Types of Catalysis

Catalysis is the process in which the rate of reaction is influenced by a substance that is not mixed or gets consumed in the all-over reaction and does not affect the final product. The process involves complicated organic substances with a different functional group. The rate of reaction depends upon various factors such as the chemical nature of the reactant, temperature, conditions, etc. The particular substance that is related to the catalysis is the catalyst that increases the production without consuming in that reaction.

History

The term catalysis was given by Jons Jacob Berzelius in 1835. In the eighteenth to nineteen centuries, various scientists observed the process of catalysis in different reactions, and they discovered different substances used as a catalyst. The first observation of the catalyst is recorded by Kirchhoff in the conversion of starch into sugar by acids. Sir Michael Faraday discovered the power of platinum in the recombination of gaseous hydrogen and oxygen.

The principle of catalysis

The catalyst can be understood by the following points:

When there is a catalyst in the reaction, it will need less free energy to reach the transition state. The working of the catalyst adjusts the environment of the reaction. A catalyst can help increase the heat of the environment, it binds the reagent to polarise the bonds, and it also helps in dissociation of reagents and formation of bonds and breaking of bonds.

The working of a catalyst can be understood by the Arrhenius equation, the cavitation energy that is Ea determines the value of rate constant K, at a given temperature. When a catalyst is added to the ration, it reduces the activation energy. Thus, it provides a mechanism for the reaction to have happened in lower activation energy.

Types of Catalysis

There are two main types of catalysts used for catalyses

1. Heterogeneous catalysis
2. Homogeneous catalysis

Heterogeneous catalysis

Heterogeneous catalysis is those which act with the different states of reactants. If the catalyst is solid, then it will work with liquid and gaseous reactants. The active site of this catalyst is on its surface. The reactants are adsorbed on the surface of these catalysts and then interact with them. Most of the catalysts are solid. Examples are zeolite, alumina, graphite, transition metal oxides, Raney nickel, vanadium oxide, etc.

The mechanisms for reactions are diverse depending upon the adsorption. The surface area of the catalyst affects the reaction. The smaller the size of the catalyst, the larger the surface area. 

An example is the Haber process. Iron acts as a catalyst in the production of ammonia from nitrogen and hydrogen. In the reaction, the gases are adsorbed on the surface of the iron. 

        N2 (g) + 3H2 (g) 2NH3 (g)

In this reaction, reactants and the product are in the gaseous phase while the catalyst Fe is in the solid phase. 

Homogenous catalysis

Homogenous catalysis work on the same phase as they are. If the catalyst is solid, then it will work on solid reactants and the same for other phases. These catalysts can be dissolved in solvents. Examples are hydrosilylation and hydroformylation. 

The process of esterification of carboxylic acid needs hydrogen ions.

Transition metals are always used as catalysts. However, some organic substances also work as a catalyst. They are called organocatalysts and come under homogeneous catalysts.

For example     CH3COOCH3(l) + H2O(l) CH3COOH(l) + CH3OH(l)

This is a hydrolysis reaction of methyl acetate which is catalysed by HCl. Here all the reactants, products and catalyst are in the liquid state. 

Significance of Catalysis

A tiny amount of catalysts can make big changes in the reactions.

Many products, when manufactured, produce a large amount of by-product that harms the environment. Catalysts increase the amount of final product and decrease the number of by-products. Thus, it saves the environment from hazardous waste.

They do not consume in the reactions, and after the reaction completes, they depart from the reactant. Thus, they do not affect the product.

Conclusion

Catalysts play an important role in many areas such as the environment, chemistry, industries, etc. They are biological and chemical catalysts. They are divided into two types based on their state of matter. One is homogenous, and the second is the heterogeneous catalyst. It helps in increasing the rate of reaction. They also help in the various reactions that happen in our bodies.