3 results
Now showing1 - 3 of 3
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Exploring structure, temperature and activity correlations in the selective oxidation of lower olefins over Bi-Mo-Co-Fe-O catalysts by spatial reactor profile measurements(Royal Society of Chemistry (RSC), 2024-01-16); ; Improving process efficiency in selective oxidation of lower olefins over mixed metal oxide catalysts requires profound knowledge of the dynamic behaviour of exothermic reactions along the reactor. For this purpose, structure-activity correlations of two Bi-Mo-Co-Fe-O model catalysts were investigated by means of structure, temperature and activity profiling in selective propylene and isobutene oxidation. Both catalysts showed pronounced differences in selectivity, which strongly affected the temperature and gas phase concentration gradients along the reactor, and thus the reaction network of each olefin oxidation process. Complementary structure profiling by synchrotron XRD identified the evolution of crystalline metal oxide phases after testing in propylene oxidation. Molybdate-based structures (e.g., α-Bi2Mo3O12, Bi3FeMo2O12) were found to moderate oxygen mobility during catalytic reaction and increase selectivity towards acrolein/methacrolein, while particularly single metal oxides (i.e., Co3O4, Fe3O4) enhanced oxygen mobility drastically and favoured total oxidation. Comparison of selective propylene and isobutene oxidation revealed the metal oxide phase ensembles within each catalyst had comparable effects on both reaction networks. Hence, the spatially-resolved testing and characterization allowed a systematic study of the catalytic processes along the reactor, showing great promise for knowledge-based optimization of selective oxidation processes.Publicationtype: Journal ArticleScopus© Citations 2 32 79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Exploring catalyst dynamics in a fixed bed reactor by correlative operando spatially-resolved structure-activity profiling(Elsevier, 2022-04); ; ; ; 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.Publicationtype: Journal Article158 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Aging of a Pt/Al2O3 exhaust gas catalyst monitored by quasi in situ X-ray micro computed tomography(Royal Society of Chemistry (RSC), 2014-12-15); ; ; ; Catalyst aging effects were analyzed using X-ray absorption micro-computed tomography in combination with conventional characterization methods on various length scales ranging from nm to mmto gain insight into deactivation mechanisms. For this purpose, a 4 wt% Pt/Al2O3 model exhaust gas catalyst was coated on a cordierite honeycomb and subjected to sequential thermal aging in static air at 950 C for 4, 8, 12 and 24 hours. The aging was followed on the one hand by traditional methods, i.e. CO-oxidation activity, scanning and transmission electron microscopy (SEM, TEM), and X-ray diffraction (XRD). On the other hand, all intermediate aging steps were captured by X-ray absorption micro-computed tomography (m-CT) with 1.27 mm voxel size using a quasi in situ approach as complementary tool. The m-CT data allowed comparing exactly the same position after each treatment using a special alignment procedure during data analysis which took into account that the sample was remounted on the sample holder. A growth of the initially nanometer-sized Pt particles into larger crystals as well as its agglomeration was found, preferentially in voids between support grains. Sintering occurred especially around the larger particles, which is in line with the Ostwald ripening mechanism reported for this system on a nanometer scale. The distribution of chemical elements in an embedded and mechanically cross-sectioned honeycomb was additionally mapped by an electron probe micro analyzer (EPMA), which in agreement to the m-CT results shows no diffusion of Pt into the cordierite. Together with studies on the nanometer scale, these results allow a more thorough multi-scale modeling of exhaust gas catalysts, especially also during aging.Publicationtype: Journal Article250 651