Wednesday , May 27 2020
Catalyst In Chemistry

Catalyst In Chemistry

A catalyst is defined as substance that 
alters the rate of the chemical reaction and remains unchanged at the end ofther chemical reaction is called Catalyst. As evident from the on top of definition, a catalyst might increase or decrease the speed of a reaction. The catalyst which enhances the rate of a reaction is called a Positive catalyst and the process Positive catalysis or simply Catalysis. A catalyst which retards the rate of a reaction is called Negative catalyst and the process Negative catalysis. 

Here we will learn the following answer of these question :

1) In chemical reaction, what does catalyst do

2) Homogeneous catalyst example

3) Heterogeneous catalyst example

4) Catalyst examples

5) Heterogeneous catalyst vs homogeneous catalyst 

We will also learn :

  • Catalyst in chemistry
  • Types of catalyst
  • Examples of catalysts in industry
Catalyst In Chemistry
Catalyst In Chemistry



According to catalyst In chemistry, there are two main types of catalysis: 
a) Homogenous catalysis 
b) Heterogeneous catalysis 

Also, there is a third type of catalyst known as Enzyme catalysis which is largely used in the biological sector.


         In homogenous catalysis, the catalyst is in the same phase as the reactants and is evenly distributed throughout. This type of catalysis can occur in the gas phase or the liquid (solution) phase. 

 Homogeneous catalyst example in Gas Phase: 

a) Oxidation of sulphur dioxide to sulphur trioxide with nitric oxide as a catalyst, 

·         2SO2 + O2 + [NO] → 2SO3  + [NO]


·         b) Decomposition of acetaldehyde with iodine as a catalyst, 
·         CH3CHO + (I2) → CH4 + CO

Example of Homogenous Catalysis in Solution Phase: 

Many reactions in solutions are catalyzed by acid and bases,

a) Hydrolysis of cane sugar in aqueous solution in the presence of mineral acid as catalyst, 

·         C12H22O11 + H2O = C6H12O6 + C6H12O+ [H2SO4]

b) Ester hydrolysis in the presence of acid or alkaline,

·         CH3COOC2H5 + H2O + [H/OH] → CH3CHO + C2H5OH

c) Decomposition of hydrogen peroxide in the presence of iodine ion as a catalyst,

·         2H2O2 + [ I­- ] → 2H2O + O2


The catalyst is called heterogeneous catalysis at different physical stage than the reactants.

The most important of such reactions are those in which the reactants are in the gas phase while the catalyst is solid. The process is also called Contact catalysis since the reaction occurs by contact of reactants with the catalyst surface. In contact catalysis, usually, the catalyst is a finely divided metal or a gauze. This form of catalysis has great industrial importance. 

Heterogeneous catalyst example 

Some example of heterogeneous catalysis with reactants in the gas, liquid or the solid phase is listed below.

1) Heterogeneous catalysis with gaseous reactant (Contact catalysis) 

a) Combination of sulphur dioxide and oxygen in the presence of finely divided platinum or vanadium pentoxide, (Contact Process for Sulphuric acid)

2SO2 + O2 + [Pt] → 2SO3 + [Pt]

b) In the presence of finely divided iron, nitrogen and hydrogen mixture to form ammonia, (Haber Process for Ammonia). 

N2 + 3H2 + [Fe] → 2NH + [Fe]

c) Oxidation of ammonia to nitric oxide in the presence of platinum gauze ( a stage in the manufacture of Nitric acid).

4NH3 + 502 + [Pt] → 4NO + 6H2O + [Pt]

d) Hydrogenation reactions of unsaturated organic compounds are catalyzed by a finely divided nickel.

H2C=CH2 + H2 + [Ni] → H3C-CH3 + [Ni]

Vegetable oils are triesters of glycerol with higher unsaturated acid. When hydrogen is passed through the vegetable oils in the presence of nickel, the carbon-carbon double bonds of the acid portions are hydrogenated to yield solid fats (Vanaspati ghee).

2) Heterogeneous catalysis with liquid reactants 

a) The decomposition of aqueous solutions of hydrogen peroxide is catalyzed by manganese dioxide or platinum in colloidal form,

 2H2O2 + [Pt] → 2H2O + O+ [Pt]

b) Benzene and ethanol chloride react in the presence of anhydrous aluminium chloride to form phenyl methyl ketone, 

C6H6 + CH3COCl  + [AlCl3]  → C6H5COCH­3 + HCl + [AlCl3]  

3) Heterogeneous catalysis with the solid reactant 

The decomposition of potassium chlorate is catalyzed by manganese dioxide.

         2KClO3 + [MnO­2] → 2KCl + 3O2 + [MnO­2]




The long chains of the enzyme (protein) molecules are coiled on each other to make a rigid colloidal particle with cavities on its surface. These cavities which are of characteristic shape and abound in active groups (NH2, COOH, SH, OH) are termed active centres. Substrate molecules which have complementary form fit into these cavities just like the key fits into lock. By virtue of the presence of active groups, the enzyme forms as the activated complex with the substrate which at once decomposes to yields to products. Thus the substrate molecules enter the cavities, forms complex and react, and at once the products get out of the cavities. 


Catalyst In Chemistry

Catalyst In Chemistry


Catalyst In Chemistry


Catalyst In Chemistry


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