Quantitative Approach to the Understanding of Catalytic Effect of Metal Oxides on the Desorption Reaction of MgH2

摘要

The hydrogen desorption reaction of magnesium hydride (MgH2), MgH2 -> Mg+H-2, 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, Delta E-M for metal ion and Delta E-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 x Delta E-O values of metal oxides. This indicates that the oxide ion in MxOy interacts mainly with hydrogen atoms in MgH2. The y x Delta E-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.