Question

# What role does adsorption play in heterogeneous catalysis?

Hint: Adsorption is the process in which molecules are held onto the surface. It is relatable to the catalytic activity by heterogeneous catalysis. It is directly related to the reaction rate of substances acting as a catalyst.

-First, let us discuss the heterogeneous catalysis. Suppose we have a chemical reaction, consisting of reactants, products, and a catalyst. In that reaction, the phase of catalyst differs from that of reactants, and products.
-We can say that if reactants, and products exist in a solid phase, then the catalyst may exist in a gaseous phase.
-As mentioned, adsorption is a surface phenomenon, it plays a major role in the heterogeneous catalysis.
-Now, in the adsorption we know molecules (reactants) are concentrated on the surface; so, it will lead to the increase in concentration of reactants.
-Thus, the catalyst adsorbs reactants, and an activated complex is formed.
-So, there is an increase in rate of reaction through catalytic adsorption.
-We can say that due to adsorption a specific molecule comes in contact with other molecules, and it also helps in dissociation of molecules into atoms, or ions.
Some of the examples of the heterogeneous catalysts are mentioned below-
1. Ammonia in Haber’s Process
Here, the catalyst iron is used which is in solid form and reactants are in gaseous form
${{N}_{2}}(g)+3{{H}_{2}}(g)\xrightarrow{Fe}2N{{H}_{3}}(g)$
2. Sulfuric Acid Manufacture
Here, the solid vanadium pentoxide is used as a catalyst whereas reactants are in gaseous phase.
$S{{O}_{2}}(g)+{{O}_{2}}(g)\xrightarrow{{{V}_{2}}{{O}_{5}}}2S{{O}_{3}}(g)$
Thus, all these factors help in increasing the rate of reaction.
In the last, we can conclude that due to adsorption, concentration of molecules on the surface increases, and then the rate of reaction too increases.

Note:
Homogeneous catalysis; the reactants, products, and catalyst exist in the same phase. Like if the reactants, and products are in gaseous phase, then the catalyst will also exist in gaseous phase.