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Catalytic Activities of Various Niobium Oxides for Hydrogen Absorption/Desorption Reactions of Magnesium.

ABSTRACT: Five types of niobium(V) oxides (Nb₂O₅) were synthesized by hydrothermal and heat treatment processes, and their structural properties and catalytic activities for the hydrogen absorption/desorption reactions of magnesium were characterized. The synthesized Nb oxides were dispersed on magnesium hydride (MgH₂), a typical hydrogen storage material, using the ball-milling method. All the synthesized Nb oxides improved the reaction kinetics of the hydrogen desorption/absorption reactions. The catalytic activities for the hydrogen desorption were comparable, while the hydrogen absorption rates were significantly different for each synthesized Nb oxide. This difference can be explained by the structural stability of Nb₂O₅, which is related to the formation of a catalytically active state by the reduction of Nb₂O₅ during the ball-milling process. Notably, the highest catalytic effect was observed for Nb₂O₅ with a highly crystalline pyrochlore structure and a low specific surface area, suggesting that pyrochlore Nb₂O₅ is a metastable phase. However, only the amorphous Nb oxide was out of order, even though there is a report on the high catalytic activity of amorphous Nb oxide. This is attributed to the initial condensed state of amorphous Nb oxide, because particle size affects the dispersion state on the MgH₂ surface, which is also important for obtaining high catalytic activity. Thus, it is concluded that Nb₂O₅ with lower stability of the crystal structure and smaller particle size shows better catalysis for both hydrogen desorption and absorption reactions.

SUBMITTER: Shinzato K

PROVIDER: S-EPMC8444326 | biostudies-literature |

REPOSITORIES: biostudies-literature

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