Solvent-Free Hydrogenation of Squalene Using Parts per Million Levels of Palladium Supported on Carbon Nanotubes: Shift from Batch Reactor to Continuous-Flow System.

The transition from batch catalytic processes to continuous flow processes requires highly active and stable catalysts that still need to be developed. The preparation and characterization of catalysts where palladium single atoms and nanoparticles are simultaneously present on carbon nanotubes were recently reported by us. These catalysts are considerably more active than commercial or previously described catalysts for the liquid phase hydrogenation of terpenes. Herein is shown that under solvent-free conditions, squalene (SQE) could be converted into squalane (SQA,>98 %) using only 300 ppm of Pd in less than 1.4 h at 20 bar H2 and 120 °C. Catalyst stability was assessed in a lab-scale flow reactor, and long-term experiments led to turnover number (TON) higher than 300000 without any detectable loss in the activity. Then, the implementation of this catalyst in a commercial intensified continuous-flow milli-reactor pilot was achieved. High purity SQA (>98 %) could be obtained by continuous hydrogenation of solvent-free SQE at 180 °C and 30 bar H2 with a contact time below 15 min. A production capacity of 3.6 kg per day of SQA could be obtained with an effective reactor volume (VR ) of 43.2 mL for this complex 3 phase reaction. Large-scale production can now be foreseen thanks to seamless scale-up provided by the continuous flow pilot supplier.

Reinvestigation of the Organocatalyzed Aerobic Oxidation of Aldehydes to Acids.

The organocatalyzed aerobic oxidation of aldehydes to acids was reproduced from the original report. In- and ex-situ analysis of the reaction mixture as the function of time reveals that, unlike the claim in the publication, the aerobic oxidation of aromatic and aliphatic aldehydes leads predominantly to the formation of peracids. The latter are transformed into the corresponding carboxylic acids during the workup procedure. The buildup of peracids in solution poses safety problems that should not be overlooked. This finding has also an influence on the way new catalysts are investigated to improve this reaction as well as on aerobic aldehyde-mediated co-oxidation.

Platinum nanoparticles in suspension are as efficient as Karstedt's complex for alkene hydrosilylation.

Colloidal suspensions of monodisperse platinum nanoparticles of 2 nm diameter have been used to catalyze the hydrosilylation of 1-octene with a polymethylhydrosiloxane. The nanoparticles were found to be as efficient as Karstedt's complex, showing that colloid formation from homogeneous species during hydrosilylation reactions is not necessarily a deactivation pathway. These results also reactivated the debate on whether Karstedt's complex was truly homogeneous or colloidal during catalysis.

A safe and efficient flow oxidation of aldehydes with O2.

A safe, straightforward, and atom economic approach for the oxidation of aliphatic aldehydes to the corresponding carboxylic acids within a continuous flow reactor is reported. Typically, the reaction is performed at room temperature using 5 bar of oxygen in PFA tubing and does require neither additional catalysts nor radical initiators except for those already contained in the starting materials. In some cases, a catalytic amount of a Mn(II) catalyst is added. Such a flow process may prove to be a valuable alternative to traditionally catalyzed aerobic processes.

High throughput screening and evolution of a library of ligands in asymmetric H-transfer reduction of acetophenone.

A library of 117 ligands was combined with three transition metals Ru, Rh and Ir and screened with three different operating conditions for the asymmetric H-transfer reduction of acetophenone into phenylethanol. The combinatorial approach was based on evolution of a first library containing 60 ligands. For the evolution, operators such as replication, regression, cross-over and mutation were used. The study was performed with a XYZ robot and fast chiral GC analysis. Over only 4 generations, the average targeted criterion, enantioselectivity, was increased from 20% to ca. 80% for the 4th generation. The best results provided enantiomeric excess up to 93%.

Design of a genetic algorithm for the simulated evolution of a library of asymmetric transfer hydrogenation catalysts.

A library of catalysts was designed for asymmetric-hydrogen transfer to acetophenone. At first, the whole library was submitted to evaluation using high-throughput experiments (HTE). The catalysts were listed in ascending order, with respect to their performance, and best catalysts were identified. In the second step, various simulated evolution experiments, based on a genetic algorithm, were applied to this library. A small part of the library, called the mother generation (G0), thus evolved from generation to generation. The goal was to use our collection of HTE data to adjust the parameters of the genetic algorithm, in order to obtain a maximum of the best catalysts within a minimal number of generations. It was namely found that simulated evolution's results depended on the selection of G0 and that a random G0 should be preferred. We also demonstrated that it was possible to get 5 to 6 of the ten best catalysts while investigating only 10 % of the library. Moreover, we developed a double algorithm making this result still achievable if the evolution started with one of the worst G0.

Gas-liquid selective oxidations with oxygen under explosive conditions in a micro-structured reactor.

The gas-liquid oxidation of cyclohexane is performed at high temperature (>200 degrees C) and pressure (up to 25 bar) using pure oxygen in a Pyrex capped silicon etched microreactor which allows convenient screen reaction conditions well above the flammability limit.

Gas-liquid and gas-liquid-solid catalysis in a mesh microreactor.

A microstructured mesh contactor that can offer residence time of more than minutes is used for gas-liquid-solid hydrogenations and gas-liquid asymmetric hydrogenations. Applications for catalyst/chiral inductor screening and for kinetic data acquisition are demonstrated.