In the context of energy carrier, storage of hydrogen is one of the key challenges for research today. The group of Mg-based hydrides stands as a promising candidate for competitive hydrogen storage with high reversible hydrogen capacity. The present studies report encouraging results for Mg-Al system with Nb(2)O(5) additive catalyst. Three nominal compositions [(Mg(x)Al(100-x))-99 + (Nb(2)O(5))-1 mol.%], X = 100 (Mg), X = 39 (beta-Mg(2)Al(3)) and X = 70 (Mg + gamma-Mg(17)Al(12)) have been investigated for their hydrogen equilibrium pressure of absorption and desorption reactions, from 250 degrees C to 400 degrees C. Decomposition of initial Nb(2)O(5) phase was shown after long annealing of samples, with reduction into other oxides. Moreover, the hydrogenation of Mg-Al alloys leads to separate initial phase(s) through several stages with the formation of MgH(2) hydride and metallic Al-fcc as the final products. This behavior is clearly visible from multi-plateaux of pressure-composition isotherm curves. In the case of the X = 70 compound, the reaction was accomplished through three reversible transformation steps. The hydrogen weight capacity of 4.7 wt.% has been found at 250 degrees C under reproducible conditions. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.