Hydrogenation

Addition of hydrogen to an unsaturated substrate. Catalyst and conditions determine which unsaturated groups are reduced; the mere presence of H2 does not guarantee chemoselectivity.

A porous nickel catalyst prepared by selective removal of aluminium from a nickel–aluminium alloy. It can catalyse hydrogenations; its use does not guarantee that every other reducible functional group will remain unchanged.

Reduction using hydrogen and a catalyst. Selectivity depends on the catalyst, pressure, solvent and functional groups: reducing an alkene while retaining a ketone is a distinct requirement from reducing a nitrile while retaining an ester.