Aluminum-doped ceria-zirconia solid solutions with enhanced thermal stability and high oxygen storage capacity
© Dong et al.; licensee Springer. 2012
Received: 23 July 2012
Accepted: 17 September 2012
Published: 1 October 2012
A facile solvothermal method to synthesize aluminum-doped ceria-zirconia (Ce0.5Zr0.5-xAl x O2-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.
KeywordsSolvothermal 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, NO x , 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, NO x , 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 . The detailed structure and property of CeO2-ZrO2 solid solutions were reported in a review article by Monte and Kaspar . 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 . Using density functional theory, Wang et al. found that in a series of Ce1-xZr x O2 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 . 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-xM x O2-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.
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.
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
OSC at 600 ° C of the CeO 2 , Ce0 .5Zr0 .5O 2 , and Ce0 .5Zr0 .3Al0 .2O1 .9calcined at 1 ,000 ° C for 20 h
OSC (μmol-O g− 1)
OSC at 600 ° C of the Ce0 .5Zr0 .4Al0 .1O1 .95, Ce0 .5Zr0 .2Al0 .3O1 .85, and Ce0 .5Zr0 .1Al0 .4O1 .8calcined at 1 , 000 ° C for 20 h
OSC (μmol-O g− 1)
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.
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).
- Yao HC, Yu YF: Ceria in automotive exhaustcatalysts: I. Oxygen storage. J Catal 1984, 86: 254. 10.1016/0021-9517(84)90371-3View Article
- 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. 10.1016/S1002-0721(08)60053-8View Article
- Steele BCH: Fuel-cell technology: running on natural gas. Nature 1999, 400: 619. 10.1038/23144View Article
- Steele BCH, Heinzel A: Materials for fuel-cell technologies. Nature 2001, 414: 345. 10.1038/35104620View Article
- Yin S, Minamidate Y, Sato T: Synthesis and morphological control of monodispersed microsized ceria particles. Surf Rev Lett 2010, 17(2):147. 10.1142/S0218625X10013552View Article
- 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.View Article
- 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. 10.1039/c2ra20280hView Article
- 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. 10.1021/am900574mView Article
- Kašpar J, Fornasiero P, Graziani M: Use of CeO2-based oxides in the three-way catalysis. Catal Today 1999, 50: 285. 10.1016/S0920-5861(98)00510-0View Article
- Kašpar J, Fornasiero P: Nanostructured materials for advanced automotive de-pollution catalysts. J Solid State Chem 2003, 171: 19. 10.1016/S0022-4596(02)00141-XView Article
- Di Monte R, Kašpar J: Heterogeneous environmental catalysis-a gentle art: CeO2-ZrO2 mixed oxides as a case history. Catal Today 2005, 100: 27. 10.1016/j.cattod.2004.11.005View Article
- Di Monte R, Kašpar J: Nanostructured CeO2-ZrO2mixed oxides. J Mater Chem 2005, 15: 633. 10.1039/b414244fView Article
- Fornasiero P, Balducci G, Di Monte R, Kašpar J, Sergo V, Gubitosa G, Ferrero A, Graziani M: Modification of the redox behaviour of CeO2induced by structural doping with ZrO2. J Catal 1996, 164: 173. 10.1006/jcat.1996.0373View Article
- 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. 10.1006/jcat.1997.1504View Article
- Kenevey K, Valdivieso F, Soustelle M, Pijolat M: Thermal stability of Pd or Pt loaded Ce0.68Zr0.32O2and Ce0.50Zr0.50 O2catalyst materials under oxidizing conditions. Appl Catal B: Environ 2001, 29: 93. 10.1016/S0926-3373(00)00196-XView Article
- 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. 10.1111/j.1551-2916.2005.00788.xView Article
- Nagai T, Nonaka T, Suda A, Sugiura M: Structure analysis of CeO2-ZrO2mixed oxides as oxygen storage promoters in automotive catalysts. R&D Rev Toyota CRDL 2002, 37: 20.
- Fornasiero P, Di Monte R, Rao GR, Kašpar J, Meriani S, Trovarelli A, Graziani M: Rh-loaded CeO2-ZrO2solid 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. 10.1006/jcat.1995.1019View Article
- 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. 10.1021/jp900942aView Article
- Taniguchi T, Watanabe T, Matsushita N, Yoshimura M: Hydrothermal synthesis of monodisperse Ce0.5Zr0.5O2metastable solid solution nanocrystals. Eur J Inorg Chem 2009, 14: 2054.View Article
- Devaraju MK, Liu XW, Yusuke K, Yin S, Sato T: A rapid hydrothermal synthesis of rare earth oxide activated Y(OH)3and Y2O3nanotubes. Nanotechnology 2009, 20: 405606. 10.1088/0957-4484/20/40/405606View Article
- Sanchez-Domingueza M, Liotta LF, Carlod GD, Pantaleob G, Veneziab AM, Solansa C, Boutonnet M: Synthesis of CeO2, ZrO2, Ce0.5Zr0.5O2, and TiO2nanoparticles by a novel oil-in-water microemulsion reaction method and their use as catalyst support for CO oxidation. Catal Today 2010, 158: 35. 10.1016/j.cattod.2010.05.026View Article
- Fuentes RO, Baker RT: Synthesis of nanocrystalline CeO2-ZrO2solid solutions by a citrate complexation route: a thermochemical and structural study. J Phys Chem C 2009, 113: 914. 10.1021/jp808825cView Article
- Yang JO, Yang HM: Investigation of the oxygen exchange property and oxygen storage capacity of CexZr1-xO2nanocrystals. J Phys Chem C 2009, 113: 6921. 10.1021/jp808075tView Article
- Teng ML, Luo LT, Yang XM: Synthesis of mesoporous Ce1-xZrxO2(x = 0.2–0.5) and catalytic properties of CuO based catalysts. Micropor Mesopor Mat 2009, 119: 158. 10.1016/j.micromeso.2008.10.019View Article
- 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 in press
- Dong Q, Yin S, Guo CS, Sato T: Ce0.5Zr0.4Sn0.1O2/Al2O3catalysts with enhanced oxygen storage capacity and high CO oxidation activity. Catal Sci Technol 2012. 10.1039/C2CY20425H
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