Hydrogenation is a chemical reaction in which hydrogen atoms add to carbon-carbon multiple bonds. In order for the reaction to proceed at a practical rate, a catalyst is almost always needed. Hydrogenation reactions are used in many industrial processes as well as in the research laboratory, and occur also in living systems.

Hydrogen gas, H₂, can react with a molecule containing carbon-carbon double or triple bonds known as an unsaturated compound. In its simplest form, a molecule with one double bond would react with one molecule of hydrogen gas. An example is shown in Figure 1.

Some carbon compounds have triple bonds and need two molecules of hydrogen to completely saturate the carbon compound with hydrogen (Figure 2).

Hydrogenation of a double or triple carbon-carbon bond will not occur unless the catalyst is present. Scientists have developed many catalysts for this kind of reaction. Most of them include a heavy...