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This article is part of the series Nano Component 2011.

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Aluminum-doped ceria-zirconia solid solutions with enhanced thermal stability and high oxygen storage capacity

Qiang Dong, Shu Yin*, Chongshen Guo and Tsugio Sato

Author Affiliations

Center for Exploration of New Inorganic Materials (CENIM), Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan

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Nanoscale Research Letters 2012, 7:542  doi:10.1186/1556-276X-7-542

The electronic version of this article is the complete one and can be found online at: http://www.nanoscalereslett.com/content/7/1/542

Received:23 July 2012
Accepted:17 September 2012
Published:1 October 2012

© 2012 Dong et al.; licensee Springer.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A facile solvothermal method to synthesize aluminum-doped ceria-zirconia (Ce0.5Zr0.5-xAlxO2-x/2, x = 0.1 to 0.4) solid solutions was carried out using Ce(NH4)2(NO3)6, Zr(NO3)3·2H2O Al(NO3)3·9H2O, and NH4OH as the starting materials at 200°C for 24 h. The obtained solid solutions from the solvothermal reaction were calcined at 1,000°C for 20 h in air atmosphere to evaluate the thermal stability. The synthesized Ce0.5Zr0.3Al0.2O1.9 particle was characterized for the oxygen storage capacity (OSC) in automotive catalysis. For the characterization, X-ray diffraction, transmission electron microscopy, and the Brunauer-Emmet-Teller (BET) technique were employed. The OSC values of all samples were measured at 600°C using thermogravimetric-differential thermal analysis. Ce0.5Zr0.3Al0.2O1.9 solid solutions calcined at 1,000°C for 20 h with a BET surface area of 18 m2 g−1 exhibited a considerably high OSC of 427 μmol-O g−1 and good OSC performance stability. The same synthesis route was employed for the preparation of the CeO2 and Ce0.5Zr0.5O2. The incorporation of aluminum ion in the lattice of ceria-based catalyst greatly enhanced the thermal stability and OSC.

Solvothermal; Aluminum; Solid solutions; Catalysis; Oxygen storage capacity; Thermal stability


Ceria (CeO2)-based materials have attracted considerable interest for more than half a century due to their far-ranging applications in catalysts, fuel cells, cosmetics, gas sensors, and solid-state electrolytes and especially their crucial application as promoters of three-way catalysts (TWCs), which are commonly used to reduce the emissions of CO, NOx, and hydrocarbons from automobile exhausts, because of their excellent oxygen storage capacity (OSC) [1-8]. Since 1990s, CeO2-ZrO2 solid solutions have gradually replaced pure CeO2 as OSC materials in the TWCs to reduce the emission of toxic pollutants (CO, NOx, hydrocarbons, etc.) from automobile exhaust and because of their enhanced OSC performance and improved thermal stability at elevated temperatures [9-13].

The redox property of CeO2 can be greatly enhanced by the incorporation of zirconium ions (Zr4+) into the lattice to form a solid solution [14-16]. Nagai et al. have suggested that enhancing the homogeneity of Ce and Zr atoms in the CeO2-ZrO2 solid solution can improve the OSC performance [17]. The detailed structure and property of CeO2-ZrO2 solid solutions were reported in a review article by Monte and Kaspar [12]. This review included the results of reducing performance for a series of samples with gradually elevated Ce contents, and a possible mechanism of structural changes in the reducing process was proposed. Fornasiero et al. 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 a considerably high redox property [18]. Using density functional theory, Wang et al. found that in a series of Ce1-xZrxO2 solutions with a content of 50%, ZrO2 possesses the lowest formation energy of the O vacancy; therefore, Ce0.5Zr0.5O2 exhibits the best OSC performance [19]. Recently, many researchers have paid much attention to prepare the Ce0.5Zr0.5O2 solutions with the homogeneity of the composition, good dispersion of particles, narrow particle size distribution, better crystallinity, and high surface area in order to improve OSC and redox property due to their catalytic applications [20-25].

