Systematic study on catalysis of group 4–6 element oxide for magnesium hydride

Abstract

In this work, systematic research on catalytic properties of group 4–6 element oxides, which are TiO2, ZrO2, HfO2, V2O5, Ta2O5, CrO3, MoO3, and WO3, for magnesium hydride (MgH2), were carried out to understand important factors for the formation of catalytic active state. Each oxide is dispersed on the MgH2 surface by the ball-milling under the same conditions. The hydrogen desorption properties are investigated, and the oxides on the MgH2 are characterized by structural and spectroscopic analyses. Although all the oxides show catalysis for the hydrogen desorption process, TiO2, V2O5, ZrO2, and CrO3 particularly reveals higher catalytic activity, resulting in the hydrogen desorption around 200 °C. For TiO2, V2O5, CrO3, ZrO2, and MoO3, a highly dispersed state of the oxides on Mg is found, suggesting that the catalysis is related to the dispersion process. Among the above oxides, only MoO3 does not show the higher catalysis even though it is highly dispersed on Mg. To know the other control factors of the catalysis, the chemical state of transition metals is investigated by X-ray photoelectron spectroscopy. As a result, it is clarified that the high catalytic activity is obtained in case the transition metals form multi oxide state especially including 2 + and 3 + oxidation states. From the above experimental facts, it is expected that the reduction and dispersion of oxides simultaneously proceed during the ball-milling process, and the oxides with intermediate oxidation states shows the high catalysis for the Mg system.