Types of Catalysis

Catalysis are easily categerozied into two different categories that are,

• Homogeneous Catalysis
• Hetrogenous Catalysis

Homogeneous Catalysis

When the reactants and catalyst are in the same phase with respect to each other (i.e. solid, liquid or gas). It is claimed that the catalysis is homogeneous. 

Some examples of homogeneous catalysis are listed below.

• In the lead chamber method, sulphur dioxide is oxidized to sulphur trioxide with oxygen in the presence of nitrogen oxides as a catalyst.

2SO₂(g)  +  O₂(g)    →   2SO₃(g) {In presence of NO(g)}

The reactants, products, and catalysts are all in the same phase or gaseous state.

• Sugar hydrolysis is catalyzed by the H+ ions produced by sulphuric acid.

C₁₂H₂₂O₁₁(l)  +  H₂O(l)   → C₆H₁₂O₆(l) + C₂H₁₂O₆(l) {In presence of H₂SO₄(l)}

Heterogeneous Catalysis

Heterogeneous catalysis is a catalytic process in which the reactants and catalysts are in different phases.

The following are some examples of heterogeneous catalysis-

• In the contact method for the synthesis of sulphuric acid, oxidation of sulphur dioxide into sulphur trioxide with platinum metal or vanadium pentaoxide as a catalyst. While the reactants are gaseous, the catalyst is solid.

SO₂(g) + O₂(g)   →  2SO₃(g) {In presence of Pt(s)}

• In Haber’s process, nitrogen and hydrogen are combined to produce ammonia in the presence of finely split iron.

N₂(g) + 3H₂(g)   →   2NH₃(g) {In presence of Fe(s)}

• In Ostwald’s procedure, ammonia is converted to nitric oxide in the presence of platinum gauze as a catalyst.

4NH₃(g) + 5O₂(g)   →   4NO(g) + 6H₂(g) {In presence of Pt(s)}

Apart form this there are also two types of catalysis that are,

• Positive Catalysis
• Negative Catalysis

Positive Catalysis

When a foreign substance accelerates the pace of a reaction, it is referred to as a positive catalyst, and the phenomenon is known as positive catalysts.

The following are some examples of Positive catalysis,

• Decomposition of H₂O₂ in presence of colloidal platinum.

2H₂O₂(l)   →   2H₂O(l) + O₂(g) {In presence of Pt}

Negative Catalysis

Certain substances, when added to the reaction mixture, slow down rather than speed up the reaction rate. Negative catalysts or inhibitors are used in this process, which is known as negative catalysis.

The following are some examples of Negative catalysis

• If some alcohol is added to chloroform, the oxidation by air is slowed.

2CHCl₃(l) +O₂(g)  →   2COCl₂(g) + 2HCl(g) {In presence of Alcohol(l)}

Catalysis in Chemistry is defined as the process in which the rate of the reaction is influenced by the presence of some specific substance. These specific substances are called Catalysts. The catalyst is never consumed during the chemical reaction.

A catalyst changes the activation energy of the reaction, i.e. the energy required for occurring the reaction. and thus alters its rate. In general, a catalyst lowers the activation energy of the chemical reaction and this process is called the Catalysis.