Research Journal of Recent Sciences ________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 178-184 (2012)
Res.J.Recent Sci.

LaCoO3 perovskite catalysts for the environmental application of
Auto motive CO oxidation
Patel Femina and Patel Sanjay
Department of Chemical Engineering, Institute of Technology, Nirma University, Ahmedabad-382481, INDIA

Available online at: www.isca.in
(Received 15th October 2011, revised 10th January 2012, accepted 25th January 2012)

Abstract
Perovskite-type oxides were synthesized through conventional citrate methods. The synthesized perovskite materials had the
nominal compositions of LaCoO3, LaCo0.8Cu0.2O3, La0.8Sr0.2CoO3 and La0.8Sr0.2Co0.8Cu0.2O3. The catalytic activity of the
perovskite samples (for CO oxidation) were measured using a stainless steel reactor with an inlet gas mixture containing
exhaust composition as gasoline engine. The prepared perovskite samples were characterized by nitrogen adsorption (BET),
EDX and XRD analyses. The perovskite catalysts showed good structural and chemical stability and high activity for the
catalytic CO oxidation reaction. The catalyst samples prepared by the citrate method achieved the same CO conversion at
lower temperatures than those prepared by the sol gel method. This was attributed to a better-formed perovskite crystals by the
citrate method. Substituted perovskite composition showed higher activity for CO conversions higher than 90%. Hence, for the
environmental application of the automotive emission control, it can completely eliminate the poisonous CO gas.
Keywords: Catalytic converter, perovskite, automotive emission, catalyst, citric acid method.

Introduction
The purification of automobile exhaust gases (carbon
monoxide (CO), unburned hydrocarbon (HC) and nitrogen
oxides (NOx)) which can cause the green house gas effect,
depletion of the ozone layer, acid rain and photochemical
smog is regarded as one of the main objectives for catalytic
control of air pollution1-3. Several series of catalytic materials
including supported noble metals, metal oxides,
mesostructured alumino-silicates, pillared clays and active
carbon were investigated as catalysts for purification of
automobile exhaust gases4.
These harmful components convert to inert gases such as
carbon dioxide in catalytic converters before the exhaust gas
emitted to the atmosphere. The catalytic converters are, in
fact reactors that consist of monolithic honeycombs skeleton
made of ceramic or metallic materials. This structure is then
coated by a ceramic substrates impregnated with Pt, Pd and
other platinum group metals (PGM) as the active catalytic
sites5-7.
However, due to the rising cost of PGM, many researchers
have been searching for alternative materials as the active
catalytic phase. Perovskite oxides, promising alternatives to
supported noble metals for exhaust gas depollution because
of their low cost, thermal stability at rather high
temperatures, great versatility and excellent redox properties.
The general chemical formula for perovskite compounds is
ABO3, where 'A' and 'B' are two cations of very different
sizes and O is an anion that bonds to both. The 'A' atoms are

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larger than the 'B' atoms. A ion can be rare earth, alkaline
earth, alkali and other large ions such as Pb+2, Bi+3 that fits in
to the dodecahedral site of the framework. The B ion can be
3d, 4d and 5d transition metal ions. The ideal cubicsymmetry structure has the B cation in 6-fold coordination
surrounded by an octahedron of anions (B surrounded by six
oxygen in octahedral coordination) and the A cation in 12fold cuboctahedral coordination (A coordinated by 12
oxygen). Many metals are stable in the ABO3 perovskite
structure provided that the A and B cations have dimension
(rA > 0.90 Å, rB > 0.51 Å) in agreement with the limits of
the so-called ―tolerance factor‖ t (0.8 < t < 1.0) defined by
Goldschimdt, as t = (rA+rO)/√2(rB+ rO), where rA, rB and rO
are the ionic radii for A, B and O, respectively7-10.
Perovskite compounds can also tolerate significant partial
substitution (A and/or B with metals A’, B’ correspondingly
of different oxidation states i.e. AA’BO3, ABB’O3 etc. or A1xA’xB1-yB’yO3±δ) and oxygen non-stoichiometry (oxygen
excess as well as deficiency) indicated by the δ subscript in
the formula while still maintaining the perovskite structure 1113
.
The catalytic properties of perovskite-type oxides basically
depend on the nature of A and B ions and on their valence
state. The A site ions are catalytically inactive. The nature of
these ions however also influences the stability of the
perovskite phase. Catalytic activity is generally determined
by the B cation. The substitution at A site with ions having
lower valence can allow the formation of structural defects
such as anionic or cationic vacancies and/or a change in the

