The formation of ceria-zirconia solid solution by the solid phase reaction of ceria and zirconia ... more 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 ap proximately 20nm, which was found asymptotically by two methods, X-ray diffraction and specific surface area measurements.
Sialon composites composed of Y- {alpha}{prime}-sialon and {beta}{prime}-sialon obtained by hotpr... more Sialon composites composed of Y- {alpha}{prime}-sialon and {beta}{prime}-sialon obtained by hotpressing powder mixtures of Si{sub 3}N{sub 4}, Y{sub 2}O{sub 3} and AlN, were annealed at 1850{degrees}C to investigate the thermal stability of Y- {alpha}{prime} -sialon. The amount of Y- {alpha}{prime} -sialon reduced and it transformed into {beta}{prime}-sialon. When the transformation proceeded, Y and N were migrated to grain boundaries and their concentration at grain boundaries increased with time. It is considered that these elements then diffuse to the remaining Y- {alpha}{prime} -sialon and dissolve again, resulting in an increase in lattice constants (solubility) of the remaining Y- {alpha}{prime} -sialon with time.
Since cracks in catalyst layers of a fuel cell affect performance and durability, it is important... more 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.
Publisher Summary This chapter summarizes process technologies for nanostructural controls using ... more 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 quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that
Spillover and Mobility of Species on Solid Surfaces, 2001
ABSTRACT Structural characterizations and dynamic OSC measurements were performed on three Pt/CeO... more ABSTRACT Structural characterizations and dynamic OSC measurements were performed on three Pt/CeO2-ZrO2 (Pt/CZ). The catalyst supports were prepared by 1) precipitation-oxidation (CZ-O), 2) high energy ball milling (CZ-D), 3) precipitation and high temperature reduction (CZ-R). XRD and TEM-EDX results revealed that the homogeneity of Zr introduction into CeO2 framework is in the order of CZ-R>CZ-D>CZ-O. Among all the catalysts, Pt/CZ-R showed both the highest OSCC under cyclic transient reaction conditions and the highest reactivity in the isotopic exchange reaction. An atomically homogeneous introduction of Zr ions into CeO2 framework enhance the reactivity and the mobility of oxygen in CZ oxides. Some kinetic data concerning oxygen storage and the thermal stability of Pt/CZ at high temperature are also discussed.
The phase transformation behavior of the superlattice structure of a CeO2–ZrO2 pyrochlore‐type bi... more 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.
Abstract To realize the high performance of the three-way catalyst, a new catalytic promoter. “AC... more Abstract To realize the high performance of the three-way catalyst, a new catalytic promoter. “ACZ” was proposed. ACZ consists of nanometer-size CeO2-ZrO2 solid solution (CZ) particles and diffusion barrier layers made of alumina (A) among the CZ particles. The specific surface area of ACZ was larger than that of the conventional CZ after durability test. The sintering of Pt on the ACZ-added catalyst is inhibited and the crystal size of CZ in the ACZ-added catalyst is smaller than that in the CZ-added catalyst. The dynamic OSC and the light off temperature of the ACZ-added catalyst are improved.
... Haruo Imagawa, Akihiko Suda, Kae Yamamura, and Shouheng Sun*. Department of Chemistry,... more ... Haruo Imagawa, Akihiko Suda, Kae Yamamura, and Shouheng Sun*. Department of Chemistry, Brown University, Providence ... 9. Hirano, M.; Fukuda, Y.; Iwata, H.; Hotta, Y.; Inagaki, M. J. Am. Ceram. Soc. 2000, 83, 1287 1289 ...
A termetallic catalyst of Pt-Ir-Au/Al 2 O 3 for NO x decomposition was prepared by loading the me... more A termetallic catalyst of Pt-Ir-Au/Al 2 O 3 for NO x decomposition was prepared by loading the metallic colloids in C 2 H 5 OH-H 2 O solution and a surfactant of polyvinyl pyrrolidone. Compared with an impregnated Pt/Al 2 O 3 catalyst, the termetallic catalyst of PtIrAu811/Al 2 O 3 , with a Pt:Ir:Au atomic ratio of 8:1:1, exhibited higher NO decomposition and selectivity to N 2 . 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/Al 2 O 3 , which correlated well with its higher catalytic performance in NO decomposition.
