Layered double hydroxides with the hydrotalcite-type structure containing Cu2+, Ni2+ and Al3+

Layered double hydroxides (LDHs) with the hydrotalcite-like structure have been prepared containing different amounts of Ni2+, Cu2+ and Al3+ in the brucite-like layers by a coprecipitation method. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis, FT-IR and UV-VIS diffuse reflectance spectroscopies, temperature-programmed reduction, and specific surface area and porosity assessment by N-2 adsorption at -196 degrees C. The nature of the phase obtained, crystallinity of the HT-like phase and thermal behaviour of these materials were influenced by M-II/Al atomic composition and concentration of bivalent metal ion. Calcination at 500 degrees C leads to mostly amorphous solids containing NiO, and also CuO (tenorite) for large Cu2+ contents (Cu/Ni molar ratio equal to 4). When the calcination temperature is increased to 850 degrees C, crystallization of well defined phases (NiO, CuO and NiAl2O4, depending on the relative amounts of Ni, Cu and Al) takes place. Reduction of Cu2+ species in these samples takes place at a lower temperature than that for Ni2+, while the temperature of reduction of nickel is increased with an increase in aluminium and copper content of the samples.