Which of the following is not an example of heterogeneous catalysis?

Options

1. A$n$\left(C{H}_{2} = C{H}_{2}\right)\overset{{R}_{3}Al + TiC{l}_{4}}{→}{\left[- C{H}_{2} - C{H}_{2} -\right]}_{4}
2. B$2S{O}_{2} + {O}_{2}\overset{Pt-Asbestos}{→}2S{O}_{3}$
3. C$RCOOR\overset{H^{+}}{\mathop{→}_{Catalyst}} RCOOH + ROH$
4. D$2{H}_{2}{O}_{2}\left(l\right)\overset{Hg\left(l\right)}{→}2{H}_{2}\text{O} + {O}_{2}$