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What Is Catalytic Hydrogenation?

Hydrogenation is one chemical process which has had a fairly large impact on people's day-to-day life. In the last century, chemists discovered that, by using catalytic hydrogenation, they could change the molecular structure and the physical properties of vegetable oils, to make them easier to use for margarine and other foods. Today scientists know that hydrogenated oils may have health issues, but hydrogenation is still used for some food products as well as different applications, such as coal processing.

Unsaturated Chemicals
- In chemistry, organic molecules are those which have carbon as their main component element. Each carbon atom in these compounds can bond with up to four other atoms. Often each carbon bond either to another carbon or to a hydrogen atom in a simple chain such as CH3CH2CH2CH3. Double bonds can also exist between adjacent carbons, however, such as CH3CH2CH=CHCH3. Since such chemicals do not contain as much hydrogen as they possibly could, they are known as "unsaturated." Chemists also call these "alkenes."
Hydrogenation
- It is possible to add hydrogen to unsaturated molecules to create saturated chemicals instead. This is done by simply mixing the alkene with hydrogen gas (H2). The reaction occurs through a complex mechanism where one of the two bonds between the carbons breaks open and the H2 molecule also splits. One hydrogen then adds to each carbon on either side of what was the double bond. The result is a single bond between the two carbons and an extra hydrogen on each.
Catalysis
- Every reaction has what is known as an activation energy, which is the energy two molecules must have in order to react. A very high activation energy can make it almost impossible for a reaction to happen, which is where catalysts come in. A catalyst is a chemical which speeds up a reaction without itself being consumed. Catalysts work by lowering the activation energy required, for example by providing a surface on which a reaction can take place more easily.
Catalytic Hydrogenation
- In hydrogenation, the activation energy is very high and so this reaction will not take place very readily without using special conditions, such as very high temperature and pressure. However, if a small amount of a metallic compound based on palladium, platinum or nickel is added to the alkene/hydrogen mixture, the hydrogenation reaction occurs much more readily. The metal acts as a catalyst for this reaction. Catalytic hydrogenation is therefore the addition of hydrogen to an unsaturated chemical compound using a metal catalyst to speed up the reaction.

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