Preparation of alumina-supported Pd and LaMnO3 catalysts with the site-selective deposition and their catalytic activity for NO-CO reaction

Article abstract of DOI:10.1016/j.cattod.2012.04.033

By the combination of the preparation techniques of intra-pore deposition of Pd and selective intra/extra-pore deposition of LaMnO₃, two types of alumina supported Pd-LaMnO₃ catalysts were successfully obtained. It was suggested from

Full text of DOI:10.1016/j.cattod.2012.04.033

Catalysis Today 201 (2013) 103–108
Contents lists available at SciVerse ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Preparation of alumina-supported Pd and LaMnO3 catalysts with the
site-selective deposition and their catalytic activity for NO–CO reaction
A. Toua, H. Einagab, Y. Teraokab,∗
a Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
b Department of Energy and Material Sciences, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
By the combination of the preparation techniques of intra-pore deposition of Pd and selective intra/extra-
pore deposition of LaMnO3, two types of alumina supported Pd–LaMnO3 catalysts were successfully
obtained. It was suggested from the reduction behavior of supported Pd–LaMnO3 catalysts that when
both Pd and LaMnO3 coexisted in the alumina pores (Pd/LaMnO3/Al2O3), Pd and LaMnO3 existed in close
proximity each other to appear the interaction and that when Pd and LaMnO3 exist separately in and out
of alumina pores, respectively (LaMnO3out/Pd/Al2O3), the existing environment of Pd was similar to that
in Pd/Al2O3. For NO–CO reaction, Pd/Al2O3 and LaMnO3out/Pd/Al2O3 showed comparable activity and
N2/N2O selectivity, and Pd/LaMnO3/Al2O3 showed higher activity than and different N2/N2O selectivity
from the two catalysts, revealing that the intimate Pd–LaMnO3 interaction is effective to modify the
catalytic property of Pd species. The excellent catalytic property of Pd/LaMnO3/Al2O3 was sustained up
to 800 ◦C of calcination temperature.
Received 16 January 2012
Received in revised form 30 March 2012
Accepted 1 April 2012
Available online 26 May 2012
Keywords:
Pd
LaMnO3
Intra/extra-pore deposition
Interaction
NO–CO reaction
© 2012 Published by Elsevier B.V.
1. Introduction
nitrates was quite effective to deposit LaFeO3 perovskite selec-
tively inside pores of alumina support (intra-pore deposition)
Platinum group metals (PGMs) play vital roles as active species
of automotive three-way catalysts (TWCs). Because of the lim-
ited supply and high cost of PGMs, it is strongly required to
reduce the amount of PGMs in TWCs. Perovskite-type oxides have
been regarded as possible substitutes for PGMs because their cat-
alytic activities per surface area are comparable to those of PGMs
[1–3]. It is also reported that the combination of perovskite-type
oxides and PGMs in both forms of the supported catalysts and
mixed metal oxides gives highly active catalysts [4–9], and recently
PGM-containing perovskite oxides have been used for commercial
automotive catalysts [5]. One of major drawbacks of perovskite-
type oxides, however, is their small specific surface areas because
relatively high calcination temperatures are necessary for the for-
mation of perovskite-type structure.
The preparation of supported perovskite catalysts in a highly
dispersed state is a possible way to increase the specific sur-
face area of perovskites and thus to obtain highly active catalysts.
We have been investigating sophisticated preparation methods of
supported perovskite catalysts, and reported that incipient wet-
ness (IW) method using mixed aqueous solution of La and Fe
[10]. The preparation of extra-pore deposited LaFeO3/Al2O3 was
also succeeded by using the hydroxide precursor of La–Fe oxides
which was obtained by the reverse homogeneous precipitation
(RHP) method [11]; the RHP-prepared hydroxide precursor is larger
in size than the pore size of the alumina support, so that the
selective extra-pore deposition of the precursor and the result-
ing perovskite-type oxides is realized. The intra-pore deposited
LaFeO3/Al2O3 with higher dispersion showed higher catalytic
activity for propane combustion than the extra-pore deposited
one [10].
