Clays, especially montmorillonite and bentonite are environmentally benign, recyclable, and economical when used as a catalyst. Heteropoly catalysts are also used in a wide variety and high potential, because of their higher catalytic activity and acidic strength than the mineral acids. By the modification of clays with a variety of HPAs, we can achieve the benefits of using both clay and HPAs. We can use various HPAs such as Silicotungstic acid (STA), Phosphotungstic acid (PTA), Silicomolybdic acid (SMA), Phosphomolybdic acid (PMA) for the modification of clay and may be obtained a series of...