Tesis sobre el tema "Diesel Oxidation Catalysts"

Worldwide usage of diesel engines has been rising rapidly and, accordingly, more stringent emission standards are introduced to lower the concentrations of diesel exhaust pollutants. NOx abatement is crucial, especially in diesel engines where controlling NOx is extremely difficult as oxygen is always in excess. The title and objective of this thesis arises from a novel approach, the diesel oxidation NOx adsorption catalyst (DONAC), where NOx is to be stored by a diesel oxidation catalyst (DOC). Supported platinum catalysts are the most used technology for diesel oxidation catalysts. Hence, the investigation of the oxidation properties of supported platinum catalysts and particularly, how these properties are affected by the support material, is of great importance. This work addresses not only the effect of the support, platinum loading, preparation method, calcination conditions and platinum precursor, but also the effect of the titania phase composition (anatase or anatase-rutile). A series of supported platinum catalysts including Pt/TiO2, Pt/SiO2, Pt/Al2O3, Pt/TiO2-SiO2 and Pt/SiO2-Al2O3 were prepared by non-aqueous impregnation and chemical vapour impregnation. In order to determine the effect of the support on the structural and electronic properties of the supported platinum catalysts detailed characterisation including XRD, BET, CO chemisorption, NH3-TPD, H2-TPR, TGA, DRIFTS, Raman, XPS, SEM, TEM and EDX was performed. Two relevant oxidation reactions, total oxidation of propane and oxidation of nitric oxide to nitrogen dioxide, were studied. It is found that the activity of supported platinum catalysts is greatly affected by the support material, in general, their performance is enhanced by addition of SiO2 to the TiO2 support. The activity of the platinum catalysts depends strongly on oxidation state, with platinum in metallic state being most active. However, it is not only the platinum oxidation state but a combination of several factors including metal dispersion, surface area, morphology and phase composition of the support that explains the variations in catalytic activity. Morphology and phase composition play an active role in the redox properties of the support and its interaction with supported metal particles. The high propane oxidation activity of Pt supported on anatase TiO2 is attributed to highly reactive oxygen species within the support. DeNOx technologies based on the concept of NOx storage have proven to be effective, however further studies are needed to succeed in finding an optimum NOx storage system. A series of metal (Cu, Fe and Pt) -exchanged zeolites with different compositions (SiO2/Al2O3 = 5.1 - 50) and frameworks (Y, ZSM-5 and BETA) were prepared by two different exchange methods (WIE and CVI). The DOE method was applied to investigate the way in which preparation experimental variables affect the NOx storage capacity of CuII/ZSM-5 (30). Evaluation of NOx storage capacity, in the presence or absence of O2, of metal-exchanged zeolites was carried out. In order to correlate the physicochemical properties of the metal-exchanged zeolites with their NOx storage performance, characterisation including XRD, BET, NH3-TPD, H2-TPR, DRIFTS, UV-Vis DRS, XPS, TEM and EDX was performed. It is found that the NOx adsorption/desorption capacity and the stability of those adsorption species formed, is greatly affected by the nature of the exchanged metal and the structure and acidity of the zeolite support. Due to the intrinsic adsorption capacity of the parent zeolite, H+-ZSM-5(23), CuII/ZSM-5(23) catalysts prepared by WIE and CVI exhibit high NOx storage capacities. The initial redox state, Cu2+/Cu+ and Fe2+/Fe3+ ratio, and bonding strength of the metal ions to the framework affect the reducibility of metal species and consequently the storage capacity. The preparation method is found to be crucial in controlling metal loading, nature and distribution of active species and crystallites size. The statistical approach allowed for a significant enhancement in the storage capacity of CuII/ZSM-5(30) and, in particular, the amount of NOx desorbed at high temperature. Temperature is found to have the greatest effect on the NOx storage capacity. In addition, its influence is dependent on the copper precursor concentration. Among the zeolite based catalysts studied, potential candidates for application under real working conditions, those that exhibit greater NOx desorption at high temperatures (T > 200°C) were found.

With mobile emission limits worldwide becoming more stringent, catalysts have increased in complexity to achieve improved activities and selectivities. This has required catalysts to be characterised under more severe conditions e.g. after extended thermal treatments to simulate catalyst lifetime. Detailed characterisation may allow a deeper understanding of the interactions within these catalysts and lead to improvements in catalyst design. The characterisation of these and other sophisticated catalysts may be improved by the development of an advanced characterisation technique using quantitative infrared spectroscopy. Bimetallic PtPd diesel oxidation catalysts which had been subjected to contrasting ageing processes were characterised using a variety of methods to study the surface composition and structure. Through FTIR studies, differences have been shown in the surface structure between the catalysts and using a semi-quantitative methodology, surface compositions have been determined. In addition to FTIR studies, characterisation has been performed using temperature programmed methods and simple oxidation reactions with in-situ diffuse reflectance spectroscopy. The results show clear evidence for the interaction of the two metals and also improved activity compared with the monometallic analogues. Simple oxidation reactions showed no significant structure sensitivity in either the CO or C3H6 oxidation reactions, however the NO oxidation reaction was shown to be sensitive to the catalyst structure following reduction. While FTIR was used to characterise the catalysts, experiments were performed with the aim to develop a quantitative methodology for FTIR applied to supported Pd catalysts. Investigations have shown the key considerations and factors required to develop an accurate quantitative method for CO adsorption on supported metal catalysts. The results of the investigations show a new method that can be applied for quantitative IR spectroscopy and the degree of complexity of the system when determining the molar absorption coefficients from complex spectra.

En raison des de l’augmentation de la pollution à l’échelle mondial du notamment aux gaz d'échappement des automobiles, de nouvelles réglementations d'émissions ont été mises en place depuis les années 1990. Ces règlementations ont conduit à une évolution des carburants traditionnels vers les biocarburants et à des systèmes de post-traitement des gaz d'échappement, notamment pour les moteurs diesel, de plus en plus sophistiqués. Ils comprennent à ce jour une série d'unités catalytiques, contenant un filtre à particules, un catalyseur d’oxydation pour traiter le monoxyde de carbone et les hydrocarbures et enfin un catalyseur pour réduire les oxydes d’azote. Dans ce travail de thèse, deux de ces systèmes catalytiques industriels ont été étudiés, les catalyseurs à l'oxydation diesel (DOC) et les catalyseurs de réduction catalytique sélective (SCR). Une attention particulière est accordée à leur performance en présence de composés métaux alcalins. En effet, les alcalins sont présent dans les biocarburants et lorsque le biodiesel est utilisé comme carburant de remplacement, ils vont donc être présents dans les gaz d’échappement et à priori dans les systèmes de post-traitement
Due to global lean exhaust gas and new emission regulations, exhaust after-treatment systems of diesel engines are getting more and more sophisticated and comprise a series of catalytic units. In the present work, two of these catalytic systems were studied, Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) catalysts. Particular attention is paid to their performance in the presence of alkali compounds when bio-diesel is utilized as the alternative fuel.Firstly, this thesis focuses on the catalytic behavior of the Diesel Oxidation Catalyst using different aging characteristics of road mileage in order to improve the efficiency of an ammonia SCR system on an after-treatment line composed by a DOC + DPF + SCR. The studied catalyst is a commercial diesel oxidation catalyst (Pt/Pd/Al2O3) provided by Continental. Hydrothermal aging under different conditions on carrots of monolith were performed. Also studied in the monolith form over the commercial DOC, the influence of the addition of different alkali metal species (K and Na) on the commercial DOC through catalytic tests performed on this structured catalyst under multicomponent (C3H6 / CO / NO / NO2) co-feeding conditions was explored. Aiming at investigating the effects of the presence of different alkali metal species on the DOC at the level of active phase, homemade bimetallic DOC is prepared and then different alkali metal species incorporated. Finally, encouraged by the evident influence of alkali compounds on DOCs, their impacts on the downstream SCR catalysts are also studied in this thesis. The studied SCR catalyst is a commercial V2O5-based catalyst provided by UMICORE company

