO = 1%, W=F ¼ 3 g-cat. min cmꢁ3
100
)
1123K
80
100
1123K
60
80
60
N2
40
20
0
N2
40
N2O
10
20
N2O
0
2
4
6
8
12
Time on stream /h
0
Figure 3. N2 yield in NO direct decomposition on LBMICu as
a function of time under coexistence of H2O, O2, and SO2. (PNO
= 1%, PO = 1%, PH O = 5%, PSO = 0.0085%)
0
20 40 60 80 100 120 140 160 180 200
Time on stream /h
2
2
2
Figure 2. Term stability of N2 and N2O yield in NO direct de-
composition on LBMICu catalyst under coexistence of H2O and
O2. (PNO = 1%, PO = 1%, PH O = 5%)
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Published on the web (Advance View) November 24, 2003; DOI 10.1246/cl.2003.1176