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.
CH3COOC2H5 + H2O → CH3COOH + C2H5OH
- 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.