Question

Give four examples of heterogeneous catalysis.

Answer 1

To solve this question, we shall require some knowledge about heterogeneous catalysis. It is a type of catalysis reaction in which the phase of catalysts differ from the phase of the reactants and products. Heterogeneous catalysts mainly involve solid phase or gas phase reactions. They can be easily separated from the reaction mixture. They are mostly transition metals with active sites all over the surface for the reactants to bind and form products.

Complete step by step answer :
As we know that, in heterogeneous catalysis, most of the reactions occur by adsorption. They may be physisorption or chemisorption. Some examples of heterogeneous catalysis are:

1.Contact Process: It is the process used for the synthesis of sulphuric acid. Gaseous phase sulphur dioxide reacts with oxygen to form sulphur trioxide, in the presence of solid state catalyst vanadium oxide. This sulphur trioxide is then treated with water to form sulphuric acid. The reaction involving the catalyst goes as:
${\text{S}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ + }}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)\xrightarrow{{{{\text{V}}_{\text{2}}}{{\text{O}}_{\text{5}}}}}{\text{S}}{{\text{O}}_{\text{3}}}\left( {\text{g}} \right)$
2.Haber - Bosch process: It is the process used for the synthesis of ammonia gas. Gaseous phase nitrogen reacts with hydrogen in the presence of iron oxides on alumina to give ammonia. The reaction goes as:
${{\text{N}}_{\text{2}}}\left( {\text{g}} \right){\text{ + 3}}{{\text{H}}_{\text{2}}}\left( {\text{g}} \right)\xrightarrow[{{\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}}]{{{\text{FeO}}}}{\text{2N}}{{\text{H}}_{\text{3}}}\left( {\text{g}} \right)$
3.Ostwald Process: It is the process used for the synthesis of nitric oxide. Gaseous phase ammonia reacts with oxygen in the presence of platinum to give nitric acid. The reaction goes as:
${\text{N}}{{\text{H}}_{\text{3}}}\left( {\text{g}} \right){\text{ + }}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)\xrightarrow{{{\text{Pt - Rh}}}}{\text{HN}}{{\text{O}}_{\text{3}}}\left( {\text{g}} \right)$
4.Alkene Polymerisation: It is the process of synthesis of polymers from their respective monomer, mostly alkene. It occurs in the presence of titanium chloride and magnesium chloride. It is also known as Ziegler Natta polymerisation. The reaction occurs as:
${\text{propylene}}\left( {{\text{aq}}} \right)\xrightarrow[{{\text{MgC}}{{\text{l}}_{\text{2}}}}]{{{\text{TiC}}{{\text{l}}_{\text{3}}}}}{\text{polypropylene}}\left( {{\text{aq}}} \right)$

Additional Note: Some other examples of heterogeneous catalysis are: hydrogen production by steam reforming in the presence of nickel, ethylene oxide synthesis in the presence of silver on alumina, hydrogen cyanide synthesis in presence of platinum etc.

Note: Heterogeneous catalysts are mostly transition metals. They are preferred due to their variable oxidation state. Hydrogenation of unsaturated hydrocarbons in th