Chemistry question!!!(please!)

Example 1:
Iron is used as the catalyst in the Haber process to produce ammonia.
nitrogen + hydrogen ⇌ ammonia .. (Fe as catalyst)
N2(g) + 3H2(g) ⇌ 2NH3(g) .. (Fe as catalyst)

Example 2:
Platinum (or copper) is used as the catalyst in the catalytic oxidation of ammonia to give nitrogen monoxide.
ammonia + oxygen → nitrogen monoxide .. (Pt or Cu as catalyst)
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) .. (Pt or Cu as catalyst)

Example 3:
Platinum (or vanadium(V) oxide) is used as the catalyst in the contact process to produce sulphur trioxide from sulphur dioxide.
sulphur dioxide + oxygen ⇌ sulphur trioxide .. (Pt or V2O5 as catalyst)
2SO2(g) + O­2(g) ⇌ 2SO3(g) .. (Pt or V2O5 as catalyst)

Example 4:
Nickel (or platinum) is used as the catalyst in the catalytic hydrogenation of ethene.
ethene + hydrogen → ethane .. (Ni or Pt as catalyst)
CH2=CH2(g) + H2(g) → CH3CH3(g) .. (Ni or Pt as catalyst)

First, you have to clear what type of catalyst you look for, there are in general 2 types of cataylst, the homogeneous and heterogeneous one.

Ususally in Al level, teachers talk heterogeneous one. Like these very good examples given above by micro.

If you are futher interesting on the homogeneous catalyst, it would a bit hard due to involved of the organometallic chemistry. If you still insteret in such catalyst, you may find some example on wiki by key word list below

Wilkinson's catalyst
Crabtree's catalyst
Grubbs' Catalyst

These three catalysts is well known and some of them still used in industry

Structure determines the nature, the nature of use. Determines the structure of the transition elements have lower activation energy of its own ability to promote thereaction. Therefore, they allow people to use it as a reaction catalyst.