Structural reversibility of a ternary CuO-ZnO-Al2O3 ex hydrotalcite-containing material during wet Pd impregnation

A Cu-Zn-Al precursor was synthesized by coprecipitation of the corresponding cations with sodium carbonate at constant pH and temperature. CuO-ZnO-Al(2)O(3) composite oxide support was obtained by calcination (673 K) of the Cu-Zn-Al precursor. Two palladium-modified CuO-ZnO-Al(2)O(3) samples were prepared by impregnation of the mixed-oxide support and further calcination (673 K). The presence of remaining CO(3)(2-) anions in the CuO-ZnO-Al(2)O(3) mixed oxide, as a result of incomplete Cu-Zn hydrotalcite phase decomposition, and the hydrothermal-like treatment during the Pd impregnation step, allow the partial reconstruction of the Cu-Zn hydrotalcite-type structure (memory effect). In addition, an enhancement in the CuO crystallinity was obtained for the Pd-modified oxides. A detailed characterization revealed that the hydrotalcite restoration enhances the crystallinity of the copper oxide as a consequence of a crystalline rearrangement of this oxidic phase.