Creat membership Creat membership
Sign in

Forgot password?

  • Forgot password?
    Sign Up
  • Confirm
    Sign In
home > search

Now showing items 17 - 24 of 24

  • Dynamic structural change in Pd-perovskite automotive catalyst studied by time-resolved dispersive x-ray absorption fine structure

    Matsumura, Daiju   Nishihata, Yasuo   Mizuki, Jun'ichiro   Taniguchi, Masashi   Uenishi, Mari   Tanaka, Hirohisa  

    Dynamic structural change in Pd-perovskite automotive catalyst, LaFe(0.9)Pd(0.1)O(3), which has a high catalytic activity during aging, was studied by in situ time-resolved dispersive x-ray absorption fine structure spectroscopy at 200-500 degrees C. An Al(2)O(3)-based conventional catalyst was also studied. In a reductive atmosphere, both catalysts showed similar temperature dependences of structural transformation from an oxide to a metal. However, different temperature dependence was observed in an oxidative atmosphere. A faster response in the structural change was observed in the Pd-perovskite catalyst than in the Pd/Al(2)O(3) catalyst. It was revealed that Pd-perovskite shows a considerably fast structural change to the oxidized state via the movement of Pd atoms into the perovskite crystal, in comparison with Pd/Al(2)O(3) showing two-step structural change for making PdO. (C) 2010 American Institute of Physics. [doi :10.1063/1.3437084]
    Download Collect
  • Direct observation of Au(111) electrode surface structure in bis(trifluoromethylsulfonyl)amide-based ionic liquids using surface X-ray scattering

    Tamura, Kazuhisa   Miyaguchi, Shin-ichiro   Sakaue, Kiyoshi   Nishihata, Yasuo   Mizuki, Jun'ichiro  

    The surface structure of Au(111) electrodes in hydrophobic ionic liquids, 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)amide ([BMP]TFSA) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide ([BMIM]TFSA) was investigated using surface X-ray scattering. In both [BMP]TFSA and [BMIM]TFSA, the reconstruction of the surface structure was observed and the phase transition between the (1 x 1) and the reconstructed structure was found to be reversible. On the other hand, the area of the reconstructed structure in [BMP]TFSA was larger than that in [BMIM]TFSA. These differences suggest that the [BMIM](+)-Au interaction is stronger than the [BMP](+)-Au interaction. (C) 2011 Elsevier B.V. All rights reserved.
    Download Collect
  • Time evolution of palladium structure change with redox fluctuations in a LaFePdO3 perovskite automotive catalyst by high-speed analysis with in situ DXAFS RID A-9953-2009

    Uenishi, Mari   Tanaka, Hirohisa   Taniguchi, Masashi   Tan, Isao   Nishihata, Yasuo   Mizuki, Jun'ichiro   Kobayashi, Tetsuhiko  

    In the LaFePdO3 perovskite catalyst, redox fluctuations of the exhaust gas suppress the growth of particles of precious metal by causing Pd to move in and out of the perovskite crystal. To observe the real movements of Pd directly, the time evolution of local structure around I'd by redox fluctuations was investigated by in situ energy-dispersive X-ray absorption fine-structure (DXAFS) analysis with a 10 ms resolution. We proved that the change in structure of Pd is sufficiently fast to respond to the control frequency (1-4 Hz) of an actual gasoline engine and that the Pd particles that segregate out are extremely fine. (C) 2007 Elsevier B.V. All rights reserved.
    Download Collect
  • Precise Observation of Growth of Surface Oxide Layer for Pd and Cu Nanoparticles During Oxidative/Reductive Gases Cyclic Flow Studied by Real-Time-Resolved XAFS Spectroscopy

    Matsumura, Daiju   Nishihata, Yasuo   Okajima, Yuka  

    We have demonstrated in situ and real-time-resolved X-ray absorption fine structure (XAFS) observation for oscillatory creation and removal reactions of surface oxide layer of Pd and Cu metal nanoparticles during cyclic flow of oxidative and reductive gases every 10 s. Pd and Cu K-edges XAFS spectra were collected at about 1-2 Hz. Precise observation of edge position was utilized for monitoring surface oxidation and reduction reactions. Reaction rate of surface oxide layer creation by NO for Pd metal nanoparticle is faster in the case of H-2/NO cyclic flow than in CO/NO. Fast and two-step surface oxidation and reduction reactions were revealed in Cu metal nanoparticles.
    Download Collect
  • Role of Cerium Oxide in the Enhancement of Activity for the Oxygen Reduction Reaction at Pt-CeOx Nanocomposite Electrocatalyst - An in Situ Electrochemical X-ray Absorption Fine Structure Study

