Interaction of hydrogen with a series of cerium nickel and zirconium (or aluminium) mixed oxides CeM0.5NixOy (M=Zr or Al, 0 <= x <= 3) has been studied in the 50-800 degrees C temperature range. Hydrogenation of 2-methyl-1,3-diene (isoprene) under helium flow in the absence of gaseous hydrogen is used to reveal and titrate reactive hydrogen species present in the solid previously treated under H-2 at various temperatures. The CeM0.5NixOy mixed oxides are large catalytic hydrogen reservoirs and among the solids studied, the highest amount of hydrogen (about 10 wt%, 540g/L) is stored in CeZr0.5Ni1Oy pretreated in H-2 at about 200 degrees C. Compared to the binary mixed oxides CeNixOy, the presence of M allows to increase the hydrogen storage and give a better stability to the system, in particular, with temperature. Different physico-chemical techniques (TPR, TGA...) have been used to characterize the solids studied. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.