Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nickel-based catalysts with perovskite like structure have shown promising application in several catalytic reactions such as in the partial oxidation of methane to obtain syngas (H2 + CO). However, these properties are potentially influenced by synthesis methods, calcinations conditions (temperature, time and atmosphere) and substitutions of sites A and/or B in the structure. The effects of these variables have been studied with the aim of improving the performance of catalysts in the production of syngas and to avoid deactivation resulting from coke deposition. In the present study, nickel-based catalysts (LaNiO3) with perovskite like structure were prepared by polymeric precursors, chelating precursors and gel modified proteic methods. All samples were subjected to thermal treatment and then calcined at 700 °C (for 1 or 2 h) to obtain the targed phase. LaNiO3 catalysts calcined at 700 °C with the lowest content of chelating agents were supported on alumina. The resulting ceramic powders were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, specific surface area, scanning electron microscopy and temperature programmed reduction tests. XRD patterns of the powders calcined at 700 °C showed the formation of perovskite phase in all samples. The characteristic peaks of perovskite phase were also found in the samples supported on alumina. Temperature programmed profiles of samples revealed the presence of two peaks with maximum at 368 °C and 482 °C. Calcined samples supported on alumina were used in the partial oxidation of methane to evaluate the level of CH4 conversion and selectivity to H2 and CO. LaNiO3 catalyst obtained through chelating precursor method showed the highest performance of methane conversion in the range of 50% and selectivity (about 60%), for 18 h of time reaction. / Os catalisadores a base de níquel com estrutura perovsquita têm se mostrado promissores na aplicação em diversas reações catalíticas, tal como, oxidação parcial do metano para obtenção de gás de síntese (H2 + CO). No entanto, as propriedades destes são potencialmente influenciadas pelo método de síntese, condições de calcinação (temperatura, tempo e atmosfera) e substituições dos sítios A e/ou B na estrutura. Os efeitos destas variáveis têm sido estudados, com o objetivo de aperfeiçoar o desempenho dos catalisadores na produção de gás de síntese e evitar a desativação destes por deposição de coque. No presente trabalho, catalisadores a base de níquel (LaNiO3) com estrutura perovsquita foram preparados através de três métodos: precursores poliméricos, precursores quelantes e gel proteico modificado. Todas as amostras foram submetidas a um tratamento térmico e, em seguida, calcinadas a 700°C (por 1 h ou 2 h) para obtenção da fase desejada. As perovsquitas do tipo LaNiO3 calcinadas a 700 °C com o menor teor de agentes quelantes foram suportadas em alumina. Os pós obtidos foram caracterizados por difratometria de raios X, espectroscopia na região do infravermelho, termogravimetria, área superficial específica, microscopia eletrônica de varredura e redução à temperatura programada. Os difratogramas dos pós calcinados a 700 °C mostraram a formação da fase perovsquita em todas as amostras. Nos difratogramas dos materiais suportados foram observados picos característicos da fase perovsquita e do suporte. Os perfis de redução à temperatura programada das amostras apresentaram dois picos de redução com máximos a 368 °C e 482 °C. As amostras calcinadas a 700 °C e suportadas em alumina foram testadas na reação de oxidação parcial do metano, sendo avaliados os respectivos níveis de conversão do metano e seletividade a CO e H2. Dentre os catalisadores estudados, o catalisador LaNiO3 obtido pelo método dos precursores quelantes e suportado em alumina foi o que apresentou maior nível de conversão de metano, na faixa de 50%, e maior seletividade ao H2 (aproximadamente 60%), durante 18 h de reação.

