In this book the modification and characterization of clays have been described. Smectite rich montmorillonite clay sample are selected for the modification and their catalytic activity studies. Clay on suitable modification generate acid sites, which make clay as potential heterogeneous acid catalysts. Clay catalysts have been prepared by modifying natural clays into different forms by cation exchange, acid activation and pillaring methods. The clay material was analyzed for its elemental analysis by X-ray fluorescence and the cation exchange capacity by barium sulphate method. The...