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Since cracks in catalyst layers of a fuel cell affect performance and durability, it is important to obtain the factors that control crack formation. Cracking characteristics are likely to differ due to the formation of agglomerates in catalyst inks. Herein, a critical crack thickness (CCT) is examined as a parameter for cracking characteristics by changing the formation of Pt/carbon by the presence or absence of an absorbed ionomer on Pt/carbon particles. The CCT was found to be four times greater for catalyst layers obtained from catalyst inks that are well dispersed by ionomer adsorption than for catalyst layers obtained from catalyst inks with a network of structured agglomerates. This shows that crack behavior can be controlled by ionomer adsorption into the Pt/carbon in catalyst ink. A well-dispersed catalyst ink produce a homogeneous Pt/carbon and ionomer distribution in catalyst layers with high fracture toughness, while catalyst inks with a network of structured agglomerates produce dense aggregates with small primary pores that generate high drying stress, and a self-organizing free ionomer that causes stress concentration in catalyst layers with a high risk of cracking. This research provided useful knowledge for controlling cracks and examining the effects of cracks on performance and durability.

A highly crystalline, 10 nm-sized red rust water oxidation catalyst composed of pure β-phase FeOOH(Cl) nanorods (ca. 3 × 13 nm) doped with Ni ions (β-FeOOH(Cl):Ni) and surface-modified with amorphous Ni(OH)2 (a-Ni(OH)2, at a Ni to Fe ratio of 22 at.%) was synthesized by a facile one-pot process at room temperature. The overpotential during the electrochemical oxygen evolution reaction (OER) over the β-FeOOH:Ni/a-Ni(OH)2 stacked nanorod anodes was 170 mV, and an OER current of 10 mA/cm2 was obtained at an overpotential of 430 mV in a 0.1 M KOH solution. X-ray absorption fine structure analysis, Mossbauer spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and impedance spectroscopy suggested that surface modification with the a-Ni(OH)2 lowered the OER overpotential of β-FeOOH(Cl):Ni, resulting in the very high current density at low potential compared with Fe-rich oxide and oxyhydroxide electrodes reported previously. Mossbauer spectroscopy suggest...

The application of the water oxidation reaction to extract electrons from water molecules is important for the future sustainable synthesis of useful chemicals such as hydrogen and organic compounds. Therefore, a cost-effective oxygen evolution reaction (OER) in alkaline, neutral or acidic solution is required, based on the use of catalysts incorporating earth abundant elements. This work demonstrates that β-FeOOH(Cl) nanorod catalysts with high crystallinity and small size (an average diameter of 3 nm and a length of 15 nm) provided the best performance in the OER activity among Fe-based oxide and (oxy)hydroxide catalysts. The pristine β-FeOOH(Cl) nanorods with the high crystallinity are realized by a new process enabling one-pot, fast, and room temperature synthesis, which is the key to forming colloidal suspensions of the highly crystallized pure-phase β-FeOOH(Cl) nanorods. The versatility of this process also enabled doping of a wide variety of transition metals. Doping of Ni2+ (at 1.2 at%) improved the OER activity and shifted the threshold potential in the negative direction by 100 mV in an alkaline electrolyte, which was comparable to that of conventional IrOx colloidal nanoparticles.

Monodisperse ceria–zirconia nanoparticles have attracted much attention as potential high-performance catalysts. Acidic aqueous solutions are generally used for peptizing aggregated precipitates during the fabrication of disperse nanoparticles. However, the peptization process requires multiple hours of aging, which significantly decreases the production efficiency. Hence, various researchers have attempted to eliminate this stage altogether by performing a coprecipitation process under ambient conditions using common salts as the starting materials. In this work, we report a continuous and direct technique for the fabrication of monodisperse composite oxide nanoparticles via coprecipitation inside a novel high-shear agitation reactor without aging. Using this method, monodisperse ceria–zirconia–yttria composite oxide nanoparticles with diameters of 3 nm were successfully synthesized.

The phase transformation behavior of the superlattice structure of a CeO2–ZrO2 pyrochlore-type binary compound (CP) was investigated so as to better understand how to improve the thermal stability of such a system. CP was synthesized through high-temperature reduction of a conventional CeO2–ZrO2 solid solution with a 1:1 molar ratio of Ce and Zr. High-resolution transmission electron microscopy and selected-area electron diffraction clearly revealed that the pyrochlore structure of CP transformed to the standard disordered cubic fluorite or tetragonal zirconia structure after having been subjected to a high-temperature durability test; moreover, it was determined that this phase transformation moves inward from the crystallite surface. This discovery suggests a new method by which to improve upon this material for practical applications.

