Publications (21)67.06 Total impact
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Article: Operando XAFS study of catalytic NO reduction over Cu/CeO(2): the effect of copper-ceria interaction under periodic operation.
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ABSTRACT: Using an operando time-resolved XAFS technique at the Cu and Ce K-edges, we have discovered that the synchronization of Cu and Ce valence change in Cu/CeO(2) under periodic (rich-lean cycling) operation can improve the catalytic activity for NO reduction at low temperature.Physical Chemistry Chemical Physics 02/2013; · 3.57 Impact Factor -
Article: Operando X-ray Absorption Spectroscopy Study of Pt/γ-Al2O3 During the Total Oxidation of C3H6
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ABSTRACT: Operando X-ray absorption fine structure (XAFS) investigations were performed on Pt/γ-Al2O3 during the total oxidation of C3H6 in reducing and oxidizing atmospheres. Study of the Pt valance state and catalytic conversion behavior as a function of temperature revealed that both the creation of metallic Pt sites and the activation of adsorbed species on Pt are important for the functioning of the catalytic reaction at low temperature.Topics in Catalysis 05/2012; 52(10):1433-1439. · 2.62 Impact Factor -
Article: Suppression of Noble Metal Sintering Based on the Support Anchoring Effect and its Application in Automotive Three-Way Catalysis
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ABSTRACT: Suppression of noble metal sintering is a very important approach in the development of automotive three-way catalysts. The investigation into the Pt sintering behavior revealed that the formed Pt–O–M (M: cation of oxide, i.e., cerium oxide) bond acted as an anchor to suppress the Pt sintering, and that the strength of the Pt-oxide-support interaction was well correlated with the electron density of oxygen in the support oxide. To achieve a good balance between catalytic activity and the sintering suppression, ceria based oxide support was verified to be suitable for Pt, and zirconia based oxide support was appropriate support for Rh. Through optimizing the configuration of Pt and Rh in the catalyst, a novel three-way catalyst was developed successfully, and this catalytic activity is far superior to the conventional catalyst, but with lower noble metal content.Topics in Catalysis 05/2012; 52(13):1967-1971. · 2.62 Impact Factor -
Article: Atmospheric pressure solvothermal synthesis of ceria–zirconia solid solutions and their large oxygen storage capacity
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ABSTRACT: 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 20mol% 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.Journal of Materials Science 04/2012; 43(7):2258-2262. · 2.02 Impact Factor -
Article: Mesoporous ferrihydrite-based iron oxide nanoparticles as highly promising materials for ozone removal.
Angewandte Chemie International Edition 06/2011; 50(32):7381-4. · 13.45 Impact Factor -
Article: Mesoporous 2-line ferrihydrite by a solution-phase cooperative assembly process for removal of organic contaminants in air.
Chemistry 01/2011; 17(4):1092-5. · 5.93 Impact Factor -
Article: Novel high-temperature reactors for in situ studies of three-way catalysts using turbo-XAS.
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ABSTRACT: Two novel high-temperature reactors for in situ X-ray absorption spectroscopy (XAS) measurements in fluorescence are presented, each of them being optimized for a particular purpose. The powerful combination of these reactors with the turbo-XAS technique used in a dispersive-XAS beamline permits the study of commercial three-way catalysts under realistic gas composition and temporal conditions.Journal of Synchrotron Radiation 10/2009; 16(Pt 5):628-34. · 2.73 Impact Factor -
Article: Real‐time XAFS analysis of Rh/alumina catalyst
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ABSTRACT: Reduction rates of rhodium supported on alumina were investigated with in situ time-resolved X-ray absorption fine structure (XAFS). The catalytic sample was prepared with 0.5-wt% rhodium on the alumina powder by a usual impregnation method. Two types of XAFS techniques were applied for the experiments: energy-dispersive XAFS and usual step-scanning XAFS. The reduction rates of the rhodium supported on alumina after oxidizing treatment at 500 °C were measured with dispersive XAFS. The reducing condition was with 3% H2 in He at various temperatures from 100 to 250oC. The spectra of Rh K-edge X-ray absorption near edge structure (XANES) were acquired every 0.2 s. The oxidation state of the rhodium was evaluated by the energy shift of Rh K-edge. The reduction rate of the rhodium was on a line in an Arrhenius plot. Reduction of the rhodium on the alumina in 3% H2 in He at 900 °C after high temperature oxidization at 900 and 1000 °C were measured with step-scan XAFS. Though a portion of the rhodium was reduced in a few minutes, the residual rhodium was hardly reduced. The hardly reducible rhodium was considered to be reacted with the alumina support and lost catalytic activities. The ratio of the deactivated rhodium has been estimated as a function of the oxidization temperature and period. Copyright © 2008 John Wiley & Sons, Ltd.Surface and Interface Analysis 12/2008; 40(13):1751 - 1754. · 1.18 Impact Factor -
Article: In situ redispersion of platinum autoexhaust catalysts: an on-line approach to increasing catalyst lifetimes?