Pour la première fois l'oxydation partielle du méthane en gaz de synthèse a été effectué en présence de pérovskites lamellaires Nd2-xCaxCoO4±δ et La2-xSrxCoO4±δ (x = 0.75; 1.0). Nouveau catalyseur d'oxydation partielle NdCaCoO3.96 de méthane a été suggéré qui permet d’obtenir la sélectivité en gaz de synthèse proche de 100% avec 90% de la conversion de CH4 (T = 900ºC; CH4/O2 = 2; W = 20 L·g-1·h-1; brevet russe № 2433950, 21/04/2010). Le catalyseur a été active et stable au moins 140 h, aucune tendance à la désactivation n’a été observée. Sur la base des analyses DRX, MEB et MET, il a été déterminé que l'activité et la sélectivité élevées de NdCaCoO3.96 ainsi que la stabilité dans l'oxydation partielle du méthane sont dues à sa transformation au cours de la réaction de la structure initiale en des nanoparticules de cobalt métallique dispersées dans Nd2O3-CaO matrice. Il a été observé que l'activité des pérovskites lamellaires dans l'oxydation partielle du méthane dépend à la fois de la taille des particules métalliques actives formées et à la stabilité de la structure initiale. / For the first time partial oxidation of methane to synthesis gas over layered perovskite-type oxides Nd2-xCaxCoO4±δ and La2-xSrxCoO4±δ (x = 0.75; 1.0) was investigated. New catalyst NdCaCoO3.96 for partial oxidation of methane was suggested allowing the selectivity toward synthesis gas close to 100% with 90% of CH4 conversion (T = 900ºC; CH4/O2 = 2; W = 20 L·g-1·h-1; Russian patent № 2433950, 21/04/2010). The catalyst was active and stable at least for 140 h, no trend to deactivation was observed. Based on XRD, SEM and TEM results it was determined that high activity and selectivity of NdCaCoO3.96 as well as stability in partial oxidation of methane are due to its transformation during reaction of initial structure to nanosized particles of metallic cobalt dispersed in Nd2O3-CaO matrix. It was observed that the activity of synthesized layered perovskite-type oxides in partial oxidation of methane depends both on the size of the formed active metallic particles and on the stability of initial structure.

No description available.

No description available.

Oxidation reactions are of prime importance at an industrial level and correspond to a huge market. Oxidation reactions are widely practiced in industry and are thoroughly studied in academic and industrial laboratories. Achievements in oxidation process resulted in the development of many new selective oxidation processes. Environmental protection also relies mainly on oxidation reactions. Remarkable results obtained in this field contributed to promote the social image of chemistry which gradually changes from being the enemy of nature to becoming its friend and savior. This study dealt with two aspects regarding oxidation process. The first aspect represented an experimental study for the partial oxidation of benzene to phenol using Pd membrane in the gaseous phase. The second part was a theoretical study for some of the advanced oxidation process (AOPs) which are applied for contaminant destructions in polluted waters. Niwa and coworkers reported a one step catalytic process to convert benzene to phenol using Pd membrane. According to their work, this technique will produce a higher yield than current cumene and nitrous oxide based industrial routes to phenol. A similar system to produce phenol from benzene in one step was studied in this work. Results at low conversion of benzene to phenol were obtained with a different selectivity from the reported work. High conversion to phenol was not obtained using the same arrangement as the reported one. High conversion to phenol was obtained using a scheme different from the one reported by Niwa et al1. It was found that producing phenol from benzene is not related to Pd-membrane since phenol was produced by passing all reactants over a Pd catalyst. Within the studied experimental conditions, formation of phenol was related to Pd catalyst since Pt catalyst was not capable of activating benzene to produce phenol. Other evidence was the result of a blank experiment, where no catalyst was used. From this experiment no phenol was produced. A kinetic model for the advanced oxidation