Descirbe some features of catalysis by zeolites.

Explanation

Zeolites are microporous aluminosilicates of the general formula `M_(x//n)[(AlO_2)_x(SiO_2)_y]mH_2O`. These are most important oxide catalysts. These are used in petrochemical industries for cracking of hydrocarbons and isomerization. The reactions in zeolites depend upon the size of the cavities (cages) or pores (apertures) present in them. The most remarkable feature of zeolite catalysis is the shape selectivity. Therefore, the selectivity of catalyst depends on the pores structure. It has been observed that the pore size in zeolites generally varies between 260 pm to 740 pm. Depending upon the size of the reactants and products compared to the size of the cages or pores of zeolite, reactions proceed in specific manner.
A zeolite catalyst called ZSM-5 converts alcohols to gasoline, by first dehydrating the alcohol by loss of water.