Quantitative approach to the understanding of catalytic effect of metal oxides on the desorption reaction of MgH₂

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, ΔE_M for metal ion and ΔE_O 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 × ΔE_O values of metal oxides. This indicates that the oxide ion in MxOy interacts mainly with hydrogen atoms in MgH₂. The y × ΔE_O 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.