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Vol. 1 (ISC-2011), 178-184 (2012)
Res. J. Recent Sci.
oxidation state of the transition metal cation to maintain the
electro neutrality of the compound. When the oxidation state
of B cation increases, the relative ease of the redox process
generates larger quantities of available oxygen at low
temperature and the overall oxidation activity enhances.
Moreover, the oxygen vacancies favour the catalytic activity
in oxidation reaction because they increase the lattice oxygen
mobility. Substitution with a cation with the same valence
state should not lead in principle, to the occurrence of the
above mentioned modifications due to the unchanged charge
balance. Moreover, B-site substitution of perovskites was
also considered an effective way to improve their catalytic
properties due to the generation of new lattice defects, mixed
valence states and nonstoichiometric oxygen.
Several synthesis methods for preparation of perovskite
phases have been proposed and developed over the years.
These methods include pyrolysis, co-precipitation, citrate
complexation, spray-drying, freeze-drying, micro emulsion,
sol–gel process etc. Among those, the benchmark methods
are co-precipitation and citrate methods14-17.
Perovskite-type oxides have been widely studied in the last
years as catalysts for CO oxidation due to their high activity
and thermal stability. It is well documented that the oxidation
activity is mainly controlled by the nature of the B-site
element with Co, Mn and Fe being usually reported as the
most effective metals when lanthanum is in the A-site11-13.
Synergistic effects can be a powerful tool of catalyst design
and effect is due to combination of two different ions at the
B-site This synergistic effect is due to bifunctional catalysis
of Mn and Cu located at B site in 1:1 atomic ratio and
exhibits a very high catalytic activity for CO oxidation18, 19 .
It has also been reported that partial substitution of transition
metal at B site with other trivalent cation can be effective to
enhance oxidation activity of perovskites. In particular,
Zhong et al. studied LaFe1−xMxO3 (M = Al, Mn, Co)
perovskites and claimed a synergistic effect due to the
presence of two types of B cations which causes an increase
in their average oxidation state resulting in better
performances for methane oxidation20.
In this work, two synthesis methods, namely citrate method
and sol gel were implemented for preparation of perovskite
catalyst samples. To study the effect of Sr and Cu
substitution for A and B cations in the ABO3 perovskite
structure were synthesized and tested for carbon monoxide
oxidation in an oxygen gas stream.

Material and Methods
Catalyst preparation: Citrate method (CT): The citrate
compound was prepared by complexation of the nitrate salts
with citric acid. A concentrated solution of the metal nitrates
was mixed with an aqueous solution of citric acid by fixing
at unity the molar ratio of citric acid to the metal cations.
Metal nitrates La(NO3)3.6H2O, Sr(NO3)2, Co(NO3)2.6H2O,