A termetallic catalyst of Pt-Ir-Au/Al2O3 for NOx decomposition was prepared by loading the metallic colloids in C2H5OH-H2O solution and a surfactant of polyvinyl pyrrolidone. Compared with an impregnated Pt/Al2O3 catalyst, the termetallic catalyst of PtIrAu811/Al2O3, with a Pt:Ir:Au atomic ratio of 8:1:1, exhibited higher NO decomposition and selectivity to N2. Transmission electron microscopy and X-ray diffraction were conducted to clarify the state of the supported metals and indicate three precious metals alloyed on the catalyst. In the study of NO-temperature programmed desorption, oxygen desorption on the PtIrAu811 catalyst shifted to the low temperature side compared to that on Pt/Al2O3, which correlated well with its higher catalytic performance in NO decomposition.

Monodisperse polyhedral nanoparticles (NPs) and nanorods (NRs) of cerium dioxide, CeO2, were synthesized by thermal decomposition of ammonium cerium(IV) nitrate, (NH4)2Ce(NO3)6, at 180 °C in an organic solution of oleylamine (OAm) and/or oleic acid (OA). The 4 nm CeO2 NPs were synthesized in diphenyl ether solution of OAm and OA with the molar ratio of Ce/OAm/OA = 1:3:3, while the 6 nm CeO2 NPs were made in 1-octadecene solution of OAm with Ce/OAm = 1:6. The NRs were formed in 1-octadecene with Ce/OAm/OA = 1:3:1.5. The CeO2 NPs were assembled on γ-Al2O3 via polyvinylpyrrolidone and were annealed at 500 °C under air to remove organic coating. They were well-dispersed on Al2O3 and showed the increased oxygen storage capacity compared to the physical mixture of aggregated CeO2 and γ-Al2O3 powder. The reported CeO2 NPs are promising for oxygen storage and release applications.

The Pt oxidation state and nanostructure on a ceria-based oxide support were characterized after sequential oxidative, reductive, and re-oxidative treatments using X-ray photoelectron spectroscopy and transmission electron microscopy. The Pt oxidation state and nanostructure depended on the treatment atmosphere: an oxidized Pt monolayer spread along the primary particle surface of the ceria-based oxide support in the oxidized catalyst, whereas metallic Pt existed as particles of 1–2 nm in diameter in the reduced catalyst. Therefore, on the ceria-based oxide surface oxidized Pt formed a nanocomposite oxide with Ce under an oxidative atmosphere and reversibly changed to metallic Pt particles under a reductive atmosphere. The formation of this surface nanocomposite oxide is evidence of the strong interaction between oxidized Pt and CeO 2 that involves the formation of a Pt–O–Ce bond, which stabilizes Pt against sintering and redisperses agglomerated Pt particles under an oxidative atmosphere.

A nanocomposite of Al2O3 and a ZrO2–TiO2 solid solution (AZT) doped with Ti (Ti–AZT) was synthesized as a support for a NOx storage-reduction (NSR) catalyst in order to achieve sulfur durability. Ti–AZT maintained the original structure of AZT after the Ti doping step and exhibited lower basicity. Energy dispersive X-ray spectroscopy revealed that the Ti concentration on the Al2O3 particles was more than 10 at.% on average for a sample containing 3.3 at.% of doped titanium. Doped titanium was homogeneously distributed on the surface without the formation of discrete TiO2 particles. SO2-temperature programmed desorption at less than 823 K indicated that the catalyst containing Ti–AZT had larger sulfur desorption than that containing AZT. After sulfur aging tests, the Ti–AZT catalyst provided a large amount of NOx storage. The improved sulfur durability in the NSR catalyst resulted from the presence of TiO2 as a Al2O3–TiO2 solid solution in Ti–AZT.

