Characterization of activated Cu/Mg/Al hydrotalcites and their catalytic activity in toluene combustion

Five hydrotalcite-type compounds containing different amounts of Cu2+ and Mg2+ cations were prepared by coprecipitation method (the molar ratio Cu2+:Mg2+:Al3+ in brucite-like layers varied as follows: 0:4:2, 1:3:2, 2:2:2, 3:1:2, and 4:0:2). The products were characterized by XRD, TG and DTA measurements. The increasing content of Cu2+ decreased both the dehydration and decomposition temperatures. Extrudates prepared from the solids were calcined at different temperatures and the properties of the resulting materials (surface area, pore volume, TPR, surface basicity and acidity) were examined. Maximum of the Mg/Al hydrotalcite surface area was observed at 400°C, basicity at 450°C and acidity at 550°C. Incorporation of Cu2+ into brucite-like layers caused a substantial decrease in both basicity and acidity. Acidity rose with increasing amounts of copper in the layers and basicity went through a local minimum. An increase in the amount of magnesium in the precursors manifested itself in a decreased reducibility of the Cu2+ component. The oxidation activity in the toluene combustion increased with increasing amounts of Cu2+ in the solids and corresponded with the amount of easily reducible copper component.