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Sr(NO3)2 and Cu(NO3)2. 3H2O) were first dissolved in
distilled water (25 ml). Citric acid (10% excess over the
number of ionic equivalents of cations) was separately
dissolved in distilled water (25 ml) and added to the
precursor solution under vigorous stirring for 15 min. Excess
water was evaporated under slow stirring in oil bath at 80 0C
until a gel was obtained. The viscous gel was then dried at
100 0C overnight in hot air oven. The obtained spongy
material was finely ground and calcined under air
atmosphere at 750 0C for 5 h.
Sol-Gel method using citric acid as complexing agents
(Sol gel): A LaCoO3 compound was synthesized by a sol–gel
method employing citric acid as complexing agent. The
required amounts of the precursor salts (La(NO3)3. 6H2O,
Co(NO3)2. 6H2O) along with citric acid were dissolved in
water at an equivalent ratio of 1:1 (metal cations : citric
acid). Ethylene glycol (25 ml) and citric acid were used to
make the gel. The Ethylene Glycol and citric acid were
added drop-wise to the nitrate solution and they were stirred
for 15 min. The resulting solutions were heated to 800C to
form a viscous gel finally yield a solid precursor upon slow
solvent evaporation at that temperature for several hours.
This gel was dried in an oven at 1000C overnight and after
thorough grinding of the resulting powder, it was finally
calcined under air at 750 0C for 5 h in order to achieve the
corresponding perovskite structure in the samples.
X-ray Diffraction: Phase analysis, lattice parameters and
particle sizes were determined by X-ray diffraction (XRD)
using PW1774 Spinner Diffractometer system XPERT-MPD
operated at 40 kV and 30 mA with Ni-filtered Cu Kα
radiation ( = 1.5406 Å). Spectra were recorded with step
scans from 20 to 990 in 2θ angle and 1 s for each 0.05 0 step.
Lattice parameters were calculated from the reflections
appearing in the 2θ = 2–990 range using the software
program. The identification of the crystal phases took place
using the JCPDS (Joint committee on Powder diffraction
standards) data bank.
Particle sizes (D) were calculated by means of the Scherrer
equation D = Kλ/βcos θ after Warren’s correction for
instrumental broadening. K is a constant equal to 0.9, λ the
wavelength of the X-ray used, β the effective linewidth of the
observed X-ray reflection, calculated by the expression β2 =
B2 − b2 (where B is the full width at half maximum (FWHM),
b the instrumental broadening determined through the
FWHM of the X-ray reflection at 2θ ≈ 280 of crystalline SiO2
with particles larger than 1000 Å, θ the diffraction angle.
Energy dispersive X-ray spectroscopy (EDX or EDS):
Energy Dispersive of X-Ray (EDX) of samples was carried
out in JEOL made instrument JEM2100 model which has
attached detector OXFORD Instrument INCA X-SIGHT
model. EDX was used to investigate the morphology as well
as the elemental composition and distribution of all the
catalyst compositional analysis.

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Vol. 1 (ISC-2011), 178-184 (2012)
Res. J. Recent Sci.
BET surface area: BET Surface area of the materials were
measured by nitrogen adsorption at the liquid nitrogen
temperature (-1960C) using a volumetric all glass apparatus.
The specific surface area of the materials calcined at 750 0C
for 5 h was determined from nitrogen adsorption isotherms
measured at -196 0C using a Micromeritics ASAP 2020
instrument. Samples were degassed at 3000C under vacuum
(10-3 Pa) until complete removal of humidity (about 3-4 h)
prior to adsorption–desorption experiments. Nitrogen
adsorption measurements were performed up to a relative
pressure P/P0 = 1. The specific surface area was determined
from the linear part of the BET curve. The pore size
distribution was calculated from the desorption branch of N2
adsorption/desorption isotherms using the Barrett–Joyner–
Halenda (BJH) formula. Pore volume and average diameter
were also obtained from the pore size distribution curves
using the software.
Catalytic activity: Before the activity tests, the catalyst in
the bed was activated by passing N 2 (90 %) and O2 (10 %) at
440 cm3 min−1 for 2 h at 500 0C below the calcinations
temperature to remove adsorbed moisture.
Catalytic activity in the combustion of carbon monoxide was
determined using a catalyst charge of about ca. 1 g
previously added with 3 g of SiO2 (0.5–1.5 mm granulate) in
order to reduce the specific pressure drop across the reactor
and to prevent thermal runaways placed between two
ceramic blanket wool and inserted into stainless steel fixed
bed reactor (I.D. 1.805 cm, O.D. 1.905 cm and L.50 cm). The
reactor operated in a down flow mode at atmospheric
pressure was placed in a tubular PID-regulated furnace. The
reaction temperature was controlled with a K type
thermocouple placed in the catalytic bed. A gas mixture 7.9
% CO, 9.64 % O2, N2 as balance with a total gas hourly space
velocity (GHSV) of 29000 Ncm3 g−1 h−1. The outlet and inlet
gas compositions were followed using gas chromatograph
equipped with Shin Carbon ST Micropacked column and a
µTCD detector. Helium was used as a carrier gas at a flow of
20 ml min-1 and the analysis is conducted isothermally at 60
0
C.
The CO conversion in activity tests was defined as:
XCO= (Ff,CO - Fp,CO)/ Ff,CO
Ff,CO: Molar flow rate of CO in feed stream, Fp,CO: Molar
flow rate of CO in product stream

