Toyoshima, Ryo

写真a

Affiliation

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

Position

Assistant Professor (Non-tenured)/Research Associate (Non-tenured)/Instructor (Non-tenured)

 

Papers 【 Display / hide

  • 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).

  • Initial oxidation of GaAs(100) under near-realistic environments revealed by in situ AP-XPS

    Toyoshima R., Murakami S., Eguchi S., Amemiya K., Mase K., Kondoh H.

    Chemical communications (Cambridge, England) (Chemical communications (Cambridge, England))  56 ( 94 ) 14905 - 14908 2020.11

    ISSN  13597345

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    In situ monitoring of initial oxidation of GaAs surfaces was performed under (near-) realistic oxidizing environments, using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). The surface chemical states drastically change with time. The oxidation process at the sub-nano-meter-scale exhibits a significantly small activation energy, which can be regarded as a quasi-barrier-less oxidation.

  • Orientation-Dependent Hindrance to the Oxidation of Pd-Au Alloy Surfaces

    Toyoshima R., Amemiya K., Mase K., Kondoh H.

    The journal of physical chemistry letters (The journal of physical chemistry letters)  11 ( 21 ) 9249 - 9254 2020.11

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    Oxidation of monometallic Pd and bimetallic Pd3Au alloy surfaces are observed by in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at an elevated pressure (100 mTorr O2 ambient). It is directly evidenced that the alloying with Au hinders the surface oxidation of Pd3Au surfaces compared with monometallic Pd surfaces. Remarkably, the oxidation behavior is clearly different between Pd3Au(111) and (100) surfaces. The (100) surface has a relatively Pd-rich surface composition, and the surface oxide layer is formed, whereas the (111) surface has a Au-rich composition, and the surface oxidation is quite limited. A combined approach of experimental and theoretical techniques reveals that Pd/Au surface composition and atomic arrangement are key factors determining the oxidation behavior.

  • In situ AP-XPS analysis of a Pt thin-film sensor for highly sensitive H<inf>2</inf> detection

    Toyoshima R., Tanaka T., Kato T., Uchida K., Kondoh H.

    Chemical communications (Cambridge, England) (Chemical communications (Cambridge, England))  56 ( 70 ) 10147 - 10150 2020.09

    ISSN  13597345

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    In situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) combined with resistivity measurement was performed for a Pt thin-film H2 gas sensor. We experimentally demonstrate that the chemical state of the Pt surface changes under working conditions, and it directly links to the sensing performance. Moreover, the operating principle is discussed at the atomic scale.

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

 

Courses Taught 【 Display / hide

  • LABORATORY IN SCIENCE

    2021

  • LABORATORIES IN CHEMISTRY 1

    2021

  • LABORATORY IN SCIENCE

    2020

  • LABORATORIES IN CHEMISTRY 1

    2020

  • LABORATORY IN SCIENCE

    2019

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