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
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