Animation showing the hydrogenation of a double bond on a metal catalyst. Hydrogenation is a reaction in which a carbon-carbon double bond is broken and replaced by two hydrogen atoms. It is performed industrially on a large scale, usually to hydrogenate vegetable oils to more solid fats. In this animation, a molecule of ethene (C2H4) is seen binding to the atoms on the metal surface, breaking its double bond. A hydrogen (H2) molecule does the same, forming two hydrogen atoms. One of these then attaches to one of the bound carbon atoms, freeing that end of the molecule, before the second hydrogen attaches to the other carbon, liberating the hydrogenated molecule, ethane (C2H6). In the food industry, nickel is often used as the catalyst.