Q.What role does adsorption play in heterogeneous catalysis?

Step 1 – Modern adsorption theory of heterogeneous catalysis. A heterogeneous catalyst works through the following steps on its surface:

1. Diffusion of reactant molecules to the catalyst surface.
2. Adsorption of reactant molecules onto the active sites of the surface.
3. Formation of an intermediate/activated complex on the surface.
4. Formation of the products on the surface.
5. Desorption of the products, freeing the surface.
6. Diffusion of the products away from the surface.

Step 2 – Why adsorption accelerates the reaction.

• Adsorption increases the concentration of reactants at the surface.
• The residual/free valencies of the surface weaken the bonds within the adsorbed reactant molecules, so they react more readily — the activation energy is lowered. …

Explain heterogeneous catalysis via the six-step adsorption theory, emphasising that adsorption both concentrates reactant …

• Describing homogeneous (intermediate-compound) catalysis instead of the surface/adsorption mechanism.
• Forgetting the desorption step that regenerates the catalyst. …