Catalytic hydrogen storage in CeMZNiXOY oxyhydrides (M = Zr or Al, z = 0 or 0.5, 0 ´ x ´ 3)
Résumé
CeMZNiXOY mixed oxides (M = Zr or Al, z = 0 or 0.5, 0 ´ x ´ 3) are large catalytic hydrogen reservoirs, called oxyhydrides, once treated in H2. A catalytic chemical reaction is used to reveal and titrate reactive hydrogen species present in the solid. The hydrogen reservoir capacity depends on the compound preparation, formulation, and activation. Among the solids studied, the highest amount of hydrogen (about 10 wt%) is stored in CeZr0.5Ni1OY pre-treated in H2 at 200°C. Different physico-chemical techniques including XPS, ion sputtering, XRD, TPR, TGA, and Inelastic Neutron Scattering (INS) have been used to characterize the solids. Depending on the composition and metal loading, a solid solution and/or a highly dispersed nickel oxide in ceria (or ceria-zirconia) can be obtained. Ion sputtering followed by XPS analysis has been very useful for estimating the size of NiO clusters (≡ 10 Å) present in the compounds. INS evidences the coexistence of different hydrogen species that can be related to hydride species, hydrogen species in interaction with metallic nickel, as well as hydrogen species from hydroxyl groups. Particular active sites, involving reactive hydrogen, are created during the activation of the mixed oxides.