Cimino et al. reported that the alumina-supported Pd–LaMnO3
catalyst showed excellent catalytic activity for methane combus-
tion because of the synergic interaction between Pd and LaMnO3
[8]. If Pd and LaMnO3 are deposited intentionally in or out of
pores of alumina supports, the catalytic property of alumina-
supported Pd–LaMnO3 catalysts must be controlled; the synergic
interaction between Pd and LaMnO3 appears when both active
species are co-deposited inside the pores but not when Pd and
LaMnO3 are separately present inside and outside of the pores,
respectively.
In this study, alumina-supported Pd–LaMnO3 catalysts with the
controlled deposition sites were prepared, and their catalytic prop-
erties were evaluated for NO–CO reaction which is one of key
reactions of three-way catalysis.
∗
Corresponding author.
E-mail address: teraoka.yasutake.329@m.kyushu-u.ac.jp (Y. Teraoka).
0920-5861/$ – see front matter © 2012 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.cattod.2012.04.033

104
A. Tou et al. / Catalysis Today 201 (2013) 103–108
Al2O3 JRC – ALO8 Vp = pore volume )
Dry impregnation with La-Mn mixed metal
Dry impregnation with Pd salt solution
(equal to 1/2Vp)
nitrate solution (equal to 1/2Vp)
Mixing
Mixing
Calcination
Calcination
Wet-impregnation
with Colloidal solution
of RHP-prepared
mixed hydroxide
precursor
Dry impregnation
with Pd salt solution
(equal to 1/2Vp)
Evaporation to
dryness
Mixing
Calcination
LaMnO3/Al2O3
( IW )
Pd/LaMnO3/Al2O3
( IW )
Pd/Al2O3
( IW )
LaMnO3out/Pd/Al2O3
( I-RHP )
-Al2O3 (Vp = pore volume)
Dry impregnation with aqueous La and Mn
nitrates (equal to 1/2Vp)
Dry impregnation with aq. Pd(NH3)4(NO3)2
(equal to 1/2Vp)
Calcination (650 oC, 5 h, in air)
Calcination (650 oC, 5 h, in air)
Wet impregnation with
colloidal solution of RHP-
prepared hydroxide precursor
Dry impregnation with
aq. Pd(NH3)4(NO3)2
(equal to 1/2Vp)
Evaporation to dryness
Calcination
Calcination
(650 oC, 5 h, in air)
(650 oC, 5 h, in air)
LaMnO3/Al2O3
Pd/LaMnO3/Al2O3
Pd/Al2O3
LaMnO3out/Pd/Al2O3
Fig. 1. Flow chart of the preparation of alumina-supported Pd and LaMnO3 catalysts.
2. Experimental
catalyst with intra-pore deposited Pd and extra-pore deposited
LaMnO3 was prepared as follows. Pd/Al2O3 was prepared by the
IW method with aqueous Pd(NH3)4(NO3)2, as described above.
Hydroxide precursor of LaMnO3 perovskite was prepared by drop-
ping a mixed aqueous solution of La and Mn nitrates into aqueous
ammonia under vigorous stirring [11]. The hydroxide precursor
and Pd/Al2O3 was dispersed into water and mixed well by ultra-
sonication. After evaporation to dryness under vigorous stirring,
the obtained solid was calcined to give LaMnO3out/Pd/Al2O3 cata-
lyst. All the powder catalysts were pressed at 35 MPa and sieved to
granules ranging from 22 to 60 meshes.
2.1. Catalyst preparation
Fig. 1 shows the preparation methods of alumina-supported
Pd and LaMnO3 catalysts. Four type catalysts were perpetrated
by using IW (dry-impregnation) and I-RHP (impregnation of
RHP-prepared hydroxide precursor) methods. ␥-Al2O3 (JRC-ALO-
8, supplied by Catalysis Society of Japan) was pretreated at 850 ◦C
for 5 h in air and used as the support. The supported catalysts
were calcined at 650 ◦C for 5 h in air, unless stated otherwise.