WRjECIÌK¥zñÌe¿ The CeO 2 ZrO 2 solid solution is the most important oxygen storage/release materi... more WRjECIÌK¥zñÌe¿ The CeO 2 ZrO 2 solid solution is the most important oxygen storage/release material for use in automobile catalysts. In particular, the ceriazirconia 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.
Ce 2 Zr 2 O 7{x jIP_fmzû®g Ce 2 Zr 2 O 7.5 m ¶¬ Oxygen absorption behavior of Ce 2 Zr 2 O 7{x (0x... more Ce 2 Zr 2 O 7{x jIP_fmzû®g Ce 2 Zr 2 O 7.5 m ¶¬ Oxygen absorption behavior of Ce 2 Zr 2 O 7{x (0x1) with an ordered arrangement of Ce and Zr ions was stu died by Xray powder diraction, electron diraction and thermogravimetric analysis. It is revealed that the oxygen absorption of Ce 2 Zr 2 O 7 during heating in oxygen proceeds mainly through two reactions: (1) reac tion from Ce 2 Zr 2 O 7 to Ce 2 Zr 2 O 7.5 around 400 K and (2) reaction from Ce 2 Zr 2 O 7.5 to Ce 2 Zr 2 O 8 around 600 K. This behavior suggests the presence of the intermediate phase of the composition, Ce 2 Zr 2 O 7.5 . The intermedi ate phase, Ce 2 Zr 2 O 7.5 , was found to give extra reections compared with Ce 2 Zr 2 O 7 , and to belong to space group F 43m. This intermediate phase was obtained by oxidation of Ce 2 Zr 2 O 7 at room temperature for about 1 year, or heating at 473 K or lower temperature in oxygen.
Lanthanum-doped hollow alumina particles A-E were made by the emulsion combustion method ECM . Po... more 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 RhA-E than for Rh-loaded A-P pellets RhA-P because of the low dispersion of Rh for RhA-E. However, a gradient of the THC conversion-temperature curve was higher for RhA-E than for RhA-P. The large pore volume can promote good gas accessibility inside the pellets for RhA-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 formation of ceria-zirconia solid solution by the solid phase reaction of ceria and zirconia ... more 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 ap proximately 20nm, which was found asymptotically by two methods, X-ray diffraction and specific surface area measurements.
Sialon composites composed of Y- {alpha}{prime}-sialon and {beta}{prime}-sialon obtained by hotpr... more Sialon composites composed of Y- {alpha}{prime}-sialon and {beta}{prime}-sialon obtained by hotpressing powder mixtures of Si{sub 3}N{sub 4}, Y{sub 2}O{sub 3} and AlN, were annealed at 1850{degrees}C to investigate the thermal stability of Y- {alpha}{prime} -sialon. The amount of Y- {alpha}{prime} -sialon reduced and it transformed into {beta}{prime}-sialon. When the transformation proceeded, Y and N were migrated to grain boundaries and their concentration at grain boundaries increased with time. It is considered that these elements then diffuse to the remaining Y- {alpha}{prime} -sialon and dissolve again, resulting in an increase in lattice constants (solubility) of the remaining Y- {alpha}{prime} -sialon with time.
Since cracks in catalyst layers of a fuel cell affect performance and durability, it is important... more 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.
Publisher Summary This chapter summarizes process technologies for nanostructural controls using ... more 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 quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that
Spillover and Mobility of Species on Solid Surfaces, 2001
ABSTRACT Structural characterizations and dynamic OSC measurements were performed on three Pt/CeO... more ABSTRACT Structural characterizations and dynamic OSC measurements were performed on three Pt/CeO2-ZrO2 (Pt/CZ). The catalyst supports were prepared by 1) precipitation-oxidation (CZ-O), 2) high energy ball milling (CZ-D), 3) precipitation and high temperature reduction (CZ-R). XRD and TEM-EDX results revealed that the homogeneity of Zr introduction into CeO2 framework is in the order of CZ-R>CZ-D>CZ-O. Among all the catalysts, Pt/CZ-R showed both the highest OSCC under cyclic transient reaction conditions and the highest reactivity in the isotopic exchange reaction. An atomically homogeneous introduction of Zr ions into CeO2 framework enhance the reactivity and the mobility of oxygen in CZ oxides. Some kinetic data concerning oxygen storage and the thermal stability of Pt/CZ at high temperature are also discussed.