The development of a more efficient oxygen storage material is a very important approach for the optimization of automotive catalysts. To investigate the influence of the physical parameters, the Pt particle size and specific surface area (SSA) on the OSC (oxygen storage capacity) performance of the Pt/CeO 2 -ZrO 2 -Y 2 O 3 (CZY) catalysts, a series of Pt/CZY catalysts were prepared and characterized. The OSC performance was evaluated by CO oxidation from 200 to 400°C, while alternately feeding CO(2.0 vol%)/N 2 and O 2 (1.0 vol%)/N 2 for 60s at a flow rate of 7.0 1/min. The CO 2 generation was analyzed continuously and used to indicate the OSC performance and oxygen storage/release behavior. The oxygen surface diffusion and bulk diffusion rates on the catalysts were further characterized by the 18 O/ 16 O isotopic exchange reaction and correlated with the OSC performances. The characterization results of the Pt particle size and SSA of the Pt/CZY catalysts indicated that the Pt particle size and SSA of Pt/CZY appeared to be a hyperbolic distribution, being interdependent and difficult to control independently. OSC performance results by CO oxidation at 200 and 300°C showed that smaller Pt particle size favored OSC performance and appeared to be the optimum around 70m 2 /g for the SSA. This corresponds with the oxygen mobility results obtained from the 18 O/ 16 O isotopic exchange reaction at 400°C, that is, the oxygen surface and bulk diffusion showed a peak at the Pt particle size of 6 nm and an SSA of 40 m 2 /g.

CeO 2 –ZrO 2 solid solution ((Ce,Zr)O 2 ) is an indispensable oxygen storage capacity (OSC) material for emission control in gasoline-fuelled automobiles. The high performance OSC material developed in this study is composed of Al 2 O 3 as “a diffusion barrier” and (Ce,Zr)O 2 particles in intervening layers on a nanometer scale, and is abbreviated as “ACZ”. The Brunauer–Emmett–Teller (BET) specific surface area (SSA) of ACZ after durability testing in air at 1000 °C was 20 m 2 /g, which is higher than that of conventional CZ (2 m 2 /g) composed of (Ce,Zr)O 2 without Al 2 O 3 . After heat treatment at 1000 °C in air, the particle size of (Ce,Zr)O 2 in ACZ was about 10 nm and that without Al 2 O 3 was one-half of the size in pure CZ. The OSC was roughly characterized by the total capacity (OSC-c1) and the oxygen release rate (OSC-r). In a fresh catalyst, ACZ and CZ had almost the same OSC-c1; however, the OSC-r of ACZ was twice as fast as CZ. After durability testing, the OSC-r of both ACZ and CZ were reduced significantly, but the OSC-r of ACZ was about five times as fast as CZ. While the OSC-c1 was hardly influenced by the (Ce,Zr)O 2 crystallite size and Pt particle size on the supports, the OSC-r was influenced by both of these parameters. The improvement of the OSC-r in the fresh catalyst and inhibition of the decrease in the OSC-r after durability testing were achieved by suppression of particle growth of (Ce,Zr)O 2 in ACZ by introducing Al 2 O 3 as a diffusion barrier with resultant inhibition of sintering of Pt particles.

Three types of CeO2–ZrO2 (Ce:Zr = 1:1 molar ratio) compounds with different oxygen storage/release capacity (OSC) were characterized by means of the Ce K-edge and Zr K-edge XAFS. In order to investigate the relationship between the OSC and local structure, the quantitative EXAFS curve-fitting analysis was applied. By enhancing the homogeneity of the Ce and Zr atoms in the CeO2–ZrO2 solid solution, the OSC performance increased. Additionally, from the XRD analysis, the homogeneous CeO2–ZrO2 solid solution has an ordered cation arrangement, and exhibits the highest OSC. The crystal structure of this CeO2–ZrO2 solid solution is usually termed as “κ-CeZrO4 phase”. However, the OSC performance of κ-CeZrO4 degrades upon a high-temperature treatment under an oxidative atmosphere. The fresh κ-CeZrO4 was aged at 973, 1,273 and 1,473 K under an oxidative atmosphere, respectively. The OSC performance deteriorated as: the fresh sample ≈973 > 1,273 > 1,473 K-aged samples. We also found that, if the temperature was beyond 1,273 K, the Ce/Zr ordered arrangement would collapse and the local structure around Ce and Zr ions would also changed remarkably. These results indicated that OSC was strongly dependent on its atomic structure.

Ceria–zirconia solid solution has a function as an oxygen storage material, which keeps air to fuel ratio (A/F) on a stoichiometric composition at the surface of three-way catalyst (TWC) for automotive exhaust. When A/F could be kept stoichiometric, TWC shows good catalytic activity. At first, ceria which dissolves 20 mol% of zirconia was developed by Ozawa et al. in 1987. After that, the ceria–zirconia solid solution was improved to achieve a complete solubility in the solid state at nano-level by surfactant modified homogeneous coprecipitation (J catal 169:490, 1997). Nano-level solid solution of ceria and zirconia could have been made by various methods. Those materials have similar amount of oxygen storage capacity (OSC). The improvement of OSC comes from the larger amount of bulk oxygen that can contributes OSC by the larger amount of zirconia dissolving into ceria (Catal Lett 33(1–2):193–200 1995). Solvothermal synthesis is usually done in a higher temperature than that can be reached under atmospheric pressure. The higher temperature accelerates generation of precipitation; however, a pressure vessel is necessary, and such a hermetically closed system is unsuitable to the material synthesis of the low-value-added product. Atmospheric pressure solvothermal (APS) synthesis was applied to ceria-zirconia solid solutions in this study. The APS ceria-zirconia showed larger amount of OSC. The excellent OSC performance was presumed to come from further uniformity of zirconium ions in the ceria lattice.

