Descirbe some features of catalysis by zeolites.

Explanation

`a.` Zeolites are hydrated alumino`-` silicates which have a three`-` dimenstional network structure containing water molecules in their pores. ltbr. `b.` To use them as catalysts, they are heated so that the water of hydration present in the pores is lost and the pores become vacant.
`c.` The size of the pores varies from 260 to `740pm.` Thus, only those molecules can be adsorbed in these pores and catalyzed whose size is small enought to enter these pores. Hence, they act as molecular sieves or shape`-`selective catalysts. ,brgt An important catalyst used in petroleum industry is `ZSM-5(` zeolite sieve of molecular porosity `5)`. It converts alcohols into petrol by first dehydrating them to form a mixture of hydrocarbons.
Alcohols `underset(Dehydration)overset(ZSM-5)rarrHydrocarbons`