Quantitative approach to the understanding of catalytic effect of metal oxides on the desorption reaction of MgH 2

The hydrogen desorption reaction of magnesium hydride (MgH 2 ), MgH 2 →Mg+H 2 , is accelerated by mixing catalytic metal oxides (e.g., Nb 2 O 5 ). This catalytic effect of metal oxides, M x O y , is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, Δ E M for metal ion and Δ 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 ×Δ E O values of metal oxides. This indicates that the oxide ion in M x O y interacts mainly with hydrogen atoms in MgH 2 . The y × Δ E O value is a measure of the magnitude of the OH interaction operating between M x O y and MgH 2 , 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. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009