Question

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How many types of Catalysis are there?

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Answer 1

Good Evening Bhai,

There are 2 types of Catalysis

1. Homogeneous Catalysis

2. Heterogeneous Catalysis

Homogeneous Catalysis

If the catalyst is present in the same phase as the reactants, it is called a homogeneous catalyst and this type of catalysis is called homogeneous catalysis. Two common examples of this type of catalysis are as follows:-

1) Oxidation of sulphur dioxide to sulphur trioxide in presence of nitric oxide as catalyst (in lead chamber process for manufacture of H₂SO₄)

→ 2SO₂ (g) + O₂ (g) ------> 2SO₃ (g)

Here, all substances are present in the gaseous phase.

Now, Similarly oxidation of CO by O takes place in presence of NO as catalyst.

→ 2 CO (g) + O₂ (g) ------> 2 CO₂ (g)

2) Decomposition of ozone in presence of NO or Cl atoms as catalyst.

→ O₃ + O -----> 2 O₂

3) Decomposition of hydrogen peroxide in presence iodide ion as catalyst.

→ 2H₂O₂ ----> 2 H₂O + O₂

4) Hydrolysis of ethyl acetate or sucrose solution in presence of dilute sulphuric acid.

⊕ CH₃COOC₂H₅ (l) + H₂O ----> CH₃COOH + C₂H₅OH (l)

⊕ C₁₂H₂₂O₁₁ (aq) + H₂O ---> C₆H₁₂O₆ (aq) + C₆H₁₂O₆ (aq)

Here, all substances are present in the liquid phase.

5) Preparation of diethyl ether from ethyl alcohol using concentrated H₂SO₄ as catalyst .

→ 2 C₂H₅OH (l) --------> C₂H₅OC₂H₅ (l) + H₂O (l)

Here, all the substances are present in the liquid phase.

Theory of Homogeneous Catalysis (Intermediate compound formation theory)

Now, According to modern views, a catalyst enters into chemical combination with one or more of the reactants forming an intermediate compound which then decomposes or combines with one of the reactants to produce the product and then catalyst is regenerated. The involvement of the catalyst in the reaction lowers the free energy of activation and hence accelerates the speed of the reaction.

1) Oxidation of SO₂ to SO₃ in presence of NO takes place as follows

⊕ O₂ (g) + 2NO (g) ----> 2NO₂ (g)

⊕ SO₂ (g) + NO₂ (g) ------> SO₃ (g) + NO (g)

2) Decomposition of H₂O₂ in presence of I⁻ ion take place as follows:-

H₂O₂ + I⁻----> H₂O₂ + IO (hypoiodite ion) IO⁻ + H₂O₂ ----> H₂O₂ + O₂+ I⁻

3) Decomposition of ozone in presence of NO take s place as follows:-

→ NO + O₃ ----> NO + O ; NO₂ + O ---> NO + O₂

4) Formation of diethyl ether from ethyl alcohol using concentrated sulphuric acid take place as follows:-

C₂H₅OH (l) + H₂SO₄ (l) ---> C₂H₅HSO₄ (aq) + H₂O(l)

2) Heterogeneous Catalysis :- If the catalyst is present in a different phase then that of the reactants, it is called a heterogeneous catalyst and this type of catalyst is called ''Heterogeneous Catalysis''

The catalyst in heterogeneous catalysis is generally solid and he reactants are mostly gases and sometimes liquids. In Heterogeneous catalysis, the reaction starts at the surface of the solid catalyst. That is why it is also known as ''Surface Catalysis''

1) Manufacture of ammonia from N and H by Haber's Process using iron as catalyst.

→ N₂ (g) + 3 H₂(g) ---> 2 NH₃ (g)

Hence, reactants are gaseous whereas catalyst is solid.

2) Synthesis of methyl alcohol(CH₃OH) from CO and H₂ using a mixture of Cu , ZnO and Cr₂O₃as catalyst.

→ CO (g) + 2 H₂ (g) ----> CH₃OH

Here, Again reactants are gaseous and catalyst is a mixture of solids.

3) Manufacture of sulphuric acid by the oxidation of SO₂ to SO₃ using platinised asbestos or V₂O₅ as catalyst.

→ 4NH₃ + O₂ -----> 2SO (g)

4) In the manufacture of nitric acid, oxidation of ammonia to nitric oxide using platinum as catalyst (''Ostwald Process'')

→ 4NH + 5O₂ -----> 4NO + 6H₂O

5) Hydrogenation of unsaturated hydrocarbon in presence of finely divided Ni, Pd or Pt ethylene (CH₂ -- CH₂) to ethane (CH₃ - CH₃) and conversion of vegetable oil into margarine (imitation butter) or ghee.

Vegetable oil (l) + H₂ (g) -----> Vegetable Ghee (s)

Here, one of the reactants is a liquid the other is gaseous whereas catalyst is ''SOLID''.

6) Polymerisation of ethylene using TiCl₄ and trialkyl aluminium as catalyst (''Ziegler - Natta catalyst).

→ n CH₂ - - CH₂ (g) -----> ( CH₂ - CH₂ )n

The catalyst is prepared by dissolving (C₂H₅)₃ Al and TiCl₄ in a hydrocarbon solvent which react exothermically to form a ''Brown Solid''

6) Cracking of hydrocarbons in the presence of hydrogen by ''ZEOLITE PROCESS''

THEORY OF HETEROGENEOUS CATALYSIS

According to this theory the ''Old Adsorption Theory'' of heterogeneous catalysis, it was believed that the reactants in the gaseous state or from the solutions are adsorbed on the surface of the catalyst. So, as a result the concentration of the reactants molecules on the surface increases and hence the rate of reactions increases. So therefore, the adsorption is always exothermic.

There are 3 theories based on the Heterogeneous Catalysis

• Old Adsorption Theory
• Intermediate Compound Formation Theory
• Modern Adsorption Theory

Hope it helps you !

Answer 2

TWO TYPES OF CATALYSIS

• homogeneous catalysts,
• heterogeneous catalysts

homogeneous catalysis ;

homogeneous catalysis is catalysis in a solution by a soluble catalyst. Homogeneous catalysis refers to catalytic reactions where the catalyst is in the same phase as the reactants. ... Enzymes are examples of homogeneous catalysts.

heterogeneous catalysis ;

heterogeneous catalysis also refers to the form of catalysis where the phase of the catalyst differs from that of the reactants. Phase here refers not only to solid, liquid, vs gas, but also immiscible liquids, e.g. oil and water.

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