Several technologies offer a promising strategy for the exhaust after-treatment of diesel engines in which continuing to further thrift Pt/Pd alloy diesel oxidation catalysts (DOC) by increasing Pd content, the prospect of an essentially Pt-free DOC catalyst is very attractive because Pd is cheaper than Pt. However, to determine the viability of this approach a much better understanding of PdO/AI20 3 chemistry and reactivity is needed. Therefore, the aim of this work is (1) to improve the catalytic performance of the Pd based ?iesel oxidation catalyst by using different preparation method and to investigate the effect of the thermal aging' on the catalyst activity towards CO and C3H6 oxidation. (2) clarify the effect of H20 and NO in the CO and C3H6 catalytic oxidation reactions in terms of reaction mechanism. (3) to investigate the catalyst deactivation induced by sulphur poisoning. It has been found that the structure, morphology and textures properties of the catalysts were significantly affected by both the preparation method and the thermal aging. In particular, the formation of highly catalytically active palladium nanoparticles showing a high density of defects and/or corners, have been observed when the sample was prepared by solution combustion synthesis and when thermal aging was carried out between 500 - 750 ·C. Regardless of the preparation method and the thermal aging, the presence of water in the reaction mixture resulted to promote the catalyst performances with the respect to CO oxidation which occurred via reaction with water derived species rather than dioxygen. Beside, water has also been found beneficial in modulating the NO, C3H6 and S02 inhibition. The formation of strongly bonded sulphate species on the catalyst surface along with the permanent loos of the structure and morphology properties of the catalyst, have been identified as the main cause of the catalyst deactivation induced by sulphur poisoning.

Abstract The combustion of fuels in motor vehicles is one of the most significant causes of air emissions. The use of oxidation catalysts in exhaust gas emission treatment can reduce hydrocarbons (HCs) and carbon monoxide (CO) emissions by more than 90%. Fuels and engine lubricants contain impurities like sulphur (S) and phosphorus (P), which can have a significant effect on the activity and durability of oxidation catalysts. This thesis aims at increasing the current knowledge of the deactivation phenomena caused by sulphur and phosphorus in diesel and natural/bio gas oxidation catalysts. Accelerated laboratory scale sulphur, phosphorus and thermal treatments in gas-phase conditions were carried out for alumina (Al2O3) based platinum (Pt) and platinum-palladium (PtPd) metallic monolith diesel and natural gas oxidation catalysts. In addition, a vehicle-aged natural gas oxidation catalyst and an engine-bench-aged diesel oxidation catalyst were studied and used as a reference for the laboratory-scale-aged catalysts. BET-BJH, FESEM, TEM, XPS and DRIFT were used as characterization techniques to determine changes on the catalysts. The effect of accelerated deactivation treatments on the catalyst activity was determined using laboratory scale measurements in CO, HC and nitric oxide (NO) oxidation. Sulphur and phosphorus were found to cause morphological and chemical changes on the studied catalysts. Sulphur was found to be adsorbed vertically throughout the entire catalyst support from the catalyst surface to the metallic monolith, while phosphorus accumulated on the surface region of the precious metal containing catalysts. Both, sulphur and phosphorus, slightly increased the average size of the precious metal particles size and are adsorbed onto the alumina by chemical bonds. In addition, a partial transformation from PdO to Pd and a change in the shape of the precious metal particles due to phosphorus were detected. Due to the detected structural and chemical changes on the catalysts, sulphur and phosphorus treatments reduced the catalytic activity of the studied diesel and natural-gas-oxidation catalysts. Correspondence between real and simulated ageing was found and thus the used accelerated laboratory scale aging method can be stated to be a good tool to simulate sulphur and phosphorus exposure
Tiivistelmä Moottoriajoneuvot ovat merkittäviä ilmapäästöjen aiheuttajia. Hapetuskatalyyttejä käyttämällä hiilimonoksidi- ja hiilivetypäästöistä pystytään poistamaan yli 90 %. Polttoaineet ja voiteluaineet sisältävät epäpuhtauksia kuten rikkiä ja fosforia, jotka voivat merkittävästi heikentää hapetuskatalyyttien aktiivisuutta ja kestävyyttä. Väitöskirjan tavoitteena on tuottaa uutta tietoa rikin ja fosforin aiheuttamasta diesel- ja maakaasukatalyyttien deaktivoitumisesta. Metalliseen monoliittiin tuettuja alumiinioksidipohjaisia platina- ja palladiumkatalyytteja ikäytetiin tekemällä niille rikki-, fosfori- ja lämpökäsittelyjä. Maantieikäytettyä maakaasuhapetuskatalyyttiä ja moottoripenkki-ikäytettyä dieselhapetuskatalyyttiä käytettiin laboratorioikäytettyjen katalyyttien referensseinä. Ikäytyskäsittelyjen aiheuttamat muutokset analysoitiin BET-BJH-, FESEM-, TEM-, XPS- ja DRIFT-menetelmillä. Käsittelyjen vaikutus katalyyttien hiilimonoksidin, hiilivetyjen ja typenoksidien hapetusaktiivisuuteen tutkittiin laboratoriomittakaavan aktiivisuuslaitteella. Rikki ja fosfori aiheuttivat rakenteellisia ja kemiallisia muutoksia tutkittuihin katalyytteihin. Rikki adsorboitui koko tukiaineeseen (tukiaineen pinnalta pohjalle), kun taas fosfori adsorboitui vain pinnan alueelle. Sekä rikki että fosfori kasvattivat jalometallipartikkeleiden kokoa sekä muodostivat alumiinioksidin kanssa yhdisteitä. Lisäksi fosforikäsittelyjen havaittiin osittain pelkistävän PdO:n Pd:ksi ja muuttavan jalometallipartikkelien muotoa. Havaitut rikin ja fosforin aiheuttamat rakenteelliset sekä kemialliset muutokset laskivat diesel- ja maakaasukatalyyttien hapetusaktiivisuutta. Laboratorioikäytyksillä havaittiin olevan hyvä korrelaatio todellisissa olosuhteissa tehtyjen ikäytysten kanssa ja tästä syystä työssä käytetyn laboratoriomittakaavan ikäytysmenetelmän voidaan todeta olevan hyvä työkalu simuloimaan rikin ja fosforin aiheuttamaa deaktivoitumista

Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains xii, 140 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-84).

