Parallel Fixed Bed Microreactors for High-Throughput Screening with Special Focus on High Corrosion Resistance and New Deacon Catalysts for Chlorine Production

In this contribution we give an overview of the developments published during the last decade on truly parallel or fast sequential fixed bed microreactors for primary or secondary high-throughput screening of heterogeneous catalysts. After a review part we focus on our own parallel reactor setups developed for the discovery and optimization of new Deacon catalysts. In hydrogen chloride recycling this oxidation reaction is energetically highly attractive, but due to extreme corrosivity of reactant / product mixtures it poses a formidable challenge on the materials of the screening reactor. The problem was solved by constructing a new parallel microreactor setup built from corrosion resistant Nibased alloys together with gas flow restriction by adjustable capillaries for a uniform gas distribution, and back pressure valves for elimination of cross contamination between the parallel reactors. Apart from catalyst screening, the setups have been used to perform ageing studies of the catalysts identified as active for the Deacon reaction. In chlorine production either by electrolysis or by the Deacon reaction, both catalyst systems contain RuO2 as essential component. RuO2 is a metallic conductor, chemically very stable in corrosive environments, but due to its low abundance its market value is subject to pronounced speculative variations. Thus, one objective of our investigations has been the reduction or even complete replacement of expensive Ru ideally accompanied by a simultaneous activity increase. To discover new Ru-free catalysts for the Deacon reaction a basic search in a wide parameter space was launched. Ru reduction was achieved by doping RuO2 with various elements. The hit and lead compositions identified were characterized by physisorption measurements as well as powder X-ray diffraction together with Rietveld refinements of the diffraction data.

Keywords: High-throughput screening, combinatorial chemistry, parallel plugflow reactor, heterogeneous catalysis, chlorine production, efficiency increase, Deacon, thermography, IR thermography, emission corrected, ecIRT, flow restrictor, sol-gel, alkoxide route, propionic acid route, ethylene glycol route, ageing reactor, Ru5Co95Ox, Ruthenium, precious metal, metal savings, corrosion, mass spectrometry, doping, 10-fold reactor.