PREPARATION AND CHARACTERIZATION OF NICKEL ALUMINUM MIXED OXIDES OBTAINED BY THERMAL-DECOMPOSITION OF HYDROTALCITE-TYPE PRECURSORS

A series of nickel-aluminum mixed hydroxides was prepared by coprecipitation and their structure and composition was examined by X-ray diffraction and thermal analysis. The homogeneity of the Ni(II) and Al(III) cations in the brucite-type layers has been verified by EXAFS spectroscopy. The hydrotalcite-type precipitates were calcined and the composition of the resulting mixed oxides investigated. The selective dissolution of a Ni-doped alumina phase has been performed in concentrated NaOH solution. The alumina phase significantly contributes to the surface area of the mixed oxides but is suggested to play a minor role for the thermal stability of nickel oxide. A model for the nickel-aluminum mixed oxides obtained from hydrotalcite decomposition is proposed to involve the formation of nickel oxide and Ni-doped alumina phases in strong interaction with partially decomposed precursor layers or with a spinal-type phase at the NiO-Al2O3 interface. The latter phase is thought to be responsible for the thermal stabilization of the nickel oxide phase. © 1992.