Catalysis: Types Of Catalysts

A substance which when used in small amount in reactions modifies the rate of a reaction without being consumed in the reaction itself is known as a catalyst and this phenomenon is known as Catalysis.

What is Catalyst?

A catalyst helps the rate of reaction to be increased and requires lesser activation energy.



Types of Catalyst:

This process can be divided into the following classes:

1. Homogeneous catalysis:

If the phase of this process and the reactant is same, then the catalyst is known as the homogeneous catalyst and the phenomenon is known as a homogeneous catalytic process. For example:

When CO is oxidized CO2 by O2 in the presence of NO as a catalyst,

i.e.,   2CO (g) + O2 (g) + NO (g) → 2CO(g)

2. Heterogeneous catalysis:

If the phase of the reactant and the catalyst is not the same, then that type of catalyst is known as a heterogeneous catalyst. In general, the catalyst is in solid-state and the reactant is in the gaseous state.

For example Hydrogenation of ethylene (unsaturated hydrocarbon) in the presence of catalysts like Ni, Pd, and Pt at 250⁰C. This is an example of heterogeneous catalytic reaction

  • Positive catalysis: When the rate of reaction is increased by the external use of other substances, then this phenomenon is known as a positive catalytic process and the substance is known as a positive catalyst. For example, Ammonia is synthesized from N2 and H2 using iron as a positive catalyst and molybdenum as a promoter.

N2 (g)+ 3H2 (g) + Fe(s), MO → 2NH3 (g)

  • Negative catalysis: A substance that reduces the rate of a reaction without undergoing a chemical reaction is known as a negative catalyst. And the phenomenon is known as the negative process. For example the presence of glycerin in the decomposition of hydrogen peroxide.

2H2O2 (l)Glycerin (l)→ 2H2O (l) + O2 (g)

  • Auto catalysis: In some types of reaction the product itself acts as a catalyst and alters the rate of reaction. This kind of substance is known as an autocatalyst and the phenomenon is known as the auto Catalysis.

For example: In the hydrolysis of ethyl acetate, ethyl alcohol and acetic acid is formed. The formation of acetic acid increases the rate of reaction.


  • Induced catalysis: When some reactions do not occur under normal condition but it occurs under the influence of another reaction then this phenomenon is known as an induced mechanism.

This was just a brief layout of the process and the different types of the catalytic process. To know more about the catalysis, its type in detail and its various theories, please visit BYJUS.

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