High‐Throughput Screening of Catalysts by Combining Reaction and Analysis

Abstract

Dedicated to Süd-Chemie on the occasion of its 150th anniversaryDiscovering new catalysts is crucial to the development of sustainable chemical processes for industrial applications as well as for broadening the spectrum of synthetic methodologies and techniques in chemistry. The prerequisite for the directed design of catalysts is understanding how the kinetics, in other words, the activation barrier, in the mechanism of catalysis is controlled by the structural parameters.[1] To identify rate-determining elementary steps and to develop models, comprehensive experimental kinetic data of a broad variety of substrates are necessary. Microfluidic devices integrating chemical synthesis and analysis on the same chip [2][3][4][5] are one promising approach for parallelized highthroughput (ht) kinetic measurements of catalysts with minute material consumption.[6] A unique technique for studying configurational changes in chiral compounds is dynamic chromatography [7] combining molecular interconversion and analysis under precisely controlled conditions. Recently, we reported [8] a unified equation to directly access reaction rate constants of first-order reactions of such experiments. However, commonly used (micro)reactors, in which the reaction, separation, and quantification of conversion are performed consecutively, are limited to the study of single reactions, because competing reactions lead to undefinable reaction kinetics. Here we show for the hydrogenation over highly active Pd nanoparticles and the ring-closing metathesis over the Grubbs second generation catalyst that the synchronous combination of catalysis and separation makes it possible to efficiently perform ht reaction rate measurements (147 reactions per hour) of substrate libraries. The catalytic systems for these multiphase reactions (gas-liquid-solid) were prepared by embedding the catalysts in polysiloxanes, which serve as both solvent and selective stationary separation phase. Furthermore this system can be used for cascade reactions or for preparative synthesis to produce the target compounds.Typically, multiphase catalytic systems, which play a predominant role in industrial processes, are difficult to investigate because the interaction of the substrate with the catalyst is controlled by the mass transfer between the different phases, and therefore the apparent reaction rate is composed of the inherent reaction rate and diffusion rates. To reduce this effect, the interfacial area must be increased. Microstructured reaction systems intrinsically have a high specific interfacial area per volume, only dependent on the radius of the reaction channels; that is, for capillaries with inner diameters between 250 and 100 mm the specific interfacial area per volume ranges from 16 000 to 40 000 m 2 m À3 . Microfluidic systems are currently revolutionizing chemical synthesis, [9][10][11][12][13] because physical processes can be more easily controlled, low operation volumes minimize reagent consumption, and detection is integrated.[14] However, there are s...

The stereodynamics of 1,2‐dipropyldiaziridines

“…This equation is an analytical solution of the theoretical plate model and is superior in precision to any computer simulation where errors arise from the imprecision of billions of floating point operations. The unified equation also opened the field to study catalytic reactions by on-column reaction chromatography [48][49][50][51][52] in a high-throughput fashion. 53 …”

Nanocatalysis in Flow

“…[81] Polysiloxanes combine catalysis and separation within the same material;t hus allowing fast reactionr ate measurements of substrate libraries. Palladium NPs were prepared by embedding the catalysts in the polymeric matrix, as outlined in Scheme 9.…”

Development of Batch and Flow Immobilized Catalytic Systems with High Catalytic Activity and Reusability

“…[92][93][94][95][96][97][98] Molecular organic transformations with heterogeneous catalystimmobilized flow microreactors are representative examples of these systems, where the efficiency of various organic transformations has been found to increase due to the vast interfacial area and the close distance of the molecular diffusion path in the narrow space of the flow microreactor. [99][100][101][102][103][104][105][106][107][108][109][110] If a heterogeneous catalyst was immobilized as a membranous composite at the interface of an organic layer and aqueous layer (the center of the microchannel), two reactants could be oppositely charged into and flow through the divided channel, all the while in contact with the vast interfacial surface of the catalytic membrane from both front and back sides, thereby realizing an instantaneous chemical reaction. This concept is shown schematically in Fig.…”