Comparative study of Mg/Al and Mg/Ga layered double hydroxides

Abstract

Three brucite-like layered Mg 2+/M 3+ (M=Al or Ga) double hydroxides were synthesized by the coprecipitation method. The hydroxides and the mixed oxides obtained by thermal decomposition at 773 K were characterized by X-ray diffraction, infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy and thermogravimetric analysis. These techniques allowed us to confirm that double hydroxides possess a brucite-like structure where tervalent cations are octahedrally arranged and that the calcination products contain a periclase MgO phase and an amorphous Al 2O 3 or Ga 2O 3 phase. The surface properties of the mixed oxides and their basicities were also determined by temperature-programmed desorption of carbon dioxide. The calcination at 773 K of synthetic LDHs gave aluminum or gallium magnesium double oxides with basic sites and high specific surface areas.