Although Ce0.5Zr0.5O2 solid solutions have been studied extensively, there are few reports on the preparation of Ce0.5Zr0.5-xMxO2-x/2 in the literature [26,27]. Considering the smaller cation radius of Al3+ (0.059 nm) compared to those of Zr4+ (0.084 nm) and Ce4+ (0.097 nm), the incorporation of Al3+ into Ce-Zr solid solutions may enhance the oxygen release reaction to form larger Ce3+. In the present work, for the first time, we describe the preparation and characterization of Ce0.5Zr0.3Al0.2O1.9 solid solutions with high surface area via a facile solvothermal route. The further experiment results show that the introduction of aluminum ion enhances the thermal stability and OSC even after calcination at a very strict condition of 1,000°C for 20 h. The OSC of CeO2, Ce0.5Zr0.5O2, and the composites which consisted of different aluminum amounts were also prepared via the same method and compared.


All chemicals used were of analytical grade and were purchased from Kanto Chemical Co. Inc., Tokyo, Japan (purity 99.999%). The chemicals were used without further purification.

Catalysts preparation

The stoichiometric amounts of (NH4)2Ce(NO3)6 (6 mmol), ZrO(NO3)2 (3.6 mmol), and Al(NO3)3·9H2O (2.4 mmol) were dissolved in 60 ml of distilled water. NH4OH solution was slowly dropped into the above mixed solution, and the pH value was maintained at 9. The yellow mixed solution was introduced in a 100-ml Teflon®-lined autoclave (SAN-AI Science, Co. Ltd, Nagoya, Japan), which was maintained at 200°C for 24 h, then cooled to room temperature naturally. The obtained products were washed with distilled water three times and dried in air at 100°C for 12 h to form the as-prepared fresh samples. Finally, the fresh samples were calcined at 1,000°C for 20 h in air atmosphere to evaluate the thermal stability. The same synthesis route was employed for the preparation of the CeO2 and Ce0.5Zr0.5O2.

OSC analysis

The OSC of the samples calcined at 1,000°C for 20 h was determined by thermogravimetric-differential thermal analysis (TG-DTA; Rigaku TAS-200, Rigaku Corporation, Tokyo, Japan) at 600°C. Before the measurements, the samples were held in flowing air at 600°C for 30 min to remove residual water and other volatile gases. The mixed gas of CO-N2 (100 cm3 min−1) and air (100 cm3 min−1) was flowed alternately at 600°C. Finally, OSC was analyzed after getting the TGA profile.


The phase composition of the sample was determined by X-ray diffraction analysis (XRD; Bruker D2 Phaser, Bruker Optik GmbH, Ettlingen, Germany) using graphite-monochromized CuKα radiation. The morphology and size of the samples were determined by transmission electron microscopy (TEM; JEOL JEM-2010, JEOL Ltd., Akishima, Tokyo, Japan). The specific surface area was measured using a BET (NOVA 4200e, Quantachrome GmbH and Co. KG, Odelzhausen, Germany) surface area and pore size analyzer.

Results and discussion

All products of (a) CeO2, (b) Ce0.5Zr0.5O2, and (c) Ce0.5Zr0.3Al0.2O1.9 consisted of a single phase of fluorite structure (Figure 1 (a) to (c)). All the diffraction patterns exhibited broad peaks, suggesting that the fresh samples were nanocrystalline materials. The calcined samples had a slight shift in diffraction peaks when compared to the pure CeO2 XRD pattern, indicating the formation of corresponding solid solutions. The calculated lattice parameters of the calcined samples of Ce0.5Zr0.5O2 (a = 0.5384 nm) and Ce0.5Zr0.3Al0.2O1.9 (a = 0.5299 nm) are smaller than that of CeO2 (a = 0.5413 nm). The shrinkage of lattice cells may be due to the substitution of the smaller cation radius of Zr4+ (0.084 nm) and Al3+ (0.0059 nm) with Ce4+ (0.097 nm). No phase separation was noticed even at such high calcination temperatures at 1,000°C for 20 h, except the increase of particle size (Figure 1 (a') to (c')). The crystal sizes of the fresh CeO2, Ce0.5Zr0.5O2, and Ce0.5Zr0.3Al0.2O1.9 calculated by Scherer's formula were 9, 5, and 3 nm, while those of the calcined CeO2, Ce0.5Zr0.5O2, and Ce0.5Zr0.3Al0.2O1.9 were 35, 10, and 8 nm, respectively.

