In emissions catalyst applications, an axial distribution of reaction, surface chemistry, and temperature all exist on or along the surface of the catalyst. Understanding these distributions is very important in developing physically relevant models of such systems. One focus of this work was developing a technique to obtain accurate temperature measurements from a catalyst during exothermic or endothermic reaction steps. IR thermography was tested as a method to evaluate spatial temperature distributions as a function of time on a diesel NOX adsorber catalyst. The technique proved accurate, relatively simple to interpret and operate, and efficient to the extent it can be used for data generation. As a continuation of the technique development, the temperature changes and gradients formed during simulated operation of a Pt/Ba/Al2O3 NOX adsorber catalyst (NAC) for diesel exhaust applications were monitored using IR thermography and standard thermocouples. NACs operate in a cyclic manner; during the lean phase, when the engine is in normal operation, the catalyst traps entering NOX; once the catalyst nears saturation, the catalyst is exposed to a rich exhaust phase, in reductant relative to oxygen, where the trapped NOX is reduced to N2; and finally the exhaust returns to the normally lean conditions thereby completing the cycle. During the rich phase, previous work has suggested that significant temperature changes might be occurring along the length of the catalyst. In this study, temporally and spatially resolved temperature distributions were obtained throughout the cycle in order to evaluate the significance of these temperature changes and their effects on the reaction chemistry. The effects of (1) reactor in the possible reaction pathways, (2) CO and O2 levels in the regeneration phase, (3) NO and NO2 as the source of NOX in the lean cycle and (4) nominal operating temperature on these temperature distributions were evaluated. The temperature gradient and distribution measurements are being used to characterize the reactions and as input into models.

In emissions catalyst applications, an axial distribution of reaction, surface chemistry, and temperature all exist on or along the surface of the catalyst. Understanding these distributions is very important in developing physically relevant models of such systems. One focus of this work was developing a technique to obtain accurate temperature measurements from a catalyst during exothermic or endothermic reaction steps. IR thermography was tested as a method to evaluate spatial temperature distributions as a function of time on a diesel NOX adsorber catalyst. The technique proved accurate, relatively simple to interpret and operate, and efficient to the extent it can be used for data generation. As a continuation of the technique development, the temperature changes and gradients formed during simulated operation of a Pt/Ba/Al2O3 NOX adsorber catalyst (NAC) for diesel exhaust applications were monitored using IR thermography and standard thermocouples. NACs operate in a cyclic manner; during the lean phase, when the engine is in normal operation, the catalyst traps entering NOX; once the catalyst nears saturation, the catalyst is exposed to a rich exhaust phase, in reductant relative to oxygen, where the trapped NOX is reduced to N2; and finally the exhaust returns to the normally lean conditions thereby completing the cycle. During the rich phase, previous work has suggested that significant temperature changes might be occurring along the length of the catalyst. In this study, temporally and spatially resolved temperature distributions were obtained throughout the cycle in order to evaluate the significance of these temperature changes and their effects on the reaction chemistry. The effects of (1) reactor in the possible reaction pathways, (2) CO and O2 levels in the regeneration phase, (3) NO and NO2 as the source of NOX in the lean cycle and (4) nominal operating temperature on these temperature distributions were evaluated. The temperature gradient and distribution measurements are being used to characterize the reactions and as input into models.

No description available.

