Hydrogenation is a chemical process in which hydrogen molecules (H₂ ) are added to unsaturated compounds, usually in the presence of a catalyst, to produce saturated compounds. This conversion reaction is widely used in various industries, such as food production, petrochemicals and pharmaceuticals, as it changes the properties of molecules, improving stability, texture and more.

Basic principles of hydrogenation

At its core, hydrogenation is a reduction reaction. During reduction, the oxidation state of atoms or molecules is reduced. In the hydrogenation of organic molecules, unsaturated compounds such as alkenes (double bonds) or alkynes (triple bonds) are reduced by adding hydrogen atoms. This leads to the formation of saturated compounds, i.e. alkanes, in which all carbon-carbon bonds are single bonds. During the hydrogenation of Fischer-Tropsch products, incorporated heteroatoms such as oxygen are also removed. Some of the hydrogen is split off as free water.

Catalysts and reaction conditions

Hydrogenation reactions are usually carried out with the help of a catalyst that accelerates the reaction without being consumed. Transition metal catalysts such as platinum (Pt), palladium (Pd) and nickel (Ni) are commonly used in hydrogenation processes. The choice of catalyst depends on factors such as reaction selectivity, substrate compatibility and reaction conditions. Catalysts can influence the stereochemistry of the products and the overall efficiency of the process.
Hydrogenation reactions are often carried out under elevated temperature and pressure conditions. The higher the temperature and pressure, the higher the conversion, but the probability of undesirable side reactions also increases. This is particularly true if some functional groups in the molecule are not to be hydrogenated.

Applications of hydrogenation 

Hydrogenation has a wide range of applications in various branches of industry:

Food industry: In the food industry, hydrogenation is used to convert liquid vegetable oils into solid or semi-solid fats using a process known as partial hydrogenation. This process produces partial trans fats, which were once widely used but are now criticized for health reasons. The selectivity in the hydrogenation process controls the formation of trans fats and is therefore minimized in the industry.

Petrochemical industry: In the petrochemical industry, hydrogenation is used to convert unsaturated hydrocarbons, such as olefins, into saturated hydrocarbons. This process can improve the quality and stability of fuels and lubricants.

Pharmaceutical industry: Hydrogenation is crucial in pharmaceutical synthesis as it enables the reduction of functional groups in drug molecules. This allows chemists to control the stereochemistry and bioavailability of drugs, which can affect their efficacy.

Chemical industry: Hydrogenation plays an important role in the production of various chemicals, including ammonia synthesis, which is an important step in the production of fertilizers. Hydrogenation is also used in the production of polymers and other industrial chemicals.

Hydrogenation of carbon dioxide

With increasing concerns about carbon dioxide emissions and global warming, researchers are looking for ways to convert CO₂ into useful products. Hydrogenation reactions are being investigated as a means of converting CO₂ into valuable chemicals such as formic acid, methanol or Fischer-Tropsch products.

Research in the field of hydrogenation is constantly evolving, with a focus on improving catalyst efficiency, selectivity and sustainability. The principles of green chemistry aim to make hydrogenation processes more environmentally friendly by using renewable resources, minimizing waste and reducing energy consumption. In addition, advances in the understanding of reaction mechanisms at the molecular level contribute to the development of more efficient catalysts.