thumbnailFigure 1. XRD patterns of fresh and calcined samples. Fresh samples: (a) CeO2, (b) Ce0.5Zr0.5O2, and (c) Ce0.5Zr0.3Al0.2O1.9. Calcined samples: (a') CeO2, (b') Ce0.5Zr0.5O2, and (c') Ce0.5Zr0.3Al0.2O1.9.

The morphology and size of the fresh and calcined samples (1,000°C for 20 h) were observed by TEM as shown in Figure 2. For the fresh samples, the particles seem to be partly dispersed and formed small agglomerates (Figure 2 (a) to (c)), and the single particle exhibited a spherical-like morphology with the diameters of 9 to 12 nm, 5 to 8 nm, and 3 to 5 nm for CeO2, Ce0.5Zr0.5O2, and Ce0.5Zr0.3Al0.2O1.9, respectively, which are in agreement with the crystallite size calculated from Scherer's formula. The particle size increased after calcination at 1,000°C for 20 h because of aggregation, and the particle sizes were found to increase to 90 to 100 nm, 50 to 55 nm, and 30 to 35 nm for the CeO2, Ce0.5Zr0.5O2, and Ce0.5Zr0.3Al0.2O1.9 samples as shown in Figure 2 (a') to (c'), respectively.

thumbnailFigure 2. TEM images of fresh and calcined samples. Fresh samples: (a) CeO2, (b) Ce0.5Zr0.5O2, and (c) Ce0.5Zr0.3Al0.2O1.9. Calcined samples: (a') CeO2, (b') Ce0.5Zr0.5O2, and (c') Ce0.5Zr0.3Al0.2O1.9.

BET nitrogen adsorption-desorption analysis was undertaken to measure the specific surface area of all samples. As a result, the fresh sample of Ce0.5Zr0.3Al0.2O1.9 showed a much higher surface area (232 m2 g−1) than those of CeO2 (119 m2 g−1) and Ce0.5Zr0.5O2 (168 m2 g−1, Figure 3 (a) to (c)). After calcinations at 1,000°C for 20 h in air, the specific surface areas of CeO2 (3 m2 g−1) and Ce0.5Zr0.5O2 (8 m2 g−1) decreased to less than 10 m2 g−1, but the sample of Ce0.5Zr0.3Al0.2O1.9 exhibited a relatively higher BET specific surface area of 18 m2 g−1 (Figure 3 (a') to (c')).

thumbnailFigure 3. BET specific surface areas of fresh and calcined samples. Fresh samples: (a) CeO2, (b) Ce0.5Zr0.5O2, and (c) Ce0.5Zr0.3Al0.2O1.9. Calcined samples: (a') CeO2, (b') Ce0.5Zr0.5O2, and (c') Ce0.5Zr0.3Al0.2O1.9.