THE EFFECTS OF CERIA ADDITION ON AGING AND SULFATION OF LEAN NOx TRAPS FOR STAND ALONE AND LNT-SCR APPLICATIONS Model powder and fully formulated monolithic lean NOx trap (LNT) catalysts were used to investigate the effect of ceria on desulfation behavior. Temperature-programmed reduction (TPR) experiments (model catalysts) showed each of the oxide phases present is able to store sulfur and possesses distinct behavior (temperature at which desulfation occurs). La-CeO2 or CeO2-ZrO2-containing samples (monoliths) showed a greater resistance to deactivation during sulfation and required lower temperatures to restore the NOx storage efficiency to its pre-sulfation value. Fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging to elucidate the effect of washcoat composition on LNT aging. Elemental analysis revealed that residual sulfur, associated with the Ba phase, decreased catalyst NOx storage capacity and that sintering of the precious metals resulted in decreased contact between the Pt and Ba phases. Spatially-resolved inlet capillary mass spectrometry (SpaciMS) was employed to understand the factors influencing the selectivity of NOx reduction in LNT catalysts degreened and thermally aged) containing Pt, Rh, BaO and Al2O3, and contained La-stabilized CeO2. Stretching of the NOx storage and reduction zone (NSR) zone resulted in increased selectivity to NH3 due to the fact that less catalyst was available to consume NH3 by either the NH3-NOx SCR reaction or the NH3-O2 reaction. Additionally, the loss of oxygen storage capacity (OSC) and NOx storage sites, along with the decreased rate of NOx diffusion to Pt/Rh sites, led to an increase in the rate of propagation of the reductant front after aging, in turn, resulting in increased H2:NOx ratios at the Pt/Rh sites and consequently increased selectivity to NH3. Finally, a crystallite scale model was used to predict selectivity to NH3 from the LNT catalysts during rich conditions after a fixed amount of NOx was stored during lean conditions. Both the experimental and model predicted data showed that the production of NH3 is limited by the rate of diffusion from the Ba storage sites to the Pt particles at 200 °C. At 300 °C, the process is limited by the rate at which H2 is fed to the reactor.

No description available.

Le catalyseur quatre voies est destiné à diminuer simultanément les émissions d’hydrocarbures, de monoxyde de carbone, d’oxydes d’azote et de suies par l’intermédiaire d’un seul monolithe catalytique. Plusieurs études sur ce type de catalyseur ont montré que la présence d’oxydes d’azote entraîne une diminution de la température d’oxydation des suies. Cependant, l’effet de la présence d’eau sur l’adsorption des oxydes d’azote n’est pas encore clair, surtout en présence de suies. Les travaux présentés dans ce manuscrit ont pour but de mettre en évidence l’influence de la présence d’eau et/ou de suies sur le fonctionnement de catalyseur «piège à NOx». Les résultats obtenus montrent que la présence d’eau entraîne une inhibition de la fonction oxydante du catalyseur, une diminution de la quantité de stockage des oxydes d’azote, et une inhibition de la formation des espèces adsorbées de surface. Ces phénomènes ont été attribués à la voix réactionnelle spécifique en présence d’eau associée à l’adsorption des oxydes d’azote. Les résultats obtenus sur le mélange noir de carbone et catalyseur montrent que la présence de noir de carbone induit une diminution de stockage des oxydes d’azote. De plus, cet effet se trouve plus important en contact fort. Les expériences réalisées sur l’adsorption des oxydes d’azote en présence simultanée de noir de carbone et d’eau ont montré un effet non cumulé de l’eau et du noir de carbone. Ce phénomène a été attribué à une compétition entre l’action de l’eau qui favorise la formation de nitrate de cœur à partir des nitrates faiblement liés et l’action du noir de carbone qui tend à déstabiliser les nitrates faiblement liés pour former les carbonates. / The four ways catalyst is used to decrease the emissions of hydrocarbon, carbon monoxide, nitrogen oxides and soot by a monolithic catalyst. Several researches on this type of catalyst have shown that the presence of nitrogen oxides involves a decrease of the soot oxidation temperature. However, the effect of the presence of water on the nitrogen oxides adsorption is not clear yet, especially with the presence of soot. The works presented in this manuscript are intended to study the influence of the presence of water or/and soot on the performance of the catalyst NOx trap. The results showed that the presence of water involves an inhibition of the oxidation function of catalyst, a decrease of the capacity of the NOx storage, and an inhibition of the formation of the surface adsorbed species. It is attributed to a special reactive way in the presence of water linked to the adsorption of nitrogen oxides. The results obtained on the mix of carbon black and catalyst showed that the presence of carbon black induce a decrease of the NOx storage capacity of catalyst. Besides, this effect was more important with a tight contact between carbon black and catalyst. The experiments realized on the adsorption of nitrogen oxides with the presence of carbon black and water simultaneously showed an effect not accumulated of the water and the carbon black. This phenomenon is attributed to a competition between the action of water which favors the formation of the bulk nitrate from the weak-linked nitrates and the action of carbon black which tend to destabilize the weak-linked nitrates to form the carbonates.

