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

Abstract

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 microm) 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 degrees C at various contact times to determine the temperature-dependent reaction rate constants and to obtain activation parameters and diffusion coefficients.

P-Stereogenic Phosphines for the Stabilisation of Metal Nanoparticles. A Surface State Study

“…Elemental analyses indicated that the Pd/L ratio found on the isolated PdNPs was: Pd/L1 = 1/0.27 and Pd/L2 = 1/0.50 (corresponding to a ratio Pd/L at the surface PdL10. 4 and PdL20.8). Concerning RuNPs, small nanoparticles were also obtained, with a mean diameter of 1.0 and 1.2 nm for RuL1 and RuL2, respectively.…”

“…Elemental analyses indicated that the Ru/L ratio found on the isolated RuNPs was: Ru/L1 = 1/0.56 and Ru/L2 = 1/0.46 (corresponding to a ratio Pd/L at the surface PdL10. 4 and PdL20.8).…”

“…The synthesis of MNPs was also run with borane-free L2 with both metal precursors, [Pd2(dba)3] and [Ru(COD)(COT)] (under the same conditions than those described above using a metal/ligand The formation of PdNPs was also monitored by the intensity decrease of the corresponding 31 P and 11 B NMR signals, in addition to the disappearance of the 1 H NMR ligand signals (see Figure S6 in the Supplementary Materials); other signals corresponding to molecular palladium species could be also observed, together with the formation of free BH 4 − , which indicates that the ligand adsorbed on the surface corresponds to the BH 3 -free phosphine. In the case of the formation of RuNPs, the differences in intensity of 31 P and 11 B NMR signals were less perceptible (see Figure S7 in the Supplementary Materials).…”

“…Even if more and more organic transformations are using metal nanoparticles (MNPs) as catalysts [1][2][3][4][5][6], few of them concern enantioselective processes (for selected reviews, see [7][8][9][10]). The enantioselective catalysis on surfaces is commonly explained by three main mechanisms: the presence of chiral crystalline atomic structures at the surface, chiral adsorbates which modify the surface and chiral modifiers which control the approach of the substrate on the surface [11,12].…”

Investigation of the Hydrogenation of 5‐Methylfurfural by Noble Metal Nanoparticles in a Microcapillary Reactor

“…These catalytic systemsw ere recently characterized in detail in our studies. [13,17,18] We reported the high activity of the Ru nanoparticles in combination with ap ronounced CO chemoselectivity.H igh turnover numbers( TONs) of up to 60 000 correlated well with more than 200 catalytic cycles corresponding to ar eaction time of about 5s.[13] Therefore, we assumethat Ru nanoparticle catalysts should provide the selective conversion of 1.S imultaneously,P di sw ell known as highlya ctive catalysti nt he total hydrogenation of furfural derivatives. [4,5,8] Ru andPdnanoparticles were prepared by the previously established method.…”