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Heterogeneous catalysis:
A catalytic process in which thecatalyst and the reactants are present in different phases is known as aheterogeneous catalysis. This heterogeneous catalytic action can be explainedin terms of the adsorption theory. The mechanism of catalysis involves thefollowing steps:
(i)┬аAdsorptionof reactant molecules on the catalyst surface.
(ii)┬аOccurrenceof a chemical reaction through the formation of an intermediate.
(iii)┬аDe-sorptionof products from the catalyst surface
(iv)┬аDiffusionof products away from the catalyst surface.
In this process, the reactantsare usually present in the gaseous state and the catalyst is present in thesolid state. Gaseous molecules are then adsorbed on the surface of thecatalyst. As the concentration of reactants on the surface of the catalyst increases,the rate of reaction also increases. In such reactions, the products have veryless affinity for the catalyst and are quickly desorbed, thereby making thesurface free for other reactants.