The surface of a catalyst is not smooth. It bears steps, cracks and comers. Hence the atoms on such locations of the surface are coordinatively unsaturated. So, they have much residual force of attraction. Such sites are called active centres. So, the surface carries high surface free energy.
The presence of such active centres increases the rate of reaction by adsorbing and activating the reactants.
The adsorption theory explains the following
- Increase in the activity of a catalyst by increasing the surface area. An increase in the surface area of metals and metal oxides by reducing the particle size increases the rate of the reaction.
- The action of catalytic poison occurs when the poison blocks the active centres of the catalyst.
- A promoter or activator increases the number of active centres on the surfaces.
