Exploring catalyst dynamics in a fixed bed reactor by correlative operando spatially-resolved structure-activity profiling
Efficient and sustainable optimization of heterogeneous catalytic processes requires a deep understanding of catalyst structure-activity relationships that occur inside catalytic reactors in space and time. Here we introduce a catalytic profile reactor capable of simultaneously measuring spatially-resolved temperature, concentration, and X-ray absorption spectroscopy (XAS) profiles through a catalytic fixed bed. Using the oxidative dehydrogenation of ethane to ethylene over MoO3/γ-Al2O3 as a test reaction, we obtained a detailed picture of local catalyst structure and activity under realistic and well-defined reaction conditions. Concentration, temperature and XAS profiles were measured up to and beyond the point of complete O2 consumption showing a distinct transition from oxidation reactions to steam reforming and water-gas shift. Profile data up to the point of complete O2 consumption were used to develop a kinetic model for the oxidation chemistry. Structural data beyond the point of complete O2 consumption were ideal for demonstrating the correlative approach but the kinetic data in the second part were not considered during modeling because industrial selective oxidation reactors are always operated at incomplete O2 consumption. The fit of kinetic models to complete reactor profiles significantly speeds up the development and accuracy of kinetic models required for any reactor design. Further, the kinetic model considers the oxidation state of molybdenum as a dynamically changing and critical catalyst property. Hence, we could predict local catalyst oxidation states and validate our model experimentally with spatially-resolved XAS. This provides a quantitative link between catalyst structure and reactivity and allows including catalyst dynamics in reactor simulations. In the current work a widely applicable methodological approach is presented to understand and optimize heterogeneous catalytic processes, e.g. in selective oxidation.
Spatial profile measurements
000: Allgemeines, Wissenschaft