Yoshiki Kubota

Osaka Prefecture University, Sakai, Ōsaka, Japan

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Publications (83)472.03 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Pd octahedrons and cubes enclosed by {111} and {100} facets, respectively, have been synthesized for investigation of the shape effect on hydrogen-absorption properties. Hydrogen-storage properties were investigated using in situ powder X-ray diffraction, in situ solid-state (2)H NMR and hydrogen pressure-composition isotherm measurements. With these measurements, it was found that the exposed facets do not affect hydrogen-storage capacity; however, they significantly affect the absorption speed, with octahedral nanocrystals showing the faster response. The heat of adsorption of hydrogen and the hydrogen diffusion pathway were suggested to be dominant factors for hydrogen-absorption speed. Furthermore, in situ solid-state (2)H NMR detected for the first time the state of (2)H in a solid-solution (Pd + H) phase of Pd nanocrystals at rt.
    Journal of the American Chemical Society 07/2014; · 10.68 Impact Factor
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    ABSTRACT: Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.
    Nature materials. 07/2014;
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    ABSTRACT: PdxRu1-x solid solution alloy nanoparticles were successfully synthesized over the whole composition range through a chemical reduction method, although Ru and Pd are immiscible at the atomic level in the bulk state. From the XRD measurement, it was found that the dominant structure of PdxRu1-x changes from fcc to hcp with increasing Ru content. The structures of PdxRu1-x nanoparticles in the Pd composition range of 30-70% consisted of both solid solution fcc and hcp structures, and both phases coexist in a single particle. In addition, the reaction of hydrogen with the PdxRu1-x nanoparticles changed from exothermic to endothermic as the Ru content increased. Furthermore, the prepared PdxRu1-x nanoparticles demonstrated enhanced CO-oxidizing catalytic activity; Pd0.5Ru0.5 nanoparticles exhibit the highest catalytic activity. This activity is much higher than that of the practically used CO-oxidizing catalyst Ru and that of the neighboring Rh, between Ru and Pd.
    Journal of the American Chemical Society 01/2014; · 10.68 Impact Factor
  • Microporous and Mesoporous Materials 01/2014; 189:83–90. · 3.37 Impact Factor
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    ABSTRACT: It is well known that the Sb–Te binary system has a large number of incommensurately or commensurately modulated structures between Sb and Sb2Te3 compounds. These structures, which are long-period trigonal stacking structures, possess their own modulation period γ, according to their composition in the thermal equilibrium. However, the structure of sputtered Sb–Te films with various compositions between the two compounds at both ends formed in a non-thermal equilibrium showed smaller γ values, than those expected from their compositions without exception. A smaller γ value implies that its structure is closer to that of Sb with the shortest period in all Sb–Te modulated structures. With increase in temperature, all these transient structures with smaller γ, however, became stable, accompanying an increase of γ to acquire their original modulated structures.
    Crystal Research and Technology 11/2013; 48(11). · 1.12 Impact Factor
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    ABSTRACT: In a model system of an O2--O2 dimer confined in the nanopores of Cu-1,4-cyclohexanedicarboxylic acid, the molecular orientation associated with the spin state was observed by precise synchrotron radiation structure analysis. The obtained charge density level structures revealed that the molecular orientation varied with increasing temperature, coupling with the spin states of the O2--O2 dimer. The magnetic properties previously reported were consistently explained by the S = 1 dimer model taking into account the molecular arrangements. The obtained gap parameters are different from those of the O2--O2 dimer confined in the nanopores of Cu-2,3-pyrazinedicarboxylate-pyrazine, which is explained by the pore deformation due to the adsorption, depending on the pore size and/or flexibility of the coordination polymer.
    Journal of the Physical Society of Japan 08/2013; 82(8):4703-. · 2.09 Impact Factor
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    ABSTRACT: We report the first discovery of pure face-centered-cubic (fcc) Ru nanoparticles. Although the fcc structure does not exist in the bulk Ru phase diagram, fcc Ru was obtained at room temperature because of the nanosize effect. We succeeded in separately synthesizing uniformly sized nanoparticles of both fcc and hcp Ru having diameters of 2-5.5 nm by simple chemical reduction methods with different metal precursors. The prepared fcc and hcp nanoparticles were both supported on γ-Al2O3, and their catalytic activities in CO oxidation were investigated and found to depend on their structure and size.
