10.2 Types of catalysis

2.1 Characteristics of Adsorption
2.2 Types of Adsorption

4.1 Freundlich adsorption isotherm
4.2 The Langmuir adsorption isotherm

7.1 Different Colloidal Systems
7.2 Classification of Colloidal System
7.3 Preparation of Colloidal System
7.4 Purification of Colloidal System
7.5 Properties of colloidal system

8.1 Protective colloids

9.1 Foams
9.2 Applications of colloids and emulsions

10.1 Positive and negative catalysis
10.2 Types of catalysis

12.1 Characteristics of Enzymes
12.2 Mechanism of enzyme catalysis
12.3 Autocatalysis
12.4 Induced catalysis

Generally there are two types of catalysis which are:

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.

According to modern vibes, 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 the 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. In other words, a new more efficient path is followed.

If the catalyst is present in a different phase than that of the reactants, it is called a heterogeneous catalyst and this type of catalysis is called heterogeneous catalysis. The catalyst in heterogeneous catalysis is generally solid and the 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.

According to 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. As a result, the concentration of the reactant molecules on the surface increases and hence the rate of the reaction increases. Further, as adsorption is always exothermic, the heat released further helps to speed up the reaction.

Question 4. Mention the catalyst used, reaction involved and the type of catalysis for the following process/reactions.

1. Haber's Process

2. Decomposition of ozone

3. Decomposition of hydrogen peroxide

4. Polymerisation of ethylene

5. Ostwald process

Solution: The catalyst used, reaction involved and the type of catalysis for the following process/reactions are:

1. Haber's process

It is a heterogeneous catalysis. It involves manufacture of ammonia from ${N_2}$ and ${H_2}$ using iron as catalyst.

\[\begin{array}{c}{{N_2}(g)}& + &{3{H_2}(g)} \end{array}\begin{array}{c}{\xrightarrow{{Fe(s)}}}&{2N{H_3}} \end{array}(g)\]

2. Decomposition of ozone

It is a homogeneous catalysis. The catalyst used for decomposition of ozone is $NO$ or $Cl$.

\[\begin{array}{c}{{O_3}}& + &O \end{array}\begin{array}{c}{\xrightarrow{{NO/Cl}}}&{2{O_2}} \end{array}\]

3. Decomposition of hydrogen peroxide

It is a homogeneous catalysis. The catalyst used for decomposition of hydrogen peroxide is iodide.

\[\begin{array}{c}{2{H_2}{O_2}}&{\xrightarrow{{{I^ - }}}} \end{array}\begin{array}{c}{2{H_2}O}& + &{{O_2}} \end{array}\]

4. Polymerisation of ethylene

It is a heterogeneous catalysis. It uses Ziegler - Natta Catalyst. The catalyst consist of ${TiC{l_4}}$ and trialkyl aluminium.

\[\begin{array}{c}{nC{H_2}C{H_2}}&{\xrightarrow{{TiC{l_4} + {R_3}Al}}}&{{{\left( {C{H_2} - C{H_2}} \right)}_n}} \end{array}\]

5. Ostwald process

It is also a heterogeneous process. In the manufacture of nitric acid, oxidation of ammonia to nitric acid using platinum as catalyst. (Ostwald process)

\[\begin{array}{c}{4N{H_3}}& + &{5{O_2}} \end{array}\begin{array}{c}{\xrightarrow{{Pt}}}&{4NO} \end{array}\begin{array}{c}+ &{6{H_2}O} \end{array}\]