Synthesis of nanosize supported hydrotalcite-like compounds coAlx(OH)2+2x(CO3)y(no 3)x-2y·nH2o on γ-Al2O3

Abstract

Nanosize (5-7 nm) supported CoIIAl-hydrotalcite-like compounds (CoIIAl-HTlcs) on γ-Al2O3 have been synthesized with a coprecipitation method in which the γ-Al2O3 acts as a source of aluminum for coprecipitation and a support for the compound formation. The synthesis parameters identified are initial concentrations of metal and base, aging time, and more importantly, the addition sequence of the metal or base solution. Using multiple characterization methods, the supported CoIIAl-HTlcs have been investigated for their structural phase and chemical composition. The chemical formula determined for these samples is CoAlx(OH)2+2x(CO3)y (NO3)x-2ynH2O/γ-Al2O 3, where x = 0.25-0.40, γ = 0.02-0.07, and n =1.3-1.7, and the distance of inter-brucite-like sheets (d003) is in the range of 7.65-7.79 Å. Because of the formation of nanosize crystallites, decomposition of the supported CoIIAl-HTlcs occurs at ≅211-217 °C, which is markedly lower than that of unsupported pure CoIIAl-HTlcs. After calcination in air, the supported CoIIAl-HTlcs are transformed into cubic spinel oxides CoIICo2-x IIIAlxO4/ γ-Al2O3 and high catalytic activity for the N2O decomposition reaction is observed for these supported spinel catalysts.