Question

How is catalysis classified on the basis of physical states of reactants and the catalyst? Give two examples of each type.

Answer 1

Catalysis is classified into two types based on the physical state of the reactants and the catalyst:

(a) Homogeneous catalysis: The catalyst and reactants are in the same physical state (usually all gases or all liquids).

Examples:

1. The oxidation of sulfur dioxide (SO₂) to sulfur trioxide (SO₃) in the lead chamber process is carried out using nitric oxide (NO) as a gaseous catalyst.

\[\ce{2SO2 + O2 ->[NO] 2SO3}\]​

2. The hydrolysis of an ester is performed in the presence of dilute sulfuric acid (H₂SO₄), where all the components are in the liquid phase.

\[\ce{CH3COOC2H5 + H2O ->[H+] CH3COOH + C2H5OH}\]

(b) Heterogeneous catalysis: The catalyst and reactants are in different physical states, usually a solid catalyst with gaseous or liquid reactants.

Examples:

1. In the Haber process, ammonia is synthesized by reacting nitrogen and hydrogen in the presence of finely divided iron as a solid catalyst.

\[\ce{N2_{(g)} + 3H2O_{(g)} ->[Fe] 2NH3_{(g)}}\]

2. The hydrogenation of oils to form fats is carried out using finely divided nickel (Ni) as a solid catalyst.

\[\ce{C = C (in oil) + H2 ->[Ni] C - C (fat)}\]