[ES] Esta tesis doctoral abarca el desarrollo de algoritmos orientados a mejorar el sistema de control de emisiones en motores Diesel. Para este propósito, la inclusión en el vehículo de sensores embarcados como los de temperatura, los de NOx o el de NH3 permite realizar diagnóstico a bordo de los sistemas de post-tratamiento foco de este trabajo, los cuales son el DOC y el SCR. Así pues, el objetivo es el de satisfacer las normativas de diagnóstico a bordo para mantener las emisiones por debajo del umbral permitido por la normativa a lo largo del tiempo. Los tests experimentales, incluyendo las medidas con analizador de gases, permiten tener una visión más amplia de las especies en la línea de escape. Complementariamente, se utilizan unidades nuevas y envejecidas para tener el efecto experimental del envejecimiento en los catalizadores. De esta manera, se analiza el efecto de la temperatura, el gasto de escape, las concentraciones de las especies y el envejecimiento en el DOC y en el SCR, así como la evaluación de algunas de las medidas relevantes realizadas por los sensores. Las temperaturas tienen una influencia destacada en el funcionamiento de los catalizadores, por lo que se requiere la evaluación de las medidas de los sensores de temperatura, junto con el desarrollo de modelos de transmisión de calor, para alimentar las funciones a continuación desarrolladas. En este sentido, la medida lenta del sensor aguas arriba del DOC se mejora en condiciones transitorias mediante una técnica de fusión de la información basada en un filtro de Kalman. Luego, se presenta un modelo de transmisión de calor 1D y un modelo agrupado 0D, en los cuales se evalúan las entradas aguas arriba según el uso del modelo. Por otra parte, se presenta una técnica para estimar el incremento de temperatura debido a la oxidación de los pulsos de post-inyección en el DOC. Se proponen modelos para ambos DOC y SCR para estimar el efecto del envejecimiento en las emisiones, en los cuales el factor de envejecimiento es modelado como un parámetro sintonizable que permite variar desde estados nuevos a envejecidos. Por una parte, un modelo agrupado 0D es desarrollado para el DOC con el propósito de estimar el desliz de HC y CO, el cual es validado en un WLTC para después ser usado en simulación. Por otra parte, un modelo 1D y un modelo 0D se desarrollan para el SCR, los cuales se usan a continuación para alimentar la estrategia de diagnóstico y para simulación. Finalmente, las estrategias de diagnóstico se presentan para fallo total o retirada de DOC, así como para la estimación de la eficiencia en DOC y SCR. Por una parte, la primera estrategia se divide en pasiva y activa, en la que se usan post-inyecciones en la activa para excitar el sistema y confirmar el fallo total si es el caso. A continuación, la eficiencia del DOC se estima a través de una técnica indirecta en la que la temperatura de activación se detecta y se relaciona con el incremento de emisiones a través del modelo. Por otra parte, se desarrolla un observador para estimar el estado de envejecimiento del SCR, el cual está basado en un filtro de Kalman extendido. Sin embargo, para evitar asociar baja eficiencia del catalizador debido a pobre calidad de la urea inyectada, a envejecimiento del SCR, un indicador de la calidad de la urea se ejecuta en paralelo.
[CAT] Esta tesi doctoral abasta el desenvolupament d'algoritmes orientats a millor el sistema de control d'emissions en motors Diesel. Per a este propòsit, la inclusió en el vehicle de sensor embarcats com els de temperatura, els de NOx o el d'NH3 permet realitzar el diagnòstic a bord dels sistemes de post-tractament focus d'este treball, els quals són el DOC i el SCR. Així doncs, l'objectiu és el de satisfer les normatives de diagnòstic a bord per a mantindre les emissions per baix de l'umbral permés per la normativa al llarg del temps. Els tests experimentals, incloent les mesures amb analitzador de gasos, permeten obtindre una visió més àmplia de les espècies en la línia d'escapament. Complementàriament, s'utilitzen unitats noves i envellides per tal de tindre l'efecte experimental de l'envelliment en els catalitzadors. D'aquesta manera, s'analitza l'efecte de la temperatura, la despesa d'escapament, les concentracions de les espècies i l'envelliment en el DOC i en el SCR, així com l'avaluació d'algunes mesures rellevants realitzades pels sensors. Les temperatures tenen una influència destacada en el funcionament dels catalitzadors, pel que es requerix l'avaluació de les mesures dels sensors de temperatura, junt amb el desenvolupament de models de transmissió de calor, per a alimentar les funcions a continuació desenvolupades. En este sentit, la mesura lenta del sensor a l'entrada del DOC es millora en condicions transitòries mitjançant una tècnica de fusió de la informació basada en un filtre de Kalman. Després, es presenta un model de transmissió de calor 1D i un model agrupat 0D, en els quals s'avaluen les entrades a l'entrada segons l'ús del model. Per altra banda, es presenta una tècnica per a estimar l'increment de temperatura degut a l'oxidació dels polsos de post-injecció en el DOC. Es proposen models per a DOC i SCR per a estimar l'efecte de l'envelliment en les emissions, en els quals es modela el factor d'envelliment com un paràmetre sintonitzable, que permet variar des d'estats nous a envellits. Per altra banda, un model agrupat 0D _es desenvolupat per al DOC amb el propòsit d'estimar la relliscada de HC i CO, el qual és validat en un WLTC per a després ser usat en simulació. Per altra banda, un model 1D i un model 0D es desenvolupen per al SCR, els quals s'usen a continuació per a alimentar l'estratègia de diagnòstic i per a simulació. Finalment, les estratègies de diagnòstic es presenten per a la fallada total o retirada del DOC, així com per a l'estimació de l'eficiència en DOC i SCR. Per altra banda, la primera estratègia es divideix en passiva i activa, en la que s'utilitzen post-injeccions en la activa per a excitar el sistema i confirmar la fallada total si es dona el cas. A continuació, l'eficiència del DOC s'estima a través d'una tècnica indirecta en la que la temperatura d'activació es detecta i es relaciona amb l'increment d'emissions a través del model. Per altra banda, es desenvolupa un observador per a estimar l'estat d'envelliment del SCR, el qual està basat en un filtre de Kalman extés. No obstant això, per a evitar associar baixa eficiència degut a pobre qualitat de l'urea injectada a l'envelliment del SCR, un indicador de la qualitat de l'urea s'executa en paral·lel.
[EN] This dissertation covers the development of algorithms oriented to improve the emission control system of Diesel engines. For this purpose, the inclusion of on-board sensors like temperature, NOx and NH3 sensors allows performing on-board diagnostics to the after-treatment systems focus of this work, which are the DOC and the SCR system. Then, the target is to meet on-board diagnostics regulations in order to keep emissions below a regulation threshold over time. Experimental tests, including gas analyzer measurements, allow having a wider view of the species in the exhaust line. Complementary, new and aged units are used in order to have the experimental effect of ageing on the catalysts. Then, the effect of temperature, exhaust mass flow, species concentrations and ageing is analyzed for DOC and SCR, in combination with the assessment of some relevant sensors measurements. As a result, the characteristics, opportunities and limitations extracted from experimental data are used as the basis for the development of models and diagnostics techniques. The assessment of temperature sensors measurements, along with the development of heat transfer models is required to feed temperature dependent functions. In this sense, the slow measurement of the DOC upstream temperature sensor is improved in transient conditions by means of a data fusion technique, based on a fast model and a Kalman filter. Then, a 1D and a 0D lumped heat transfer models are presented, in which the upstream inputs are assessed in relation to its use. On the other hand, a technique to estimate the temperature increase due to post-injection pulses oxidation is also presented. Both DOC and SCR models are proposed in order to estimate the effect of ageing on emissions, in which an ageing factor is modelled as a tunable parameter that allows varying from new to aged states. On the one hand, a 0D lumped model is developed for DOC in order to estimate the HC and CO species slip, which is validated in a WLTC and is then used for simulation. On the other hand, a 1D and a 0D models are developed for SCR, which are then used to feed the diagnostics strategy and for simulation. Finally, diagnostics strategies are presented for total failure or removal of DOC, as well as for efficiency estimation of DOC and SCR. On the one hand, the former strategy is separated into passive and active diagnostics, in which post-injections are used in active diagnostics in order to excite the system and confirm a total failure, in case. Then, the DOC efficiency estimation is done by means of an indirect technique in which the light-off temperature is detected and an emissions increase is related by means of the DOC ageing model. On the other hand, an observer to estimate the SCR ageing state is developed, which is based on an extended Kalman filter. However, in order to avoid associating low SCR efficiency to ageing, an indicator of the injected urea quality is developed to run in parallel.
Mora Pérez, J. (2018). Control-oriented modelling and diagnostics of diesel after-treatment catalysts [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115937
TESIS

