When nickel is the catalyst for the hydrogenation of ethene, the reactants are absorbed onto the surface.

1
Transition metals make good heterogeneous
catalysts because of their 4s and 3d electrons.
A catalyst speeds up a reaction because it
decreases the enthalpy change for the reaction.
Transition metal ions make good homogeneous
catalysts because of their variable oxidation
states.
When nickel is the catalyst for the hydrogenation
of ethene, the reactants are absorbed onto the
surface.
The catalyst in a catalytic converter is a
homogeneous catalyst.