Question

Explain Adsorption theory of heterogeneous catalysis.

Hint:

Remember the three steps: Adsorption of reactants → Reaction on surface → Desorption of products.

Answer 1

Step 1: Understanding heterogeneous catalysis.
Heterogeneous catalysis occurs when the catalyst is in a different phase from the reactants. Usually, solid catalysts act on gaseous or liquid reactants. Step 2: Adsorption theory.
The adsorption theory explains catalysis in terms of adsorption of reactant molecules on the surface of the solid catalyst: \begin{enumerate} \item Reactant molecules are adsorbed on the surface of the catalyst. \item Adsorption weakens the chemical bonds in reactant molecules, lowering activation energy. \item The adsorbed reactants combine to form products. \item The product molecules desorb (leave) from the catalyst surface, making it free for the next reaction. \end{enumerate} Step 3: Example.
In the Haber process, \( N_2 \) and \( H_2 \) gases are adsorbed on finely divided Fe catalyst. Their bonds weaken, allowing formation of \( NH_3 \). Conclusion:
The adsorption theory provides a clear explanation for the mechanism of heterogeneous catalysis, showing how catalysts work by adsorption, bond weakening, and product desorption.