Reduction of impregnated NiO/α-A12O3 association of A13+ ions with NiO Original Research Article

Contrary to common belief that α-Al2O3 is an inert support for the impregnation of base metal species, evidence is presented for the incorporation of Al3+ ions into NiO impregnated on α-Al2O3, thereby causing the observed increase in reduction temperature. In agreement with this proposed model of support dissolution/incorporation into the impregnated material, temperature programmed reduction measurements on samples of NiO prepared by coprecipitation with small amounts of Al3+ and by multiple impregnation of α-Al2O3 gave similar results. As predicted, treating α-Al2O3, in the form of rings or powder, with HNO3 extracted small amounts of Al3+ at 30°C and larger amounts at 90°C. During the calcination step following impregnation with Ni(NO3)2,6H2O, NiO is formed as the Ni(NO3)2 crystals decompose and Al3+ ions are extracted from the surface. These Al3+ ions are then retained either in or in the vicinity of evolving NiO crystallites. Successive impregnation steps result in further Al3+ extraction from the support and additional increases in reduction temperature.