What are the theories that explain the working of the catalyst?

Several theories have been proposed to explain the working of the catalyst. However, none are comprehensive enough to explain the diverse types of catalysis processes. Two of the most widely-accepted theories that explain the working of a catalyst are the Intermediate Compound Theory and the Adsorption Theory. 

Intermediate Compound Theory

The intermediate compound theory focuses on the mechanism of homogenous catalysis in which the catalyst and the reactants are in the same state. This theory proposes that the catalyst acts by providing a new path with low activation energy. The catalyst participating in the reaction reacts with one of the reactants, forming a temporary intermediate compound. This intermediate compound decomposes to produce new substances, regenerating the catalyst in the process. 

The limitation of this theory is its inability to explain the mechanism of heterogeneous catalysis. 

Adsorption Theory

The adsorption theory explains the action of the catalyst in heterogeneous catalysis based on adsorption. 

According to this theory, the reactant molecules diffuse and are adsorbed on the surface of the catalyst where they are activated and form activated complexes. The activated complex subsequently decomposes to form new products. The new product molecules are desorbed and the product diffuses away from the catalyst’s surface.