Synthesis of nanosize supported hydrotalcite-like compounds coAl_x(OH)_2+2x(CO₃)_y(no ₃)_x-2y·nH₂o on γ-Al₂O₃

Nanosize (5-7 nm) supported Co^IIAl-hydrotalcite-like compounds (Co^IIAl-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 Co^IIAl-HTlcs have been investigated for their structural phase and chemical composition. The chemical formula determined for these samples is CoAl_x(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 Co^IIAl-HTlcs occurs at ≅211-217 °C, which is markedly lower than that of unsupported pure Co^IIAl-HTlcs. After calcination in air, the supported Co^IIAl-HTlcs are transformed into cubic spinel oxides Co^IICo_2-x^IIIAl_xO₄/ γ-Al₂O₃ and high catalytic activity for the N₂O decomposition reaction is observed for these supported spinel catalysts.