The hydrogen desorption reaction of magnesium hydride (MgH2), MgH2→Mg+H2, is accelerated by mixing catalytic metal oxides (e.g., Nb2O5). This catalytic effect of metal oxides, MxOy, is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, ΔEM for metal ion and ΔEO for oxide ion in various metal oxides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption rate increases monotonously with increasing y × ΔEO values of metal oxides. This indicates that the oxide ion in MxOy interacts mainly with hydrogen atoms in MgH2. The y × ΔEO value is a measure of the magnitude of the O-H interaction operating between MxOy and MgH2, and hence, it is indeed a good parameter to show the catalytic activities of metal oxides. This approach is useful for the analysis of other catalyst and catalytic reactions.
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