The nominal contents of LaMnO3 and Pd were set at 10 wt% and
1 wt%, respectively. Intra-pore deposition of LaMnO3 was per-
formed by the IW method as in the case of the deposition of
LaFeO3 [10]. ␥-Al2O3 was dry-impregnated with an aqueous solu-
tion of La and Mn nitrates (La(NO3)2 6H2O, Mn(NO3)2 6H2O,
Wako, >99%). The calcination of the dry-impregnated sample gave
intra-pore deposited LaMnO3/Al2O3 catalyst. Pd/LaMnO3/Al2O3 in
which both Pd and LaMnO3 were co-deposited in the alumina
pores were prepared by the dry-impregnation of LaMnO3/Al2O3
with Pd salt solution (Pd(NH3)4(NO3)2, Aldrich, density of
10 wt%) and the subsequent calcination. The LaMnO3out/Pd/Al2O3
2.2. Characterization of catalysts
The crystal structure of the catalysts was examined by pow-
der X-ray diffractometer (RINT2200, Rigaku) using Cu K␣ radiation.
Nitrogen adsorption isotherms for the catalysts were measured at
−196 ◦C (BEL-SORP mini, BEL Japan), and specific surface areas and
pore size distribution were determined by the BET and BJH meth-
ods, respectively.
Temperature programmed reduction by hydrogen (H2-TPR)
was carried out in a flow of 5% H2 in N2 (30 mL min−1) at a

A. Tou et al. / Catalysis Today 201 (2013) 103–108
105
3. Results and discussion
: Al2O3
: PdO
: LaMnO
3.15
a
3.1. Selective deposition of LaMnO3 and Pd in or out of alumina
pores
b
c
We have reported that LaFeO3 was selectively deposited in and
out of pores of alumina by IW and I-RHP methods, respectively [10].
In the IW (dry-impregnation) method, the metal nitrates as start-
ing materials are present in the pores of alumina and therefore the
perovskite is formed there after calcination. By I-RHP method, on
the other hand, the hydroxide precursors cannot go into the pores
because the size of the aggregates of hydroxide precursors is larger
than the pore size of alumina, and thus perovskite was formed
not inside but outside of pores. In the research, the appearance
of XRD peaks from the perovskite-phase was the clearest results to
judge the place of deposition of the perovskite; XRD peaks were not
observed in the case of intra-pore deposition, but they were clearly
observed with the extra-pore deposited oxide.
Fig. 2 shows XRD patterns of the prepared catalysts with dual
active components, Pd/LaMnO3/Al2O3 and LaMnO3out/Pd/Al2O3,
and a single active component, Pd/Al2O3 and LaMnO3/Al2O3. Small
peaks of PdO were detected in all the Pd-containing catalysts,
but almost all Pd species might be present in the alumina pores
because they were deposited by the IW method. As for perovskite,
on the other hand, diffraction peaks assignable to oxygen-rich
phase of LaMnO3.15 were observed only with LaMnO3out/Pd/Al2O3,
and the average crystallite size of perovskite oxides formed in
LaMnO3out/Pd/Al2O3 was estimated to be 24.6 nm. The pore sizes
of Al2O3 support ranged from 2 to 100 nm with a maximum at
20 nm. The average size of perovskite crystallite was slightly larger
than the size of the most populated pores, which might support
the presence of LaMnO3 not in the pores but out of pores. In
LaMnO3/Al2O3 and Pd/LaMnO3/Al2O3 for which the IW method
was employed to deposit LaMnO3, no peak from perovskite phase
was observed, indicating that LaMnO3 phase smaller than the XRD-
detectable size is highly dispersed inside of alumina pores. The
formation of the perovskite phase in LaMnO3/Al2O3 was confirmed
by transmission electron microscope and electron diffraction (data
are not shown).
d
20
30
40
50
60
70
80
2θ/ deg.
