Hydrotalcites were prepared by coprecipitation from aqueous solutions at room temperature. Solution A containing nitrate precursors (Al/(Mg + Al) = 0.20, 0.25 or 0.33 and [Mg + Al] = 1.5 M) was slowly dropped (1 mL min− 1) under vigorous stirring to solution B containing appropriated amounts of Na2CO3 and NaOH (CO32−/Al3+ = 0.375 and OH−/Al3+ = 6.3). The gel formed was aged for 18 h at 60 °C. The solid obtained was then filtered and washed with distilled water (90 °C) until pH 7. The HTs so obtained were then dried at 100 °C overnight, followed by calcination at 200 °C for 12 h to remove water molecules in the interlayer space. The sample with Al/(Mg + Al) ratio of 0.33 was also calcined at 400 and 600 °C.
The prepared catalysts were labeled as HTXXX, where x = 0.20, 0.25 or 0.33 depending on Al/(Mg + Al) atomic ratio of the synthesis gel.