Ceria-zirconia solid solution is one of the most important components of three way catalyst (TWC) for cleaning automotive exhaust. Ceria-zirconia solid solution has a function as an oxygen storage material, which keeps air to fuel ratio (A/F) at the surface of TWC on a stoichiometric composition. The dissolved zirconia into ceria lattice makes cerium ions to be reduced easier and enhances especially bulk oxygen to release. However, there is a large difference of oxygen storage capacity (OSC) between a theoretical value and that of the prior ceria zirconia solid solutions. The cause of the large difference of OSC might be come from the inhomogeneous dispersion of Zr ions in ceria lattice. Atmospheric pressure solvothermal (APS) process was applied to ceria-zirconia solid solutions in this study. The APS ceria-zirconia showed excellent OSC. The excellent OSC performance was presumed to come from further uniformity of zirconium ions in the ceria lattice.

This research focuses on investigating the influence of the various compositions of TiO2 and ZrO2 on the NOx removal ability over a sulfur-treated NSR catalyst. On the NSR catalyst, potassium was loaded as the NOx storage material and platinum as the precious metal, and the ZrO2 content was varied from 0 to 100 wt%. A relatively high NOx removal ability above 500 °C was obtained with the 60 to 80 wt% ZrO2 content, and the maximum value was 70 wt%, while the TiO2-rich supports were superior below 400 °C when compared to the ZrO2-rich supports. K/Pt/ZrO2 had a poor NOx removal activity over the entire temperature range. The analysis of the sulfur-aged catalysts with the supports of 70 wt%ZrO2-30 wt%TiO2, pure TiO2, and ZrO2 indicated that the TiO2 support presented a higher resistance to potassium sulfate-formation, while the ZrO2 support suppressed the solid phase reaction with potassium. The catalyst with 70 wt%ZrO2-30 wt%TiO2 retained the highest amount of remaining potassium, which was neither the formed-sulfate nor the solid-phase-reacted potassium. The sulfur-deactivation of the potassium sites could increase the activity of the metallic platinum, and a suitable combination of metallic platinum with the adequate potassium sites lead to a higher NOx removal activity for the TiO2-rich catalysts at low temperatures. In the case of the K/Pt/ZrO2 catalyst, almost all the potassium changed into sulfate, which caused a poor de-NOx ability over the entire temperature range. The support's acidity is an important factor regarding the sulfur tolerance of the NSR catalyst. The ZrO2-TiO2 catalyst containing 70 wt% ZrO2 was verified to have the highest acid amount among the sample supports, and was supposed to be the best support against sulfur-poisoning. In addition, this support contained 60 mol% ZrO2, and favorably suppressed the solid phase reaction with potassium. These properties of the ZrO2-TiO2 support containing 60 mol% ZrO2 balanced the sulfur tolerance and thermal resistance, and led to its highest NOx purification ability at high temperatures following the sulfur-aging treatment.

Innovative three-way catalysts containing ceria-zirconia solid solutions (CZ) with a ZrO 2 content ranging from 5 to 75 mol% were developed. Such catalysts have very high oxygen storage/release capacity (OSC). The OSC of'catalysts containing first-generation CZ was found to increase linearly with the amount of zirconia dissolved in the solid solution in the 0-20 mol%( ZrO 2 range. The thermal stability of the catalyst containing first-generation CZ was higher than that containing ceria. Second-generation CZ with greater OSC than first-generation CZ was developed by a homogeneous coprecipitation process, followed by heat-treatment below 1000 °C, enabling dissolution of zirconia into ceria up to 75 mol% zirconia as estimated by XRD. Third-generation CZ, CZ-doped alumina (ACZ), was developed by homogeneous coprecipitation based on the "diffusion barrier concept". The OSC of ACZ was 23 times larger than that of pure ceria. The NOx emission over the catalyst containing ACZ was reduced by about a factor of five compared with that containing pure ceria. Toyota Motor Corp. has put three-way catalysts containing first-, second-, and third-generation CZ into practical use globally.

