What do you understand by shape selective catalysis? Why are zeolites good shape selective catalysts?

Explanation

The catalytic reaction which depends upon pore structure of catalyst and the size of the reactant and product molecules is known as shape selective catalysts. Zeolites are good shape selective catalyst because of honey comb like structure.
(i) They are microporous aluminosilicates with Al-O-Si framework and general formula `M_(x//n)[(AlO_(2))_(x)(SiO_(2))_(y)]mH_(2)O`
(ii) The reactions taking place in zeolites depend upon the size and shape of the reactant and product molecules as well as upon the pores and cavities of the zeolites.
(iii) Zeolites are widely used as catalysts in petrochemical industries for cracking of hydrocarbonds and isomerisation. They are also used for removing permanent hardness of water.
(iv) e.g., ZSM-5 is a catalyst used in petroleum industry
Alcohols `underset("Dehydration")(overset(ZSM-5)(to))` Gasoline(petrol) (A mixture of hydrocarbons)