Step 1:

The catalytic process in which the reactants and the catalyst are in different phases is known as heterogeneous catalysis. 

Step 2:

The example of heterogenous catalysis are as follows:

(i)
Oxidation of sulphur dioxide to form sulphur trioxide. In this reaction, Pt acts as a catalyst. 

Here reactant and product are in the gaseous phase and the catalyst is in solid phase.

$2{\mathrm{SO}}_{2\left(\mathrm{g}\right)}\stackrel{{\mathrm{pt}}_{\left(\mathrm{s}\right)}}{\to }2{\mathrm{SO}}_{2\left(\mathrm{g}\right)}$

(ii) 
Formation of ammonia by the combination of dinitrogen and dihydrogen in the presence of finely divided iron.  

Here reactant and product are in the gaseous phase and the catalyst is in the solid phase.

$4{\mathrm{NH}}_{3\left(\mathrm{g}\right)}+3{\mathrm{H}}_{2\left(\mathrm{g}\right)}\stackrel{{\mathrm{Fe}}_{\left(\mathrm{s}\right)}}{\to }2{\mathrm{NH}}_{3\left(\mathrm{g}\right)}$

This process is called Haber’s process.

(iii) 
Hydrogenation of vegetable oils in the presence of Ni. 

$\mathrm{Vegetable} {\mathrm{oil}}_{\left(\mathrm{l}\right)}+{\mathrm{H}}_{2\left(\mathrm{g}\right)}\stackrel{{\mathrm{Ni}}_{\left(\mathrm{s}\right)}}{\to }\mathrm{Vegetable} {\mathrm{ghee}}_{\left(\mathrm{s}\right)}$

Here reactants are in the liquid and gaseous phase but the catalyst is in the solid phase.

${}_{}$(iv)
Oxidation of ammonia into nitric oxide in the presence of platinum gauze in Ostwald’s process. The reaction is as follows

\(4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \stackrel{\mathrm{Pt}(\mathrm{s})}{\longrightarrow} 4 \mathrm{NO}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})\)

The reactants are in gaseous state while the catalyst is in the solid state.