Types of Catalysts

Catalysts are compounds that affect the rate of a process by changing the nature of a reaction. A catalyst is frequently used to speed up or increase the rate of a chemical process. There are many types of catalysts in solid, liquid, and gaseous states. Metals and semi-metallic elements like aluminium and silicon are considered solid catalysts. Catalysts can be a gas or liquid when in their pure form. In these notes on the types of catalysts, we will uncover how these compounds trigger a catalytic reaction.

What Is a Catalyst in Chemistry?

A catalyst is required to break or mend chemical bonds between the atoms of molecules of specific elements or compounds during a chemical reaction. Catalysts encourage molecules to react, simplifying and speeding the whole reaction process.

Catalysts in the liquid or gas phase are more likely to be made up of a single element. However, they may be mixed with solvents and other materials. Solid catalysts may be dispersed inside a solid or liquid substrate known as catalyst support.

A catalytic reaction is one where a catalyst is used in the reaction. A catalyst is renewed when a reaction between both reactants takes place.

Catalysts accelerate reactions by reducing activation energy (Ea) of a process that would take much longer to complete without the catalyst. Such reactions produce a product or products with lower total energy than the reactant or reactants; if this were not the case, these reactions would not occur without external energy input.

Types of Catalysts

Catalysts and catalytic processes are classified into homogeneous catalysts, heterogeneous catalysts, and biocatalysts (usually called enzymes). Photocatalysis, environmental catalysis, and green catalytic processes are less prevalent but still essential forms of catalyst activity. 

Depending on the attributes of the chemical reaction, there are many types of catalysts. Some are given below:

• Negative Catalysts

A negative catalyst is a type of catalyst that slows down the pace of the chemical reaction. It lowers the rate of chemical reactivity by upgrading the activation of energy stoppage, which decreases the number of molecules that react can be transformed into products.

Example: Acetanilide is used as a negative catalyst to reduce the rate of decomposition of hydrogen peroxide

• Positive Catalysts

A positive catalyst paces or accelerates the rate of a chemical reaction taking place. It advances the chemical reaction by lowering activation energy resistances. A positive catalyst lets a high number of reactive molecules be transformed into products by increasing the percentage of product outcome.

Examples: In Haber’s method, iron oxide works as a positive catalyst.

• Accelerator or Promoter

A promoter or accelerator is a substance in chemistry that powers up the activity of the catalyst.

Examples: Molybdenum is used as a promoter in Haber’s process. 

• Homogeneous Catalyst

Both the reaction mixture and the catalyst are contained in the same phase in homogeneous catalysis. The catalyst and reactants have a high degree of homogeneity, which results in a high level of contact between them. Thus, there is high reactivity and selectivity of the reaction under moderate reaction conditions.

Examples: Carbonic anhydrase, which catalyzes the release of CO2 into the lungs from the bloodstream.

• Heterogeneous Catalyst

In heterogeneous catalysis, catalysts reside in a distinct phase from the reaction mixture.

Examples: The Haber-Bosch process to synthesise ammonia, the Fischer–Tropsch process to produce a variety of hydrocarbons, etc.

• Biocatalysts

Biocatalysts are natural enzymes or nucleic acids that catalyse certain chemical processes outside living cells. Animal tissues, plants, and microorganisms are all sources of enzymes (bacteria, yeast, or fungi).

Examples: Trypsin, amylase.

Conclusion

This module has covered most of the topics, types and concepts related to the types of catalysts in chemistry.

Catalysts are chemicals that change the nature of a reaction to modify the rate of a process. The employment of a catalyst to speed up or raise the rate of a chemical reaction is common. Catalysts come in a variety of solid, liquid, and gaseous forms. Solid catalysts include metals and semi-metallic components such as aluminium and silicon. In their purest form, catalysts might be a gas or a liquid. We have learned how these substances cause a catalytic reaction in these notes on the many sorts of catalysts.