Characterization of calcined and reduced multi-component Co-Ni-Mg-Al-layered double hydroxides

Several Co-Ni-Mg-Al-layered double hydroxides (LDH) have been synthesized b y coprecipitation at constant pH = 9. All samples present well crystallized , layered structures, no excess phases were detected by X-ray diffraction, and the lattice a parameter followed the Vegard correlation. The cations th us belong to the same, brucite-like, lattice. Calcined samples exhibit XRD patterns of the crystallographic phase preferentially adopted by the major cation in the LDH: i.e., a mixed oxide of the rock salt type in the case of Ni or Mg, and a spinel-like structure for Co. Surface areas reached maximu m values in the range of 200-300 m(2)g(-1) after calcination at 573 K. They were stabilized with increasing Ni or Mg content, as higher amounts of mix ed oxide phase were formed. Programmed temperature reduction showed two dom ains of H-2 consumption, assigned to reduction of CO3-xNixO4 species below 720 K, and to NiMg(Al)O and Co3-x-yNixMgyAlO6, of rock salt type and spinel -like structures respectively, above this temperature. These assignments ar e in agreement with the XRD patterns and show that Ni and Co are associated in the same crystallographic phases.