Are Catalysts Inhibitors or Poisons

Surface chemistry is one of the essential scoring topics in chemistry. Concepts like adsorption, dispersion, desorption, absorbent, and adsorbent or occlusion are crucial aspects of surface chemistry. One of the most critical topics among them is catalysis. In order to understand catalysis, it is essential to understand what a catalyst is and what are catalyst poisons or inhibitors. It is equally important to know how inhibitors function, the types of inhibitors, and the difference between inhibitors and poisons. 

According to scientific definition, a catalyst is a foreign substance added to a reaction to accelerate or retard the rate of reaction. A negative catalyst slows down the chemical reaction, while a positive catalyst accelerates it. Homogeneous, heterogeneous, positive, negative, auto-catalyst and induced catalysts are a few types of catalysts.

Essential Features of Catalysts and Catalytic Inhibitors 

A  catalyst retains its mass and composition till the completion of a chemical reaction and cannot initiate a reaction or change the equilibrium’s position. Catalysts are specific in nature. 

A catalytic inhibitor is a chemical substance that affects the catalyst’s efficiency by slowing it down. In simple words, it is a substance that destroys the catalyst’s activity by its presence. 

How do Catalytic Inhibitors Reduce a Catalyst’s Efficiency

We know that a catalyst has some active sites present on its surface. An active site is a specific region of an enzyme where the substrate or the reactant species binds up, and the catalysis process or the chemical reaction occurs. An inhibitor affects a catalyst’s efficiency by binding up with the active sites on its surface. 

Most of the catalytic inhibitors act by preventing the reactants from coming closer to each other by binding with one of the reactants permanently or temporarily. They can coordinate with the active sites to slow down the reaction process. 

An example of a catalytic inhibitor is methotrexate – a chemotherapy drug that acts as a competitive Inhibitor.

The leading causes of inhibition are a decrease in the concentration of one of the reactants in the chemical reaction, a decrease in the concentration of an active catalyst, or termination of a chain reaction.

 Types of Catalytic Inhibitors

Chemical catalytic inhibitors are broadly divided into two types

• Reversible Catalytic inhibitor
•  Irreversible Catalytical inhibitors

Reversible Catalytic Inhibitor

Reversible catalytic inhibitors slow down the reaction instead of completely stopping the reaction process. After removing this kind of inhibitor, the affected enzymes start working again. Essentially, they do not have a permanent effect on the chemical reaction. Reversible inhibitors are further classified into competitive, non-competitive, and uncompetitive inhibitors.

Irreversible Catalytical Inhibitor

Inhibitors that stop the occurrence of unwanted reactions in the primary reaction are irreversible catalytic inhibitors. They simply deactivate the enzyme by binding to the active sites. Again, there are three types of irreversible inhibitors: group-specific reagents, reactive substrate analogs, and suicide inhibitors.

Catalytic Poisons

Substances that destroy the activity of the catalyst by their presence are known as catalytic poisons. The poisoning of catalysts takes place due to the preferential adsorption of poison on its surface, thus reducing the space available for the adsorption of the reacting molecules. In simple words, catalytic poisons are substances that change the composition of the reaction.

Some examples of catalytic poisons are carbon monoxide, halides, sulphides, sulfites, phosphates, phosphites, and organic molecules such as nitriles, nitro compounds, oximes, and nitrogen heterocycles.

Conclusion

A catalyst is a foreign chemical substance that helps alter or change the rate of a chemical reaction. Usually, a catalyst is used in a chemical reaction to increase the speed of a chemical reaction. Six common catalysts are homogeneous, heterogeneous, induced, auto-catalyst, negative, and positive. On the other hand, catalytic inhibitors affect a catalyst’s activity in a chemical reaction, and catalytic poisons stop an unwanted reaction in the primary chemical reaction.  

The main difference between a catalytic inhibitor and a catalytic poison is that the inhibitor slows down the catalytic reaction by affecting the activity of the catalyst. On the other hand, poisons directly stop unwanted reactions from occurring.