Radiation-induced synthesis of α-Al2O3 supported nickel clusters: Characterization and catalytic properties

A series of Ni aggregates supported on α-Al2O3 at different nickel contents are prepared by ionic exchange of Ni2+ followed by γ-irradiation under inert atmosphere. Characterization techniques are used at each step to select the elaboration conditions optimized for their use as catalysts. X-ray diffraction demonstrates the presence, after the Ni2+ adsorption step, of the phases (NiO)2(Al2O3)9 and (NiO)(Al2O3)16 that are favourable to further performances of the catalyst. After radiolysis, the phases of the oxide NiO and the metal Ni are observed. The relative amount of the Ni metal phase increases with the initial Ni2+ content. The nickel clusters (prepared from the complex [Ni(NH3)6]2+), imaged by Scanning Electron Microscope (SEM)/EDS, are highly dispersed. The H2 adsorption and thermodesorption study by chemisorption and H2-TPD indicates that the sites of the catalyst are occupied by hydrogen generated during irradiation. After H2 treatment at 350 °C, it shows high hydrogen adsorption/desorption capacity. When tested in the steam-reforming methane reaction (CH4+H2O→CO+3H2), the radiolytic Ni/α-Al2O3 samples exhibit quite promising catalytic properties, namely a high activity and a remarkably high selectivity in CO even at moderate temperature (80% at 550 °C with a conversion of 60%).