PREPARATION, BULK CHARACTERIZATION AND SURFACE-CHEMISTRY OF HIGH-SURFACE-AREA COBALT ALUMINATE

A coprecipitation procedure for the preparation of high area CoAl2O4 is described. This procedure involves the precipitation of a crystalline precursor, that has been characterized by XRD, IR and TG-DTA analyses to be a layered mixed hydroxy-carbonate having a structure related to that of the mineral hydrotalcite. Calcination of this compound leads to high area CoAl2O4 spinels (120-40 m2/g). HREM micrographs of the powder calcined at 1073 K evidences that (111) and (400) planes are predominantly exposed at the surface. Structural data derived from XRD and IR analyses evidence that these materials are partly inverse spinels. The surface chemistry data obtained by FT-IR spectra of surface hydroxy-groups and of adsorbed pyridine and carbon monoxide show the location at the surface of reducible Co2+ cations and of Al3+ in both tetrahedral and octahedral unsaturated environments.