Angewandte Chemie International Edition 11/2008; 47(48):9303-6. · 13.45 Impact Factor -
Article: XAFS and XRD Analysis of Ceria–Zirconia Oxygen Storage Promoters for Automotive Catalysts
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ABSTRACT: 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 1,473K under an oxidative atmosphere, respectively. The OSC performance deteriorated as: the fresh sample ≈973>1,273>1,473K-aged samples. We also found that, if the temperature was beyond 1,273K, 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.Topics in Catalysis 03/2008; 47(3):137-147. · 2.62 Impact Factor -
Article: Origin and dynamics of oxygen storage/release in a Pt/ordered CeO2-ZrO2 catalyst studied by time-resolved XAFS analysis.
Angewandte Chemie International Edition 02/2007; 46(48):9253-6. · 13.45 Impact Factor -
Article: Characterization and dynamic behavior of precious metals in automotive exhaust gas purification catalysts
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ABSTRACT: Both the behaviors of sintering and reactivation of Pt and Rh on various metal oxide supports were investigated by TEM, CO pulse chemisorption and XAFS analysis. The results suggest that phenomenon of reversible sintering and re-dispersion to reduced, active metallic sites is related to the electron density of O atoms in support and to the crystal structure of support.As a result of in situ XAFS and in situ TEM analysis, Pt reversible sintering and re-dispersion phenomenon was observed on CeO2 based metal oxide. The Pt re-dispersion process proceeds by the repetition of (1) migration of Pt oxide from the surface of large Pt particles, (2) adsorption of Pt oxide on the surface of CeO2 based metal oxide by strong Pt–O–Ce interaction and (3) reduction Pt oxide and Pt–O–Ce bond.To achieve a good balance between activity and the sintering suppression, CeO2 based metal oxide is selected as Pt support, and ZrO2 is used as Rh support. The blended catalyst of Pt on ceria based oxide and Rh on ZrO2 has higher activity after aging.Catalysis Today 164(1):467-473. · 3.41 Impact Factor -
Article: Dynamic in situ observation of automotive catalysts for emission control using X-ray absorption fine structure
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Article: Dynamic oxygen mobility and a new insight into the role of Zr atoms in three-way catalysts of Pt/CeO2–ZrO2
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ABSTRACT: 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 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.Catalysis Today. -
Article: Reversible changes in the Pt oxidation state and nanostructure on a ceria-based supported Pt
Journal of Catalysis. 266(2):182-190. -
Article: Oxidation selectivity between n-hexane and sulfur dioxide in diesel simulated exhaust gas over platinum-supported zirconia catalyst
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ABSTRACT: We examined the oxidation reaction of n-C6H14 and SO2 over two types of Pt/ZrO2 catalysts with low (8 m2/g) and high (75 m2/g) surface areas of the ZrO2 supports (referred to as ZrO2-8 and ZrO2-75, respectively). The catalytic activity was evaluated under simulated diesel exhaust gas which simultaneously contained n-C6H14 and SO2. The Pt/ZrO2-75 exhibited a desirably higher selectivity for the complete oxidation of n-C6H14 than that of SO2, as compared with the Pt/ZrO2-8. In order to clarify the cause of this selective oxidation, we investigated the Arrhenius parameter for these oxidation reactions and characterized these catalysts using X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Transmission electron micrograph (TEM), IR and CO2 temperature-programmed desorption (CO2-TPD) methods. The amount of Pt0 (metal) in the Pt/ZrO2-75 was significantly lower than that in Pt/ZrO2-8, because the high basicity of the ZrO2-75 support stabilized the high oxidation state of Pt such as Pt2+ and Pt4+. It was concluded that the difference in the number of Pt0 sites as catalytic active sites causes the apparent selectivity to change due to the much slower reaction rate for the SO2 oxidation than that for the n-C6H14 oxidation.Applied Catalysis B: Environmental. 39(2):149-155. -
Article: Ideal Pt loading for a Pt/CeO2-based catalyst stabilized by a Pt–O–Ce bond
