This GIF illustrates the process of Hydrogenation of an ethene to an ethane using Nickel Catalyst:
Ni
CH2 = CH2 + H2 ----> CH3CH3
1) Ethene molecules are adsorbed onto the surface of nickel catalyst
2) Hydrogen molecules are also adsorbed onto the surface of nickel catalyst
3) When a hydrogen atom diffused close to one of the bonded carbons, the bond between carbon and nickel will be replaced by one between carbon and hydrogen
4) Eventually both ends will break free as another hydrogen bonds with the carbon
5) There is now a space on the surface of the nickel catalyst for the new reactant molecules
Ni
CH2 = CH2 + H2 ----> CH3CH3
1) Ethene molecules are adsorbed onto the surface of nickel catalyst
2) Hydrogen molecules are also adsorbed onto the surface of nickel catalyst
3) When a hydrogen atom diffused close to one of the bonded carbons, the bond between carbon and nickel will be replaced by one between carbon and hydrogen
4) Eventually both ends will break free as another hydrogen bonds with the carbon
5) There is now a space on the surface of the nickel catalyst for the new reactant molecules