Fig. 2. XRD patterns of alumina-supported Pd and LaMnO3 catalysts ((a)
LaMnO3/Al2O3; (b) Pd/Al2O3; (c) Pd/LaMnO3/Al2O3; (d) LaMnO3out/Pd/Al2O3).
ramping rate of 5 ◦C min−1 (BEL-CAT, BEL Japan). Granules of cat-
alysts were packed in a tubular quartz reactor and heat-treated
at 600 ◦C for 30 min in a flow of air. After cooling down to 40 ◦C
in air and the stabilization of the TCD signal in He, the H2-TPR
measurement was started. The concentration of H2 in the efflu-
ent was measured by a thermal conductivity detector (TCD), and
the amount was determined by the standard quantification curve
prepared by the reduction of CuO.
Pd dispersion was measured by CO pulse method at 40 ◦C (BEL-
CAT, BEL Japan). Because CO adsorbed on both Pd and LaMnO3,
the surface of LaMnO3 was blocked with CO2 prior to CO adsorp-
tion. The CO2 blockage method was developed to measure the
dispersion of PGMs on CeO2-containing supports [12], and the
CO2-preadsorption conditions were optimized for the present
alumina-supported Pd and LaMnO3 catalysts. Granules of catalysts
which were packed in a tubular quartz reactor were heat-treated at
300 ◦C for 5 min in a flow of air. After cooling down to 40 ◦C, the sam-
ple was exposed to a flow of CO2 for 60 min and then of 5%H2/N2 for
5 min. After flushing with He, the pulse adsorption measurement
of CO was started. The stoichiometry of one CO molecules on one
Pd atom was used for the calculation of Pd dispersion.
FTIR spectra were recorded on FT/IR 430 (JASCO corp.) with an
MCT detector at a resolution of 0.5 cm−1. A self-supporting disk of
the sample was placed in an IR reactor cell equipped with a heater
and ZnSe windows. After successive pretreatments of heating at
400 ◦C under flowing He for 0.5 h and reduction under flowing 5%
H2/N2 at 40 ◦C for 0.5 h, CO was adsorbed on the catalysts by flowing
1% CO/He gas at 40 ◦C for 1 h. FTIR measurements were carried out
at 40 ◦C under flowing He.
Specific surface areas (SBET) and pore volumes of the alumina-
supported catalysts calcied at 650 ◦C are listed in Table 1. The
SBET values were in the order of Al2O3 > Pd/Al2O3 > LaMnO3out/
Pd/Al2O3 > LaMnO3/Al2O3 > Pd/LaMnO3/Al2O3. The reduction of
SBET by the deposition of 10 wt% LaMnO3 (LaMnO3/Al2O3) was more
prominent than that of 1 wt% Pd (Pd/Al2O3). The smallest SBET value
and pore volume of Pd/LaMnO3/Al2O3 suggests that both Pd and
LaMnO3 are present in the pores of the alumina support. The SBET
value and pore volume of LaMnO3out/Pd/Al2O3 were higher than
2.3. Catalytic reaction
Catalytic NO–CO reaction was carried out with a fixed-bed
flow reactor in a flow of NO(0.51%)–CO(0.49%)–He (100 ml min−1
)
with a contact time of 0.06 g s cm−3. The reaction gases were
analyzed by gas chromatograph equipped with TCD (Shimadzu
GC-8A). All the catalysts were heat-treated at 400 ◦C in air and
then maintained 350 ◦C under a flow of He before the catalytic
activity test.
LaMnO3/Al2O3
Pd/Al2O3
Pd/LaMnO3/Al2O3
Table 1
Specific surface area, pore volume and Pd dispersion of catalysts.