Le travail au présent surligne la cérine nanostructurée et bien-définie ; une morphologie qui promeut une haute activité catalytique de la cérine dans l’oxydation des suies. Le travail présente également l’introduction des métaux pour le dopage, tels que praséodyme et zirconium, à la surface de la cérine pour améliorer la réductibilité, la stabilité thermique, et la capacité du stockage d’oxygène. L’oxydation à température programmée a été utilisée pour analyser l’activité catalytique. Au premier étage de la recherche, on a découvert que l’oxyde en mélange équimolaire de la cérine et de l’oxyde de praséodyme en nanostructure (indiqué comme Ce50Pr50-NP) possède la quantité d’espèces oxygénées à la surface la plus haute, la réductibilité la plus haute et l’activité catalytique la plus haute dans l’oxydation normale des suies. Il a été conclu que la nanostructure soulève la fonctionnalité du praséodyme dans la cérine. Le travail introduit également des nanoparticules (NPs) de Pt stabilisée par n-octylsilane. Pendant la calcination, les ligands silyliques se transforment aux « patches » de la silice qui leur évitent le frittage. Des NPs de Cu ont été préparées avec la même façon ; néanmoins elles ont souffert de sintering. Les NPs de Pt sont très actives dans l’oxydation de tous les polluants modèles des véhicules Diesel, spécifiquement l’oxydation des suies en présence de NOx, et elles fonctionnent mieux avec la cérine nanostructurée. Comme attendu, Ce50Pr50-NP donne l’activité catalytique plus haute que les catalyseurs à base du platine. La haute conversion du NO et l’adsorption du NO2 sur la surface sont la raison majeure de l’activité marquante
The present work highlights well-defined nanostructured ceria; a morphology that bestows exceptional catalytic activity on ceria towards soot oxidation. The work includes also introduction of promoting foreign metals, such as praseodymium and zirconium, to well-defined nanostructured ceria as a means of improving reducibility, thermal stability and oxygen storage capacity of the catalyst. Temperature-programmed oxidation (TPO) has been used for analyzing catalytic activity. At the first stage of the research, nanostructured equimolar ceria-praseodymia (denoted as Ce50Pr50-NP) was found to have the highest amount of surface oxygen, the highest reducibility and the highest catalytic activity towards soot oxidation. The nanostructured morphology has been proven to raise the functionality of praseodymia as the foreign metal in ceria. The work also introduces small, silane-stabilized Pt nanoparticles. Upon calcination, silyl ligands are transformed into siliceous patches that prevent the particle from migrating/coalescing. Cu nanoparticles have been prepared the same way as Pt nanoparticles; however, they sinter even under milder thermal treatment. The small Pt-NPs are proven active towards all pollutant oxidations, including NOx-assisted soot oxidation, and they function better with nanostructured ceria as the support. Unexpectedly, Ce50Pr50-NP gives higher activity towards NOx-assisted soot oxidation than Pt catalysts. Intense NO conversion and NO2 adsorption on the surface of Ce50Pr50-NP are the reason behind its high activity

Les normes plus restrictives visent à réduire les émissions de polluants, en particulier le CO2, favorisant l'usage des biocarburants. Cependant, le biodiesel contient des éléments inorganiques (Na, K, Ca et P) qui réduisent la durabilité des systèmes de post-traitement. Dans ce travail sont évalués les performances des catalyseurs d'oxydation diesel (DOCs, catalyseur de référence PtPd/CeZrO2/La-Al2O3). Les résultats de caractérisation ont montré l’influence de ces impuretés sur les propriétés physico-chimiques et catalytiques. Bien que la structure cristalline du catalyseur de référence ne change pas après l'incorporation des impuretés, la surface spécifique diminue. La capacité redox a diminué lorsque les impuretés Na, K et Ca sont présents du à leur faible électronégativité, ce qui augmente l'interaction avec l'oxygène. Cette interaction semble être responsable de l’augmentation de la vitesse de réaction de C3H6. Les résultats NO-TPD ont montré que la forte basicité ces impuretés entraînait une plus forte adsorption du NO. Par DRIFT il a été aussi montré que l’adsorption des intermédiaires du NO, associée au champ électrostatique créé par ces cations, empêche l'oxydation de NO. L'adsorption de CO a été favorisée, améliorant la conversion du CO. La formation de phosphate de cérium observée pourrait stabiliser l'état d'oxydation de Ce3+ (vérifié par XPS), en diminuant l'oxydation de NO due au blocage des sites catalytiques. Néanmoins, les co-oxydations de CO et de C3H6 ont été améliorées en évitant l'auto-empoisonnement. Après vieillissement hydrothermal, l'effet des impuretés a été masqué par le frittage de Pt/Pd, ce qui diminue les performances catalytiques
The more restrictive regulations to reduce pollutants emissions, especially CO2, promote the use of biofuels. However, biodiesel contains inorganic elements (Na, K, Ca and P) that reduce the durability of the after-treatment catalysts. This work aims to evaluate the performance of Diesel Oxidation Catalysts (DOCs, PtPd/CeZrO2/La-Al2O3 reference catalyst). The characterization results have shown that the above-mentioned impurities affect the physico-chemical, redox, surface and catalytic properties. Although the catalyst crystalline structure of reference catalyst did not change after impurities incorporation, the specific surface area decreased. The redox ability was also decreased when Na, K and Ca impurities are present due to their low electronegativity, which increased the oxygen interaction. This high interaction seems to be responsible of the enhanced C3H6 reaction rate. NO-TPD results evidenced that the high basicity of Na, K and Ca impurities resulted in an increase of NO adsorption strength. Accordingly, DRIFT results showed the presence of NO intermediates adsorption associated to the electrostatic field created by these cations, hindering NO oxidation. CO adsorption was also promoted, enhancing CO reaction rate. The formation of cerium phosphate was also observed, which could stabilize the Ce3+ oxidation state (checked by XPS), decreasing NO oxidation due to the blockage of catalytic sites. Nevertheless, CO and C3H6 co-oxidations were enhanced by avoiding self-poisoning. After catalyst hydrothermal aging, the effect of impurities was masked by the sintering of Pt/Pd active sites, which decreases the DOC catalytic performances

In order to obtain a deeper understanding of the performance of a diesel oxidation catalyst (DOC), techniques are developed which help to bridge the gap in the development of catalyst technology from the laboratory bench-top to an application on a real 2.0 litre diesel engine. The methodology is illustrated using a full-scale DOC (106 mm diameter; length 114 mm), from which sections are cut and then examined using a variety of techniques, including: optical measurement, SEM, TEM, FTIR, CO chemisorption, pore size and pore volume measurements. These provide valuable information on the characteristics of the Pt catalyst, in the actual form (on supportlwashcoat) that it will be used in a commercial application. In addition, a transient chromatographic technique was tested to measure the effective diffusivity in the washcoat layer. These experiments were performed using sections of v-alumina washcoated (:::::50/lm thick) monolith (1 mm channels), which were mounted in a 570 mm long housing - unfortunately this did not work. The technique was improved, and short sections of monolith, with a larger channel diameter (2.64 mm) and with a thicker washcoat (:::::475/lm) were mounted in a 1 m long sleeve - although better results were obtained, this technique still needs to be improved. A methodology was then described, in which a short section of DOC (5 mm long) was cut from the full-scale DOC, and this was connected to a live 2.0 litre diesel engine. It was shown how experiments (with gas inlet temperatures varying from 150 to 270 QC) can be performed, and in combination with a modelling technique, the information gathered can be used to test the validity of rate expressions. It was shown: (a) that the Langmuir-Hinshelwood-Hougen-Watson (LHHW) form of rate expression is clearly unsuitable for transient simulations, whereas mechanistic forms can provide a better match to the experimental data, and (b) how to tune the coefficients to match points of ignition-extinction in the light-off hysteresis cycle.

