J. Phys. Chem. B, ASAP Article 10.1021/jp026339k S1089-5647(02)06339-3
Web Release Date: November 6, 2002

First Principles Study of the Structure and Chemistry of Mg-Based Hydrotalcite-Like Anionic Clays

Andrea Trave (1,2), Annabella Selloni (2), Annick Goursot (2,3), Didier Tichit (2), and Jacques Weber (3)

We use variable-cell first principles molecular dynamics as an optimization tool to investigate the structural and electronic properties of Mg-based anhydrous hydrotalcite-like compounds. The formation energy as a function of the ratio R between di- and trivalent cations shows a minimum at R ~ 3, in good agreement with experimental stability ranges for these materials. At the same value R ~ 3, a maximum is found in the calculated interlayer distance, suggesting a correlation between energetic stability and structure. The energies and character of the electronic states of hydrotalcites containing different interlayer anions and trivalent cations have been compared. The nature of the anions is found to have a major influence on the electronic properties. In particular, OH^- anions, rather than, e.g., Cl^-, lead to a significantly smaller HOMO-LUMO gap, with a LUMO spatially more localized in the interlayer region. These features are related to the observed differences in the catalytic properties of hydrotalcites containing OH^- vs Cl^- anions.