LaMnO3out/Pd/Al2O3
SBET/m2g−1
Pore volume/cm3g−1
Pd dispersion/%
A12O3
LaMnO3/Al2O3
Pd/Al2O3
Pd/LaMnO3/Al2O3
LaMnO3out/Pd/Al2O3
134
110
126
107
116
1.0
0.8
0.9
0.5
0.7
n.d.
n.d.
33
33
24
0
100 200 300 400 500 600 700 800 900
Temperature / oC
Fig. 3. H2-TPR profiles of alumina-supported Pd and LaMnO3 catalysts.

106
A. Tou et al. / Catalysis Today 201 (2013) 103–108
those of Pd/LaMnO3/Al2O3. This is probably due to the fact that
LaMnO3 in LaMnO3out/Pd/Al2O3 is deposited outside the pores.
The dispersions of Pd were also listed in Table 1. The same
Pd dispersion in Pd/Al2O3 and Pd/LaMnO3/Al2O3 catalysts sug-
gests that LaMnO3 which has been deposited in advance of Pd
deposition has little influence on the Pd dispersion even they coex-
ist in pores. The dispersion of Pd in LaMnO3out/Pd/Al2O3 was
slightly lower than the dispersions in the other two catalysts.
Since LaMnO3out/Pd/Al2O3 experienced two calcination processes
at 650 ◦C after Pd deposition, the growth and/or aggregation of Pd
particles might occur. The average particle size of Pd was estimated
to be 3 nm for 33% dispersion (Pd/LaMnO3/Al2O3 and Pd/Al2O3) and
5 nm for 24% dispersion (LaMnO3out/Pd/Al2O3).
that in Pd/Al2O3 and therefore Pd in the pores are present inde-
pendent from extra-pore deposited LaMnO3. The reduction of the
La–Mn perovskite in LaMnO3out/Pd/Al2O3 occurred at lower tem-
perature than that in LaMnO3/Al2O3. Hydrogen is activated on Pd
surface and the activated hydrogen enhances the reduction of the
La–Mn perovskite.
The profile for Pd/LaMnO3/Al2O3 was different from that for
LaMnO3out/Pd/Al2O3. Just after the appearance of a small negative
peak, the reduction of the La–Mn perovskite started. This can be
explained if one assume that the reduction of the La–Mn perovskite
starts at the temperature lower than 60 ◦C and adsorbed hydrogen
on Pd is consumed by the reduction before desorption during the
H2-TPR process. This event may occur when Pd is located in close
proximity to LaMnO3 in such Pd/LaMnO3/Al2O3 catalyst that both
Pd and LaMnO3 coexist in alumina pores.
3.2. Reduction behavior
H2-TPR of the alumina-supported catalysts (Fig. 3) gave the use-
ful information about the location and the interaction of LaMnO3
and Pd on the alumina support. Only a negative peak below 60 ◦C
due to H2 desorption was observed for Pd/Al2O3. This indicates that
PdO is reduced to metallic Pd during the pretreatment process in
H2/N2 flow at 40 ◦C and hydrogen adsorbed on or absorbed in Pd
desorbs during heating [13] in the TPR experiment. The profile for
LaMnO3/Al2O3 exhibited two positive peaks due to H2 consump-
tion in the temperature range of 150–550 ◦C. The reduction peak at
around 215 ◦C was ascribed to the reduction of Mn4+ to Mn3+ and
that at higher temperature (370 ◦C) was due to the reduction of
Mn3+ to Mn2+ [14–18]. This is consistent with the XRD result of the
formation of the oxygen-rich La–Mn–O perovskite which contains
3.3. Catalytic activity
Fig. 4 shows the activities of the supported catalysts for NO–CO
reaction. Pd-deposited catalyst exhibited the activity for NO–CO
reaction at the temperatures higher than 150 ◦C and the conver-
sion increased with an increase in the reaction temperature. On
the other hand, LaMnO3/Al2O3 showed no activity even at 300 ◦C,
indicating that Pd serves as the active site for NO–CO reaction
under the present condition and in the supported Pd–LaMnO3
catalysts. Pd/LaMnO3/Al2O3 catalyst showed the highest activity
among the catalysts. Table 2 compares TOFsNO (turnover frequen-
cies for NO conversion per a surface Pd site) for Pd-deposited
catalysts at the reaction temperature of 200 ◦C. The comparable
TOFNO of LaMnO3out/Pd/Al2O3 and Pd/Al2O3 is in accordance with
the same existing atmosphere suggested by the reduction behav-
ior. The higher TOFNO of Pd/LaMnO3/Al2O3 as compared with the
both Mn4+ and Mn3+
.
