Papers by Author: Ryosuke Nakanishi

Abstract: . Preferential oxidation (PROX) of CO in the presence of H2 is an important reaction to maintain stable operation of polymer electrolyte fuel cells (PEFCs) since their anode catalyst can be poisoned by trace amount of CO. In this study, we examined PROX reactions mediated by Pt catalysts prepared using several mesoporous silica and aluminosilicate supports such as imogolite (IM), allophane (AP), silica aerogel (SAG), and an amorphous hydroxyl aluminosilicate developed in our research group (HAS). The selectivity of CO oxidation gradually decreased from 80 to 60 % with increasing temperature from 323 to 473 K for Pt/HAS catalyst whereas it increased with temperature from 10 to 40 % for Pt/IM, Pt/AP, Pt/SAG catalysts. These results indicate that Pt supported on HAS may be effective for low-temperature PROX reactions.

Abstract: The effects of the Zn content on the aging behavior of Mg–Zn alloys was examined by means of Vickers microhardness measurements and high-resolution transmission electron microscopy (HRTEM). The hardness of Mg–Zn alloys with high Zn concentrations increased markedly on aging at 473 K. A higher maximum hardness was obtained at an earlier aging time for alloys with high Zn concentrations. The aging response of Mg–4.7mass%Zn alloy aged at 473 K and quenched in chilled water differed from that of a specimen both aged and quenched at 473 K up to the maximum hardness. HRTEM images of the monolayers on the { }Mg planes were recorded for specimens quenched in chilled water; ' and ' phases were found to exist in the maximally aged specimen. Compared with the specimen quenched in water, the number of ' phases was lower in the specimen that was both aged and quenching at 473 K. It was suggested that the difference in the aging response is related to the formation of monolayers in the early stage of aging.