Hydrogenation of Renewables

Hydrogenation reactions have a variety of applications in the chemical industry which is shown by the corresponding products, such as ammonia, methanol, and polyamides. In petrochemistry, the addition of hydrogen is used to adjust properties of product mixtures, e.g. in the hydrocracking or hydrotreating. For renewables the same is already feasible or first proofs of concept were already shown. Therefore, hydrogenations indicate ways to increase the availability and enhance handling of products from natural resources. Heterogeneously catalysed hydrogenations with renewables are realised already in big scale, e.g. in the production of margarine or sorbitol. In general, hydrogenation is the addition of hydrogen to C–C-, C–O-, C–N-, or N–O-multiple bonds. If the bond is broken, the reaction is referred to as hydrogenolysis [1]. Hydrogenation reactions are usually exothermic; therefore, low temperatures favour the reaction over its corresponding back reaction, which is dehydrogenation (Fig. 2.1). Hydrogenations on industrial scale are mostly heterogeneously catalysed but lack of reactivity at mild reaction conditions or selectivity. Therefore, homogeneous catalysed hydrogenations are needed for more specialised reactions, which are required for the valorisation of renewables. Common catalyst metals for homogeneous hydrogenations are platinum, palladium, rhodium, iridium, and ruthenium. But also non-precious metal systems as nickel, copper and other transition metals, such as molybdenum and cobalt have found applications in industrial processes. Frequently used homogeneous catalyst complexes in hydrogenation are as follows: