Optimized Palladium on activated carbon formulation for N-hydrogenolysis reactions
Palladium on carbon (Pd/C) is by far the most commonly used catalyst in hydrogenolysis process steps. Since the palladium price is increasing strongly, this reaction was investigated in some detail aiming to map the parameters important to the catalyst efficiency, ultimately to bring down the palladium metal usage and costs. N-benzyl piperidine was selected as a model substrate, representing a large range of relevant intermediates in fine-chemical processes. For this reaction, it is found that the application of a pre-reduction step significantly decreased the activity of the catalyst. Catalyst optimization is also done by the choice of carbon type and by optimizing the palladium metal dispersion. This resulted in an optimized 3% Pd/C formulation that showed superior N-hydrogenolysis activity. This formulation is compared to other catalysts in several solvents. Also, functional group effects are investigated on the N-piperidine ring.
The application of carbon supported palladium catalysis in fine chemical applications is widespread (1). In 10 to 15% of all the preparation pathways described in the “Thomson-Reuters-Integrity” database palladium on carbon is used as a catalyst (2). In comparison, Pt/C is only used in ~1% and Rh/C only in ~0.2% of the cases. The majority of Pt/C applications related to nitrate reductions, some alkene hydrogenations (especially to Michael systems) and a range of niche applications were found. Rh/C is mainly used for the hydrogenation of specific aromatic rings. In some cases also alcohol oxidations are applied using Rh/C. Looking at the applications for Pd/C usage the next 6 mostly applied applications could be defined:
- O- and N-