Journal of Alloys and Compounds 470 (2009) 387–392
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Synthesis and characterization of Al O -Ce Zr O powders prepared by
2
3
0.5
0.5
2
chemical coprecipitation method
Chia-Che Chuang , Hsing-I Hsiang , Jenn Shyong Hwang , Tai Shen Wangb
a
a,∗
b
a
Particulate Materials Research Center, Department of Resources Engineering, National Cheng Kung University,
No. 1 University Road, Tainan 70101, Taiwan
b
Department of Physics, National Cheng Kung University, No. 1 University Road, Tainan 70101, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Al O -Ce0.5Zr0.5O2 catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical
2
3
Received 22 November 2007
Received in revised form 20 February 2008
Accepted 22 February 2008
Available online 16 April 2008
mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spec-
troscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al ions
affected the phase development, texture and oxygen storage capacity (OSC) of the Ce0.5Zr0.5O2 powder.
3+
Single phase of ACZ-C could be maintained without phase separation and inhibit ␣-Al2O3 formation up
◦
2
2
to 1200 C. The specific surface area value of ACZ-C (81.5 m /g) was larger than that of ACZ-M (62.1 m /g)
Keywords:
2
◦
and Ce0.5Zr0.5O2 (17.1 m /g) powders, which were calcined at 1000 C. In comparison with ACZ-C and
Al2O3, which were calcined at high temperature (900–1200 C), it was found that the degradation rate
Al2O3-Ce0.5Zr0.5O2
Co-precipitation method
Thermal stability
◦
of specific surface area of ACZ-C was lower than that of Al2O3. ACZ-C sample showed a higher thermal
stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity
property for Ce0.5Zr0.5O2 powders.
Oxygen storage capacity
©
2008 Elsevier B.V. All rights reserved.
1
. Introduction
can improve OSC performance. Besides, Fornasiero et al. [2] have
reported that an optimum composition, like Ce0.5Zr0.5O2 (molar
ratio of Ce:Zr = 1:1) can exist as a cubic phase, which can have
best redox property. Therefore, the homogeneity of the composi-
Promoting the catalyst conversion performance of the vehicle
exhaustis important for the increasinglyrestrictedemission regula-
tions. The next generation of emission catalysts must have following
two characteristics: (i) high thermal stability to resist the high tem-
perature sintering and the deactivation resulting from the closely
coupled converter (CCC), (ii) high surface area to increase the reac-
tion efficiency, and achieve higher noble metal dispersion, thereby
decreasing noble metal usage [1].
tion and crystalline phase play crucial roles in the CeO –ZrO2 solid
2
solution for TWC applications. Some researches [1,3,8,9] have pro-
posed that addition of Al O can promote the thermal stability and
2
3
specific surface area of CeO –ZrO2 solid solution. Various prepara-
2
tion methods (coprecipitation, impregnation and sol–gel methods)
[9,10] have been employed in order to synthesize a homogeneous
CeO -ZrO /Al O catalyst. These methods can both combine the
CeO has been widely applied in many fields, including catalysis,
2
2
2
2
3
fuel cell and glass polishing technologies. In current three-way cat-
alyst (TWC) for automotive pollution control, the unique reducing
and oxidizing properties of CeO2 allow the catalyst to enlarge the
operating air/fuel (A/F) ratio window [2]. In a reducing atmosphere,
advantages of high specific surface area of Al O3 and high OSC
2
property of the CeO –ZrO2 solid solution.
2
Recently, Morikawa et al. [11] investigated the effect of intro-
ducing alumina into CeO –ZrO solid solution as a diffusion barrier
2
2
CeO2 releases oxygen to form CeO
(x < 2). However, CeO
can
on the physical properties and OSC characteristics and observed
that the improvement of OSC could be achieved by suppression of
grain growth of CeO –ZrO2 and Pt particles via introducing Al O3
2−x
2−x
easily absorb oxygen and form CeO2 in an oxidizing atmosphere.
This is the so-called oxygen storage capacity (OSC) characteris-
tics.
2
2
as a diffusion barrier at nanometer scale. However, the effects of
alumina doping and mixing extent of Al3+ on the development
of phase separation and texture characteristics of Ce0.5Zr0.5O2 are
not clear. Therefore, in this study, the effect of mixing extent of
The redox property of CeO is greatly enhanced by incorpo-
2
ration of zirconium ions (Zr4 ) into the lattice to form a solid
+
homogeneity of Ce and Zr atoms in the CeO –ZrO2 solid solution
3+
Al ions on the crystallite size, phase development and texture
2
◦
characteristics of Ce0.5Zr0.5O2 after heat treatment at 500–1200 C
were investigated. In addition, the effects of these microscopic char-
acteristics on the macroscopic OSC property were discussed as
well.
∗ Corresponding author. Tel.: +886 6 27527575x62821; fax: +886 6 2380421.
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.02.078