Torsten Zech

Miniaturization of screening devices for the combinatorial development of heterogeneous catalysts

The present work is focused on the determination of the advantages, bottlenecks and challenges of miniaturized screening systems which are essential to the success of combinatorial high-throughput methodologies in heterogeneous catalysis. Two different reactor configurations with different degrees of miniaturization were developed for the parallel and fast screening of heterogeneously catalyzed gas phase reactions: a monolithic reactor system acting as a multichannel reactor and a microreaction system based on microfabrication techniques. In both cases, a scanning mass spectrometry technique was successfully applied for quantitative product analysis within 60 s per catalyst. Due to its flexibility and high spatial resolution, this three dimensional scanning MS can be used with different and highly parallel reactor arrays. Many experiments were carried out to study the efficiency and reliability of the different screening systems, with the oxidation of methane, the oxidation of CO, and the oxidative dehydrogenation of i-butane as model reactions. Moreover, chip modules in silicon–glass technology having a number of parallel microchannels were developed, each of them containing a different catalyst. Using this approach, “catalysis-on-a-chip” proved in methane oxidation was possible. Finally, a multibatch reactor consisting of a number of parallel mini autoclaves was developed and tested in the liquid-phase hydrogenation of citral in order to overcome the lack of parallel and fast screening procedures for heterogeneously catalyzed gas–liquid reactions widely spread in the chemical industry.

Simultaneous Screening of Catalysts in Microchannels: Methodology and Experimental Setup

Given the excellent properties of microfluidic reactors our project aims to develop a fast and parallelized catalyst screening unit. In a first step the channel- walls of microstructured wafers are coated with catalytic active species. For the screening of catalytic properties a stack of 35 catalyst wafers is operated under steady-state conditions and continuous flow. Each wafer is exposed to the same amount of reactant gases at the same time, temperature and pressure. The product analysis is carried out using mass spectrometry for each catalyst wafer in order to gain full chemical information of the product distribution, conversion degrees and selectivities. A fast, sequentially sampling device is used to sample each catalyst wafer at least every 60 minutes.