The rate of a chemical reaction changes due to the participation of heterogeneous catalyst. The product generally desorbs from the surface of the catalyst and diffuses away after the completion of reaction. The catalytic site determined the surface area of the catalyst and hence it is very critical and important. Adsorption and desorption are the two phenomena associated with the heterogeneous catalysts functions. The two processes help in the reaction of molecules to make them attract and attach to one another. Homogeneous catalysts are in the same phase as the reactants. When catalysis in a single liquid phases this type of catalyst is called homogeneous cataly­sis. Table 15.3 shows the comparison of main advantages/disadvantages of homoge­neous vs. heterogeneous catalysts. A main disadvantage of homogeneous catalysts is the problem of their recovery from the reaction medium because of its hygro­scopic nature along with its hazardous nature for the environment as compared to heterogeneous catalysts; this led to flourishing activity attempting to heterogenize homogeneous catalysts.