CHE 598 Seminar: Rate-and-Selectivity Oscillations in the Fischer Tropsch Reaction
About the event
SPEAKER: Norbert Kruse, Emeritus Professor, Voiland School of Chemical Engineering and Bioengineering, WSU
BIOGRAPHY:
Norbert Kruse studied Chemistry and Chemical Engineering at the Technical University of Berlin, Germany, and graduated with a PhD in Chemical Engineering in 1980 after a thesis at the Fritz Haber Institute of the Max Planck Society. After his habilitation he became a university lecturer in Marseille, France, and ETH Zurich, Switzerland, before accepting a full professorship in 1994 for “Chemical Physics of Materials” at the Free University (ULB) in Brussels, Belgium. He was awarded the title of a First Officer of the King of Belgium in 2012. In 2013 he was appointed Voiland Distinguished Professor at the Washington State University in the USA and became a Fellow of the Pacific Northwest National Laboratories. He served as an Editor-in-Chief of the Catalysis Letters and Topics in Catalysis from 2009 to 2013. From 2008 to 2014 he was the President of the International Field Emission Society and since 2015 he is an Inaugural Fellow of this Society. He retired from WSU in 2022 and is now an invited professor at ULB in Belgium.
ABSTRACT:
Catalytic reactions occur far from equilibrium and may therefore exhibit multiple steady states leading to hysteresis or even oscillatory behavior and chaos. Different levels of complexity may be encountered depending on the catalyst formulation and the choice of the control parameters. The most detailed insight into oscillatory reaction kinetics and their feedback mechanisms was so far obtained in single crystal work under low pressure conditions. Oscillatory behaviors in studies of catalyst powders at atmospheric pressure conditions usually imply a considerably higher level of complexity because heat and mass transport limitations may come into play and mask the possible influence of surface chemistry and reconstruction effects for feedback control. To demonstrate the level of complexity in oscillatory behaviors, we start by looking into earlier single crystal work in which rate oscillations were observed at low pressures under strictly isothermal conditions using imaging techniques that provide nanoscale spatial resolution to identify local oscillators and there coupling through surface diffusion. Next, we move to the case of rate-and-selectivity oscillations of the Fischer-Tropsch reaction (FT) over Co-based powder catalysts. These oscillations are non-isothermal and self-sustained for many hours time-on-stream depending on the catalyst composition and the choice of the vector gas (Ar or He) in H2/CO flows. The thermokinetic origin of rate-and-selectivity oscillations in FT synthesis can be demonstrated by phase portraits from extended time series of reactants and products. Rate-and-selectivity oscillations have been modeled with a kinetic scheme based on the CO insertion mechanism for hydrocarbon chain lengthening, the thermal activation of C–O bond breaking, and periodic temperature forcing. The agreement between experimental results and theoretical modelling is excellent.