Lanthanum-doped hollow alumina particles (A-E) were made by the emulsion combustion method (ECM). Powder characteristics and three-way catalytic performance were evaluated and compared with those of precipitation-made alumina (A-P). The A-E powder was gamma alumina and 40 m 2 /g in specific surface area (SSA). The unique hollow structure resulted in a broad peak at 130 nm in the pore size distribution and a large pore volume (3.0 cm 3 /g) with pore diameters of >20 nm. The A-E powder primarily maintained its shape, crystalline phase and SSA up to 1200°C, indicating high thermal stability. Conversion of total hydrocarbon (THC) started at higher temperatures for the Rh-loaded A-E pellets (Rh/A-E) than for Rh-loaded A-P pellets (Rh/A-P) because of the low dispersion of Rh for Rh/A-E. However, a gradient of the THC conversion-temperature curve was higher for Rh/A-E than for Rh/A-P. The large pore volume can promote good gas accessibility inside the pellets for Rh/A-E, resulting in the high gradient of the THC conversion-temperature curve and thus the high activity at high temperatures where gas diffusion is likely to determine the conversion efficiency. The conversion-temperature curves of CO and NO X showed primarily similar behavior to the THC ones.

The CeO 2 -ZrO 2 solid solution is the most important oxygen storage/release material for use in automobile catalysts. In particular, the ceria-zirconia solid solution with a pyrochlore structure exhibits the highest oxygen storage capacity (OSC). In this study, CeO 2 -ZrO 2 solid solutions containing Y 2 O 3 were synthesized and their OSCs were measured to clarify the influence of an ordered arrangement of Ce and Zr ions on the OSC. As a result of this study, it is concluded that an ordered arrangement of Ce and Zr ions markedly improves the OSC of CeO 2 -ZrO 2 solid solutions.

As an important oxygen storage material, ceria-zirconia solid solution is widely used in automotive three-way catalysts. For the Ce-Zr solid solution being usually used with a noble metal, the evaluation of oxygen storage capacity (OSC) should be conducted with the Ce-Zr solid solution loaded with a noble metal. The measured OSC of noble-metal-loaded Ce-Zr solid solution consists of two parts: the stored oxygen within the solid solution itself and the adsorbed oxygen on the loaded noble metal particles. Therefore, it is very necessary to clarify the influence of metal loading on the measured OSC in order to ascertain the exact OSC of the solid solution itself. In this research, the authors attempted to clarify the above issues by characterizing the OSC performance of Ce-Zr solid solutions with platinum (Pt) loading from 0.0001-10 mass%. We found that increasing the amount of Pt loading increases the oxygen storage and release rates and that increasing the temperature also increases the oxygen storage rate, although the oxygen release rate is not affected by increasing the temperature. The apparent OSC reached saturation over a certain amount of Pt loading and temperature. The saturated OSC increased with increasing temperature.

Ceria-zirconia (Ce-Zr) solid solution is widely used as an oxygen storage material, which is a key component in the automotive three-way catalysts. The Ce-Zr solid solution is usually used with noble metals supported on their surface. Thus the evaluation of oxygen storage capacity (OSC) should be conducted on the Ce-Zr solid solution loaded with a noble metal. The measured OSC of noble-metal-loaded Ce-Zr solid solution consists of two parts; one is the stored oxygen within the solid solution itself, and the other is the adsorbed oxygen on the surface of the supported noble metal particles. Therefore, it is necessary to clarify the influence of the noble metal on the measured OSC, and this will also help to ascertain the exact OSC of the solid solution itself. In this research, the authors tried to clarify the above issues by characterizing the OSC performance on Ce-Zr solid solutions with Pt loading from 0.0001 to 10 wt%. We found that, increasing the Pt loading makes the oxygen storage and release rate higher. Temperature increase also makes the oxygen storage rate higher, however, the oxygen release rate is not affected by the temperature. The apparent OSC saturated above a certain level of Pt loading and temperature. The saturated OSC increased with increasing temperature.

Three types of CeO2–ZrO2 (Ce:Zr=1:1 molar ratio) compounds with different oxygen storage/release capacities (OSCs) were characterized by means of the Ce K-edge and Zr K-edge X-ray absorption fine structure (XAFS). In order to investigate the relationship between the OSC and local structure, the quantitative EXAFS curve-fitting analysis was applied. By enhancing the homogeneity of the Ce and Zr atoms in the CeO2–ZrO2 solid solution, the OSC performance increased. Especially, the atomically homogeneous Ce0.5Zr0.5O2 solid solution exhibited the highest OSC among these CeO2–ZrO2 samples. Additionally, the local oxygen environment around Ce and Zr was remarkably modified by enhancing the homogeneity of the CeO2–ZrO2 solid solution. It was postulated that the enhancement of the homogeneity of the CeO2–ZrO2 solid solution and the modification of the oxygen environment would be the source for the OSC improvement.

