Adsorption Theory of Heterogeneous Catalysis – Class 12 | Chapter – 5 | Surface Chemistry | Chemistry Short Notes Series PDF for NEET & JEE

Adsorption Theory of Heterogeneous Catalysis: The adsorption theory of heterogeneous catalysis is a fundamental concept that explains how catalysts accelerate chemical reactions on their surfaces. This theory proposes that the reactant molecules, also known as adsorbates, adsorb onto the surface of a solid catalyst, where the reaction takes place. The adsorption of reactant molecules onto the catalyst surface is a crucial step in the catalytic process, as it allows the reactants to come into close proximity and interact with each other more effectively, leading to a faster reaction rate.

Adsorption Theory of Heterogeneous Catalysis

  • Adsorption of Reactants: In heterogeneous catalysis, the reactant molecules from the gas or liquid phase are adsorbed onto the active sites of the solid catalyst surface. Active sites are specific regions on the catalyst surface with suitable electronic and geometric properties that allow the adsorption of reactant molecules. The nature of these active sites and their affinity for the reactants depends on the specific catalyst and the reaction being catalyzed.
  • Formation of the Transition State: Upon adsorption, the reactant molecules experience changes in their electronic configuration and bonding. These changes facilitate the formation of an intermediate state known as the transition state. The transition state represents a high-energy, activated complex where the reactants are partially transformed into the products.
  • Facilitation of Reaction Pathway: The presence of the catalyst and the adsorbed reactants on its surface lowers the activation energy required for the reaction to proceed. This is one of the key roles of the catalyst in the adsorption theory. By providing an alternative reaction pathway with lower activation energy, the catalyst increases the rate of the reaction, making it more favorable and efficient.
  • Desorption of Products: Following the reaction at the transition state, the products are formed. These products then desorb from the surface of the catalyst, leaving the catalyst surface unchanged and available to catalyze further reactions.

The adsorption theory of heterogeneous catalysis explains why certain substances can act as effective catalysts for specific reactions, while others may not. For a catalyst to be effective, it must have suitable active sites that can accommodate and adsorb the reactant molecules involved in the desired reaction. Additionally, the strength of adsorption and desorption of the reactants and products on the catalyst surface plays a crucial role in determining the overall reaction rate and efficiency of the catalytic process.

Understanding the adsorption theory of heterogeneous catalysis has significant practical implications for the design and optimization of catalysts in various industrial processes, including petrochemical refining, ammonia synthesis, hydrogenation reactions, and environmental applications like catalytic converters. By tailoring catalysts to have optimal active sites and adsorption properties, researchers can develop more efficient and selective catalysts to enhance the performance of chemical processes and reduce energy consumption.

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By Team Learning Mantras