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

Abstract

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.