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ABSTRACT: Pt–O–Ce bond formation under suitable oxidative conditions on the surface of a catalyst support inhibits Pt particle sintering and promotes the redispersion of agglomerated Pt particles. In the present study the influence of Pt loading on changes in the catalytic activity and Pt particle size was evaluated for aged and regenerated Pt/CeO2-based catalysts. Catalysts with a lower Pt loading exhibited less catalytic deactivation and Pt sintering. There was an ideal Pt loading for which regeneration restored the Pt particle size and the catalytic activity to the same values as for the fresh state. This ideal Pt loading is discussed in terms of Pt anchor sites by considering the structure and composition around Pt on a CeO2-based catalyst.Graphical abstractThe experimental ideal Pt load for Pt/CeO2-based catalysts is discussed in terms of Pt anchor sites based on the structure and composition of the Pt neighborhood on the support.Research highlights▶ Structure of Pt–O–Ce anchor site was simulated using DFT. ▶ 5 Ce atoms interact with one Pt atom to form a Pt anchor site. ▶ The experimental ideal Pt loading was same with simulated one.Applied Catalysis B: Environmental. 99:336-342. -
Article: Low temperature CO pulse adsorption for the determination of Pt particle size in a Pt/cerium-based oxide catalyst
Applied Catalysis A: General. 370:108-113. -
Article: Physicochemical Study of Automotive Catalysts for Emission Control
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ABSTRACT: 学位授与年月日: 2007-07-23 ; 学位の種類: 新制・論文博士 ; 学位記番号: 論工博第3967号 Preface: This thesis is concerning the automotive catalysts to remove the harmful emission from automotive engines. Today, the automobile society is growing on the global scale, and vehicles are essential to make our living more convenient and richer. On the other hand, vehicles have a great effect on the global environment and natural resources. Recently, due to increasing demands for global environmental protection, more stringent regulations have been imposed on the automobile industry. Automobile companies are striving to purify automobile exhaust emissions. Consequently, there is a strong demand to produce more advanced automotive catalysts by technical innovation. Here, the author presents the physicochemical study of automotive catalysts. Using advanced analysis techniques such as synchrotron radiation analysis can make it possible to design catalysts for practical use, rather than adopting a trial-and-error approach. The author hopes that his studies can pave the way for planed catalytic design in the future. In the near future, this approach of designing catalysts at an atomic level by using advanced synchrotron radiation analysis must enable the realization of an ultimate clean car which completely removes harmful components from exhaust gases. The present study has been carried out in the catalyst laboratory at the TOYOTA Central R&D Labs. Inc. (TCRDL) during the years 1999-2006. During this time, the author has been in charge of the development of new automotive catalysts. The main subject of his work was “Synchrotron radiation analysis of automotive catalysts”. The aims of the project were the knowledge on the relationship between catalytic activity and the atomic structure, and the development of more advanced catalysts. The author started the synchrotron radiation analysis at SPring-8 (Hyogo, Japan) in 1999. After that, he also carried out the synchrotron radiation experiment at ESRF (Grenoble, France) and PF (Tsukuba, Japan). The author has met many people and gained a lot of experience. Kyoto University (京都大学) 0048 新制・論文博士 博士(工学) 乙第12102号 論工博第3967号 新制/工/1417 UT51-2007-M982 2007-07-23 -
Article: Sintering inhibition mechanism of platinum supported on ceria-based oxide and Pt-oxide–support interaction
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ABSTRACT: Sintering inhibition mechanism of Pt in Pt/ceria-based oxide catalyst under oxidizing condition at high temperature was studied by several analysis techniques. Pt in a Pt/ceria-based oxide catalyst did not sinter after aging treatment at 800 °C in air, but did sinter in a Pt/Al2O3 catalyst. Using X-ray absorption analysis, we found that the PtOCe bond (i.e., the Pt-oxide–support interaction) acted as an anchor and inhibited the sintering of Pt particles on ceria-based oxide. As a result of further systematic investigation on various Pt catalysts, clearly there was an excellent correlation between the strength of the Pt-oxide–support interaction and the electron density of oxygen in the support oxide. The sintering inhibition effect on Pt can be controlled by the electron density of oxygen in the support through the Pt-oxide–support interaction.Journal of Catalysis.
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Institutions
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2008–2013
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Toyota Central R & D Labs., Inc.
Nagoya-shi, Aichi-ken, Japan
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