process using ultraviolet light and hydrogen peroxide (UV/H2O2) in a completely mixed batch reactor has been tested for the destruction of humic acid in aqueous solutions. Known elementary chemical reactions with the corresponding rate constants were taken from the literature and used in this model. Photochemical reaction parameters of hydrogen peroxide and humic acid were also taken from the literature. Humic acid was assumed to be mainly destroyed by direct photolysis and radicals. The rate constant for the HA- reaction was optimized from range of values in the literature. Other fitted parameters were the rate constant of direct photolysis of hydrogen peroxide and humic acid. A series of reactions were proposed for formation of organic byproducts of humic acid destruction by direct photolysis and radicals. The corresponding rate constants were optimized based on the best fit within the range of available published data. This model doesn't assume the net formation of free radicals species is zero. The model was verified by predicting the degradation of HA and H2O2 for experimental data taken from the literature. The kinetic model predicted the effect of initial HA and H2O2 concentration on the process performance regarding the residual fraction of hydrogen peroxide and nonpurgeable dissolved organic carbon (NPDOC). The kinetic model was used to study the effect of the presence of carbonate/bicarbonate on the rate of degradation of NPDOC using hydrogen peroxide and UV (H2O2/UV) oxidation. Experimental data taken from literature were used to test the kinetic model in the presence of carbonate/bicarbonate at different concentrations. The kinetic model was able to describe the trend of the experimental data. The kinetic model simulations, along with the experimental data for the conditions in this work, showed a retardation effect on the rate of degradation of NPDOC due to the presence of bicarbonate and carbonate. This effect was attributed to the scavenging of the hydroxyl radicals by carbonate and bicarbonate. A kinetic model for the degradation of methyl tert-butyl ether (MTBE) in a batch reactor applying Fenton's reagent (FeII/ H2O2) and Fenton-like reagent (Feo/ H2O2) in aqueous solutions was proposed. All of the rate and equilibrium constants for hydrogen peroxide chemistry in aqueous solutions were taken from the literature. Rate and equilibrium constants for ferric and ferrous ions reactions in this model were taken from the reported values in the literature, except for the rate constant for the reaction of ferric ions with hydrogen peroxide where it was fitted within the range that was reported in the literature. Rate constant for iron dissolution was also a fitted parameter. The mechanism of MTBE degradation by the hydroxyl radicals was proposed based on literature studies. The kinetic model was tested on available experimental data from the literature which involved the use of Fenton's reagent and Fenton-like reagent for MTBE degradation. The degradation of MTBE in Fenton's reagent work was characterized to proceed by two stages, a fast one which involved the reaction of ferrous ions with hydrogen peroxide (FeII/H2O2 stage) and another, relatively, slower stage which involved the reaction of ferric ions with hydrogen peroxide (FeIII/H2O2 stage). The experimental data of MTBE degradation in the FeII/H2O2 stage were not sufficient to validate the model, however the model predictions of MTBE degradation in the FeIII/H2O2 stage was good. Also, the model was able to predict the byproducts formation from MTBE degradation and their degradation especially methyl acetate, and tert-butyl alcohol. The effect of each proposed reaction on MTBE degradation and the byproducts formation and degradation was elucidated based on a sensitivity analysis. The kinetic model predicted the degradation of MTBE for Fenton-like reagent for the tested experimental data. Matlab (R13) was used to solve the set of ordinary nonlinear stiff differential equations that described rate of species concentrations in each advanced oxidation kinetic model. Niwa, S. et al., Science 295 (2002) 105