    Masuda, Takuya   Fukumitsu, Hitoshi   Fugane, Keisuke   Togasaki, Hirotaka   Matsumura, Daiju   Tamura, Kazuhisa   Nishihata, Yasuo   Yoshikawa, Hideki   Kobayashi, Keisuke   Mori, Toshiyuki   Uosaki, Kohei  

    In situ electrochemical X-ray absorption fine structure (XAFS) measurements were performed at the Pt L-3 and Ce L-3 edges of the Pt-CeOx/C catalyst, which was prepared by a combined process of precipitation and coimpregnation methods, as well as at the Pt L-3 edge of the conventional Pt/C catalyst in oxygen-saturated H2SO4 solution to clarify the role of CeOx in the reduction of the overpotential for the oxygen reduction reaction (ORR) at the Pt-CeOx nanocomposite compared with the conventional Pt/C catalyst. XAFS measurements clearly show that the enhancement of ORR activity is attributed to the inhibition of Pt oxide formation by the CeOx layer, of which Ce3+ was oxidized to Ce4+ instead of Pt at the Pt oxide formation potential.
    Download Collect
  • Magnetic and dielectric study of R(0.5)Sr(0.5)MnO(3) (R = Gd, Tb and Dy)

    Yoshii, Kenji   Hiramitsu, Yusuke   Okajima, Yuka   Yoneda, Yasuhiro   Nishihata, Yasuo   Mizuki, Jun'ichiro   Nakamura, Akio   Shimojo, Yutaka   Ishii, Yoshinobu   Morii, Yukio   Ikeda, Naoshi  

    Magnetic and dielectric properties of perovskite manganites R(0.5)Sr(0.5)MnO(3)(R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at T(g) similar to 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R(3+) and Sr(3+) settled randomly at the same crystallographic site. Dielectric constants for each material were similar to 1000-10,000 between similar to 50 and similar to 300 K and showed broad maximums above T(g). Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan delta and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons. (C) 2010 Elsevier Ltd. All rights reserved.
    Download Collect
  • Growth of perovskite (Bi, Ln)(Ni0.5Ti0.5)O-3 thin films by RF magnetron sputtering

    Fukushima, Koji   Kobune, Masafumi   Yamaji, Toru   Tada, Hideto   Mineshige, Atsushi   Yazawa, Tetsuo   Fujisawa, Hironori   Shimizu, Masaru   Nishihata, Yasuo   Mizuki, Jun'ichiro   Yamaguchi, Hideshi   Honda, Koichiro  

    The epitaxial growth and formation mechanism of the partially La- and Nd-substituted perovskite structures, and the ferroelectric properties of bismuth lanthanoid nickel titanate [(Bi1-xLax)(Ni0.5Ti0.5)O-3; BLNT and (Bi1-xNdx)(Ni0.5Ti0.5)O-3; BNNT] based solid solution films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction. transmission electron microscope, and polarization-electric field hysteresis loop measurements. BLNT samples at x >= 0.3 and BNNT samples at x >= 0.4 were confirmed to have a single-phase perovskite structure. This small difference is speculated that it is related to metal-oxygen bond dissociation energy. The sample substituted with La exhibited the best hysteresis loop at x = 0.5 with a remanent polarization of P, = 12 mu C/cm(2) and the sample substituted by Nd exhibited the best hysteresis loop at x = 0.4 with a remanent polarization Of P-r = 2 mu C/cm(2).
    Download Collect
  • Magnetic and Dielectric Properties of R(0.5)Ca(0.5)MnO(3) (R = Eu-Lu)

    Yoshii, Kenji   Hiramitsu, Yusuke   Yoneda, Yasuhiro   Okajima, Yuka   Nishihata, Yasuo   Mizuki, Jun'Ichiro   Ikeda, Naoshi  

    The magnetic and dielectric properties of perovskite manganites R(0.5)Ca(0.5)MnO(3) (R = Eu-Lu), which show charge ordering of the Mn-3d electrons below room temperature, have been investigated. Their dielectric constants were similar to 1000-10000 at around room temperature. Inflections or peaks of temperature dependences of the dielectric constants were observed at around the charge-ordering temperatures. Analyses of tan delta for R = Eu-Lu and EXAFS spectra for R = Dy suggested that the dielectric properties of the present system are rooted in a special arrangement and transfer of the Mn-3d electrons. The two-peak structure of tan d indicates that dielectric measurement can be used to observe homogeneity or inhomogeneity of sample, as mentioned in our previous paper on the ruthenium perovskite oxides.
    Download Collect
1 2


If you have any feedback, Please follow the official account to submit feedback.

Turn on your phone and scan

Submit Feedback