A clear negative peak was observed for LaMnO3out/Pd/Al2O3,
indicating that the existing state or atmosphere of Pd is similar to
100
100
: Pd/LaMnO3/Al2O3
: Pd/LaMnO3/Al2O3
: LaMnO out/Pd/Al2O3
3
: LaMnO out/Pd/Al2O3
80
3
80
: Pd/Al2O3
: Pd/Al2O3
: LaMnO /Al2O3
3
: LaMnO /Al2O3
3
60
40
20
0
60
40
20
0
150
200
250
300
350
150
200
250
300
350
Temperature / oC
Temperature / oC
(a) NO conversion
(c) NO into N2 conversion
100
80
60
40
20
0
100
80
60
40
20
0
: Pd/LaMnO /Al2O3
: LaMnO ou3t/Pd/Al2O3
: Pd/LaMnO /Al2O3
3
3
: LaMnO out/Pd/Al2O3
3
: Pd/Al2O3
: Pd/Al2O3
: LaMnO /Al2O3
3
: LaMnO /Al2O3
3
150
200
250
300
350
150
200
250
300
350
Temperature / oC
Temperature / oC
(d) NO into N2O conversion
(b) CO conversion
Fig. 4. Catalytic reaction of NO–CO reaction over alumina-supported Pd and LaMnO3 catalysts.

A. Tou et al. / Catalysis Today 201 (2013) 103–108
107
Table 2
Calcination
temperature
Turnover frequency of NO conversion at 200 ◦C.
Sample name
TOFnO × 104/s−1
650oC
Pd/Al2O3
Pd/LaMnO3/Al2O3
LaMnO3out/Pd/Al2O3
0.2
1.9
0.3
700oC
800oC
900oC
other two catalysts indicates that the coexistence of Pd and LaMnO3
inside the alumina pores is effective in improving the activity of Pd
through the chemical synergic interaction.
The NO–CO reaction includes the following two reactions.
0
100
200
300
400
500
600
700
800
900
NO + CO → N2 + CO2
(1)
(2)
Temperature / oC
2NO + CO → N2O + CO2
Fig. 6. H2-TPR profiles Pd/LaMnO3/Al2O3 calcined at 650, 700, 800 and 900 ◦C.
LaMnO3out/Pd/Al2O3 and Pd/Al2O3 showed similar N2/N2O
selectivity, indicating that extra-pore deposited LaMnO3 has no
effect not only on the activity but also on the selectivity in NO–CO
reaction. With Pd/LaMnO3/Al2O3 catalyst, on the other hand, N2
and N2O conversions were higher and the temperature depen-
dences of NO conversion into N2 and N2O were different as
compared with the other catalysts. These results suggest that syn-
ergic interaction between Pd and LaMnO3 in the alumina pores
also modifies the selectivity in NO–CO reaction. FTIR investiga-
tion showed that wavenumbers of stretching vibration of linearly
adsorbed CO on Pd were 2069 and 2080 cm−1 on Pd/Al2O3 and
Pd/LaMnO3/Al2O3 catalysts, respectively. This suggests that elec-
tronic density of Pd in Pd/LaMnO3/Al2O3 is lower than that in
Pd/Al2O3 and that the interaction between Pd and LaMnO3 exists
in Pd/LaMnO3/Al2O3. The implication of the interaction with the
catalytic property will be revealed in a future study.
