Solids containing Co(II) and Fe(III) with molar ratios of2/1, 3/2, 1/1, 2/3 and 1/2 have been synthetised by coprecipitation at constantpH. All they displayed a hydrotalcite-like structure with interlayer carbonate,which crystallinity decreases as the iron content was increased. No othercrystalline phase was identified, even in the Fe-rich samples. They have beencharacterised by powder X-ray diffraction, FT-IR spectroscopy, thermal analysis(differential thermal analysis, thermogravimetric analysis andtemperature-programmed reduction), in addition to specific surface areaassessment by nitrogen adsorption at -196_C. A minor oxidation of Co(II) toCo(III) is observed in the Co-rich samples, although it reverses again to Co(II)upon calcination in oxygen at ca. 850_C. Thermal decomposition takes place in asingle step up to ca. 350_C, and the specific surface area increases with theiron content, probably because of the presence of hydrated amorphous ironoxides. The solids calcined at 1200_C in air contain crystalline CoO, Co3O4and CoFe2O4 (spinel), this one being the dominant phase,and only phase detected for large Fe contents. Metallic species are more easilyreduced in the original solids than in the calcined ones, and in all cases ironseems to be reduced at a higher temperature than cobalt.
