(l) Heterogeneous catalysis In a reaction, the catalyst is present in a different phase i.e. it is not present in the same phase as that of reactants or products. This is generally referred as contact catalysis and the catalyst present is in the form of finely divided metal or as gauze Illustration (i) In the manufacture of sulphuric acid by contact process SO is prepared by the action of SO and O in the presence of Pt or V O as a catalyst. XII U10-Surface XII U10-Surface - - - - ( (s) (s) ( ) ( ) Pt or V O 2SO +O 2SO g g g → ii) In the Haber’s process for the manufacture of ammonia, iron is used as a catalyst for the reaction between Hydrogen and Nitrogen.
+3H Fe 2NH (s) ( ( ( g g g iii) Oxidation of ammonia is carried out in presence of platinum gauze 4NH +5O 4NO +6H O Pt (s) ( ) ( ) ( ) ( ) g g g g iv) The hydrogenation of unsaturated organic compounds is carried out using finely divided nickel as a catalyst. CH =CH +H CH -CH Ni (s) ( ) ( ) ( ) g g g v) Decomposition of H O occurs in the presence of the Pt catalyst Pt (l) H O 2H O (g) +O (l) (s) vi) In the presence of anhydrous AlCl , benzene reacts with ethanoyl chloride to produce acetophenone AlCl anhydrous + CH Cl acetophenone + HCl (l) (l) (l) (l) (s) . . Characteristics of catalysts .
For a chemical reaction, catalyst is needed in very small quantity. Generally, a pinch of catalyst is enough for a reaction in bulk. . There may be some physical changes, but the catalyst remains unchanged in mass and chemical composition in a chemical reaction.
. A catalyst itself cannot initiate a reaction. It means it can not start a reaction which is not taking place. But, if the