The function of oxygen storage capacity (OSC) is very important to improve a performance for an automobile exhaust catalyst. CeO2-ZrO2 solid solution has an excellent OSC, and is available for a catalytic promoter. In this paper, OSC of the CO reduced CeO2-ZrO2 solid solution having various composition loaded with Pt was estimated by thermo gravimeter, and the phases and the crystalline structure of the reduced CeO2-ZrO2 solid solution were studied by X-ray diffraction method. The maximum total OSC-value of the reduced material occurs at the composition of 50mol% CeO2-50mol% ZrO2. The maximun value is about 753μmol O2/g-solid solution, which is about twice the value (416μmol O2/g-solid solution) of the attritionmilled CeO2-ZrO2 solid solution, and 5 times higher than that (150μmol O2/g-solid solution) of the material synthesized by conventional impregnation. The reduced material consists of Ce2Zr2O8 and CeO2 solid solution in the composition range from 30 to 50mol% ZrO2. The reduced material consists of the mixture, Ce2Zr2O8 and ZrO2 in the composition range from 50mol% ZrO2 to 100mol% ZrO2. The presence of Zr4+ near Ce4+ makes the expansion easier enhancing further valence change, because Zr4+ is very small in volume. Regular distribution of Ce and Zr ions would make it possible to place Zr4+ in the nearest position to Ce ion. This would be the reason why the partial OSC of Ce2Zr2O8 is much higher than the complete solid solution.

The oxidation behavior of reduced CeO2 and CeO2-ZrO2 solid solution (CZS) was studied by measuring the weight and temperature change during oxidization, in the near-room-temperature range. A flaming oxidation at close to room temperature was observed in some of the reduced CZS. This oxidation takes place in the CZS reduced at much lower temperatures, 800°C and 1000°C, compared with CeO2, for which the temperature of 1400°C or so is required for the occurrence of the flaming oxidation. The oxidation was not observed in the CZS reduced at a temperature higher than 1200°C. The material, which exhibited the flaming oxidation, possessed a high oxygen storage capacity (OSC) and a large specific surface area. The dissolution of ZrO2 into CeO2 results in an increase of OSC and in the retardation of grain growth. These two effects lead reduced CZS to a flaming oxidation at close to room temperature.

The formation of ceria-zirconia solid solution by the solid phase reaction of ceria and zirconia powders near room temperature during wet attrition milling was recently reported. The solid phase reaction occurred as a result of a large plastic deformation, breaking and mutual combining on the ceria particle as well as the solid solution. The size of the particle in which the solid phase reaction can occur was examined in this study. The reaction that forms ceria-zirconia solid solution from large ceria particles (4m2/g) begins when the average particle size reaches 28nm or smaller. The reaction does not occur in CeO2 powder with particle size larger than 30nm. The critical particle size of ceria powder to begin the reaction with zirconia is thought to be approximately 20nm, which was found asymptotically by two methods, X-ray diffraction and specific surface area measurements.

Capability of oxygen store and release of ceria-zirconia solid solution made by attrition mill process was measured by thermo-gravimeter with 1mass% of Pt. Ceria-zirconia solid solution made by conventional heating method of ceria powder with zirconium salt was also characterized for comparison. Capability of oxygen store and release of ceria-zirconia solid solution made by attrition mill process is about three times larger than that of conventionally made samples. And, the point, where zirconium content is 100% on the relation between capability of oxygen store and release and zirconia content in the ceria-zirconia solid solution, corresponds to the state in which the valence of all the cerium ion being contained in the solid solution is 3. This fact suggests that the mechanism, that the increase of capability of oxygen store and release by dissolving zirconia into ceria, is that zirconium ions, which are smaller than cerium ions of the valence 4, release the strain caused by the expansion due to a reduction of cerium ions.

