Klink, Miriam
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Klink, Miriam
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Klink, Miriam
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Klink, M.
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Item type:Publication, The origin of a large apparent tortuosity factor for the Knudsen diffusion inside monoliths of a samaria-alumina aerogel catalyst: a diffusion NMR study(RSC, Royal Society of Chemistry, 2015-09-23); ; ; ; Pulsed field gradient (PFG) NMR was applied to measure tortuosity factors for carbon dioxide diffusion in the Knudsen and gas regimes inside monoliths of a samaria-alumina aerogel catalyst, a high porosity material containing micropores in addition to meso- and macropores. The apparent tortuosity factor obtained from PFG NMR measurements for the Knudsen diffusion in the meso- and macropores of the catalyst has an unexpectedly large value of approximately 6 if carbon dioxide adsorption in the micropores and other types of surface adsorption sites of the catalyst is ignored. At the same time, the corresponding apparent tortuosity factor in the gas regime was found to be around 2. Application of a proposed model which describes fast molecular exchange between the surface adsorption sites and the main pore volume of the catalyst yields corrected tortuosity factors which depend only on the pore system geometry. Using this model, the corrected tortuosity factors were found to be around 2 for both diffusion regimes, in agreement with the expectations based on a high porosity of the studied catalyst.journal article83 119 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, NMR imaging of gas phase hydrogenation in a packed bed flow reactorIn situ analysis of heterogeneously catalyzed gas phase reaction systems is becoming a valuable aid to their modeling and optimization. The commonly applied methods are either invasive, do not provide spatial information or are not applicable for optically inaccessible systems. This work investigates the possibility to use NMR imaging to study gas phase reaction processes in situ, spatially resolved and non-invasively. A multislice NMR spectroscopic imaging pulse sequence, which was optimized to realize ultrashort echo time TE, was employed to study the ethylene hydrogenation reaction in an NMR-compatible packed bed flow reactor. The catalyst bed, containing inactive γ-Al2O3 pellets and Pt-Al2O3 pellets, was subdivided into several sections in order to identify reaction zones that depend on initial conditions. Spatial mapping of the chemical composition was demonstrated on the basis of two experiments with varying initial volume flow and ethylene conversion. The inlet and outlet temperature of the catalyst bed was simultaneously detected by analyzing the spectra of inserted glycol capsules. The resulting spatial shift of the reactive zones in both experiments could be proven by the spatially resolved concentration measurements and the temperature measurements. The locations of single active catalyst pellets were also detectable by the same measure. The quantitative results of product gas composition of both experiments were in good agreement with accompanying mass spectrometric measurements. The results demonstrate the applicability of NMR imaging methods to investigate gas phase reaction processes and can help to establish these methods as a standard tool to map chemical transformations in gas flow reactors.journal articleBand:502142 157