The OSC values of the calcined samples were determined at 600°C with a continuous flow of CO-N2 gas and air alternately. Figure 4 shows the typical TG profiles of the CeO2, Ce0.5Zr0.5O2, and Ce0.5Zr0.3Al0.2O1.9 samples. The TG profile shows the oxygen release/storage performance of the CeO2, Ce0.5Zr0.5O2, and Ce0.5Zr0.3Al0.2O1.9 samples at 600°C with time. As a result, Ce0.5Zr0.3Al0.2O1.9 exhibited a higher OSC of 427 μmol-O g−1, when compared to those of the CeO2 (25 μmol-O g−1) and Ce0.5Zr0.5O2 (350 μmol-O g−1) samples (Table 1). It is accepted that the OSC is dependent on the specific surface area; it is obvious that Ce0.5Zr0.3Al0.2O1.9 exhibited the highest specific surface area and highest OSC values even after calcination at such high temperature as 1,000°C for 20 h. In order to examine OSC performance stability, oxygen release/storage cycle measurement was tested, and Ce0.5Zr0.3Al0.2O1.9 retained the same OSC even after 22 cycles (Figure 5). The result indicates that Ce0.5Zr0.3Al0.2O1.9 has good OSC performance stability.

thumbnailFigure 4. TG profiles of calcined samples ( 1 , 000 ° C , 20 h ) at 600 °C, which show oxygen release / storage properties. (a) CeO2, (b) Ce0.5Zr0.5O2, and (c) Ce0.5Zr0.3Al0.2O1.9.

Table 1. OSC at 600 ° C of the CeO 2 , Ce 0 .5 Zr 0 .5 O2 , and Ce 0 .5 Zr 0 .3 Al 0 .2 O 1 .9 calcined at 1 ,000 ° C for 20 h

thumbnailFigure 5. TG profiles during measurement ofOSC at 600°C for Ce0.5Zr0.3Al0.2O1.9 (1,000°C, 20 h) after 22 cycles. The profiles show oxygen release/storage properties.

The amount of incorporated aluminum was also controlled to test its effect on the OSC of the calcined sample as shown in Figure 6 and Table 2. As a result, Ce0.5Zr0.3Al0.2O1.9 exhibited the highest OSC of 427 μmol-O g−1 (Table 1), when compared to those of the Ce0.5Zr0.4Al0.1O1.95 (378 μmol-O g−1), Ce0.5Zr0.2Al0.3O1.85 (389 μmol-O g−1), and Ce0.5Zr0.1Al0.4O1.8 (261 μmol-O g−1) samples (Table 2), Therefore, in Ce0.5Zr0.5-xAlxOy (0.1 <x < 0.5, x is the amount of incorporated aluminum), the most appropriate amount of incorporated aluminum might be around x = 0.2.

thumbnailFigure 6. TG profiles during measurement ofOSC at 600°C for calcined samples(1,000°C, 20 h). The profiles show oxygen release/storage properties. (a) Ce0.5Zr0.4Al0.1O1.95, (b) Ce0.5Zr0.2Al0.3O1.85, and (c) Ce0.5Zr0.1Al0.4O1.8.

Table 2. OSC at 600 ° C of the Ce 0 .5 Zr 0 .4 Al 0 .1 O 1 .95 , Ce 0 .5 Zr 0 .2 Al 0 .3 O1 .85 , and Ce 0 .5 Zr 0 .1 Al 0 .4 O 1 .8 calcined at 1 , 000 ° C for 20 h


Ce0.5Zr0.3Al0.2O1.9 solid solutions with high surface area were successfully synthesized via a facile solvothermal method. The structures of the fresh samples and calcined samples were characterized by X-ray diffraction. The lattice parameters of the Ce0.5Zr0.3Al0.2O1.9 solid solution are smaller than those of CeO2 and Ce0.5Zr0.5O2, suggesting the incorporation of the Al3+ into Ce-Zr solid solutions. The fresh particles showed spherical-like morphology with a diameter of 3 to 5 nm determined by TEM. The Ce0.5Zr0.3Al0.2O1.9 solid solutions exhibited a remarkably higher oxygen storage capacity than those of the CeO2 and Ce0.5Zr0.5O2 samples prepared via the same method, even after calcination at 1,000°C for 20 h, indicating the improvement of the OSC and thermal stability due to the incorporation of aluminum. An appropriate amount of incorporated aluminum is also suggested.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

QD participated in the design of the study, carried out the total experiments, and performed the result analysis as well as drafted the manuscript. SY participated in the design of the study, gave the theoretical and experimental guidance, and made the corrections of manuscript. CG mainly helped in the experiments and measurements. TS gave the theoretical and experimental guidance and helped to amend the manuscript. All authors read and approved the final manuscript.

