Which one is an example of heterogenous catalysis?

Oxidation of sulphur dioxide into sulphur trioxide in the presence of oxides of nitrogen.

Hydrolysis of sugar catalysed by $\displaystyle \mathrm{H}^{+}$ ions.

Decomposition of ozone in presence of nitrogen monoxide.

Combination between dinitrogen and dihydrogen to form ammonia in the presence of finely divided iron.