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Item type:Publication, Access status: without files , Selective Oxidation of Ethylene to Ethylene Oxide on Silver Catalysts at Industrial Conditions: Reactor Profiles, Kinetics, and Chlorine Inhibition(American Chemical Society (ACS), 2024-03-06); ; ; 143 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , What happens in a catalytic fixed-bed reactor for n-butane oxidation to maleic anhydride? Insights from spatial profile measurements and particle resolved CFD simulations(2018-10-15); ; ; ; Industrial catalytic reactors are made of steel, operate at high temperatures and pressures and contain hazardous chemicals. What happens inside remains hidden. Reactor optimization requires costly trial and error or is based on simplified mathematical models employing more or less accurate transport correlations and reaction kinetics. In the present work a pilot-scale fixed-bed reactor was developed for measuring concentration and temperature profiles for n-butane oxidation to maleic anhydride on vanadyl pyrophosphate catalyst pellets under industrially-relevant conditions. The reactor was equipped with five heating zones. The reactor was modeled by particle-resolved computational fluid dynamics. The catalyst bed was created by discrete element simulation and the result was validated by comparison with experimental radial porosity profiles. Catalytic chemistry was included by a kinetic model of intrinsic reaction rates. Transport resistances and packing deviations were lumped in reaction rate multipliers determined by fitting the model to profiles measured at a uniform reactor wall temperature. Simulation results reveal strong inhomogeneities inside the bed. A hot-spot develops at uniform wall temperature. At this hot-spot temperature differences of 40 K exist on one and the same pellet with negative impact on maleic anhydride selectivity and catalyst lifetime. An optimized wall temperature profile was derived by combining knowledge from the experimental profiles at uniform wall temperature and the CFD results. A gradual increasing temperature was predicted by the model to eliminate the hot-spot and increase integral maleic anhydride selectivity at constant n-butane conversion. This prediction was confirmed by experiment. At 80% n-butane conversion the maleic anhydride selectivity could be improved by 2%. Facing the scale of the process, this improvement translates into significant n-butane savings, reduced COx emissions and increased revenue.Publicationtype: Journal Article185 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Sites for methane activation on lithium-doped magnesium oxide surfaces(Wiley, 2014-08-11); Zavyalova, UlyanaDensity functional calculations yield energy barriers for H abstraction by oxygen radical sites in Li-doped MgO that are much smaller (12±6 kJmol-1) than the barriers inferred from different experimental studies (80-160 kJmol-1). This raises further doubts that the Li +O.- site is the active site as postulated by Lunsford. From temperature-programmed oxidative coupling reactions of methane (OCM), we conclude that the same sites are responsible for the activation of CH 4 on both Li-doped MgO and pure MgO catalysts. For a MgO catalyst prepared by sol-gel synthesis, the activity proved to be very different in the initial phase of the OCM reaction and in the steady state. This was accompanied by substantial morphological changes and restructuring of the terminations as transmission electron microscopy revealed. Further calculations on cluster models showed that CH4 binds heterolytically on Mg2+O 2- sites at steps and corners, and that the homolytic release of methyl radicals into the gas phase will happen only in the presence of O 2. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Publicationtype: Journal Article27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fuel-rich methane oxidation in a high-pressure flow reactor studied by optical-fiber laser-induced fluorescence, multi-species sampling profile measurements and detailed kinetic simulations(Elsevier, 2014-02-05); ; ; ; A versatile flow-reactor design is presented that permits multi-species profile measurements under industrially relevant temperatures and pressures. The reactor combines a capillary sampling technique with a novel fiber-optic Laser-Induced Fluorescence (LIF) method. The gas sampling provides quantitative analysis of stable species by means of gas chromatography (i.e. CH4, O2, CO, CO2, H2O, H2, C2H6, C2H4), and the fiber-optic probe enables in situ detection of transient LIF-active species, demonstrated here for CH2O. A thorough analysis of the LIF correction terms for the temperature-dependent Boltzmann fraction and collisional quenching are presented. The laminar flow reactor is modeled by solving the two-dimensional Navier-Stokes equations in conjunction with a detailed kinetic mechanism. Experimental and simulated profiles are compared. The experimental profiles provide much needed data for the continued validation of the kinetic mechanism with respect to C1 and C2 chemistry; additionally, the results provide mechanistic insight into the reaction network of fuel-rich gas-phase methane oxidation, thus allowing optimization of the industrial process. © 2014 The Combustion Institute.Publicationtype: Journal Article40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Resolving kinetics and dynamics of a catalytic reaction inside a fixed bed reactor by combined kinetic and spectroscopic profilingThe oxidative dehydrogenation of ethane to ethylene was studied using a MoO3 based catalyst supported on γ-alumina spheres. The measurement of species and temperature profiles through a fixed bed reactor shows for the first time the reaction pathways inside the catalyst bed directly. Oxidative dehydrogenation of ethane to ethylene and water occurs on the redox sites of MoO3 only in the presence of gas phase oxygen. Further oxidation of the product ethylene to carbon dioxide occurs as a subsequent reaction step by lattice oxygen of MoO3. Deep oxidation of ethylene to CO2 is the only existing reaction in the absence of gas phase oxygen reducing MoO3 to MoO2. Oxidation of CO and C 2H6 by lattice oxygen does not occur. The reduction of the catalyst can be followed by in situ fiber Raman spectroscopy as a function of the oxygen partial pressure. The in situ Raman measurements are complemented by ex situ micro-Raman spectroscopy and X-ray diffraction. The combined measurement of kinetic and spectroscopic reactor profiles presents a novel approach in in situ catalysis research to establish catalyst structure-function relationships under technically relevant conditions of temperature and pressure. © The Royal Society of Chemistry 2013.Publicationtype: Journal Article41 - 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 , 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 , Morphology and microstructure of Li/MgO catalysts for the oxidative coupling of methane(Wiley, 2011-06-14); ; 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Reactor for in situ measurements of spatially resolved kinetic data in heterogeneous catalysis(American Institute of Physics (AIP), 2010-06-01); ; ; 18 - 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