Synthesis and characterization of hydrotalcites: [Zn_1-xAl_x(OH)₂](CO₃)_X/2.mH₂O; x = 0.25-0.66

In this work a series of [Zn_1-xAl_x(OH)₂](CO₃)_x/2·mH₂O; x = 0.25-0.66 were prepared at constant pH in order to study the effect of the thermal treatment on their crystalline structure. It was found that is possible to obtain pure Zn-Al hydrotalcite materials within a x = 0.25-0.50 range in comparison with Mg-Al hydrotalcites which yield pure phases in more restricted x ranges (0.25-0.33). All Zn-Al hydrotalcites lost their layered structure at temperatures above 473 K being less stable than their parental Mg-Al hydrotalcite (623 K). Specific surface areas of these materials depended strongly on the Zn/Al ratio and calcination temperature, ranging from 280 to 20 m²/g. ZnO and ZnAl₂O₄ compounds were detected as the calcination products at temperatures higher than 873 K.