Relationship between Al/Mg Ratio and the Stability of Single-layer Hydrotalcite

On the basis of a single-layer hydrotalcite model, various computations with density functional theory (DFT) were carried out for the purpose of investigating the relationship between the Al/Mg molar ratio and the stability of single-layer hydrotalcite. With the increase in the Al/Mg molar ratio, both Al-O and Mg-O distances gradually became large and reached maximum at the ratio of 7:12. However, once the Al-O-Al triple was formed by continuously increasing the ratio, the case was dramatically different and the hydrotalcite structure phase dissolved. In consideration of the difference of the bond energy between Al-O and Mg-O, the structures formed at Al/Mg molar ratios of 6:13 and 7:12 were much more stable among all the constructed ones. In fact, if these results are extended to single layer hydrotalcite, high symmetry structures with ratios of 1:2 and 1:3 will be easily obtained in experiment. Therefore, in the case, where the formation of the Al-O-Al triple is avoided, the best synthesizing scheme may be heightening the ratio of Al/Mg.