What is the adsorption theory of heterogeneous catalysts?
According to the traditional adsorption theory of heterogeneous catalysts, reactants in their gaseous or dissolved state in any solution are adsorbed onto the solid surface of a suitable catalyst. As a result of an increase in the concentration of the reactants on the surface of the catalyst, the availability and probability of a reaction between two species rise, and consequently, so does the rate of the reaction. In addition, as the reactants cling to the surface of the catalyst, a small amount of exothermic energy is generated. This combined heat is employed in the interaction between the two species, hence accelerating the process.
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According to the intermediate compound hypothesis of catalysis, the intended reaction is accomplished through the creation of an intermediate compound and its subsequent breakdown into the desired products. After the reaction is complete, the catalyst is replenished in this procedure.
Heterogeneous Catalysis Steps
Now, according to the modern adsorption theory, which is a blend of the old theory of adsorption and the intermediate theory of compound synthesis, heterogeneous catalysis occurs in five stages.
- The reactants diffuse to the catalysts’ surface. In this procedure, the reactants initially come into touch with the exterior surface, and then a portion of them pass through the barrier and enter the inner exposed surface, which includes channels and fissures on the exterior surface.
- Then, these molecules adhere to the accessible sites that are suited for adsorption.
- When reactants are attached to a surface, there is a greater likelihood that they will react with one another, resulting in the formation of an intermediate molecule.
- After this procedure, the intermediate chemical is desorbed from the surface, making it once again accessible for adsorption by subsequent molecules.
- The intermediate chemical subsequently decomposes into the end products, which diffuse out of the catalyst’s internal pores and an exterior surface.
Here, we observe that the catalyst remains unaltered and is recovered in its original state when the reaction is complete. The catalyst’s mass and chemical composition remain unchanged throughout the process. Through the contemporary theory of adsorption, the concept of catalytic promoters and inhibitors cannot be explained.
Examples of some heterogeneous catalyst
Reactants and catalysts are at various phases during the heterogeneous catalytic process. Here are some instances of heterogeneous catalysis:
In the presence of platinum metal or vanadium pentoxide as a catalyst, sulfur dioxide is converted to sulfur trioxide. Here, the reactants are in gaseous form and the catalyst is solid.
In the presence of finely split iron, nitrogen and hydrogen combine to generate ammonia in the Haber process.
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Frequently Asked Questions – FAQs
Q.1 What is adsorption theory?
According to the adsorption principle, adhesion is the consequence of molecular interaction between two materials and the development of surface forces. The adsorption of sticky molecules on a substratum and the attractive forces that arise are often referred to as secondary or van der Waals forces.
Q.2 Why are heterogeneous catalysts preferred?
Heterogeneous catalysts play an important role in industrial chemical processing. As a result of their durability and lower operating costs, they are favored, especially because their simpler recovery/separation from the products facilitates the simplification of chemical processes.
Q.3 What does heterogeneous mean?
Heterogeneous describes a structure that appears aberrant or varied due to the presence of diverse components or features. For instance, a dermoid cyst displays uneven CT attenuation. It is the antonym for homogenous and refers to a system with identical components. Heterogeneous describes a system with an alien origin.
Q.4 What are the two types of catalysts?
It is feasible to divide catalysts into heterogeneous and homogeneous categories. In a heterogeneous reaction, the catalyst exists in a distinct phase from the reactants. In a homogeneous reaction, the catalyst is in the same phase as the reactants.
Q.5 What are the most common types of heterogeneous catalysts?
In homogeneous catalysis, the catalyst occurs concurrently with the reactants. In heterogeneous catalysis, the catalyst occurs at a step separate from that of the reactants. Solid catalysts are the most prevalent type of heterogeneous catalyst.