Authors’ information

QD, SY, CG, and TS are an assistant professor, an associate professor, a Ph.D. candidate, and a full professor, respectively, at the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University.


This work was supported by the Rare Metal Substitute Materials Development Project of New Energy and Industrial Technology Development Organization (NEDO), Japan and the Management Expenses Grants for National Universities Corporations from the Ministry of Education, Culture, Sports and Science for Technology of Japan (MEXT).


  1. Yao HC, Yu YF: Ceria in automotive exhaustcatalysts: I. Oxygen storage.

    J Catal 1984, 86:254. Publisher Full Text OpenURL

  2. Di Monte R, Kasper J, Bradshaw H, Norman C: A rationale for the development of thermally stable nanostructured CeO2 -ZrO2 -containing mixed oxides.

    J Rare Earth 2008, 26:136. Publisher Full Text OpenURL

  3. Steele BCH: Fuel-cell technology: running on natural gas.

    Nature 1999, 400:619. Publisher Full Text OpenURL

  4. Steele BCH, Heinzel A: Materials for fuel-cell technologies.

    Nature 2001, 414:345. PubMed Abstract | Publisher Full Text OpenURL

  5. Yin S, Minamidate Y, Sato T: Synthesis and morphological control of monodispersed microsized ceria particles.

    Surf Rev Lett 2010, 17(2):147. Publisher Full Text OpenURL

  6. Yin S, Minamidate Y, Sato T: Synthesis of monodispersed plate-like CeO2 particles by precipitation process in sodium hydrogen carbonate solution.

    Adv Sci Technol 2010, 63:30. OpenURL

  7. Yin S, Minamidate Y, Tonouchi S, Goto T, Dong Q, Yamane H, Sato T: Solution synthesis of homogeneous plate-like multifunctional CeO2 particles.

    RSC Adv 2012, 2:5976. Publisher Full Text OpenURL

  8. Devaraju MK, Yin S, Sato T: Morphology control of cerium oxide particles synthesized via a supercritical solvothermal method.

    Appl Mater Interfaces 2009, 1(11):2694. Publisher Full Text OpenURL

  9. Kašpar J, Fornasiero P, Graziani M: Use of CeO2 -based oxides in the three-way catalysis.

    Catal Today 1999, 50:285. Publisher Full Text OpenURL

  10. Kašpar J, Fornasiero P: Nanostructured materials for advanced automotive de-pollution catalysts.

    J Solid State Chem 2003, 171:19. Publisher Full Text OpenURL

  11. Di Monte R, Kašpar J: Heterogeneous environmental catalysis-a gentle art: CeO2 -ZrO2 mixed oxides as a case history.

    Catal Today 2005, 100:27. Publisher Full Text OpenURL

  12. Di Monte R, Kašpar J: Nanostructured CeO2 -ZrO2 mixed oxides.

    J Mater Chem 2005, 15:633. Publisher Full Text OpenURL

  13. Fornasiero P, Balducci G, Di Monte R, Kašpar J, Sergo V, Gubitosa G, Ferrero A, Graziani M: Modification of the redox behaviour of CeO2 induced by structural doping with ZrO2.

    J Catal 1996, 164:173. Publisher Full Text OpenURL

  14. Yao MH, Baird RJ, Kunz FW, Hoost TE: An XRD and TEM investigation of the structure of alumina-supported ceria-zirconia.

