Answer:

Adsorption plays an important role in heterogeneous catalysis. Adsorption is surface phenomenon in which the substances (reactants) get concentrated only on the surfaces of solid adsorbents and do not penetrate into it.This increases concentration of reactants and there is a great probability of occurrence of reaction. The catalyst adsorbs reactants and forms a intermediate compound known as activated complex. Following are various ways in which catalytic adsorption increases the reaction rate:
(i) The concentration of reactants on surface of solid adsorbent increases and it becomes easier for molecules to attack each other for effective collisions, forming products.

(ii) A particular part of reactant molecule may come in contact with other molecules which otherwise is difficult.

(iii) Some adsorbed molecules dissociate into atoms or free radicals which are very reactive and thus increase the reaction rate.

(iv) Heat of adsorption released provides activation energy for formation of activated complex and then increase the rate of reaction.