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Item type:Publication, Access status: without files , Resolving gradients in an ammonia oxidation reactor under industrial conditions: A combined experimental and simulation studyThe industrial production of nitric acid by the Ostwald process is a major emission source of the potent green-house gas nitrous oxide that is formed during the catalytic oxidation of ammonia. A systematic knowledge-based optimization of industrial ammonia oxidation, e.g. with respect to minimizing nitrous oxide formation, is hindered by the limited fundamental process understanding resulting from a lack of experimental insight into the reaction at industrial conditions. Here we bridge this gap of knowledge by resolving concentration and temperature profiles in a bench-scale reactor setup under industrial conditions using capillary profile measurements in combination with detailed CFD simulations. The profile measurement technique has a spatial resolution sufficient to resolve the steep gradients around single catalyst gauze wires. The influence of the sampling orifice diameter and reaction conditions on the sampling region and the resulting spatial resolution is discussed. The importance of the sampling orifice to gauze positioning in order to measure well averaged concentration profiles is shown. A comparison of simulated and experimental profiles demonstrates that the most widely used surface mechanism in CFD simulations of ammonia oxidation, the Kraehnert and Baerns model, shows the correct trends but cannot capture the product distribution quantitatively. The approach presented in this article provides detailed experimental insight into ammonia oxidation under industrial conditions required to develop and validate future kinetic models for knowledge-based optimization of industrial ammonia oxidation.Publicationtype: Journal Article89 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Catalytic partial oxidation of methane on platinum investigated by spatial reactor profiles, spatially resolved spectroscopy, and microkinetic modeling(2013); ; Kandemir, TimurSpatially resolved profile measurements, Raman spectroscopy, electron microscopy, and microkinetic modeling have been used to study the catalytic partial oxidation of methane on Pt. The measured species profiles through Pt coated foam catalysts exhibit a two-zone structure: an abrupt change in reaction rates separates the fast exothermic oxidation chemistry at the entrance of the reactor from the slow endothermic reforming chemistry. Spatially resolved Raman spectroscopy and electron microscopy confirm that the position of the mechanistic change could be correlated with Pt transportation and formation of carbonaceous deposits blocking the majority of active Pt sites in the reforming zone. The species profiles were simulated using a pseudo-2D heterogeneous model, which includes heat and mass transport limitations, and two state-of-the-art chemical kinetic mechanisms. Although both mechanisms are in quantitative agreement with the oxygen profiles, the two mechanisms differ substantially in their predictions of the branching ratio between partial and complete oxidation, as well as surface site coverages. The experimentally observed change in reaction rates is attributed to carbon formation, which the mechanisms are unable to reproduce, since they do not include carbon-carbon coupling reactions.Publicationtype: Journal Article28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Carbon formation in catalytic partial oxidation of methane on platinum : model studies on a polycrystalline Pt foilA polycrystalline Pt foil has been investigated as model catalyst in methane catalytic partial oxidation to synthesis gas. It is demonstrated that a substantial amount of carbonaceous deposits forms on the Pt foil upon reaction light-off blocking a large fraction of Pt surface atoms. By using in situ Raman spectroscopy and quantitative spectral analysis the evolution and spatial distribution of these carbonaceous compounds with reaction temperature and reaction time have been characterized. The chemical composition of the carbon material changes from highly reactive and strongly disordered directly after reaction light-off to highly ordered, oxidation and steam reforming resistant after several hours time on stream at 800 °C reaction temperature. Remarkably the carbon distribution at the Pt surface was found to be inhomogeneous and related to the nature of the microcrystals forming the polycrystalline foil in a yet unknown manner.Publicationtype: Journal Article8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Measurement and analysis of spatial reactor profiles in high temperature catalysis research(Elsevier, 2011-10-01); ; 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In-situ investigation of gas phase radical chemistry in the catalytic partial oxidation of methane on Pt(2009-04-15); ; ; ; The catalytic partial oxidation of methane on platinum was studied in situ under atmospheric pressure and temperatures between 1000 and 1300 °C. By combining radical measurements using a molecular beam mass spectrometer and threshold ionization with GC, GC-MS and temperature profile measurements it was demonstrated that a homogeneous reaction pathway is opened at temperatures above 1100 °C, in parallel to heterogeneous reactions which start already at 600 °C. Before ignition of gas phase chemistry, only CO, H2, CO2 and H2O are formed at the catalyst surface. Upon ignition of gas chemistry, CH3-radicals, C2 coupling products and traces of C3 and C4 hydrocarbons are observed. Because the formation of CH3-radicals correlates with the formation of C2 products it can be concluded that C2 products are formed by coupling of methyl radicals in the gas phase followed by dehydrogenation reactions. This formation pathway was predicted by numerical simulations and this work presents an experimental confirmation under high temperature atmospheric pressure conditions.Publicationtype: Journal Article19