Récemment, les constructeurs automobiles se sont intéressés au développement des catalyseurs appelés quatre voies, destinés à diminuer simultanément les émissions polluantes des moteurs diesels par l'intermédiaire d'un seul monolithe catalytique. Dans cet objectif, plusieurs études ont montré que la capacité de stockage des NOx de ces catalyseurs est inhibée par la présence de suies. Les travaux présentés dans ce manuscrit s'inscrivent dans la compréhension des phénomènes en cause. Les résultats obtenus montrent que la présence de noir de carbone entraîne une diminution de la stabilité des nitrates adsorbés par les systèmes catalytiques étudiés et, ainsi, de leur capacité de stockage des NOx. Ce phénomène a été attribué à une réduction des espèces nitrates adsorbées à la surface des matériaux par les particules de carbone adjacentes. La présence d'une particule Pt à proximité d'un site de carbone favorise la formation de complexes oxygénés de surface, limitant l'effet réducteur du carbone envers les nitrates adsorbés. La perte de capacité d'adsorption des NOx des catalyseurs étudiés, observée lors de leur mise en contact avec du noir de carbone, s'est révélée irréversible à l'issue de l'oxydation du carbone. La caractérisation des matériaux par microscopie à transmission (MET) a révélé une modification importante de la structure des matériaux. Un frittage des particules de platine et une modification de la structure des particules de Ba entraînent en effet la perte irréversible de l'activité des matériaux vis-à-vis de l'adsorption des NOx. / Recently, car manufacturers have developed "4 way" catalytic converters in order to couple hydrocarbon and CO oxidation, soot combustion and DeNOx fonctions on a single monolith. Several studies showed that the NOx storage capacity of NSR catalysts is reduced in the presence of soot. The aim of this work is to investigate the effect of carbon­ NSR catalyst contact on the ability of the catalyst to store NOx. The results show that the presence of carbon black in the catalytic bed involves a decrease of adsorbed nitrates stability and of the NOx storage capacity of materials. It is proposed that the proximity of the carbon particles and NOx adsorbents sites leads to a reduction of the stored nitrates species. The decrease of the NOx storage capacity is Jess important when platinum is present in the catalytic material composition. In agreement with previous studies on the catalytic combustion of soot, it is suggested that platinum increases the number of surface-oxygen complexes -C(O), which thus led to a decrease in the reducing character of carbon. Our study reveals that the deactivation of the NOx storage activity due to carbon-catalyst contact is an irreversible phenomena, and thus even when all carbon is burnt. Characterization of materials by transmission electron microscopy (TEM) showed that sintering of the platinum particles and a structural modification of the barium particles occurs after that the catalysts was in contact with carbon. The decrease in the NOx storage activity of the materials is then assigned to a lesser proximity of the oxidizing sites (Pt) and adsorption sites (Al or Ba).

Dans cette étude, on s'est intéressé à la modélisation réduite et au contrôle d’organes intervenant dans la réduction des émissions de polluants des véhicules automobiles à basse consommation. Il s’agit des réacteurs catalysés de type « piège à NOx » et SCR, utilisés dans les architectures de post-traitement des gaz d’échappement des véhicules Diesel. Ces systèmes ont en commun la nécessité de contrôler les niveaux des émissions de polluants stockés sur les sites catalytiques et l’optimisation du fonctionnement du GMP en vue d’approcher les futures normes Euro et les nouvelles incitations sur les émissions de gaz à effet de serre.Le piège à NOx est un système catalytique dont la fonction première est de collecter les oxydes d’azote (NOx) des gaz d’échappement afin qu’ils ne soient pas rejetés dans l’environnement. Le réacteur SCR est un système catalytique qui utilise le principe de réduction sélective des NOx par l’ammoniac (NH3), initialment produit et délivré à partir d’un stock d’urée embarqué.La similitude des technologies a permis la mise en œuvre de méthodologies communes de modélisation cinétique et de réduction de modèles, basées sur l’étude thermochimique et cinétique des réseaux réactionnels. Après application aux systèmes respectifs de piège à NOx et SCR, nous avons obtenus des modèles réduits qui ont pu être identifiés, validés et appliqués à l’observation et au contrôle des niveaux de stock des polluants (respectivement NOx et NH3). / The purpose of this study is to develop mathematical reduced order models for components of low consumption motor vehicles : the lean NOx trap and the SCR catalysts, used in the exhaust of Diesel engines and involved in the reduction of pollutants in exhaust emissions. These systems have in common that they aim at controling the boundaries on pollutant emissions in order to achieve the forthcoming Euro standards and they allow the optimization of the aftertreatment systems to reduce greenhouse gases.The lean NOx trap catalyst aims at collecting the NOx in order to avoid the pollution of the environment and the SCR catalyst uses the selective reduction of the NOx by the ammonia (NH3), initially produced by an embedded urea system. The similarity between the two technologies allow the implementation of common methodologies for reduced order modeling of catalytic reactors based on thermochemical and kinetic studies. After application, respectively to the NOx trap and the SCR, we obtain reduced order models which were identified, validated and implemented for the control and diagnosis of the amount of stock of the pollutants (respectively NOx and NH3).