320
: Pd/LaMnO3/Al2O3
: Pd/Al2O3
300
280
260
240
600
700
800
900
Calcination temperature / oC
3.4. Thermal stability
Fig. 7. Catalytic activity for NO–CO reaction of Pd/LaMnO3/Al2O3 calcined at 650,
700, 800 and 900 ◦C. The activity is expressed by the temperature of 50% NO con-
version.
Thermal stabilities of Pd/Al2O3 and Pd/LaMnO3/Al2O3 were
investigated by the characterization and activity evaluation of the
catalysts calcined at 650, 700, 800 and 900 ◦C in air. Characteri-
zation results are summarized in Table 3. Specific surface areas
were not so much changed by the calcination at higher temper-
atures. With an increase in calcination temperature, Pd dispersions
decreased steadily up to 800 ◦C and suddenly at 900 ◦C. This is con-
sistent with XRD results (Fig. 5) that the peak intensity from PdO
increased with increasing calcination temperature and that incre-
ment between 800 and 900 ◦C was prominent. It should be noted
that the decrease in Pd dispersion in Pd/LaMnO3/Al2O3 up to 800 ◦C
was more moderate than that in Pd/Al2O3. This indicates that the
interaction between Pd and LaMnO3 in the alumina pores has pos-
itive effect in suppression of sintering of Pd species.
Fig. 6 shows H2-TPR profiles for Pd/LaMnO3/Al2O3 calcined at
different temperatures. The reduction behavior changed gradually
with increasing calcination temperature; the negative peak became
intense and the reduction peak of La–Mn perovskite became higher
with increasing calcination temperature. Taking the above discus-
: Al2O3
: PdO
700oC
800oC
900oC
20
30
40
50
2θ / deg.
60
70
80
Fig. 5. XRD patterns of Pd/LaMnO3/Al2O3 calcined at 700, 800 and 900 ◦C.
Table 3
Characterization of Pd/Al2O3 and Pd/LaMnO3/Al2O3 calcined at different temperatures.
Sample name
Calcination
XRD phases
SBET/m2g−1
Pd dispersion/%
temperature/◦C
650
700
800
900
PdO, A12O3
PdO, A12O3
PdO, A12O3
PdO, A12O3
126
115
102
102
33
12
11
3
Pd/Al2O3
650
700
800
900
PdO, A12O3
PdO, A12O3
PdO, A12O3
PdO, A12O3
107
102
102
94
33
21
18
3
Pd/LaMnO3/Al2O3

108
A. Tou et al. / Catalysis Today 201 (2013) 103–108
sion into account, it can be said that the interaction between Pd and
LaMnO3 becomes weaker with increasing calcination temperature
and practically disappears at calcination temperature of 900 ◦C.
Fig. 7 shows the relationship between calcination temperature
and the catalytic activity for NO–CO reaction which is represented
by the temperature of 50% NO conversion. The abrupt drop of the
activity at 900 ◦C is reasonably ascribable to the prominent growth
of particles of Pd species. Pd/LaMnO3/Al2O3 showed higher activity
than Pd/Al2O3 at all the calcination temperatures, suggesting the
sustainment of the Pd–LaMnO3 interaction at higher calcination
temperatures.
study in more details between Pd/LaMnO3/Al2O3 and
LaMnO3out/Pd/Al2O3 with the same composition but different
location of or interaction between Pd and LaMnO3 is under-
going to clarify the origin of the synergic action of Pd and
LaMnO3.
References
[1] J.M.D. Tascón, L.G. Tejuca, C.H. Rochester, Journal of Catalysis 95 (1985)
558–566.
[2] M.A. Pen˜a, J.M.D. Tascón, J.L.G. Fierro, L. González Tejuca, Journal of Colloid and
Interface Science 119 (1987) 100–107.
[3] N. Yamazoe, Y. Teraoka, Catalysis Today 8 (1990) 175–199.
