Synthesis and characterization of layered double hydroxides containing Nickel in unstable oxidation state + 3 in cationic sites

Highlights: • LDH containing Ni3+ in brucite-like layers were synthesized in oxidizing medium; • Detailed characteristics of Mg/AlNi-LDHs confirmed their structure and properties; • Ni³⁺ cations appear to be rather stable in hydrotalcite structure. - Abstract: A series of layered double hydroxides (LDH) with molar ratio M²⁺/M³⁺ = 3:1 and different degrees of aluminum substitution in the cationic sites by Ni³⁺ were prepared by precipitation from solution in the presence of sodium hypochlorite as an oxidizing agent. The synthesized samples were characterized by various techniques including powder X-ray Diffraction (XRD), Thermogravimetric and Differential Thermal Analysis (TG-DTA), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and inverse Temperature-programmed Reduction (iTPR). The results indicate that single-phase LDHs were formed during synthesis and they were of a high degree of crystallinity. The thermal stability of LDHs did not decrease essentially with increasing Ni³⁺ content. The calcination at 600 °C led to the complete destruction of the layered structure and formation of mixed oxide phases. In iTPR experiments for as-synthesized LDHs the reduction of Ni³⁺ to Ni²⁺ took place above 400 °C, and the reduction of Ni²⁺ to Ni° occurred above 600 °C.