New magnesium cobalt iron double hydroxides with hydrotalcite structure: Synthesis and characterization

Series ol layered double hydroxides (LDHs) of the hydrotalcite family simultaneously containing iron and cobalt cations in the positions of triply charged metal ions of the brucite-like sheets, were prepared by coprecipitation of the components from solution in an oxidative medium. The materials prepared have been characterized by X-ray powder diffraction, temperature-programmed reduction (TPR), and temperature-programmed destruction (TPD); their behavior during dehydration-rehydration cycling was studied. The layered double hydroxides were shown to be reducible when heated in flowing hydrogen. Heating to 600°C induced the reduction of cobalt and iron to doubly charged cations, and at temperatures higher than 600°C the reduction yielded the metals. The thermal destruction products of the LDHs prepared are capable of recovering their layered structure when reacted with aqueous sodium carbonate solutions; however, this capability is reduced as the cobalt content in the sample increases.