Akihiko Suda

X-ray absorption fine structure analysis of local structure of CeO2–ZrO2 mixed oxides with the same composition ratio (Ce/Zr=1)

Abstract 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.

Extra-Low-Temperature Oxygen Storage Capacity of CeO2 Nanocrystals with Cubic Facets

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.

Local structure analyses of Ce0.5Zr0.5O2 mixed oxides by XAFS.

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 Ce(0.5)Zr(0.5)O2 solid solution at atomic level exhibited the highest OSC among these CeO2-ZrO2 with the same composition (Ce/Zr = 1).

Development of Three-way Catalyst Using Composite Alumina-Ceria-Zirconia

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.

Highly crystalline β-FeOOH(Cl) nanorod catalysts doped with transition metals for efficient water oxidation

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.

91 Development of three-way catalyst using composite alumina-ceria-zirconia

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.

High Oxygen Storage Ceria-Zirconia Solid Solutions Synthesized by Atmospheric Pressure Solvothermal Process

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.

Continuous Fabrication of Monodisperse Ceria–Zirconia–Yttria Composite Oxide Nanoparticles Using a Novel High-Shear Agitation Reactor

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.

CONTROL OF NANOSTRUCTURE OF MATERIALS

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.

EVALUATION METHODS FOR PROPERTIES OF NANOSTRUCTURED BODY

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.