K. Mimori

Tokyo Institute of Technology, Edo, Tokyo, Japan

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Publications (5)14.32 Total impact

  • K. Mimori · T. Togawa · N. Hasegawa · M. Tsuji · Y. Tamaura
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    ABSTRACT: An endothermic chemical system composed of pulverized iron-based oxide and carbon powder has been investigated by using the temperature swing method (TSM) at 700–800 °C. Ferrites of Zn, Mn, and Ni, and magnetite were studied. The magnetite showed the most promising result. In the TSM, magnetite as the working material was reduced to wüstite and carbon was concurrently oxidized to CO in a flow of N2 at 800 °C; this process is referred to as an activation step of the metal oxide. In the reverse process, in a flow of CO2, the wüstite was oxidized to magnetite and the injected CO2 was reduced to CO at 700 °C. The total amount of oxygen donated to carbon during the activation step was the same as that taken from the magnetite during the reduction step. In this system, the following net reaction is realized at temperatures of 700–800 °C: C + CO2 → 2CO. The process will therefore serve for the utilization of coal and other carbonaceous compounds at much lower temperatures than are employed in the traditional water-gas and producer-gas reactions.
    No preview · Article · Jul 1994 · Energy
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    ABSTRACT: Methanation reactivity was studied for the surface carbon deposited from CO2 on the surface of Rh-bearing activated magnetite. The most active material (Rh=0.83 wt %) for methanation was prepared by the impregnation method at 60C and showed 98% conversion at 300C. The surface carbon was composed of elemental carbon (-carbon) and polymerized carbon (-carbon), the proportion being dependent on the density of carbon deposited. In temperature-programmed surface reaction, the extent of conversion of the - and -carbon to CH4 was 0.34 (-carbon) and 0.53 (-carbon), respectively, and the total conversion was 0.87. This result indicates that not only elemental carbon but polymerized carbon (-carbon) could be converted to CH4 on the Rh-bearing activated (-carbon) magnetite, whereas -carbon is not hydrogenated on activated magnetite.
    No preview · Article · Dec 1993 · Journal of Materials Science
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    ABSTRACT: An oxygen-deficient Mn(II) ferrite (Mn0.97Fe2.02O3.92) was synthesized and its reactivity to reduce CO2 gas into carbon was studied at 300°C. The oxygen-deficient Mn(II) ferrite was obtained by flowing H2 gas through Mn(II) ferrite with a nearly stoichiometric composition of Mn0.97Fe2.02O4.00 at 300° C. The lattice constant of the oxygen-deficient Mn(II) ferrite (0.8505nm) is larger than that of the Mn(II) ferrite with a nearly stoichiometric composition (0.8498nm). The chemical composition of the Mn(II) ferrite changed from Mn0.97Fe2.02O4.00 to Mn0.97Fe2.02O3.92 during the H2 reduction process, indicating that the oxygen is deficient in the spinel structure of the Mn(II) ferrite. This was confirmed by Mössbauer spectroscopy and X-ray diffractometry. The efficiency of CO2 decomposition into carbon at 300°C with the oxygen-deficient Mn(II) ferrite was much lower by about 105 than that of oxygen-deficient magnetite. This is considered to be due to the difference in electron conductivity between Mn(II) ferrite and magnetite, which determines the reductivity for CO2 into carbon by donation of an electron at the adsorption site.
    No preview · Article · Feb 1993 · Journal of Materials Science
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    ABSTRACT: The reduction of CO2 to carbon was studied in oxygen-deficient Mn(II)-bearing ferrites (Mn x Fe3-x O4-, Ox1, >0) at 300 C. They were prepared by reducing Mn(II)-bearing ferrites with H2 gas at 300C. The oxygen-deficient Mn(II)-bearing ferrites showed a single phase with a spinel structure having an oxygen deficiency. The decomposition reaction of CO2 to carbon was accompanied by oxidation of the oxygen-deficient Mn(II)-bearing ferrites. The decomposition rate slowed when the Mn(II) content in the Mn(II)-bearing ferrites increased. A Mssbauer study of the phase changes of the solid samples during the H2 reduction and CO2 decomposition indicated the following. Increases in the Mn(II) content lowered the electron conductivity of the Mn(II)-bearing ferrites. Increases in the oxygen deficiency, , contributed to an increase in electron conductivity and suggested that electron conduction due to the electron hopping determines the reductivity of CO2 to carbon by the donation of an electron at adsorption sites.
    No preview · Article · Dec 1992 · Journal of Materials Science
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    ABSTRACT: The CO2 decomposition into carbon with the rhodium-bearing activated magnetite (Rh-AM) was studied in comparison with the activated magnetite (AM). The Rh-AM and the AM were prepared by flowing hydrogen gas through the rhodium-bearing magnetite (Rh-M) and the magnetite (M), respectively. The rate of activation of the Rh-M to the Rh-AM was about three times higher than that of the M to the AM at 300 C. The reactivity for the CO2 decomposition into carbon with the Rh-AM (70% CO2 was decomposed in 40 min) was higher than that with the AM (30% in 40 min) at 300 C. The Rh-M was activated to the Rh-AM at a lower temperature of 250 C, and the Rh-AM decomposed CO2 into carbon at 250 C. On the other hand, the M was little activated at 250 C.
    No preview · Article · Dec 1992 · Journal of Materials Science