Results and Discussion
Catalyst characterization: XRD measurement of LaCoO3,
LaCo0.8Cu0.2O3, La0.8Sr0.2CoO3 and La0.8Sr0.2Co0.8Cu0.2O3
(calcined at 750 0C for 5 h) were prepared by citrate method,
LaCoO3 prepared by sol gel method (calcined at 750 0C for 5
h) and its XRD patterns are presented in figure - 1. The
comparison of these spectra with JCPDS charts indicates that
all Co based samples except La0.8Sr0.2CoO3 are essentially

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perovskites type mixed oxides (JCPDC card 00-025-1060,
00-006-0491). Other phases such as SrCoO2.8 (JCPDS card
00-039-1084) in the case of La0.8Sr0.2CoO3 was detected in
addition to the major ABO3 Perovskite phase.
Phase formation is closely related to the calcination
temperature. At 750 0C, all the catalyst samples except
La0.8Sr0.2CoO3 completely transformed lanthanum and cobalt
nitrates into LaCoO3 perovskite phase. No spinel phase
La2CoO4 (that normally tends to form at higher temperatures)
was observed in these samples.
Moreover, a small shift of diffraction peaks in XRD patterns
of Cu substituted samples to low diffraction angle (2θ) with
respect to unsubstituted one implied that Cu had indeed been
introduced into the perovskite lattice. The crystallite sizes of
prepared perovskites calculated by Scherrer’s equation after
Warren’s correction of instrumental broadening are also
reported in table - 1.
The results for the nitrogen isothermal sorption at 77 K for
LaCoO3, LaCo0.8Cu0.2O3 perovskite- type mixed oxides
prepared by citrate method and LaCoO3 prepared by sol gel
method are presented in figure -2, respectively. All the
isothermal results show hysteresis loops, whose
characteristics exhibit dependence on the structure of the
samples which are confirmed to be with a porous
morphology. The specific surface area (BET surface area),
pore size and pore volume of the samples synthesized by
citrate method and sol gel method after calcinations at 750 0C
for 5 h are listed in table - 1.
Adsorption-desorption isotherms of the catalysts have shown
similar characteristics. Barett-Joyner- Halendar (BJH)
analysis showed that catalyst pores were meso size and the
average pore sizes were found to be in between 2 and 27 nm.
Catalytic oxidation of CO: The catalytic activity of the
perovskite samples chiefly depends on three factors:
chemical composition, degree of crystallinity and the crystals
morphology (including particle sizes, pore size distribution
and specific surface area of the perovskite catalyst). All these
factors are affected by the synthesis method and the specific
synthesis operating conditions.
The temperature corresponding to 50% conversion of CO is
defined as the catalyst ―light off‖ temperature and it is an
important parameter in catalytic reactions. The lower the
light off temperature, the more active the catalyst is. The
light off temperature for a catalyst prepared by citrate
method is around 420 0C for CO conversion (shown in figure
- 3) in case of LaCoO3 prepared by citrate method which
lower than the perovskite prepared by sol gel. The
enhancement of catalytic activity may attribute to both the
higher BET surface of the perovskite used and large number
of active sites available in case of citrate method.

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Res. J. Recent Sci.

(a)

(b)

(c )

(d)

(e)

Figure - 1
XRD patterns of (a) LaCoO3 by CT (b) LaCo0.8Cu0.2O3 by CT (c) La0.8Sr0.2CoO3 by CT
(d) La0.8Sr0.2Co0.8Cu0.2O3 by CT and (e) LaCoO3 by sol gel

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Vol. 1 (ISC-2011), 178-184 (2012)
Res. J. Recent Sci.