The objective of this study was onboard testing of a mixed metal oxide diesel soot oxidation catalyst composing of oxides of lead and cobalt previously developed in our lab, by mounting a diesel particulate filter (DPF), which is coated with this catalyst, to the exhaust stream of a diesel vehicle. Commercial wall flow type DPF&rsquo
s (Corning EX-80) were coated with the catalyst by a slurry wash-coating procedure and then mounted on the exhaust stream of a diesel light duty vehicle (LDV) provided by TOFAS (FIAT Doblo 1.9 JTD). These vehicles were driven on the rollers of the chassis dynamometer at constant speed and gear for two different loading conditions and on a standard driving cycle (NEDC) in the Test and Emission Laboratory of TOFAS-FIAT. The exhaust gases were analyzed for NOx, CO, CO2, THC and PM. The pressure drop caused by the filter was monitored during these tests as an indication of soot accumulation on the filter with the help of pressure sensors placed before and after the filter. Also temperatures before, inside and after the filter were monitored by means of thermocouples. Three different filters were tested in this manner: (1) Monocoated (CoOx), (2) Sequential PbOx coated over CoOx (PbOx/CoOx), (3) Simultaneously coated (PbCoOx). Also tests with the uncoated filter were performed to determine the pressure drops as a result of non-catalytic soot oxidation. The performances of the catalytic filters were evaluated by determining the temperature at which the soot oxidation rate on the filter equals the soot production rate in the engine (balance point temperature-Tbal). This temperature was used for comparing the catalytic activity of the supported catalyst with that of the powder form tested in the laboratory, i. e. Tpeak. The results of the onboard test were in parallel with the previous laboratory studies with similar catalytic activity temperatures. The continuous regeneration temperatures (Tbal) obtained in onboard tests with PbOx/CoOx and PbCoOx filters of about 370oC, which was close to the values attained in the lab study with the same mixed metal oxide catalyst having a Tpeak value of 385oC. Also the PM emissions during the tests were complying with the current EURO-IV emission limits.

In this thesis, the experimental test facilities consisted of a well instrumented live Ford 2.0 litre turbocharged diesel engine connected to a specially made exhaust can, which contained a diesel oxidation catalyst (DOC). Experiments were performed on DOCs, which were specially prepared by Johnson Matthey, and had thermocouples mounted in their walls to measure axial temperature profiles. These DOCs consisted of a Pt catalyst dispersed in an alumina washcoat on a cordierite monolith supports, and were representative of a commercial application. Experiments were performed on Full-scale DOCs (o.d. = 106 mm, length = 114 mm), and also on Thin-slice DOCs (length = 5 and 10 mm), which generate some interesting data, and enabled a technique that is normally only used in laboratory bench-top experiments to be applied to a live engine. A number of different methodologies were developed based on (a) the operation of the engine at pseudo-steady-state operating conditions, and (b) transient experiments (e.g. a pulse of CO was injected into the exhaust gas just before the DOC). For example, it was shown how experiments on a live engine can be used to explore: (a) the hysteresis between light-off and extinction curves, (b) how catalyst temperature rise during warm-up of a DOC, (c) the promotion effect that hydrogen has on the conversion of CO, (d) the extent of competition for active catalytic sites, e.g. between CO, THCs, propane or hydrogen. The main findings are: (a) the hysteresis between light-off and extinction curves are mainly caused by CO inhibition, (b) the promotion effect of hydrogen on CO oxidation is largely attributed to thermal effect, (c) LHHW form rate expression is not adequate for catalytic converter modelling under transient conditions, (d) the competition for active catalytic sites is not apparent at the test conditions performed in this thesis. Moreover, a number of case studies were also used to illustrate how the experimental results/techniques developed in this thesis, may be used to support modelling studies. iii

Scania provides sustainable transport systems powered by bioethanol, biogas, biodiesel along with hybrid and conventional solutions. Today Scania offers the largest variety of engines operating on alternative fuels in the market. The number of the alternative fuel operated vehicles sold in 2016 increased by 40 % [1]. Nevertheless, one of the alternative fuels – biodiesel - is a source of inorganic contaminants. These impurities can detrimentally affect the diesel truck after-treatment system that is responsible for harmful emission abatement. As a consequence, better understanding of the alternative fuel impact on the after-treatment system is necessary for further development of a sustainable transportation system. This thesis is focused on the diesel oxidation catalyst (DOC) that is one of the major components in the diesel truck after-treatment system. Catalyst performance due to chemical deactivation of biodiesel derived inorganic contaminants (P, Na and Ca) is determined and analysed. The study covers PtPd/Al 2O3 DOC preparation and poisoning by the incipient wetness impregnation method, monolith dip-coating, fresh and poisoned catalyst characterization (BET, CO chemisorption, TPR, ICP-OES, TEM-EDS, SEM-EDS, XRD). Catalyst activity tests in a laboratory scale activity testing rig are performed to study carbon monoxide, nitric oxide and propylene oxidation reactions before and after the poisoning. Sulphur effect on the catalyst activity is determined after the gas-phase poisoning with SO2.

Abstract Exhaust gas emissions, e.g. nitrogen oxides (NOx), hydrocarbons (HCs) and carbon monoxide (CO), are harmful to human health and the environment. Catalysis is an efficient method to decrease these emissions. Unfortunately, the fuels and lubricant oils may contain chemical impurities that are also present in exhaust gases. Thus, catalytic materials with high activity and chemical resistance towards impurities are needed in the abatement of exhaust gas emission. In this thesis, the aim was to gain new knowledge about the effects of chemical impurities on the behaviour and activity of the catalysts. To find out these effects, the impurities existing in the exhaust gas particulate matter after combustion of biofuels and fossil fuels were analysed. The studied zeolite (ZSM-5), cerium-zirconium mixed oxides (CeZr and ZrCe) and silicon-zirconium oxide (SiZr) based catalysts were also treated with impurities to simulate the poisoning of the catalysts by, e.g. potassium, sodium, phosphorus and sulphur, using gas or liquid phase treatments. Several characterization techniques were applied to find out the effects of impurities on catalysts’ properties. The activity of catalysts was tested in laboratory-scale measurements in CO and HC oxidation and NOx reduction using ammonia (NH3) and hydrogen (H2) as reductants. The results revealed that the CeZr based catalysts had a high activity in NOx reduction by NH3 and moderate activity by H2. Sulphur was proven to enhance the activity of CeZr catalysts in NOx reduction. This is due to an increase in chemisorbed oxygen after the sulphur treatment on the catalyst surface. Instead, in HC and CO oxidation reactions, sulphur had a negligible impact on the activity of the SiZr based diesel oxidation catalyst. Thus, both CeZr and SiZr based catalysts can be utilized in exhaust gas purification when sulphur is present. ZSM-5 based catalysts were proven to be resistant to potassium and sodium. Alternatively, the activity of SiZr based catalysts decreased due to phosphorus. Thus, the removal of biomaterial-based impurities from the exhaust gases is needed to retain high catalyst activity in the exhaust gas after-treatment system
Tiivistelmä Pakokaasupäästöissä olevat typen oksidit (NOx), hiilivedyt (HCs) ja hiilimonoksidi (CO) ovat haitallisia ihmisten terveydelle ja ympäristölle. Katalyysi on tehokas menetelmä vähentää näitä päästökomponentteja. Polttoaineet ja voiteluöljyt sisältävät epäpuhtauksia, jotka siirtyvät myös pakokaasuihin. Tästä johtuen pakokaasupäästöjen hallinnassa tarvitaan katalyyttimateriaaleja, joilla on hyvä vastustuskyky myrkyttymistä vastaan. Tavoitteena oli saada uutta tietoa kemiallisten epäpuhtauksien vaikutuksesta katalyyttien toimintaan. Biopolttoaineiden sisältämät mahdolliset epäpuhtaudet selvitettiin analysoimalla fossiilisen ja biopolttoaineen palamisessa muodostuvia partikkeleita ja vertaamalla niitä polttoaineiden hivenaineanalyysiin. Tutkimuksessa käytetyt zeoliitti (ZSM-5), cerium-zirkonium-sekaoksidi (CeZr) ja pii-zirkonium-oksidipohjaiset (SiZr) katalyytit käsiteltiin epäpuhtauksilla (kalium, natrium, fosfori ja rikki) kaasu- ja nestefaasissa. Tutkimuksessa käytettiin useita karakterisointitekniikoita, joiden avulla selvitettiin epäpuhtauksien vaikutuksia katalyyttien ominaisuuksiin. Katalyyttien toimintaa testattiin laboratoriomittakaavan kokeissa CO:n ja HC-yhdisteiden hapetuksessa sekä NOx:ien pelkistyksessä käyttäen ammoniakkia (NH3) tai vetyä (H2) pelkistimenä. Tulokset osoittavat, että CeZr-pohjaisten katalyyttien aktiivisuus NOx:ien pelkistyksessä oli hyvä käytettäessä pelkistimenä NH3:a ja kohtalainen käytettäessä vetyä. Rikki paransi CeZr-katalyyttien aktiivisuutta NOx:ien pelkistyksessä, mikä johtui kemiallisesti sitoutuneen hapen osuudesta katalyyttien pinnoilla. Vastaavasti hiilivetyjen ja CO:n hapetusreaktioissa rikki ei vaikuttanut SiZr-pohjaisten dieselhapetuskatalyyttien aktiivisuuteen. Sekä CeZr- ja SiZr-pohjaisia katalyytteja voidaan siten käyttää rikkiä sisältävien pakokaasujen puhdistuksessa. SiZr-pohjaisten katalyyttien aktiivisuus laski fosforin vuoksi. ZSM-5-pohjaiset katalyytit olivat vastustuskykyisiä kaliumille ja natriumille. Kestäviä katalyyttejä on siten kehitettävä, mikäli biopolttoaineiden sisältämien epäpuhtauksien poistaminen polttoaineista ei ole mahdollista

