Synthesis of nanosize supported hydrotalcite-like compounds CoAlx(OH)2+2x(CO3)y(NO3)x-2y•nH2O on γ-Al2O3

Nanosize (5-7 nm) supported (CoAl)-Al-II-hydrotalcite-like compounds ((CoAl)-Al-II-HTlcs) on gamma -Al2O3 have been synthesized with a coprecipitation method in which the gamma -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 (CoAl)-Al-II-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-2y). nH(2)O/gamma -Al2O3, where x = 0.25-0.40, y = 0.02-0.07, and n = 1.3-1.7, and the distance of inter-brucite-like sheets (d(003)) is in the range of 7.65-7.79 Angstrom. Because of the formation of nanosize crystallites, decomposition of the supported (CoAl)-Al-II-HTlcs occurs at approximate to 211-217 degreesC, which is markedly lower than that of unsupported pure (CoAl)-Al-II-HTlcs. After calcination in air, the supported (CoAl)-Al-II-HTlcs are transformed into cubic spinel oxides (CoCo2-xAlxO4)-Co-II-Al-III/gamma -Al2O3 and high catalytic activity for the N2O decomposition reaction is observed for these supported spinel catalysts.