(a)

(b)

(c)
Figure - 2
N2 adsorption-desorption isotherm of (a) LaCoO3 by CT
(b) LaCo0.8Cu0.2O3 by CT (c) LaCoO3 by sol gel

Sr.
No.

Sample

1
2
3

LaCoO3
LaCo0.8Cu0.2O3
La0.8Sr0.2CoO3

4
5

La0.8Sr0.2Co0.8Cu0.2O3
LaCoO3 (sol gel)

Table - 1
Properties of Co-based catalysts after calcinations at 750 0C for 5 h
Calcination
Crystallite
Phases
Specific Surface
Pore
T
Size (nm)
area (m2/g)
diameter
(nm)
750 0C
35-56
P
8.78
9.77
29-42
P
3.04
11.29
25-56
P+O
3.91
8.32
(SrCoO2.8)
25-34
35-42

Adding impurities to the benchmark LaCoO3 perovskite
sample, in general may enhance the rate of combustion due
to an increase in the oxygen mobility in the bulk of the solid.
Partial substitution of transition metal at B site with other
cation (Cu) can be effective to enhance oxidation activity of
perovskites due to synergistic effect (due to combination of
two different ions at the B-site). Synergistic effect is due to
the presence of two types of B cations which causes an
increase in their average oxidation state resulting in better
performances for carbon monoxide oxidation. This is

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P
P

3.75
5.22

9.97
27.42

Pore
volume
(cm3/g)
0.0214
0.0086
0.0081
0.0093
0.0358

probably the reason that perovskite composition of La
Co0.8Cu0.2O3 has resulted in the best CO oxidation
performance compare to unsubstituted LaCoO3 prepared by
citrate method. Activity tests of the catalysts shows that
LaCoO3 has 50 % conversion for CO at 420 0C and the
maximum conversion was found around 58% even it has
large surface area due to less active site available for
catalytic activity and also low residence time of the reactants
in the bed.

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Vol. 1 (ISC-2011), 178-184 (2012)
Res. J. Recent Sci.
100
90
CO conversion %

80

(a)
(b)
(c)

70
60
50
40
30
20
10
0
0

100

200

300

400

Temperature,

500

600

700

0C

Figure - 3
CO conversion as function of temperature for LaCoO 3 perovskites prepared by
(a) CT : CO: 7.9 %, O2 : 9.64 %, N2 : 82.39 %, SV : 29000 Ncm3g-1h-1) and
(b) Sol gel (CO: 7.9 %, O2 : 9.64 %, N2 : 82.39 %, SV : 29000 Ncm3g-1h-1),
(c) LaCo0.8Cu0.2O3 by CT : CO : 6.8 %, O2 : 17.6 %, N2: 85.67 %, SV = 48810 Ncm3g-1h-1

Conclusion
Perovskite samples were synthesized by the citrate (LaCoO 3,
LaCo0.8Cu0.2O3, La0.8Sr0.2CoO3 and La0.8Sr0.2Co0.8Cu0.2O3)
and sol gel (LaCoO3) methods and tested toward CO
oxidation reaction using a gas mixture.
Various
characterization techniques confirmed that the citrate method
produces lower crystallinity and higher surface are than the
sol gel method. The oxidation catalytic activity of the
substituted samples produce by the citrate method was higher
than the samples produced by sol gel due to synergistic effect
in case of substituted catalyst.

3.

Heck R. and Farrauto R., Automobile exhaust
catalysts, Applied Catalysis A: General, 221, 443457 (2001)

4.

Traa Y., Burger B. and Weitkamp J., Zeolite-based
materials for the selective catalytic reduction of NOx
with hydrocarbons, Microporous and Mesoporous
Materials, 30, 3–41 (1999)

5.

Zhang R., Villanueva A., Alamdari H. and Kaliaguine
S., Catalytic reduction of NO by propene over LaCO1xCuxO3 perovskites synthesized by reactive grinding,
Applied Catalysis B: Environmental, 64, 220-233
(2006)

6.

Seyfi B., Baghalha M. and Kazemian H., Modified
LaCoO3
nano-perovskite
catalysts
for
the
environmental application of automotive CO
oxidation, Chemical Engineering Journal, 148, 306311 (2009)

7.