Στην παρούσα διδακτορική διατριβή έγινε η μελέτη της φύσης των επιφανειακών ειδών άνθρακα που δημιουργούνται στην επιφάνεια κεραμομεταλλικών υλικών βασισμένα στο Ni-YSZ κατά την θερμοδυναμική ισορροπία της διασπαστικής ρόφησης του μεθανίου. Κύριος στόχος της μελέτης ήταν να διερευνηθεί η επίδραση της παρουσίας ενός δεύτερου μετάλλου στο Ni-YSZ, όσον αφορά τον σχηματισμό και/ή την αναστολή του ανενεργού άνθρακα. Η επικάλυψη της επιφάνειας του Ni με μικρή ποσότητα Au (≤1%at σε σχέση με το Ni) επηρέασε σημαντικά την κινητική της διασπαστικής ρόφησης του CH4 και την ενέργεια δεσμού των ροφημένων ειδών CHx στην επιφάνεια του Ni. Ο σχηματισμός γραφιτικού άνθρακα παρεμποδίστηκε, ενώ η επιφανειακή δραστικότητα για την υδρογόνωση των CHx προς CH4 ήταν χαμηλότερη από ότι στον Ni-YSZ. Αυτό έχει ως αποτέλεσμα την υψηλότερη σταθερότητα και την επιμήκυνση του χρόνου ζωής των CHx πάνω στην επιφάνεια του NiAu/YSZ πριν την διάσπαση τους προς επιφανειακά καρβιδικά είδη. Με βάση τις πειραματικές μετρήσεις, προτάθηκε κινητικό μοντέλο για την περιγραφή της μερικής οξείδωσης του μεθανίου για την παραγωγή αερίου σύνθεσης. Οι αντιδράσεις οξείδωσης περιλαμβάνουν την οξείδωση των ειδών CHx προς CHxO και την επακόλουθη διασπασή τους σε υψηλές θερμοκρασίες (700 Κ) προς CO και H2, ενώ τα καρβιδικά είδη οξειδώνονται εκλεκτικά προς CO2 από χαμηλότερες θερμοκρασίες (500 Κ). Από αυτή την άποψη, η εκλεκτικότητα ως προς το αέριο σύνθεσης εξαρτάται από δύο παράγοντες: (i) τον χρόνο ζωής και την επιφανειακή συγκέντρωση των ειδών CHx, και (ii) τη θερμοκρασία διάσπασης των ειδών CHxO. Ως γενικό συμπέρασμα, ο ηλεκτροκαταλύτης Ni(1%at Au)/YSZ αναμένεται να έχει υψηλή αντοχή στην εναπόθεση άνθρακα όπως και εκλεκτικότητα για την μερική οξείδωση του CH4 προς αέριο σύνθεσης. / In order to investigate the possibility of the direct introduction of CH4 into a SOFC, the dissociative adsorption of CH4 and the nature of the various carbon adspecies on Ni-based cermets were studied in the present thesis by means of thermodynamic equilibrium measurements and temperature programming methods. The aim of this study was mainly to elucidate the effect of a second metal addition on Ni-YSZ, regarding the formation and/or inhibition of inactive carbon. The decoration of the Ni surface with very small quantity of Au (≤1at% with respect to Ni) affected significantly both the kinetics of CH4 dissociative adsorption and the binding strength of the adsorbed CHx species on the Ni surface. The formation of graphitic carbon was significantly inhibited, while the surface reactivity towards the hydrogenation of CHx species into CH4 was lower than on the unmodified Ni/YSZ surface. This resulted in the higher stability and elongation of the CHx species life time on the NiAu/YSZ surface prior to their decomposition into surface carbidic species. Based on the experimental results and discussion, a kinetic model is proposed for the description of the partial oxidation of methane towards the production of synthesis gas. The oxidation reactions involve both the oxidation of CHx species into CHxO and its subsequent decomposition at elevated temperatures (700 K) into CO and H2, while carbidic species are selectively oxidized into CO2 at temperatures as low as 500 K. In this respect, the selectivity towards synthesis gas depends on two factors: (i) the lifetime and surface concentration of CHx species, and (ii) the decomposition temperature of the CHxO species. As a conclusion, the Ni(1%at Au with respect to Ni)/YSZ catalyst is expected to be highly carbon tolerant and selective catalyst/electrode for the CH4 partial oxidation reaction for the production of synthesis gas.

Η τεχνολογία κυψελίδων καυσίμου στερεού ηλεκτρολύτη είναι αρκετά ελκυστική για την συμπαραγωγή αερίου σύνθεσης και ηλεκτρικής ενέργειας. Το κυριότερο μειονέκτημα είναι η εναπόθεση άνθρακα στο ανοδικό ηλεκτρόδιο λόγω της διασπαστικής ρόφησης του CH4. Σε μια θεωρητική μελέτη, οι Besenbacher et al συμπέραναν ότι η παρουσία μικρής ποσότητας Αu σε υποστηριγμένο καταλύτη Ni οδηγεί σε σημαντική μείωση την εναπόθεση άνθρακα. Σε αντίστοιχα συμπεράσματα κατέληξαν και οι Τριανταφυλλόπουλος και Νεοφυτίδης μελετώντας τα είδη του άνθρακα που δημιουργούνται πάνω στο Ni(1%at Au)-YSZ κατά την διασπαστική ρόφηση του μεθανίου. Στην παρούσα εργασία μελετήθηκε