PREPARATION, CHARACTERIZATION AND MICROCALORIMETRIC STUDIES OF NICKEL-IRON HYDROTALCITES AND THEIR DECOMPOSITIONS

Ni-Fe hydrotalcites with Ni/Fe molar ratios of 1, 2, 3, 6 and 10 were prepared by coprecipitation. TG-DTA results showed that the hydrotalci tes decomposed in two stages, corresponding to two endothermic peaks a round 200 and 300 degrees C. After calcination at 400 degrees C, the h ydrotalcites were converted to NiFeO mixed oxides with high surface ar eas around 100 m(2)/g, which exhibited the XRD pattern of NiO only. TP R studies of the mixed oxides indicated that the reduction temperature s decreased with increasing Ni content, inconsistent with the in situ Mossbauer spectroscopic results which showed that the mixed oxide (Ni/ Fe = 2) was easier to reduce than the Fe2O3 sample. Microcalorimetric adsorption of NH3 and CO2 revealed that the mixed oxide (Ni/Fe = 2) di splayed intermediate acidity and basicity between those of the pure ox ide NiO and Fe2O3. The mixed oxides after calcination at 800 degrees C possessed the phases of NiO and NiFe2O4 with the surface area around 15 m(2)/g, which exhibited moderate basicity with only a little weak a cidity. (C) 1997 Elsevier Science B.V.