Sharma S., Hegde M., Das R. and Pandey M.,
Hydrocarbon oxidation and three-way catalytic
activity on a single step directly coated cordierite
monolith: High catalytic activity of Ce0.98Pd0.02O2,
Applied Catalysis A: General, 337, 130–137 (2008)

8.

H. Iwakuni, Shinmyou Y., Yano H., Matsumoto H.
and Ishihara T., Direct decomposition of NO into N 2
and O2 on BaMnO3 – based perovskites oxides,
Applied Catalysis B: Environmental, 74, 299-306
(2007)

Acknowledgement
The work described above was fully supported by a research
grant from the Nirma University.

References
1.

Shinjoh H., Rare earth metals for automotive exhaust
catalysts, Journal of Alloys and Compounds, 408-412,
1061-1064 (2006)

2.

Thakur
Prabhat, Rahul Mathur Anil and
Balomajumder Chandrajit, Biofiltration of volatile
organic compounds (VOCs) – An overview, Research
Journal of Chemical Sciences, 1(8), 83-92 (2011)

International Science Congress Association

183

Research Journal of Recent Sciences ____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 178-184 (2012)
Res. J. Recent Sci.
9.

10.

11.

12.

Ciambelli P., Cimino S., De Rossi S., Lisi L., Minelli
G., Porta P. and Russo G., AFeO3 (A= La, Nd, Sm)
and LaFe1−xMgxO3 perovskites as methane
combustion and CO oxidation catalysts: structural,
redox and catalytic properties, Applied Catalysis B:
Environmental, 29, 239–250 (2001)
Ciambelli P., Cimino S., Lisi L., Faticanti M., Minelli
G., Pettiti I. and Porta P., La, Ca and Fe oxide
perovskites: preparation, characterization and
catalytic properties for methane combustion, Applied
Catalysis B: Environmental, 33, 193–203 (2001)
Alifanti M., Blangenois N., Florea M. and Delmon B.,
Supported Co-based perovskites as catalysts for total
oxidation of methane, Applied Catalysis A: General,
280, 255–265 (2005)
Thomas Screen, Platinum group metal perovskite
catalysts – Preparation and Application, Platinum
Metals Review, 51(2), 87–92 (2007)

13.

Nishihata Y., Cleaning up catalyst, News and views,
Nature, 418, 138 (2002)

14.

Zhang R., Alamdari H. and Kaliaguine S., Fe-based
perovskites substituted by copper and palladium for
NO+ CO reaction, Journal of Catalysis, 242, 241–253
(2006)

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15.

Asuman C., Canan K., Askar K. and Nesrin O.,
Catalytic Combustion of Methane over LaαCeβCo(2-αPerovskite Catalysts, Third European
β)O3±δ
combustion meeting ECM , (2007)

16.

Paolo C., Stefano C., Sergio D., Marco F., Luciana L.,
Giuliano M., Ida P., Piero P., Gennaro R. and Maria
T., AMnO3 (A=La, Nd, Sm) and Sm1−xSrMnO3
perovskites as combustion catalysts: structural, redox
and catalytic properties, Applied Catalysis B:
Environmental, 24, 243–253 (2000)

17.

Ozuomba J. O. and Ekpunobi A. J., Sol-Gel Derived
Carbon Electrode for Dye-Sensitized Solar Cells,
Research Journal of Chemical Sciences, 1(8), 76-79
(2011)

18.

Tanakaa H. and Misono M., Advances in designing
perovskite catalysts, Current Opinion in Solid State
and Materials Science, 5, 381–387 (2001)

19.

Strobel R., Baiker A. and Pratsinis S. E., Aerosol
flame synthesis of catalysts, Advanced Powder
Technology, 17(5), 457–480 (2006)

20.

Lima R. K. C. de , Batista M. S., Wallau M., Sanches
E. A. , Mascarenhas Y. P. and Urquieta-Gonza lez E.
A. lez, High specific surface area LaFeCo perovskites
— Synthesis by nanocasting and catalytic behavior in
the reduction of NO with CO, Applied Catalysis B:
Environmental , 90, 441–450 (2009)

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