The phase transformation behavior of the superlattice structure of a CeO2–ZrO2 pyrochlore‐type bi... more 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.
Abstract To realize the high performance of the three-way catalyst, a new catalytic promoter. “AC... more Abstract To realize the high performance of the three-way catalyst, a new catalytic promoter. “ACZ” was proposed. ACZ consists of nanometer-size CeO2-ZrO2 solid solution (CZ) particles and diffusion barrier layers made of alumina (A) among the CZ particles. The specific surface area of ACZ was larger than that of the conventional CZ after durability test. The sintering of Pt on the ACZ-added catalyst is inhibited and the crystal size of CZ in the ACZ-added catalyst is smaller than that in the CZ-added catalyst. The dynamic OSC and the light off temperature of the ACZ-added catalyst are improved.
... Haruo Imagawa, Akihiko Suda, Kae Yamamura, and Shouheng Sun*. Department of Chemistry,... more ... Haruo Imagawa, Akihiko Suda, Kae Yamamura, and Shouheng Sun*. Department of Chemistry, Brown University, Providence ... 9. Hirano, M.; Fukuda, Y.; Iwata, H.; Hotta, Y.; Inagaki, M. J. Am. Ceram. Soc. 2000, 83, 1287 1289 ...
A termetallic catalyst of Pt-Ir-Au/Al 2 O 3 for NO x decomposition was prepared by loading the me... more A termetallic catalyst of Pt-Ir-Au/Al 2 O 3 for NO x decomposition was prepared by loading the metallic colloids in C 2 H 5 OH-H 2 O solution and a surfactant of polyvinyl pyrrolidone. Compared with an impregnated Pt/Al 2 O 3 catalyst, the termetallic catalyst of PtIrAu811/Al 2 O 3 , with a Pt:Ir:Au atomic ratio of 8:1:1, exhibited higher NO decomposition and selectivity to N 2 . 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/Al 2 O 3 , which correlated well with its higher catalytic performance in NO decomposition.
WRjECIÌK¥zñÌe¿ The CeO 2 ZrO 2 solid solution is the most important oxygen storage/release materi... more WRjECIÌK¥zñÌe¿ The CeO 2 ZrO 2 solid solution is the most important oxygen storage/release material for use in automobile catalysts. In particular, the ceriazirconia 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.
Ce 2 Zr 2 O 7{x jIP_fmzû®g Ce 2 Zr 2 O 7.5 m ¶¬ Oxygen absorption behavior of Ce 2 Zr 2 O 7{x (0x... more Ce 2 Zr 2 O 7{x jIP_fmzû®g Ce 2 Zr 2 O 7.5 m ¶¬ Oxygen absorption behavior of Ce 2 Zr 2 O 7{x (0x1) with an ordered arrangement of Ce and Zr ions was stu died by Xray powder diraction, electron diraction and thermogravimetric analysis. It is revealed that the oxygen absorption of Ce 2 Zr 2 O 7 during heating in oxygen proceeds mainly through two reactions: (1) reac tion from Ce 2 Zr 2 O 7 to Ce 2 Zr 2 O 7.5 around 400 K and (2) reaction from Ce 2 Zr 2 O 7.5 to Ce 2 Zr 2 O 8 around 600 K. This behavior suggests the presence of the intermediate phase of the composition, Ce 2 Zr 2 O 7.5 . The intermedi ate phase, Ce 2 Zr 2 O 7.5 , was found to give extra reections compared with Ce 2 Zr 2 O 7 , and to belong to space group F 43m. This intermediate phase was obtained by oxidation of Ce 2 Zr 2 O 7 at room temperature for about 1 year, or heating at 473 K or lower temperature in oxygen.
Lanthanum-doped hollow alumina particles A-E were made by the emulsion combustion method ECM . Po... more 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 RhA-E than for Rh-loaded A-P pellets RhA-P because of the low dispersion of Rh for RhA-E. However, a gradient of the THC conversion-temperature curve was higher for RhA-E than for RhA-P. The large pore volume can promote good gas accessibility inside the pellets for RhA-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.
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