In a reaction, if the catalyst is present in the same phase as the reactants, it is called a homogeneous catalyst and the phenomenon is homogeneous catalysis. Such catalysis can take place in gaseous reaction or reactions in solution. This type of catalysis can sometimes be explained in terms of the formation of an intermediate compound, or ion or a radical. These chemicals help in attaining the equilibrium more quickly by increasing the rates of both the forward and reverse reactions to an extent. Examples of homogeneous catalysis in the gas phase are:
(a) Oxidation of sulphur dioxide, SO2, by oxygen to sulphur trioxide, SO3, in presence of nitric oxide, NO, in the Chamber Process for sulphuric acid manufacture.
2SO2 (g) + O2 (g) → 2SO3 (g)
Here NO acts as a catalyst.
(b) The following reaction in the gas phase is catalysed by traces of chlorine gas, particularly in presence of tight.
2N2O (g) → 2N2 (g) + O2 (g)
In presence of light chlorine forms chlorine radicals, which react with N2O forming the intermediate radical ClO*. The proposed mechanism is:
- Step 1: N2O (g) + Cl* (g) → N2 (g) + ClO*(g)
- Step 2: 2ClO*(g) → Cl2 (g) + O2 (g)
(c) Some examples of homogeneous Catalysis in solution are as follows:
(i) Hydrolysis of ester in presence of acid and alkali:
CH3COOC2H5 (l) + H2O (l) → CH3COOH (aq) + C2H5OH (aq)
(ii) Hydrolysis of sucrose (cane sugar) into glucose and fructose in presence of minerals acids acting as catalysts:
C12H22O11 (aq) (cane sugar) + H2O (l) → C6H12O6 (aq) (glucose) + C6H12O6 (aq) (fructose)