    Journal of the American Chemical Society 04/2013; · 10.68 Impact Factor
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    ABSTRACT: The crystal structure of a phase-change recording material (the compound Ag(3.4)In(3.7)Sb(76.4)Te(16.5)) enclosed in a vacuum capillary tube was investigated at various temperatures in a heating process using a large Debye-Scherrer camera installed in BL02B2 at SPring-8. The amorphous phase of this material turns into a crystalline phase at around 416 K; this crystalline phase has an A7-type structure with atoms of Ag, In, Sb or Te randomly occupying the 6c site in the space group. This structure was maintained up to around 545 K as a single phase, although thermal expansion of the crystal lattice was observed. However, above this temperature, phase separation into AgInTe(2) and Sb-Te transpired. The first fragment, AgInTe(2), reliably maintained its crystal structure up to the melting temperature. On the other hand, the atomic configuration of the Sb-Te gradually varied with increasing temperature. This gradual structural transformation can be described as a continuous growth of the modulation period γ.
    Acta crystallographica. Section B, Structural science 12/2012; 68(Pt 6):559-70. · 1.80 Impact Factor
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    ABSTRACT: Spinel Compound CuV2S4 exhibits incommensurate charge-density wave (CDW) transition at Tt ~ 90 K accompanied by a structural phase transition. We have performed synchrotron powder diffraction experiments in order to determine the crystal structure for low temperature phase. The CDW phase has an orthorhombic symmetry with the superspace group Imm2(0β0). It was found that the crystal structure is characterized by the significant change of bond lengths between vanadium atoms along a-axis. We suggested that this change is related to the orbital ordering of t2g orbitals, which is the origin of the formation of the CDW.
    Journal of Physics Conference Series 12/2012; 391(1):2095-.
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    ABSTRACT: An ordered mesoporous MFI zeolite material (Meso-MFI) was prepared by using CMK-type mesoporous carbons as a hard template. The Meso-MFI exhibits both structural and adsorption differences compared to the conventional bulk MFI zeolite. To study the argon (Ar) adsorption process in Meso-MFI, an in situ gas adsorption powder X-ray diffraction (XRD) analysis was performed using synchrotron X-ray source. Structural rearrangement of the mesoporous MFI zeolite upon Ar adsorption at low temperature (83 K) was intensively studied together with Ar adsorption process in Meso-MFI. We observed that a structural transition of the Meso-MFI zeolite framework from monoclinic (P21/n) to orthorhombic (Pnma) occurred at around 126 Pa at 83 K. Positions of Ar atoms are determined as a function of the Ar gas pressure through Rietveld refinement of powder XRD data. Ar atoms are observed at straight channels, sinusoidal channels, and the intersection of these channels at low pressure. As gas pressure increases, Ar atoms in the pore intersection are pulled off from the intersection toward the straight and sinusoidal channels. The pore shape of the straight channel is changed accordingly with the amount of adsorbed Ar atoms within the pores from circular to oval. These results indicate that Ar adsorption induces not only continuous rearrangement of framework atoms but also symmetry change in the Meso-MFI. A molecular simulation study combined with Rietveld refinement of in situ XRD data provided a full understanding of the adsorption process of Ar in Meso-MFI.
    The Journal of Physical Chemistry C. 11/2012; 116(48):25300–25308.
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    ABSTRACT: By adopting a ligand-based solid solution approach, the sulphonic acid functional group can be successfully incorporated into a porous coordination polymer with UiO-66 structure type. Zr(6)O(4)(OH)(4)(BDC-SO(3)H)(1.1)(BDC)(4.9) possesses enhanced heat of adsorption for carbon dioxide and acetone compared to Zr(6)O(4)(OH)(4)(BDC)(6).
