Monday, November 18, 2013

Theories Of Catalysis

  • Intermediate compound formation theory.
  • Adsorption theory.
Intermediate compound formation theory:
          This theory was proposed by Clement and Desormes in 1806. In general , the intermediate compound formation theory applies to homogeneous catalyst reactions. According to this theory, the catalyst form an intermediate with one of the reactants. But the intermediate compound is unstable. So that the intermediate compound combines with other reactant to form the desired product and the catalyst is regenerated. 
Example: ( Reaction Type )

Example :

                                       2NO     +     O2     →     2NO2
                                    (catalyst)                      (Intermediate compound)
                                      NO2     +SO2     →     SO3     +     NO
                                                                      (product)       (catalyst)

Adsorption Theory:
             In general adsorption theory applies to heterogeneous catalytic reactions. The catalyst functions by the adsorption of the reacting molecules on its surface.

The adsorption reaction undergoes four types of steps.
( i) Adsorption of reactant molecule:
                 The reactant molecules A and B strike the surface of the catalyst. The reaction molecules held up by the partial chemical bond.

( ii ) Formation of intermediate complex:
                 The reactant molecule adjacent one another join to form an intermediate complex ( A-B ). The intermediate complex is unstable.

( iii ) Decomposition of intermediate complex:
                The intermediate complex breaks to form the products C and D. The product molecules hold to the catalyst surface by partial chemical bond.

( iv ) Release of product:
                The product particles are released from the surface.

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