Toyoshima, Ryo

写真a

Affiliation

Faculty of Science and Technology, Department of Chemistry (Yagami)

Position

Research Associate/Assistant Professor/Instructor

 

Papers 【 Display / hide

  • XPS and HAXPES analyses for pre-sputtered InP surface and InP/Pt interface

    Saito Y., Uemura S., Kagiyama T., Toyoshima R.

    Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)  61 ( 3 )  2022.03

    ISSN  00214922

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    The state of the pre-sputtered indium phosphide (InP) surface was analyzed by X-ray photoelectron spectroscopy, employing synchrotron-based relatively low-energy X-ray. It was found that the pre-sputtering treatment induced the phosphorus vaporization and made the surface composition In-rich, which was thought to promote oxidation of InP surface in atmosphere. The state of the interface between InP and Pt was also investigated nondestructively, by using hard X-ray photoemission spectroscopy. As a result, it was demonstrated that the interfacial layer was composed of the native oxide (In-O, P-O) and metallic state (In-Pt or In-In, P-P) and that the pre-sputtering treatment increased significantly the amount of the P-O, In-Pt or In-In, and P-P. From a simplified calculation, assuming a Pt/In-Pt/In-P layer stacking structure and neglecting the In-O and P-O components, the thickness of the interfacial layer was estimated to be approximately 3.0 nm.

  • A newly designed compact CEY-XAFS cell in the soft X-ray region and its application to surface XAFS measurements under ambient-pressure conditions without photoinduced side effects

    Shimizu H., Toyoshima R., Isegawa K., Mase K., Nakamura J., Kondoh H.

    Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics)  24 ( 5 ) 2988 - 2996 2022.02

    ISSN  14639076

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    We report a newly designed compact cell to measure XAFS spectra with the conversion electron yield (CEY) method in the soft X-ray region under ambient-pressure gas conditions. Secondary electrons generated from the gas and sample by collision of X-ray-absorption-induced Auger electrons are collected by a positively biased collector electrode to obtain XAFS spectra. It was confirmed that this cell is applicable to soft X-ray surface XAFS measurements for different types of materials such as insulating organic materials and metal oxides under 1 bar gas conditions. During the measurements, photoinduced side effects were observed; i.e. photoinduced degradation of organic materials and photoinduced reduction/oxidation of metal oxides. We found that these photoinduced side effects can be sufficiently suppressed by controlling the measuring conditions. The presented measuring approach will enable surface XAFS spectra to be obtained in the soft X-ray region for various types of functional materials under ambient-pressure working conditions. This journal is

  • Ligand effects on surface oxide at RhPd(100) alloy surfaces: A density functional theory calculation study

    Shirahata N., Toyoshima R., Yoshida M., Ueda K., Mase K., Mun B.S., Kondoh H.

    Surface Science (Surface Science)  716 2022.02

    ISSN  00396028

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    Density functional theory calculations were applied to a study on ligand effects on a Pd surface oxide formed on RhPd(100) alloy surfaces. It was found that chemical composition of the topmost layer of alloy significantly influences on the electronic structure of the Pd surface oxide. Such interlayer ligand effects are originating from the Rh−O and Pd−O interactions between the topmost layer of alloy and the Pd surface oxide. These effects give rise to substantial changes in binding energies of adsorbates and could change catalytic activity depending on atomic fraction of the Rh−Pd alloy.

  • In situ AP-XPS study on reduction of oxidized Rh catalysts under CO exposure and catalytic reaction conditions

    Toyoshima R., Ueda K., Koda Y., Kodama H., Sumida H., Mase K., Kondoh H.

    Journal of Physics D: Applied Physics (Journal of Physics D: Applied Physics)  54 ( 20 )  2021.05

    ISSN  00223727

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    Reduction of oxidized Rh catalysts under carbon monoxide (CO) exposure and reaction conditions were studied by using ambient-pressure x-ray photoelectron spectroscopy. First, Rh powders pressed into a pellet were deeply oxidized and the reduction process under 100 mTorr CO environment was monitored in situ at different temperatures. The oxidized Rh surfaces are composed of Rh2O3 and RhO2, the latter of which is more segregated near the surface. Both oxide species are reduced simultaneously to the metallic state; kinetic analyses indicate that the activation energy of the reduction of the Rh oxides is 1.68 eV, which is a little larger than those for Pd oxides, probably due to a stronger Rh-O interaction. Reduction of oxidized Rh nano-particles deposited on SiO2 under two reaction conditions (CO + O2 and CO + NO + O2) was observed with increasing temperature. It was found that the reduction temperature shifts to the higher temperature in the presence of NO, even though the S-factors are almost the same. The NO molecule more strongly prevents the reduction of oxidized Rh catalyst compared to O2.

  • Detailed Characterization of MoO<inf>x</inf>-Modified Rh Metal Particles by Ambient-Pressure XPS and DFT Calculations

    Toyoshima R., Kawai J., Isegawa K., Kondoh H., Junkaew A., Nakayama A., Asano T., Tamura M., Nakagawa Y., Yabushita M., Tomishige K.

    Journal of Physical Chemistry C (Journal of Physical Chemistry C)  125 ( 8 ) 4540 - 4549 2021

    ISSN  19327447

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    © 2021 American Chemical Society. Characterization of Mo species on Rh metal particles in Rh-MoOx/C catalyst for C-O hydrogenolysis reactions was carried out with in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory (DFT) calculations. The as-prepared Rh-MoOx/C sample with high oxidation states of Rh3+, Rh4+ and Mo6+ was reduced with 0.2 Torr of H2. All the Rh species and most Mo species were reduced to Rh0 and Mo4+ during the heating to 570 K. The thickness of the Mo layers after the reduction was calculated by a numerical analysis based on the XPS intensity ratio and a uniform adlayer stacking model. The calculated averaged thickness was about 0.3 nm, suggesting the formation of Mo species with a monolayer order on the metallic Rh particle surface. The O 1s XPS showed the presence of Mo-OH and Mo-O oxygen species with a ratio of 1.4 in reduced Rh-MoOx/C. Considering the presence of residual Mo6+ species with a large number of Mo6+-O bonds, the ratio of Mo4+-OH to Mo4+-O is estimated to be 2, suggesting the formation of MoO(OH)2. The DFT calculations of various monomeric MoOxHy species on the Rh(111) surface were carried out, and the stability was examined by the ab initio thermodynamic approach. The relative stability is changed when the surface coverage of hydrogen atoms is taken into account. The MoO(OH)2 species is calculated to be the most stable species in the presence of surface hydrogens over a wide range of conditions, including those for the catalytic reaction (ca. 400 K, 100-1 MPa H2).

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Papers, etc., Registered in KOARA 【 Display / hide

 

Courses Taught 【 Display / hide

  • LABORATORY IN SCIENCE

    2022

  • LABORATORIES IN CHEMISTRY 1

    2022

  • LABORATORY IN SCIENCE

    2021

  • LABORATORIES IN CHEMISTRY 1

    2021

  • LABORATORY IN SCIENCE

    2020

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