Oxidation filters are used to decrease particulate emissions commonly. In this study, design of a particulate trap to produce an alternative, low cost filter has been aimed. An experimental setup has been installed according to standards to carry out tests of these designed filters. Electronic measurement and control systems have been attached to this setup to increase efficiency of experiments. Two filter designs have been used in the experiments. First design consists of aluminum wire cloth. Second design is sheet metal structure, which includes three longitudinal cells. Metal chip is used as filter material. Empty filter tests have been performed firstly, and then experiments have been repeated with aluminum, iron, and copper chip addition in filter. Copper chip test results are better than other metal chip for first experiments. Afterwards, experiments have been repeated with varying copper chip amount. Suitable copper chip amount was determined based on fuel consumption rate of the engine. As a result, designed filter reduce the particulate emissions with high efficiency. Although, carbon monoxide, and carbon dioxide gaseous emissions increase with designed filter, hydro carbon emissions decrease.

L’amélioration de la qualité de l’air est un enjeu majeur pour la santé et l’environnement. Le challenge pour les fabricants de convertisseurs catalytiques pour la dépollution automobile est d’optimiser leur formulation pour répondre aux normes réglementant les émissions polluantes se durcissant, tout en rentabilisant l’utilisation de métaux précieux dont les ressources s’épuisent. Dans cette thèse, un nouveau support catalytique MgAl2O4 méso-poreux a été synthétisé par atomisation d’un sol aqueux contenant un copolymère tri-blocs. Les nano-cristallites de MgAl2O4 en contact quasi-ponctuel permettent d’atteindre des taux de dispersion de la phase active Pt-Pd supérieurs à ceux d’un catalyseur d’oxydation Diesel commercialisé, pris comme référence par la société Renault. La phase active d’un catalyseur 2,5%m.PtPd(3:2)[450°C]/MgAl2O4[900°C] présente une stabilité hydrothermale similaire à celle ce dernier grâce aux ancrages chimiques (croissance épitaxiale, solutions solides) et mécaniques (marches atomiques, pores). Bien que la totalité des métaux précieux ne soit pas accessible (insertion, encapsulation) pour l’oxydation du CO, des HC et de NO, les performances catalytiques atteintes par ce catalyseur au cours de vieillissements hydrothermaux sont comparables à celle d’un DOC de référence. La conversion des HC est similaire à celle du DOC de référence et dépendante de la concentration locale des sites actifs. La conversion du CO est légèrement pénalisée car les particules sont de trop petite taille et à l’état oxydé. Enfin, ce catalyseur ne réduit pas les NOx, en revanche il assure une oxydation plus importante de NO en NO2 après vieillissement hydrothermal que le DOC de référence, ainsi que le stockage de NO2. Cela représente un avantage majeur pour le bon fonctionnement du filtre à particules situé en aval du DOC
The improvement of air quality is a major issue for the health and the environment. The challenge for the manufacturers of catalytic converters for automotive depollution is to optimize their formulation to meet the standards regulating the polluting emissions hardening, while making a profitable use of the precious metals whose resources are becoming exhausted. In this thesis, a new, mesoporous, MgAl2O4, catalytic support was synthesized by atomization of an aqueous sol containing a tri-block copolymer. The MgAl2O4 nanocristallites in point contact enable to reach higher dispersion rates of the Pt-Pd active phase than those of a commercialized DOC taken as reference by Renault. The active phase of the 2,5%m.PtPd(3:2)[450°C]/MgAl2O4[900°C] catalyst presents similar hydrothermal stability to that of the reference DOC thanks to chemical anchoring (epitaxial growth, solid solutions) and mechanical anchoring (atomic steps, pores). Although the totality of the precious metal content is not accessible (insertion, encapsulation) for CO, HC and NO oxidation, the catalytic performances reached by this catalyst during hydrothermal aging are comparable with that of the reference DOC. The conversion of the HC is similar to that of the reference DOC and depends on the local concentration of the active sites. The CO conversion rate is slightly penalized since the particles are too smalls and in an oxidized state. Lastly, this catalyst does not reduce NOx but ensures a more important oxidation of NO in NO2 after a hydrothermal aging than the reference DOC and also the storage of NO2 which have a positive impact on the proper functioning of the downstream diesel particulate filter

