Zeolites are microporous alumino silicates with three dimensional network in which some Si atoms are replaced by Al atoms giving Al-O-Si frame work.
They are heated in vacuum so that water of hydration is lost and they become porous. The size of pores varies between 260 pm- 740 pm which allows only those molecules to be adsorbed whose size is small enough to enter these pores.
Thus, the reactions taking place in zeolites depend upon the size and shape of the reactant and product molecules and upon the pores and cavities of the zeolites.
ZSM-5 which converts alcohols directly into gasoline (petrol) by dehydrating them to give a mixture of hydrocarbons.