Comparative study of Mg Al and Mg Ga layered double hydroxides

Three brucite-like layered Mg2+/M3+ (M = Al or Ga) double hydroxides were s ynthesized by the coprecipitation method. The hydroxides and the mixed oxid es obtained by thermal decomposition at 773 K were characterized by X-ray d iffraction, infrared spectroscopy, solid-state nuclear magnetic resonance s pectroscopy and thermogravimetric analysis. These techniques allowed us to confirm that double hydroxides possess a brucite-like structure where terva lent cations are octahedrally arranged and that the calcination products co ntain a periclase MgO phase and an amorphous Al2O3 or Ga2O3 phase. The surf ace properties of the mixed oxides and their basicities were also determine d by temperature-programmed desorption of carbon dioxide. The calcination a t 773 K of synthetic LDHs gave aluminum or gallium magnesium double oxides with basic sites and high specific surface areas. (C) 1999 Elsevier Science B.V. All rights reserved.