The surprisingly low temperature (-323K) synthesis of the ceria-zirconia solid solution upon milling ceria powder with zirconia mill and zirconia balls (in ethanol and/or water) was studied. Solid solutions up to 60mol%ZrO2 were obtained, whose formation was proved to result from solid phase reaction between ceria and zirconia powders, enhanced by contact stress (either shear or compressive one). Furthermore, the occurrence of large plastic deformation, breaking and mutual combining was found on the ceria powder before and after solid solution. The grain size of ceria-zirconia solid solution was ≤20nm, which would cause on easy rearrangement of low diffusion atoms of cerium and zirconium to form the solid solution at such a low temperature. In addition, the possible existence of a solid solution for which the migration of the constituents is much faster (or the stability of the solid at the composition is much higher) than that of other composition, was suggested around 50mol%CeO2-50mol%ZrO2.

High temperature oxidation test of α'/β' Sialon composite containing small a amount of Y-α'-sialon was conducted between 1200 and 1400°C for up to 96 hours in static air. When the oxidation temperature was higher than 1300°C, many voids were formed on the surface and the strength after oxidation decreased drastically due to the formation of pit in the matrix near surface. It is thought that these pits are formed by the local destruction of the oxidized layer during oxidation. A large amount of Y and Al diffused from inside of matrix to the surface, and concentrated in the oxidized layer.

SiAlON composites composed of Y-α′-SiAlON and β′-SiAlON were fabricated by hot-pressing mixtures of Y-α′-SiAlON and α-Si3N4. The amount of Y-α′-SiAlON decreased during sintering. The lattice constant (solubility) of Y-α′-SiAlON after sintering depended on the initial amount of Y-α′-SiAlON and was lower than that before sintering. On the other hand, the lattice constant (solubility) of β′-SiAlON remained constant. It is thought that Y-α′-SiAlON with lower solubility was formed by the reaction between the Y-α′-SiAlON and α-Si3N4.

A sialon composite consisting of Y-α'-sialon and β'-sialon is obtained by hot-pressing mixtures of Si 3 N 4 , Y 2 O 3 and AlN powders. In this study, the effect of the presence of a small amount of SiO 2 on the reaction during sintering, especially on the formation of Y-α'-sialon, is investigated. The sinterability of mixtures of Si 3 N 4 :Y 2 O 3 and AlN powders was remarkably improved by the addition of a small amount of SiO 2 . The amount of Y-α'-sialon after sintering decreases with increasing amounts of SiO 2 added to the starting mixtures, while the lattice constants, hence the solubility of Y-α'-sialon and β'-sialon, remain unchanged.

The sintering behavior of Y-α'-sialon powder during hot-pressing was investigated. Y-α'-sialon powder was consolidated by hot-pressing without any additive. Although the intermediate phases were formed during sintering, only Y-α'-sialon was observed as crystalline phase after sintering. The lattice constant of Y-α'-sialon was constant before and after sintering. This means that the solid solubility of Y- α'-sialon remains constant during sintering.

The oxygen storage capacity (OSC) of CeO 2 -ZrO 2 solid solutions that were directly formed as nanocrystals by thermal hydrolysis of acidic aqueous solutions of (NH 4 ) 2 Ce(NO 3 ) 6 and ZrOCl 2 at 150°C increased from 94 μmol of O 2 /g for pure CeO 2 to >400 μmol of O 2 /g for compositions of CeO 2 /ZrO 2 with molar ratios (C/Z) from 74.1/25.9 to 41.7/58.3 (maximum value of 431 μmol O 2 /g was reached at the composition C/Z = 51.7/48.3) and then decreased with increased ZrO 2 content in the solid solutions. As compared with pure CeO 2 , the CeO 2 -ZrO 2 solid solutions that contained

Herein we demonstrate the extra-low-temperature oxygen storage capacity (OSC) of cerium oxide nanocrystals with cubic (100) facets. A considerable OSC occurs at 150 °C without active species loading. This temperature is 250 °C lower than that of irregularly shaped cerium oxide. This result indicates that cubic (100) facets of cerium oxide have the characteristics to be a superior low-temperature catalyst.

Electron-cyclotron-resonance (ECR) plasma etching was applied to gas pressure sintered Si3N4, β′-SiAlON and α′/β′ composite SiAlON. The etching was successfully performed within about 15min, and the shapes of Si3N4 and SiAlON grains were clearly observed. Also the grains of α′-SiAlON were distinguishable from β′-SiAlON grains and grain boundaries. The volume ratio of α′ phase to β′ phase obtained from the area of the etched surface was almost consistent with the value obtained from X-ray diffraction. However, the grain boundary area observed from the etched surface did not correspond to that obtained from back scattered electron image.

