1. We need to identify the incorrect pair.

2. Check each option:

   A: Haber process – Iron
   In the Haber process for ammonia synthesis, finely divided iron is used as the catalyst.
   So, A is correct.

   B: Polythene preparation – $\mathrm{TiCl}_4, \mathrm{Al}(\mathrm{CH}_3)_3$
   These are Ziegler–Natta catalyst components used for polymerization of ethene to form polythene.
   So, B is correct.

   C: Photography – AgBr
   Silver bromide, $\mathrm{AgBr}$, is a photosensitive compound used in photography.
   So, C is correct.

   D: Wacker process – $\mathrm{PtCl}_2$
   The Wacker process involves oxidation of ethene to acetaldehyde using $\mathrm{PdCl}_2$ and $\mathrm{CuCl}_2$, not $\mathrm{PtCl}_2$.
   Hence, D is incorrect.

3. Therefore, the incorrect pair is:

$\boxed{\text{D}}$