[ES] La preocupación mundial por el cambio climático y la calidad del aire se refleja en normativas para la regulación de emisiones en el sector del transporte cada vez más estrictas, situando el desarrollo de sistemas propulsivos sostenibles como el objetivo fundamental. En el caso de los motores de combustión interna, el uso de sistemas de postratamiento de gases de escape, necesario para cumplir con los límites impuestos a las emisiones contaminantes, ha añadido mayor complejidad a la línea de escape. Una correcta comprensión de la respuesta de estos sistemas y su interacción con el motor requiere un profundo conocimiento de los procesos termo-fluidodinámicos y químicos que tienen lugar en los mismos. Su estudio indica que las mayores contribuciones a la reducción de las emisiones consisten en conseguir una activación más rápida de los catalizadores. Sin embargo, por lo general, las estrategias empleadas para alcanzar este fin se traducen en una penalización del consumo de combustible y, por consiguiente, de las emisiones de CO2. En este contexto, el objetivo de esta tesis doctoral es contribuir a la comprensión de los fenómenos presentes en los reactores monolíticos de flujo continuo utilizados en los motores de combustión pobre. En primer lugar, se presenta el desarrollo de una herramienta computacional para el modelado de los reactores estándar, es decir, los monolitos con recubrimiento catalítico monocapa, con un coste computacional bajo que permite responder de manera oportuna a las nuevas condiciones de contorno. El modelo se construyó dentro del entorno de modelo de motor virtual VEMOD, un software de dinámica de gases desarrollado por el I.U.I. CMT-Motores Térmicos para la simulación termo-fluidodinámica de motores de combustión interna y sus componentes. Apoyada sobre experimentos específicos para su calibración y validación en catalizadores de oxidación y de reducción de NOx, la herramienta computacional permite la identificación y el estudio de los parámetros que determinan la eficiencia de conversión de los sistemas de postratamiento. De esta forma, se aplica, con un enfoque de cálculo de valor medio, al análisis, en primer lugar, del impacto de la meso-geometría y el material de catalizadores de oxidación en condiciones dinámicas en función de la forma del canal. También se aborda el estudio de la sensibilidad a la composición de los gases de escape considerando diversas estrategias de combustión comparadas con el diésel convencional, así como el empleo de combustibles alternativos. Por último, se explora experimentalmente la importancia de la ubicación en la línea de escape de un catalizador de oxidación para discutir el efecto sobre las emisiones y el rendimiento del motor de la ubicación pre-turbina, por los beneficios que a nivel térmico tiene esta localización para el postratamiento. Todo ello sirve como fuente de desarrollos tecnológicos y científicos en el área de control de emisiones para el uso y comprensión de la nueva generación de sistemas de postratamiento. / [CA] La preocupació mundial pel canvi climàtic i la qualitat de l'aire es reflecteix en normatives per a la regulació d'emissions en el sector del transport cada vegada més estrictes, situant el desenvolupament de sistemes propulsius sostenibles com l'objectiu fonamental. En el cas dels motors de combustió interna, l'ús de sistemes de posttractament de gasos de fuita, necessari per a complir amb els límits imposats a les emissions contaminants, ha afegit major complexitat a la línia de fuita. Una correcta comprensió de la resposta d'aquests sistemes i la seua interacció amb el motor requereix un profund coneixement dels processos termo-fluidodinámicos i químics que tenen lloc en aquests. El seu estudi indica que les majors contribucions a la reducció de les emissions consisteix a aconseguir una activació més ràpida dels catalitzadors. No obstant això, en general, les estratègies emprades per a aconseguir aquest objectiu es tradueixen en una penalització del consum de combustible i, per consegüent, de les emissions de CO2. En aquest context, l'objectiu d'aquesta tesi doctoral és contribuir a la comprensió dels fenòmens presents en els reactors monolítics de flux continu utilitzats en els motors de combustió pobra. En primer lloc, es presenta el desenvolupament d'una eina computacional per al modelatge dels reactors estàndard, és