[4] N. Guilhaume, S.D. Peter, M. Primet, Applied Catalysis B: Environmental 10
(1996) 325–344.
4. Conclusions
[5] Y. Nishihata, J. Mizuki, T. Akao, H. Tanaka, M. Uenishi, M. Kimura, T. Okamoto,
N. Hamada, Nature 418 (2002) 164–167.
[6] K. Zhou, H. Chen, Q. Tian, Z. Hao, D. Shen, X. Xu, Journal of Molecular Catalysis
A: Chemical 189 (2002) 225–232.
[7] A. Eyssler, A. Winkler, P. Mandaliev, P. Hug, A. Weidenkaff, D. Ferri, Applied
Catalysis B: Environmental 106 (2011) 494–502.
[8] S. Cimino, M.P. Casaletto, L. Lisi, G. Russo, Applied Catalysis A: General 327
(2007) 238–246.
[9] S. Cimino, F. Donsì, G. Russo, D. Sanfilippo, Catalysis Letters 122 (2008)
228–237.
[10] T. Asada, T. Kayama, H. Kusaba, H. Einaga, Y. Teraoka, Catalysis Today 139 (2008)
37–42.
[11] Y. Teraoka, S. Nanri, I. Moriguchi, S. Kagawa, K. Shimanoe, N. Yamazoe, Chem-
istry Letters 29 (2000) 1202–1203.
[12] T. Takeguchi, S. Manabe, R. Kikuchi, K. Eguchi, T. Kanazawa, S. Matsumoto, W.
Ueda, Applied Catalysis A: General 293 (2005) 91–96.
[13] A. Baylet, P. Marecot, D. Duprez, P. Castellazzi, G. Groppi, P. Forzatti, Physical
Chemistry Chemical Physics 13 (2011) 4607–4613.
LaMnO3was selectively deposited inside or outside the pores
of alumina by using IW and I-RHP methods, respectively. By the
combination of intra-pore deposited Pd, two types of alumina sup-
ported Pd–LaMnO3 catalysts were successfully obtained; in one
catalyst (Pd/LaMnO3/Al2O3), both Pd and LaMnO3 coexist in the
alumina pores, and in the other (LaMnO3out/Pd/Al2O3), Pd and
LaMnO3 exist separately in and out of alumina pores, respectively.
The close proximity and interaction between Pd and LaMnO3 in the
intra-pore co-deposited catalyst were suggested by the reduction
behavior of supported Pd–LaMnO3 catalysts. For NO–CO catalytic
reaction, Pd/LaMnO3/Al2O3 showed higher activity than and differ-
ent N2/N2O selectivity from Pd/LaMnO3 and LaMnO3out/Pd/Al2O3,
revealing that the intimate Pd–LaMnO3 interaction is effective to
modify the catalytic property of Pd species. The excellent catalytic
property of Pd/LaMnO3/Al2O3 was sustained up to 800 ◦C of calci-
nation temperature.
[14] W. wang, H. Zhang, G. Lin, Z. Xiong, Applied Catalysis B: Environmental 24
(2000) 219–232.
[15] E.M. Vogel, D.W. Jonson Jr., P.K. Gallagher, Journal of the American Ceramic
Society 60 (1977) 31–33.
[16] J.L.G. Fierro, J.M.D. Tascon, L.G. Tejuca, Journal of Catalysis 89 (1984) 209–216.
[17] L. Lisi, G. Bagnasco, P. Ciambeli, S.D. Rossi, P. Porta, G. Russo, M. Turco, Journal
of Solid State Chemistry 146 (1999) 176–183.
[18] M.L. Rojas, J.L.G. Fierro, L.G. Tejuca, A.T. Bell, Journal of Catalysis 124 (1990)
41–51.
The present study has revealed that the interaction between Pd
and LaMnO3 effectively appears when they coexist in alumina pores
in close proximity and that the interaction promotes the catalytic
property for NO–CO reaction of Pd species. The comparative