The hydrogen desorption (or decomposition) reaction of NaAlH 4 is expressed as NaAlH 4 ! 1=3Na 3 AlH 6 þ 2=3Al þ H 2 , and its desorption rate is accelerated by mixing metal chloride catalysts (e.g., TiCl 3 ). This catalytic effect of metal chlorides, MCl n , is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, DE M for metal ion and DE Cl for chloride ion in various metal chlorides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption reaction rate increases with increasing n  DE M values of metal chlorides. This indicates that the metal ion in MCl n interacts mainly with hydrogen or [AlH 4 ] À complex anion in NaAlH 4 . To confirm this calculated result, experiments are performed using NaAlH 4 mixed with Ti-based catalysts. The hydrogen desorption rate is enhanced in the order, TiCl 3 > TiO 2 > Ti metal nanopowder, indicating that the Ti ions in TiCl 3 or TiO 2 work to promote the catalytic reaction more effectively than the neutral Ti atoms in Ti metal nanopowder. V C 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: [950][951][952][953][954][955][956][957][958][959][960] 2011