η ηλεκτροχημική δραστικότητα διμεταλλικών ηλεκτροδίων Ni(Au1%at)-YSZ και Ni(Ag1%at)-YSZ για την μερική οξείδωση του μεθανίου καθώς και για την εσωτερική αναμόρφωση του μεθανίου με ατμό σε κυψελίδες καυσίμου στερεού ηλεκτρολύτη. Τα ηλεκτρόδια παρασκευάστηκαν με τη μέθοδο της επιτόπου πυρανάφλεξης (in situ combustion synthesis, μέθοδος σχετικά χαμηλής θερμοκρασίας που δημιουργεί νανοδομημένα ηλεκτρόδια) και μελετήθηκαν ως προς την ηλεκτροκαταλυτική συμπεριφορά τους για την εσωτερική αναμόρφωση του μεθανίου με ατμό. Τα πειράματα θερμοσταθμικής ανάλυσης, τα κινητικά πειράματα καθώς και οι ηλεκτροχημικές μετρήσεις που πραγματοποιήθηκαν, συντέλεσαν το καθένα με το τρόπο του, στην εξαγωγή του γενικότερου συμπεράσματος ότι τα διμεταλλικά ηλεκτρόδια Ni(Au1%at)-YSZ και Ni(Ag1%at)-YSZ είναι πολύ πιο σταθερά και ανθεκτικά στην εναπόθεση άνθρακα από το ‘συμβατικό’ ηλεκτρόδιο Ni-YSZ υπό τις συνθήκες της εσωτερικής αναμόρφωσης μεθανίου με ατμό που μελετήθηκαν. Τα ανοδικά αυτά ηλεκτρόδια επομένως φαίνεται να αποτελούν ενδιαφέρουσες επιλογές για χρήση στις κυψελίδες καυσίμου στερεού ηλεκτρολύτη που λειτουργούν με μεθάνιο ακόμη και σε αρκετά υψηλές θερμοκρασίες (μέχρι και 1173K) για τα NiAu-YSZ, ή σε χαμηλότερες (έως 973-1023K) για τα NiAg-YSZ. / The technology of solid oxide fuel cells seems quite attractive for the cogeneration of synthesis gas and electrical energy. A major bottleneck that has delayed the widespread use of this technology has always been the anode’s contamination with carbon due to the dissociative adsorption of methane. In a theoretical study, Besenbacher et al concluded that small quantities of Au on a supported Ni catalyst can minimize carbon deposition. Triantafyllopoulos and Neophytides reached similar results while studying the carbon adspecies that are formed on a Ni(1%at Au)-YSZ electrocatalyst during the dissociative adsorption of methane. The present study focused on the electrochemical activity of Ni(Au1%at)-YSZ and Ni(Ag1%at)-YSZ bimetallic electrodes under internal steam reforming conditions of methane in solid oxide fuel cells. The bimetallic electrodes were prepared by the combustion synthesis method, which is a relatively low temperature procedure that produces nanostructured electrodes, and their electrochemical behavior was investigated under internal steam reforming conditions. The thermogravimetric analysis, the electrochemical experiments as well as the kinetic measurements that were conducted, each one of them helped in reaching the general conclusion that the Ni(Au1%at)-YSZ and Ni(Ag1%at)-YSZ bimetallic electrodes are much more stable and carbon tolerant than the conventional Ni-YSZ electrode, at least under the steam reforming conditions of methane that they were studied. So these anodic electrodes seem to be interesting candidates for use in solid oxide fuel cells that operate with methane feed even at high temperatures (such as 1173K) for the NiAu-YSZ anodes, or at lower temperatures (up to 973-1023K) for the NiAg-YSZ anodes.

Made available in DSpace on 2014-12-17T15:01:22Z (GMT). No. of bitstreams: 1 KalyanneKPG_ate o resumo.pdf: 69797 bytes, checksum: 49f1d53a5fe82cc0c03f9f579c34a190 (MD5) Previous issue date: 2006-09-12 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The nanostructures materials are characterized to have particle size smaller than 100 nm and could reach 1 nm. Due to the extremely reduced dimensions of the grains, the properties of these materials are significantly modified relatively when compared with the conventional materials. In the present work was accomplished a study and characterization of the molybdenum carbide, seeking obtain it with particles size in the nanometers order and evaluate its potential as catalyst in the reaction of partial methane oxidation. The method used for obtaining the molybdenum carbide was starting from the precursor ammonium heptamolybdate of that was developed in split into two oven, in reactor of fixed bed, with at a heating rate of 5?C/min, in a flow of methane and hydrogen whose flow was of 15L/h with 5% of methane for all of the samples. The studied temperatures were 350, 500, 600, 650, 660, 675 and 700?C and were conducted for 0, 60, 120 and 180 minutes, and