    J Catal 1997, 166:67. Publisher Full Text OpenURL

  15. Kenevey K, Valdivieso F, Soustelle M, Pijolat M: Thermal stability of Pd or Pt loaded Ce0.68 Zr0.32 O2 and Ce0.50 Zr0.50 O2 catalyst materials under oxidizing conditions.

    Appl Catal B: Environ 2001, 29:93. Publisher Full Text OpenURL

  16. Zhang F, Chen CH, Hanson JC, Robinson RD, Herman IP, Chan SW: Phases in ceria-zirconia binary oxide (1-x)CeO2 -xZrO2 nanoparticles: the effect of particle size.

    J Am Ceram Soc 2006, 89:1028. Publisher Full Text OpenURL

  17. Nagai T, Nonaka T, Suda A, Sugiura M: Structure analysis of CeO2 -ZrO2 mixed oxides as oxygen storage promoters in automotive catalysts.

    R&D Rev Toyota CRDL 2002, 37:20. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  18. Fornasiero P, Di Monte R, Rao GR, Kašpar J, Meriani S, Trovarelli A, Graziani M: Rh-loaded CeO2 -ZrO2 solid solutions as highly efficient oxygen exchangers: dependence of the reduction behavior and the oxygen storage capacity on the structural properties.

    J Catal 1995, 151:168. Publisher Full Text OpenURL

  19. Wang HF, Gong XQ, Guo YL, Guo Y, Lu GZ, Hu P: A model to understand the oxygen vacancy formation in Zr-doped CeO2 : electrostatic interaction and structural relaxation.

    J Phys Chem C 2009, 113:10229. Publisher Full Text OpenURL

  20. Taniguchi T, Watanabe T, Matsushita N, Yoshimura M: Hydrothermal synthesis of monodisperse Ce0.5 Zr0.5 O2 metastable solid solution nanocrystals.

    Eur J Inorg Chem 2009, 14:2054. OpenURL

  21. Devaraju MK, Liu XW, Yusuke K, Yin S, Sato T: A rapid hydrothermal synthesis of rare earth oxide activated Y(OH)3 and Y2 O3 nanotubes.

    Nanotechnology 2009, 20:405606. PubMed Abstract | Publisher Full Text OpenURL

  22. Sanchez-Domingueza M, Liotta LF, Carlod GD, Pantaleob G, Veneziab AM, Solansa C, Boutonnet M: Synthesis of CeO2 , ZrO2 , Ce0.5Zr0.5 O2 , and TiO2 nanoparticles by a novel oil-in-water microemulsion reaction method and their use as catalyst support for CO oxidation.

    Catal Today 2010, 158:35. Publisher Full Text OpenURL

  23. Fuentes RO, Baker RT: Synthesis of nanocrystalline CeO2 -ZrO2 solid solutions by a citrate complexation route: a thermochemical and structural study.

    J Phys Chem C 2009, 113:914. Publisher Full Text OpenURL

  24. Yang JO, Yang HM: Investigation of the oxygen exchange property and oxygen storage capacity of Cex Zr1-x O2 nanocrystals.

    J Phys Chem C 2009, 113:6921. Publisher Full Text OpenURL

  25. Teng ML, Luo LT, Yang XM: Synthesis of mesoporous Ce1-x Zrx O2 (x = 0.2-0.5) and catalytic properties of CuO based catalysts.

    Micropor Mesopor Mat 2009, 119:158. Publisher Full Text OpenURL

  26. Dong Q, Yin S, Guo CS, Sato T: A new oxygen storage capacity material of tin doped ceria-zirconia supported paradium-alumina catalyst with high CO oxidation activity.

    Chem Lett

    in press


  27. Dong Q, Yin S, Guo CS, Sato T: Ce0.5 Zr0.4 Sn0.1 O2 /Al2 O3 catalysts with enhanced oxygen storage capacity and high CO oxidation activity.

    Catal Sci Technol 2012. Publisher Full Text OpenURL