Thermal effects on gas transport in catalytic membranes

In chemical engineering, heterogeneous catalysts are of central importance in numerous fields of application involving chemical energy conversion and storage. They make a significant contribution to the production of chemicals and to technical measures for environmental protection. A prerequisite for the efficient use of these mostly cost-intensive catalytic materials is the uninterrupted transport of reactants to and products from the catalyst surface, where the reaction is catalyzed and thus initiated.

Under real reaction conditions, however, the transport processes within a reactor often deviate significantly from the ideal case. In particular, the diffusion of gas molecules within the boundary layer is often slower than the chemical reaction itself, so that mass transport rather than kinetics limits the conversion rate. The targeted improvement of transport properties within such boundary layers therefore represents a central challenge in catalytic research and forms the core of this research project.

The focus is on the use of a physical phenomenon known as the Knudsen pumping effect (KPE) to specifically improve gas transport. Using ethene hydrogenation as a model reaction, the influence of this effect on reaction rates will be investigated experimentally. Under diluted gas conditions, KPE enables the directed transport of gas molecules from cold to hot areas and thus against a temperature gradient generated on a solid body. Although the Knudsen Pumping Effect has already been the subject of numerous fundamental studies, this project aims to transfer this physical phenomenon to an application-oriented environment. In a first step, the effect will be detected in a continuously flowing reactor using magnetic resonance imaging (MRI) as an imaging method, and the optimal conditions for its occurrence will be systematically investigated. In a further step, KPE will be used specifically to actively transport the reactants of ethene hydrogenation to the hot catalyst surface and overcome existing mass transport limitations.