Three types of CeO2-ZrO2 with the same composition (Ce/Zr = 1) were prepared by different methods, exhibited the different oxygen storage/release capacity (OSC). To investigate the relationship between the OSC and the local structure, the Ce and Zr K-edges XAFS spectra for these samples were measured. The features of Fourier transforms of these samples were different from each other. This suggested that the OSC was remarkably exerted by the local structure around Ce and Zr. The quantitative curve-fitting analysis of EXAFS was applied, and it was concluded that homogeneous Ce0.5Zr0.5O2 solid solution at atomic level exhibited the highest OSC among these CeO2-ZrO2 with the same composition (Ce/Zr = 1).

Publisher Summary The functions inherent in nanoparticles can be maintained while lowering their reactivity by fabricating nanoparticles into nanostructures. Stable nanostructured materials, fully utilizing the functions of nanoparticles, can be created by fabricating composite and bulk materials from nanoparticles, depending on their intended use. This chapter deals with such nanostructured materials and their various functions and the characteristic evaluation by function. It summarizes the nature of nanostructures, relevant examples of the relations between nanostructures and their characteristics, and the functionality and the evaluation of the characteristics of nanostructures. The chapter describes an electrode of a solid oxide fuel cell (SOFC), the structure of which is controlled using surface-coating type composite particles and the inner-dispersion type composite particles, as an example to explain the relation between nanostructures and their functional performance. In fabricating nanostructures in the application of nanoparticles, new functionalities are expected to produce many applications ranging over almost all fields in the coming years, with the advancement of technology. The chapter discusses the functional characteristics that are expected to be implemented in nanostructures in the coming future, including mechanical characteristics, thermal characteristics, electrical characteristics, electrochemical characteristics, electromagnetic characteristics, optical characteristics, catalytic characteristics, and gas permeability and separation characteristics.

Publisher Summary This chapter summarizes process technologies for nanostructural controls using mainly fine particles including nanoparticles as a starting material. The assembly structures of nanoparticles are discussed, introducing nanobiotechnologies and colloid processes. In addition, there is an explanation of fractal structures, rather than periodic or random structures, and optical properties. The chapter looks at nanoporous structures and their control technologies, including zeolite, creation technologies of nanoporous structures by dry processes, control technologies of nanoporous structures, and the control of tubular porous structures. The relation between nanocomposite structures used in catalysts and fuel cell electrodes and their functions is explained together with polymer nanocomposite technologies. In addition, plastic deformation technologies are discussed for controlling the nanostructures of metal and alloy. The distinctive process technologies of sintering and bonding of nanoparticle assembly and self-organization of nanoparticles are covered. The latest information is also introduced on various technologies useful for forming nanostructures, including sintering technologies of nanoparticles, low temperature sintering technologies of ceramics, aerosol deposition, colloid chemical processes, self-organization phenomena of nanoparticles in liquid phase, assembly patterning technologies, and organic/inorganic mesoporous materials.

The oxidation of Y-α′-SiAlON and α-Si3N4 powders was investigated in air in the temperature range 800 to 1000°C. The oxidation rate was evaluated by determining the change in oxygen content of the powders during oxidation. It was found that Y-α′-SiAlON powder was more easily oxidized than the α-Si3N4 powder and the oxidation law of these powders was of a parabolic type. Diffusion of oxygen through the oxide layer formed on the specimen surface was thought to be the rate controlling step. The apparent activation energies for the oxidation process were -126kJ/mol and 147kJ/mol for Y-α′-SiAlON powder and α-Si3N4 powder, respectively.

SSCI-VIDE+CARE+CDS; International audience; The dynamic oxygen mobility and oxygen storage capacity (OSC) on three-model three-way catalysts of Pt/CeO2-ZrO2 (CZ-O, CZ-D and CZ-R) was characterized by the O-18/O-16 isotopic exchange (IE) reaction combined with CO oxidation. The measured oxygen surface and bulk diffusion coefficients, OSC, and oxygen release rates were correlated with XRD spectra, surface areas, metal dispersions and the other physical parameters. We found that the oxygen mobility was parallel to the structural homogeneity of Zr introduction into the CeO2 framework, decreasing as CZ-R > CZ-D > CZ-O. The oxygen diffusion coefficients over CeO2-ZrO2 oxides hinted us that oxygen species are mobile in the oxide support. In addition to the contribution to the space effect, we proposed a new insight to the role of zirconium atoms as carriers for the oxygen transfer, although further investigation is necessary. These results showed that the combined IE reaction could be counted as a reliable technique for qualifying the oxygen mobility, the OSC and oxygen release rates, and is expected to be a direct probe into the nature of CeO2-ZrO2 oxygen storage materials and further development of more efficient oxygen storage materials. (C) 2004 Elsevier B.V. All rights reserved.