Q.

A substance which increases rate of reaction without consuming itself is called catalyst. This
phenomenon is called catalysis.
It is classified into two types
1) Homogeneous catalysis
2) Heterogenous catalysis
Homogeneous catalysis :
→ Catalyst and reactants are in same phase
Ex : $2{\mathrm{SO}}_{2( \mathrm{g})}+{\mathrm{O}}_{2( \mathrm{g})}\stackrel{\mathrm{NO}\left(\mathrm{g}\right)}{\to }2{\mathrm{SO}}_{3( \mathrm{g})}$
$2{\mathrm{CO}}_{\left(\mathrm{g}\right)}+{\mathrm{O}}_{2( \mathrm{g})}\stackrel{\mathrm{NO}\left(\mathrm{g}\right)}{\to }2{\mathrm{CO}}_{2( \mathrm{g})}$
Heterogeneous Catalysis:-
→ Catalyst and reactants are in different phase
Ex: ${\mathrm{N}}_{2( \mathrm{g})}+3{\mathrm{H}}_{2( \mathrm{g})}\stackrel{\mathrm{Fe}\left(\mathrm{s}\right)}{⟶}2{\mathrm{NH}}_{3( \mathrm{g})}$
$2{\mathrm{SO}}_{2( \mathrm{g})}+{\mathrm{O}}_{2( \mathrm{g})}\stackrel{\mathrm{Pt}\left(\mathrm{s}\right)}{⟶}2{\mathrm{SO}}_{3( \mathrm{g})}$