Mg-Al hydrotalcites have demonstrated their superior performance in numerous base-catalyzed applications, especially their meixnerite-type analogues. The effect of using mechanical stirring or ultrasound during reconstruction of the mixed oxides leads to an enhancement in the catalytic activity. This can be correlated to modifications in the structure and basicity of the resulting materials, together with an increased surface area and improved accessibility to the active sites. However, increasing the rehydration time during stirring or sonication strongly affects the final catalyst, as observed by high-resolution transmission electron microscopy. An important amount of defects in the lamellar structure of the small hydrotalcite nanoplatelets are likely responsible of the presence of stronger and more accessible active basic sites, as determined by CO2-TPD and benzoic acid titration. The greater performance of these materials has been disclosed for the epoxidation of styrene. (C) 2007 Elsevier Inc. All rights reserved.