Synthesis and characterization of Ni/Mg/Al mixed oxides obtained by co-precipitation

Ni/Mg/Al mixed oxides were obtained from hydrotalcite-like precursors by thermal decomposition at 400°, 600° and 800 ⁰C using co-precipitation method at pH 7. The mixed oxides were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) techniques. XRD analysis revealed the formation of Ni _xMg _1-xO (x = 0-1), α-Al ₂O ₃ and traces of MgAl ₂O ₄ (NiAl ₂O ₄) phases. The diffraction peak positions for MgO or NiO oxides were shifted towards 2θ values higher than simulated for pure bulk oxides that can be attributed to the possible presence of lattice vacancies or surface compressive stress. The evaluated grain size by XRD technique was about 8-10 nm. It was also detected the presence of microstrains that can be associated with the presence of extended defects in the grains. SEM observations showed that the particles of oxides are formed as agglomerates with the particle sizes of 50 nm up to 200 nm. EDS detected the presence of Mg ²⁺, Ni ²⁺, and Al ³⁺ cations and oxygen in all particles independently on their size. The obtained results revealed the presence of mixture of Ni/Mg/Al oxides in each particle obtained. The oxides calcined at temperatures of 400° and 600°C were unstable and under air storage they revert to the precursor. The incorporation of Ni ²⁺ in Mg-Al mixed oxides leads to stability of the compounds calcined at 800°C.