Temperature-programmed-reduction studies of nickel oxide/alumina catalysts: effects of the preparation method

Two series of NiO Al₂O₃ catalysts with various metal loadings were prepared by incipientwetness impregnation and coprecipitation methods. The reducibilities of NiO over these catalysts were investigated by the temperature-programmed reduction (TPR) technique. For impregnated Ni Al₂O₃ catalysts, more than one species was detected by TPR. At low nickel loadings, the NiOAl₂O₃ interaction is strong, and at high Ni loadings NiO is observed. NiAl₂O₄ was not detected at all Ni loadings. For precipitated Ni Al₂O₃ catalysts, three NiO species are present in the TPR profiles. NiAl₂O₄ was detected at all Ni loadings. The rate of reduction of NiO on the support depends not only on the chemical nature of the NiO species but also on the rate of nucleation of metallic nickel. At high nickel loadings, owing to the presence of easily reduced Ni species, the rate of reduction is enhanced.