Le nouveau mode de combustion HCCI est adapté pour réduire les émissions d’oxydes d’azote et de particules fines issues de moteurs Diesel afin de respecter les futures normes d’émission Euro de plus en plus drastiques. Ce type de combustion se traduit par l’augmentation des émissions de monoxyde de carbone et des hydrocarbures et par une faible température des gaz d’échappement retardant ainsi leur conversion par le catalyseur d’oxydation Diesel (DOC). C’est dans ce contexte environnemental et économique que le couplage plasma-catalyseur apparait comme une solution intéressante afin d’améliorer l’efficacité du traitement des gaz d’échappement Diesel. Cette thèse est dédiée à l’étude du couplage d’un plasma non-thermique de type décharge à barrière diélectrique (DBD) et d’un catalyseur d’oxydation Diesel (Pt-Pd/Al2O3) pour le traitement de mélanges gazeux représentatifs d’un échappement de moteur Diesel HCCI (O2-NO-H2O-CO-CO2-CH4-C3H6- C7H8-C10H22-N2). Les expériences avec un réacteur plasma pilote ont été menées sur deux bancs expérimentaux : le premier à l’échelle laboratoire en vue de comprendre la physico-chimie impliquant le plasma et le catalyseur avec une attention particulière pour les sous-produits de réaction, et le second à l’échelle industriel afin de déterminer l’efficacité et la faisabilité d’un tel couplage dans les conditions de débit et de température les plus proches possibles de celles rencontrées en sortie moteur véhicule. L’étude menée en fonction de la puissance injectée dans le milieu, la VVH, la température des gaz, ainsi que la nature du cycle de roulage a permis de montrer l’efficacité du plasma pour abaisser de façon significative la température d’activation du DOC pour l’oxydation de CO et des hydrocarbures. Aussi, la présence du plasma en amont du DOC a permis, sur un cycle NEDC simulé, une réduction de 68% et 42% des masses de CO et des hydrocarbures émis en accord avec la norme Euro6 (2014). L’efficacité du plasma pour l’oxydation des hydrocarbures et de NO à basse température dans ces conditions de débits élevés (jusqu’à 900 Lmin−1 sur le cycle NEDC) a été confirmée et les principaux produits de réaction identifiés et quantifiés
The new HCCI combustion mode is well adapted to improve nitrogen oxide and particulate matter reduction from Diesel engine in order to meet future emission regulations adopted in the Euro zone. However, HCCI engines emit relatively high amounts of unburned hydrocarbons and carbon monoxide due to lower engine exhaust temperature increasing the catalyst light-off time and decreasing the average efficiency of the Diesel oxidation catalyst (DOC). In this environmental and economic context, the combination of plasma with DOC has been considered especially for intermittent use during the cold start. The thesis presents the combination of nonthermal plasma upstream Diesel oxidation catalyst (Pt-Pd/Al2O3) applied to the treatment of simulating Diesel HCCI exhaust gas (O2-NO-H2O-CO-CO2-CH4-C3H6-C7H8-C10H22-N2). The studies were conducted at atmospheric pressure with a pilot-scale dielectric barrier discharge reactor (DBD) on two experimental devices. The first is a laboratory scale set-up (low flow rate : 20 Lmin−1) used to understand the physico-chemical involving the plasma and the catalyst by focusing on the by-products reactions. The second is an industrial scale (gas flow rate up to 260 Lmin−1) used to study the feasibility and the efficiency of the plasma-DOC system under conditions similar to those encountered in Diesel exhaust engine. The effects of the plasma, the DOC and the plasma-DOC systems on the exhaust gas have been investigated under various conditions. The main contribution of the plasma was to give a « thermal » and a chemical « push » to the DOC resulting in the decrease of light-off temperature for CO and HC oxidation. These improvements were shown to depend on the treatment conditions (injected energy i.e. energy density, space velocity, gas temperature and nature of the driving cycle). It is shown that for a simulated European Driving Cycle (NEDC), the combination of plasma upstream DOC reduces the cumulative mass of CO and hydrocarbons by about 68% and 42%, respectively, in accordance with the Euro 6 standard (2014). The efficiency of plasma for hydrocarbons and NO oxidation at low temperature in high flow conditions (up to 900 Lmin−1 on the NEDC) has been confirmed and the main reaction products identified and quantified

The scope of this dissertation work is a description of modern methods of reducing exhaust emission in diesel engines. The fundamental part is the application of these methods for diesel engines for off-road use that means for engines that are used in tractors and road machines. The mentioned evidence for the practical utility of the results of this dissertation thesis in practice and their verification on the actual engine are given in the conclusion.

L’hybridation électrique de la chaîne de traction automobile est l’une des solutions adoptées pour respecter les règlementations futures sur ses émissions. La stratégie de supervision de la chaîne de traction hybride répartit la puissance produite par le moteur à combustion interne et la machine électrique. Elle répond habituellement à un problème d’optimisation où l’objectif est de réduire la consommation de carburant mais nécessite à présent d’y ajouter les émissions polluantes. La chaîne de dépollution, placée à l’échappement du moteur, permet de diminuer la quantité de polluants émise dans l’atmosphère. Cependant, elle n’est efficace qu’à partir d’un seuil de température, et dépend de la chaleur apportée par les gaz d’échappement du moteur thermique. La première partie de ce travail est donc consacrée à la modélisation de la consommation énergétique et des émissions polluantes de la chaine de traction hybride. La modélisation de l’efficacité de la chaîne de dépollution est réalisée selon deux contextes. Le modèle zéro-dimensionnel est adapté aux contraintes de calcul de la commande optimale. Le modèle unidimensionnel associé à un estimateur d’état permet d’être embarqué et calculé en temps réel. À partir de ces travaux, la seconde partie de cette thèse déduit des stratégies de supervision à l’aide de la théorie de la commande optimale. Dans un premier cas, le principe de Bellman permet de calculer la commande optimale d’un véhicule hybride Diesel selon des critères de supervision ayant plus ou moins connaissance de l’efficacité de la chaîne de dépollution des émissions de NOX. Dans un second cas, une stratégie issue du Principe du Minimum de Pontryagin, embarquée sur un véhicule hybride essence, fonctionnant en temps réel et calibrée selon deux paramètres est proposée. L’ensemble de ces travaux est validé expérimentalement au banc moteur et montre une réduction significative des émissions polluantes pour une faible pénalité de carburant
Powertrain hybridization is a solution that has been adopted in order to conform to future standards for emissions regulations. The supervisory strategy of the hybrid powertrain divides the power emitted between the internal combustion engine and the electric machine. In past studies, this strategy has typically responded to an optimization problem with the objective of reducing consumption. However, in addition to this, it is now necessary to take pollutant emissions into account as well. The after-treatment system, placed in the exhaust of the engine, is able to reduce pollutants emitted into the atmosphere. It is efficient from a certain temperature threshold, and the temperature of the system is dependent on the heat brought by the exhaust gas of the engine. The first part of this dissertation is aimed at modelling the energy consumption and pollutant emissions of the hybrid powertrain. The efficiency model of the after-treatment system is adapted for use in two different contexts. The zero-dimensional model conforms to the constraints of the optimal control calculation. The one-dimensional model associated with a state estimator can be embedded in a vehicle and calculated in real time. From this work, the second part of this dissertation deduces supervisory strategies from the optimal control theory. On the one hand, Bellman’s principle is used to calculate the optimal control of a Diesel hybrid vehicle using different supervisory criteria, each having more or less information about the after-treatment system efficiency over NOX emissions. On the other hand, a strategy from Pontryagin’s minimum principle, embedded in a gasoline hybrid vehicle, running in real time and calibrated with two parameters, is proposed. The whole of this work is validated experimentally on an engine test bed and shows a significant reduction in pollutant emissions for a slight fuel consumption penalty

