Hydrogenation


The catalytic hydrogenation is the largest application of homogeneous catalysis in industry. For the addition of hydrogen to unsaturated compounds (like alkenes, alkynes, ketones, nitriles, and imines) mainly Platinum, Palladium, Rhodium (Wilkinson's catalyst), Ruthenium and Iridium (Crabtree's catalyst) are used. The mechanism using the Wilkinson catalyst RhCl(TPP)3 is shown in the following figure.

The Wilkinson mechanism

If the hydrogenation catalyst is modified with a chiral diphosphine ligand, enantioselective hydrogenation of double bounds can be achieved with high selectivity. The Nobel Prize for chemistry in 2001 was rewarded for the development of such chiral catalyst complexes to W.S. Knowles, R. Noyori and K.B. Sharpless. Today, a plethora of chiral ligands exists, sometimes tailor-made for the desired reaction.
In two research projects, the SILP technology is applied for hydrogenation reactions. In the selective hydrogenation of arenes and conjugated double bonds both in slurry and fixed bed reactors the selectivity toward intermediates is the major goal.

Reaction network for the selective hydrogenation of aromatic compounds using heterogeneous Ru catalysts.

The catalysts used in this study are mainly based on Raney Nickel and Palladium on porous support. When using Raney Nickel, the ionic liquid film acts as a diffusion barrier for oxygen and moisture, thus preventing the ignition of the pyrophoric catalyst. The coating has been patented recently.
When using Palladium catalyst on porous supports the ionic liquid film can enhance selectivity toward the intermediate species by acting as an extraction medium for the intermediate, thus lowering the concentration around the metal centre. First results from batch slurry experiments verified the applicability of the SILP concept for these systems.

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