Zeolites are aluminosilicates i.e. three dimensional net work silicates in which some silicon atoms are replaced by aluminium atoms. They are found in nature as well as synthesized in the laboratory. They form an important class of oxide catalyst. Zeolites to be used as a catalyst are heated in vacuum so that the water of hydration is lost. As a result, zeolite becomes porous i.e. the cavities in the cage like structure which were occupied by the water molecules become vacant. The size of the pores generally varies between 260 pm and 740 pm. Thus only those molecules can be absorbed in these pores whose size is small enough to enter these cavities and also leave easily.
Zeolites are being very widely used as catalyst in petrochemical industries for cracking of hydrocarbons and isomerization. An important zeolite catalyst used in the petroleum industry is ZSM – 5. It converts alcohols directly into gasoline by first dehydrating them so that a mixture of hydrocarbons is formed.