    Dalton Transactions 08/2012; · 3.81 Impact Factor
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    ABSTRACT: We present a modeling scheme to analyze cagelike silica mesoporous crystals based on in situ X-ray diffraction (XRD) data collected during gas adsorption-desorption (physisorption) processes. Nitrogen physisorption on a silica mesoporous crystal of SBA-16 was directly monitored by using synchrotron in situ powder XRD measurements conducted at SPring-8. SBA-16 is a well-ordered mesoporous silica in which three-dimensional interconnected cagelike primary mesopores are located at the body-centered cubic lattice points. In addition, the surrounding silica matrix contains random microporous and mesoporous intrawall porosities that are significantly influential to the diffusion properties, and thus important to be quantified for this media. The in situ XRD data exhibits seven Bragg reflections throughout the measurements, and the present method allows one to obtain the maximal and stand-alone information about the pore structure (for example, the mesopore size, the matrix density, the intrawall porosity, and pore surface roughness) together with the nitrogen film evolution in the primary mesopores and the intrawall pore-filling in the silica matrix. We furthermore observe a macroscopic amount of nitrogen adsorbed assuming the density of the fluid, and confirm that the XRD "isotherm" recalculated from the analysis result is consistent with the conventional nitrogen isotherm on a semi-quantitative level; however, these results suggest that the intrawall pores would have a greater contribution to the adsorption than considered based on the conventional isotherm analyses. The present method is readily extendable to any ordered mesopores wrapped by the wall matrix containing a certain intrawall porosity.
    Chemistry 07/2012; 18(33):10300-11. · 5.93 Impact Factor
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    ABSTRACT: The mesoscale design of domain assembly is crucial for controlling the bulk properties of solids. Herein, we propose a modular design of domain assembly in porous coordination polymer crystals via exquisite control of the kinetics of the crystal formation process. Employing precursors of comparable chemical reactivity affords the preparation of homogeneous solid-solution type crystals. Employing precursors of distinct chemical reactivity affords the preparation of heterogeneous phase separated crystals. We have utilized this reactivity-directed crystallization process for the facile synthesis of mesoscale architecture which are either solid-solution or phase-separated type crystals. This approach can be also adapted to ternary phase-separated type crystals from one-pot reaction. Phase-separated type frameworks possess unique gas adsorption properties that are not observed in single-phasic compounds. The results shed light on the importance of crystal formation kinetics for control of mesoscale domains in order to create porous solids with unique cooperative functionality.
    Journal of the American Chemical Society 07/2012; 134(32):13341-7. · 10.68 Impact Factor
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    ABSTRACT: We have synthesized and characterized homogeneous solid-solution alloy nanoparticles of Pd and Rh, which are immiscible with each other in the equilibrium bulk state at around room temperature. The Pd-Rh alloy nanoparticles can absorb hydrogen at ambient pressure and the hydrogen pressure of Pd-Rh alloys for hydrogen storage is dramatically decreased by more than 4 orders of magnitude from the corresponding pressure in the metastable bulk state. The solid-solution state is still maintained in the nanoparticles even after hydrogen absorption/desorption, in contrast to the metastable bulks which are separated into Pd and Rh during the process.
    Journal of the American Chemical Society 07/2012; 134(30):12390-3. · 10.68 Impact Factor
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    ABSTRACT: The crystallization of a sputtered Sb(8)Te(3) film was examined in an X-ray powder diffraction experiment. An as-sputtered, amorphous Sb(8)Te(3) film crystallized during heating into a structure of Sb-Te homologous series modulated along the stacking direction. During heating the lattice parameters and the modulation period γ were found to change significantly and continuously; this observation suggests a continuous change in the stacking sequence. A superspace analysis revealed that with heating the modulation period γ increased to a value that seemed to be determined by the atomic composition. Once γ reached this value it remained unchanged with cooling. A three-dimensional projection of the converged four-dimensional superspace structure corresponded to the homologous Sb(8)Te(3) structure.
    Acta crystallographica. Section B, Structural science 10/2011; 67(Pt 5):381-5. · 1.80 Impact Factor
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    ABSTRACT: The development of a new methodology for visualizing and detecting gases is imperative for various applications. Here, we report a novel strategy in which gas molecules are detected by signals from a reporter guest that can read out a host structural transformation. A composite between a flexible porous coordination polymer and fluorescent reporter distyrylbenzene (DSB) selectively adsorbed CO₂ over other atmospheric gases. This adsorption induced a host transformation, which was accompanied by conformational variations of the included DSB. This read-out process resulted in a critical change in DSB fluorescence at a specific threshold pressure. The composite shows different fluorescence responses to CO₂ and acetylene, compounds that have similar physicochemical properties. Our system showed, for the first time, that fluorescent molecules can detect gases without any chemical interaction or energy transfer. The host-guest coupled transformations play a pivotal role in converting the gas adsorption events into detectable output signals.