a dir, els monòlits amb recobriment catalític monocapa, amb un cost computacional baix que permet respondre de manera oportuna a les noves condicions de contorn. El model es va construir dins de l'entorn de model de motor virtual VEMOD, un programari de dinàmica de gasos desenvolupat per l'I.U.I. CMT-Motors Tèrmics per a la simulació termo-fluidodinámica de motors de combustió interna i els seus components. Recolzada sobre experiments específics per al seu calibratge i validació en catalitzadors d'oxidació i de reducció de NOx, l'eina computacional permet la identificació l'estudi dels paràmetres que determinen l'eficiència de conversió dels sistemes de posttractament. D'aquesta manera, s'aplica, amb un enfocament de càlcul de valor mitjà, a l'anàlisi, en primer lloc, de l'impacte de la meso-geometria i el material de catalitzadors d'oxidació en condicions dinàmiques en funció de la forma del canal. També s'aborda l'estudi de la sensibilitat a la composició dels gasos de fuita considerant diverses estratègies de combustió comparades amb el dièsel convencional, així com l'ús de combustibles alternatius. Finalment, s'explora experimentalment la importància de la ubicació en la línia de fuita d'un catalitzador d'oxidació per a discutir l'efecte sobre les emissions i el rendiment del motor de la ubicació pre-turbina, pels beneficis que a nivell tèrmic té aquesta localització per al posttractament. Tot això serveix com a font de desenvolupaments tecnològics i científics en l'àrea de control d'emissions per a l'ús i comprensió de la nova generació de sistemes de posttractament. / [EN] The global concern on climate change and air quality is reflected over increasingly strict emission regulations in the transportation sector, making the development of sustainable propulsion systems the key objective. In the case of internal combustion engines, the use of aftertreatment systems (ATS), necessary to comply with the limits imposed on pollutant emissions, has added further complexity to the exhaust line. A correct comprehension of the response of these systems and their interaction with the engine requires an in-depth knowledge of the thermo-fluid-dynamic and chemical processes taking place inside them. Their study indicates that the major contributions to emission reduction rely on driving the catalysts to a faster light-off. However, in general, the strategies employed to achieve this goal involve a fuel consumption penalty and, consequently, CO2 emissions increase. In this context, the aim of this Ph.D. thesis is to contribute to the understanding of the phenomena present in flow-through catalysts used in lean burn combustion engines. First, the development of a computational tool for modelling the standard devices, i.e. mono-layers washcoat catalysts, is presented, with flexible and low computational cost, enabling timely response to the new boundary conditions. The model was built inside the Virtual Engine Model VEMOD, an open-source gas dynamics software developed by I.U.I. CMT-Motores Térmicos for thermo-fluid-dynamic simulation of internal combustion engines and their components. Supported by specific experiments for its calibration and validation on oxidation and NOx reduction catalysts, the computational tool allows the identification and study of the parameters that determine the conversion efficiency of the ATS. In the first instance it is used to analyze the impact of meso-geometry and oxidation catalyst material under dynamic conditions as a function of the channel shape. The study of the sensitivity to exhaust gas composition is also addressed considering various combustion strategies compared to conventional diesel, as well as the use of alternative fuels. Finally, the importance of the position in the exhaust line of an oxidation catalyst is explored experimentally to discuss the effect on emissions and engine performance of the pre-turbine location, because of the thermal benefits of this location for the aftertreatment. All of this serves as a source of technological and scientific developments in the area of emissions control for the use and comprehension of the new generation of aftertreatment systems. / Ruiz Lucas, MJ. (2023). Modelling and analysis of conversion efficiency in flow-through catalysts for lean-burn combustion engines [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/194012