Hyrogenation is a reductive chemical reaction which results in an addition of hydrogen (H2) usually to saturate organic compounds. The process constitutes the addition of hydrogen atoms to the double bonds of a molecule through the use of a catalyst. Hydrogen also adds to triple bonds if they are present. Typical substrates include alkenes, alkynes, ketones, nitriles, and imines. Most hydrogenations involve the direct addition of diatomic hydrogen (H2) but some involve the alternative sources of hydrogen, not H2: these processes are called transfer hydrogenations. The reverse reaction, removal of hydrogen, is called dehydrogenation. A reaction involving hydrogen and cleavage of a carbon-oxygen bond or carbon-nitrogen bond is called Hydrogenolysis. Hydrogenation differs from protonation or hydride addition (e.g. use of sodium borohydride): in hydrogenation, the products have the same charge as the reactants.