Give four examples of heterogeneous catalysis.

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

$2 \mathrm{SO}_{2(g)} \stackrel{\mathrm{Pr}_{(0)}}{\longrightarrow} 2 \mathrm{SO}_{3(g)}$

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

$\mathrm{N}_{2(g)}+3 \mathrm{H}_{2(g)} \stackrel{\mathrm{Fe}_{(0)}}{\longrightarrow} 2 \mathrm{NH}_{3(g)}$

This process is called the Haber’s process.

(iii) Oswald’s process: Oxidation of ammonia to nitric oxide in the presence of platinum.

$4 \mathrm{NH}_{3(g)}+5 \mathrm{O}_{2(g)} \stackrel{\mathrm{P}_{(k)}}{\longrightarrow} 4 \mathrm{NO}_{(g)}+6 \mathrm{H}_{2} \mathrm{O}_{(g)}$

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

Vegetable oil $_{(i)}+\mathrm{H}_{2(\mathrm{~s})} \stackrel{\mathrm{Ni}_{(i)}}{\longrightarrow}$ vegetable ghee $_{(s)}$