High-Throughput Kinetic Study of Hydrogenation over Palladium Nanoparticles: Combination of Reaction and Analysis

The hydrogenation of 1‐acetylcyclohexene, cyclohex‐2‐enone, nitrobenzene, and trans‐methylpent‐3‐enoate catalyzed by highly active palladium nanoparticles was studied by high‐throughput on‐column reaction gas chromatography. In these experiments, catalysis and separation of educts and products is integrated by the use of a catalytically active gas chromatographic stationary phase, which allows reaction rate measurements to be efficiently performed by employing reactant libraries. Palladium nanoparticles embedded in a stabilizing polysiloxane matrix serve as catalyst and selective chromatographic stationary phase for these multiphase reactions (gas–liquid–solid) and are coated in fused‐silica capillaries (inner diameter 250 μm) as a thin film of thickness 250 nm. The palladium nanoparticles were prepared by reduction of palladium acetate with hydridomethylsiloxane–dimethylsiloxane copolymer and self‐catalyzed hydrosilylation with methylvinylsiloxane–dimethylsiloxane copolymer to obtain a stabilizing matrix. Diphenylsiloxane–dimethylsiloxane copolymer (GE SE 52) was added to improve film stability over a wide range of compositions. Herein, we show by systematic TEM investigations that the size and morphology (crystalline or amorphous) of the nanoparticles strongly depends on the ratio of the stabilizing polysiloxanes, the conditions to immobilize the stationary phase on the surface of the fused‐silica capillary, and the loading of the palladium precursor. Furthermore, hydrogenations were performed with these catalytically active stationary phases between 60 and 100 °C at various contact times to determine the temperature‐dependent reaction rate constants and to obtain activation parameters and diffusion coefficients. Active service: Hydrogenation over highly active Pd nanoparticles has been studied by synchronous catalysis and separation in microcapillaries (see picture). High‐throughput reaction‐rate measurements of reactant libraries show that the size and morphology of the nanoparticles and hence the catalytic activity depends on the ratio of the two stabilizing polysiloxanes, the activation temperature, and the loading of the Pd precursor.