Abstract
Clay minerals are solid acids with Brφnsted and/or Lewis acid sites. The Brφnsted acidity arises usually from the permanent negative charge sites, the exchangeable cations with hydration shell (hydrated Lewis acid), and the silanol groups located on the broken edges, etc., and the Lewis acidity from the exchangeable cations, such as Al, Fe, and Mg, exposed at the broken edges. With such acidities together with large surface areas, clay minerals, especially montmorillonite, have long been used as catalysts for organic reactions, such as oxidation, addition, dehydration, and polymerization. In recent years, much attention has been drawn into the catalytic ability of pillared clay minerals and their acidities.