the percent amount and the crystallite size of the intermediate phases were determined by the Rietveld refinement method. The carbide obtained at 660?C for 3 hours of reaction showed the best results, 24 nm. Certain the best synthesis condition, a passivating study was accomplished, in these conditions, to verify the stability of the carbide when exposed to the air. The molybdenum carbide was characterized by SEM, TEM, elemental analysis, ICP-AES, TG in atmosphere of hydrogen and TPR. Through the elemental analysis and ICP-AES the presence carbon load was verified. TG in atmosphere of hydrogen proved that is necessary the passivating of the molybdenum carbide, because occur oxidation in room temperature. The catalytic test was accomplished in the plant of Fischer-Tropsch of CTGAS, that is composed of a reactor of fixed bed. Already the catalytic test showed that the carbide presents activity for partial oxidation, but the operational conditions should be adjusted to improve the conversion / Os materiais nanoestruturados s?o caracterizados por terem um tamanho de cristalito inferior a 100 nm podendo atingir 1 nm. Devido ?s dimens?es extremamente reduzidas dos cristalitos, as propriedades destes materiais s?o significativamente modificadas relativamente ?s dos materiais convencionais. No presente trabalho foi realizado um estudo de s?ntese e caracteriza??o do carbeto de molibd?nio, visando obt?-lo com tamanho de part?culas na ordem de nan?metros e avaliar seu potencial como catalisador na rea??o de oxida??o parcial do metano. O m?todo utilizado para obten??o do carbeto de molibd?nio foi a partir do precursor heptamolibdato de am?nio que foi desenvolvida em forno bipartido, em reator de leito fixo, com uma taxa de aquecimento de 5?C/min, em um fluxo de metano e hidrog?nio cuja vaz?o foi de 15L/h com 5% de metano para todos os ensaios. As temperaturas estudadas foram 350, 500, 600, 650, 660, 675 e 700?C e nos tempos de isoterma de 0, 60, 120 e 180 minutos, sendo que a determina??o das fases presentes, estrutura cristalina e tamanho de cristalitos foram obtidos por refinamento de estrutura pelo m?todo de Rietveld. O carbeto obtido a 660?C e 3 horas de rea??o foi o que apresentou menor tamanho de cristalito 24 nm. Determinada a melhor condi??o de s?ntese foi realizado um estudo de passivac?o, nestas condi??es, para verificar a estabilidade do carbeto ao ser exposto ao ar. O carbeto de molibd?nio foi caracterizado por MEV, MET, an?lise elementar, ICP-AES, TG em atmosfera de hidrog?nio e RTP. Atrav?s da an?lise elementar e ICP-AES foi verificada a presen?a de carbono livre. A TG em atmosfera de hidrog?nio comprovou que ? necess?ria a passivac?o do carbeto de molibd?nio, pois ele ? oxidado em temperatura ambiente. O teste catal?tico foi realizado na planta semipiloto de Fischer-Tropsch do CTGAS, que ? composta de um reator de leito fixo. O teste catal?tico mostrou que o carbeto apresenta atividade para oxida??o parcial, mas as condi??es operacionais devem ser ajustadas para melhorar a convers?o

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17555号 / 工博第3714号 / 新制||工||1566(附属図書館) / 30321 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 中部 主敬, 教授 牧野 俊郎, 教授 小森 悟 / 学位規則第4条第1項該当

Vergasungsprozesse, bei denen kohlenstoffhaltige Ausgangsstoffe in ein vorwiegend aus Wasserstoff und Kohlenmonoxid bestehendes Synthesegas umgewandelt werden, stellen eine Schlüsseltechnologie für eine zukünftige nachhaltige Rohstoffnutzung dar. Der Grund für den Einsatz von Hochdruckverfahren liegt in der Steigerung der Wirtschaftlichkeit. Die numerische Simulation der Hochdruckvergasung hat große Schnittmengen mit der Verbrennungssimulation. So kann die Flammenzone mit Hilfe von Verbrennungsmodellen beschrieben werden. In der Arbeit wurden Simulationen einer Versuchsanlage für Hochdruckvergasung mit Hilfe kommerzieller CFD-Codes und mit Hilfe des quelloffenen Codes OpenFOAM durchgeführt. Eine Analyse des Verbrennungsmodells ergab, dass die wesentlichen Reaktionen im Reformierungsbereich, wo kein freier Sauerstoff mehr vorhanden ist, nur unzureichend abgebildet wurden. Durch die Verwendung eines alternativen Ansatzes konnte der Modellierungsfehler deutlich reduziert werden.