Acidity in pillared clays: Origin and catalytic manifestations

Acidity in pillared clays is a broad topic, and one which has been reviewed before [1-3]. Since it is difficult to be exhaustive, the present contribution is divided in two parts. The first one tries to establish relationships between observed acidity and structural data in the only case which is sufficiently understood to date, i.e., [Al-13] in smectite clays. The second part is concerned with the acid catalytic properties of pillared clays. They are classified according to the types of reactions. While most references are concerned with [Al-13]@smectites, other systems will be considered too as the need arises.