    Nature Material 09/2011; 10(10):787-93. · 35.75 Impact Factor
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    ABSTRACT: We report the first example of nanosize-induced hydrogen storage in a metal that does not absorb hydrogen in its bulk form. Rhodium particles with diameters of <10 nm were found to exhibit hydrogen-storage capability, while bulk Rh does not absorb hydrogen. Hydrogen storage was confirmed by in situ powder X-ray diffraction, solid-state (2)H NMR, and hydrogen pressure-composition isotherm measurements. The hydrogen absorption capacity could be tuned by controlling the particle size.
    Journal of the American Chemical Society 06/2011; 133(29):11034-7. · 10.68 Impact Factor
  • Angewandte Chemie International Edition 10/2010; 49(42):7660-4. · 11.34 Impact Factor
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    ABSTRACT: Rh and Ag are the elements neighboring Pd, which is well known as a hydrogen-storage metal. Although Rh and Ag do not possess hydrogen-storage properties, can Ag-Rh alloys actually store hydrogen? Ag-Rh solid-solution alloys have not been explored in the past because they do not mix with each other at the atomic level, even in the liquid phase. We have used the chemical reduction method to obtain such Ag-Rh alloys, and XRD and STEM-EDX give clear evidence that the alloys mixed at the atomic level. From the measurements of hydrogen pressure-composition isotherms and solid-state (2)H NMR, we have revealed that Ag-Rh solid-solution alloys absorb hydrogen, and the total amount of hydrogen absorbed reached a maximum at the ratio of Ag:Rh = 50:50, where the electronic structure is expected to be similar to that of Pd.
    Journal of the American Chemical Society 10/2010; 132(45):15896-8. · 10.68 Impact Factor
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    ABSTRACT: The crystal structures of GeSb(6)Te(10) and GeBi(6)Te(10) were scrutinized using an X-ray powder diffraction method, which revealed that these compounds crystallize in trigonally distorted cubic close-packed structures with a 51-layer period (R3m). Each layer consists of a triangular atomic net; Te atoms occupy their own specific layers, whereas Ge, Sb and Bi atoms are located in the other layers. In these pseudobinary compounds, random atomic occupations of Ge and Sb/Bi are observed and the layers form two kinds of elemental structural blocks by their successive stacking along the c axis. These compounds can be presumed to be isostructural. It is known that the chemical formula of the chalcogenide compounds with the homologous structures found in these pseudobinary systems can be written as (GeTe)(n)(Sb(2)Te(3))(m) or (GeTe)(n)(Bi(2)Te(3))(m) (n, m: integer); the GeSb(6)Te(10) and GeBi(6)Te(10) investigated in this study, which correspond to the case in which n = 1 and m = 3, naturally have 3 x l = 51-layer structures according to a formation rule l = 2n + 5m commonly found in the compounds of these chalcogenide systems (l represents the number of layers in the basic structural unit). Calculations based on the density functional theory revealed that these materials are compound semiconductors with very narrow band gaps.
    Acta crystallographica. Section B, Structural science 08/2010; 66(Pt 4):407-11. · 1.80 Impact Factor

Publication Stats

1k Citations
472.03 Total Impact Points

Institutions

  • 2006–2014
    • Osaka Prefecture University
      • • Department of Physical Science
      • • Graduate School of Science
      Sakai, Ōsaka, Japan
    • Stockholm University
      • Department of Physics
      Stockholm, Stockholm, Sweden
  • 2003–2013
    • Kyoto University
      • • Division of Chemistry
      • • Department of Synthetic Chemistry and Biological Chemistry
      Kyoto, Kyoto-fu, Japan
  • 2012
    • Korea Advanced Institute of Science and Technology
      • Graduate School of EEWS
      Seoul, Seoul, South Korea
  • 2008–2010
    • Kyushu University
      • Faculty of Sciences
      Fukuoka-shi, Fukuoka-ken, Japan
    • Università degli Studi di Milano-Bicocca
      • Department of Materials Science
      Milano, Lombardy, Italy
  • 2000–2004
    • Osaka Women's University
      Sakai, Ōsaka, Japan
    • The University of Tokyo
      • Department of Advanced Materials Science
      Tokyo, Tokyo-to, Japan
  • 1999
    • Shimane University
      • Interdisciplinary Faculty of Sciences and Engineering
      Matsu, Shimane Prefecture, Japan
  • 1998
    • Nagoya University
      Nagoya, Aichi, Japan