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Saravanan G.,Japan National Institute of Materials Science | Abe H.,Japan National Institute of Materials Science | Xu Y.,Japan National Institute of Materials Science | Sekido N.,Japan National Institute of Materials Science | And 4 more authors.
Langmuir | Year: 2010

A platinum-based intermetallic phase with an early d-metal, Pt 3Ti, has been synthesized in the form of nanoparticles (NPs) dispersed on silica (SiO2) supports. The organometallic Pt and Ti precursors, Pt(1,5-cyclooctadiene)Cl2 and TiCl 4(tetrahydrofuran)2, were mixed with SiO2 and reduced by sodium naphthalide in tetrahydrofuran. Stoichiometric Pt 3Ti NPs with an average particle size of 2.5 nm were formed on SiO2 (particle size: 20-200 nm) with an atomically disordered FCC-type structure (Fm3̄m; a = 0.39 nm). A high dispersivity of Pt 3Ti NPs was achieved by adding excessive amounts of SiO2 relative to the Pt precursor. A 50-fold excess of SiO2 resulted in finely dispersed, SiO2-supported Pt3Ti NPs that contained 0.5 wt % Pt. The SiO2-supported Pt3Ti NPs showed a lower onset temperature of catalysis by 75 °C toward the oxidation reaction of CO than did SiO2-supported pure Pt NPs with the same particle size and Pt fraction, 0.5 wt %. The SiO2-supported Pt3Ti NPs also showed higher CO conversion than SiO2-supported pure Pt NPs even containing a 2-fold higher weight fraction of Pt. The SiO2-supported Pt3Ti NPs retained their stoichiometric composition after catalytic oxidation of CO at elevated temperatures, 325 °C. Pt3Ti NPs show promise as a catalytic center of purification catalysts for automobile exhaust due to their high catalytic activity toward CO oxidation with a low content of precious metals. © 2010 American Chemical Society. Source


Tsujimoto Y.,Japan National Institute of Materials Science | Sathish C.I.,Hokkaido University | Sathish C.I.,Japan National Institute of Materials Science | Hong K.-P.,Korea Atomic Energy Research Institute | And 11 more authors.
Inorganic Chemistry | Year: 2012

The crystal structure of the layered cobalt oxyfluoride Sr 2CoO 3F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr 2CoO 3F is an antiferromagnetic insulator with the Néel temperature T N = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ B at 3 K, consistent with the high spin electron configuration for the Co 3+ ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt. © 2012 American Chemical Society. Source


Tominaka S.,Japan International Center for Materials Nanoarchitectonics | Tsujimoto Y.,Japan National Institute of Materials Science | Matsushita Y.,NIMS Beamline Station at SPring 8 | Yamaura K.,Japan National Institute of Materials Science
Angewandte Chemie - International Edition | Year: 2011

Reduction without particle growth: Ti 2O 3 nanoparticles of corundum structure were synthesized by reducing TiO 2 nanoparticles of rutile structure with CaH 2 powder at a low temperature of 350 °C. The morphology of the reduced oxide was the same as that of the precursor, though the crystal structure was transformed from the tetragonal to the hexagonal system (see picture). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Tsujimoto Y.,Japan National Institute of Materials Science | Yamaura K.,Japan National Institute of Materials Science | Yamaura K.,Transformative Research Project on Iron Pnictides TRIP | Hayashi N.,Kyoto University | And 8 more authors.
Chemistry of Materials | Year: 2011

Topotactic reaction of the n = 2 Ruddlesden-Popper phase Sr 3Fe2O7-δ (δ ≈ 0.18) with polytetrafluoroethylene (PTFE) yields a highly fluorinated phase Sr 3Fe2O5+xF2-x (x ≈ 0.44), compared with Sr3Fe2O6F0.87 prepared by the reaction of Sr3Fe2O6 and F2 gas. Structure analyses based on powder neutron diffraction, synchrotron powder diffraction, and 57Fe Mössbauer spectroscopy measurements demonstrate that the new oxyfluoride perovskite has no anion deficiencies and adopts the tetragonal structure (space group I4/mmm) with the lattice constants a = 3.87264(6) Å and c = 21.3465(6) Å at room temperature. The fluoride ions preferentially occupy the terminal apical anion sites with oxide ions in a disordered manner, which results in square pyramidal coordination around iron. The present compound also shows an antiferromagnetic order with a Néel temperature (TN) of 390 K, in sharply contrast to Sr 3Fe2O6F0.87, which has a T N value that is lower than room temperature. © 2011 American Chemical Society. Source


Tsujimoto Y.,Japan National Institute of Materials Science | Li J.J.,Japan National Institute of Materials Science | Li J.J.,Hokkaido University | Li J.J.,Transformative Research Project on Iron Pnictides TRIP | And 11 more authors.
Chemical Communications | Year: 2011

The first Ruddlesden-Popper type layered cobalt oxyfluoride, Sr 2CoO3F, has been synthesized under a pressure of 6 GPa at 1700 °C and shown to adopt a K2NiF4-type structure with distorted square pyramidal coordination around Co and with O/F disorder at the apical sites. © 2011 The Royal Society of Chemistry. Source

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