C3H6 oxidation over a Pt/Al2O3 catalyst with or without NOx present was investigated. In particular, its reaction mechanism was studied using diffuse reflectance infrared spectroscopy (DRIFTS), a reactor system designed for monolith-supported catalysts and a micro-reactor system designed for powder catalysts referred to as CATLAB. These experiments reveal that C3H6 oxidation is inhibited by the presence of NO, NO oxidation is inhibited by the presence of CeH6, and that adsorbed NOx can react with gas phase C3H6. DRIFTS and CATLAB results confirm the reaction between C3H6 and nitrates, which are formed during NOx adsorption, with linear nitrites observed as reaction products. Therefore, a reaction route is proposed for C3H6 oxidation in the presence of NOx, namely, nitrates acting as oxidants. Using NO2 instead of NO, or using a high NOx/C3H6 ratio, which is beneficial for nitrate formation, favors this reaction pathway. Data also showed that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant. Reaction kinetics studies of C3H6 oxidation over Pt/Al2O3 and Pt/SiO2 catalysts were performed in CATLAB using a temperature-programmed oxidation method with different oxidants: O2, NO2 and nitrates. The reaction kinetics of these possible reactions were compared in order to determine which reaction is more important. NOx adsorption does not occur on the SiO2 surface so the reaction between C3H6 and NO2 could be isolated and the effect of nitrates could be observed as well when compared to the results from Pt/Al2O3. The Pt dispersions were determined using H2 chemisorption and were 1.3 and 1.6% for Pt/Al2O3 and Pt/SiO2, respectively. C3H6 oxidation starts at a lower temperature with O2 than with NO2 but the activation energy was lower with NO2. This gives indication that hydrocarbons must be activated first for NO2 to be favored in hydrocarbon oxidation. When the experiment was done with C3H6 and nitrates, the reaction did not occur until NOx started to desorb from the catalyst at higher temperatures, when nitrates become unstable and decompose. Therefore, O2 was added to the system and the reaction began at even lower temperature than with just C3H6 and O2. This proved that hydrocarbons need to be activated in order for surface nitrates to affect C3H6 oxidation and this reaction also resulted in a lower activation energy than with just C3H6 and O2. Nitrate consumption was also observed as less NOx desorbed from the catalyst at the later stage of the temperature ramp compared to the amount desorbed when the catalyst was not exposed to C3H6.

Increasingly stringed regulations for diesel engine emissions have a significant impact on the required efficiency of DOC. Lowered DOC oxidation efficiency due to thermal aging effects influences the efficiency of the exhaust aftertreatment systems downstream of the DOC. In this work carried out in the Jean Le Rond d’Alembert Institute the effect of hydrothermal aging on the reactivity and structure of a commercial DOC was investigated. The characterization of the catalytic performance was carried out on a synthetic gas bench using carrots catalyst under conditions close to the realistic conditions i.e. using a synthetic gas mixture, representative of the exhaust gases from diesel engines. Different structural characterization techniques were performed: textural and morphological proprieties were analyzed by BET and TEM, the characterization of the presented crystallographic phases was performed by DRX and the determination of the number of reducible species was possible by TPR. TEM results shown, an increase of the metal particle size with the aging caused by the agglomeration of metal particles, revealing the presence of metal sintering. DRX results also suggest the presence of support sintering. Furthermore, DRX and BET results unexpectedly reveal that the most drastic aging conditions used actually activated the catalyst surface. As expected, the aging affected negatively the catalyst performance on the oxidation of methane and CO, however an improvement of the NO oxidation performance with the aging was observed. Nevertheless, for the aging conditions used, catalytic activity results show that the influence of aging in DOC performance was not significant, and therefore, more drastic aging conditions must be used.

There has been a growing interest in using lean-burn engines due to their higher fuel economy and associated lower CO2 emissions. However, there are challenges in reducing NOX in an O2-rich (lean-burn) exhaust, and in low temperature soot oxidation. NOX storage/reduction (NSR) and selective catalytic reduction (SCR) are commercial NOX reduction technologies, and both are more efficient with levels of NO2 that are higher than those that are in engine exhaust (engine-out NO2 levels are ~10% of the total NOX). Therefore diesel oxidation catalysts are installed upstream of these technologies to provide NO2 through NO oxidation. The motivation behind this research project was two-fold. The first was to gain a better understanding of the effect of hydrocarbons on NO oxidation over a monolithic diesel oxidation catalyst. The second was to spatially resolve competitive oxidation reactions as a function of temperature and position within the same diesel oxidation catalyst (as that used in the first part). A technique known as spatially resolved capillary-inlet mass spectrometry (SpaciMS) was used to measure the gas concentrations at various positions within the catalyst. Diesel engine exhaust contains a mixture of compounds including NO, CO and various hydrocarbons, which react simultaneously over a catalyst, and each can influence the oxidation rates of the others. While studying the effect of hydrocarbons on NO oxidation in this project, propylene was found to have an apparent inhibition effect on NO oxidation, which increased with increasing propylene concentration. This apparent inhibition is a result of the NO2, as a product of NO oxidation, reacting with the propylene as an oxidant. Experiments with NO2 demonstrate a significant temperature decrease in the onset of NO2 reduction when propylene was present, which decreased further with increasing amounts of propylene, verifying NO2 as an oxidant. Similar results were observed with m-xylene and dodecane addition as well. The results also demonstrate that NO2 was consumed preferentially relative to O2 during hydrocarbon oxidation. With low inlet levels of O2, it was evident that the addition of NO2 had an apparent inhibition effect on propylene oxidation after the onset of NO2 reduction. This subsequent inhibition was due to the NO formed, demonstrating that C3H6 results in reduced NO2 outlet levels while NO inhibits C3H6 oxidation. The development of new models as well as validation of existing models requires the ability to spatially resolve oxidation reactions within a monolith. Spatially-resolved data will also give catalyst manufacturers insight into the location of active fronts, thereby directing the design of more efficient catalysts. In this research project, spatially resolving the oxidation reactions demonstrated that H2 and CO are oxidized prior to C3H6 and C12H26 and clearly show back-to-front ignition of the reductant species. An enhancement in NO oxidation was observed at the same time as dodecane oxidation light off, likely related to dodecane partial oxidation products.

The Diesel Oxidation Catalyst (DOC) is a key component in the exhaust after-treatment system of diesel engines. In this study two aspects of a DOC were investigated: catalyst distribution and reactant species interactions. In the first part, the effect of an axial Pt distribution along a DOC was investigated by comparing a standard sample, with a homogeneous Pt distribution along the length, with a zoned sample, where the Pt was non-homogeneously distributed along the length. Temperature-programmed oxidation (TPO) and spatially-resolved gas-phase concentration measurement experiments were used to compare the CO, C3H6 and NO oxidation performance of the standard and zoned catalysts. Both catalyst types had the same total amount of Pt but different distributions. The zoned catalyst, with more Pt located in the upstream portion, showed better performance than the standard catalyst, especially at high total flow rate and when a mixture of the reactants were used. The superior performance of the zoned sample is due to a larger, localized exotherm in the upstream region, where more Pt is located, and a decrease in the self-poisoning effect downstream, where reaction light-off occurs. In addition, catalyst durability against thermal degradation was tested by exposing the whole catalyst (homogeneous aging) and part of the catalyst (heterogeneous aging) to high temperatures. In general, the zoned catalyst showed better performance than the standard catalyst after thermal aging, especially after heterogeneous aging. The reason for the superior performance of the zoned catalyst, especially after heterogeneous aging, is that the back of the catalyst, which is exposed to higher temperature, contains less Pt than the front; therefore, most of the Pt particles in the zoned catalyst were not affected by thermal aging. However, after homogeneous aging, the performance of the standard catalyst was better than the zoned catalyst at higher flow rate and temperature most likely due to the different sintering rates in the zoned sample compared to the standard one. In the second part of this research, the interactions between CO, C3H6, H2, and NO were tested over a commercial Pt/Al2O3 monolith sample by studying these reactions during ignition and extinction (warm-up and cool-down). Results showed that CO, C3H6, and NO inhibit their own oxidation and each other’s oxidation due to the self-poisoning effect and competitive adsorption over active sites. In the case of a CO + C3H6 mixture, interesting CO and C3H6 oxidation trends were observed during the extinction phase. As the C3H6 concentration increased in the mixture, the catalytic activity of CO oxidation during the extinction phase decreased until it was actually poorer than that during the ignition phase. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed different C3H6 oxidation intermediates during the extinction phase on the catalyst surface, thus blocking active sites and lowering catalyst activity.

Zone-coated diesel oxidation catalysts (DOCs) can be used to obtain overall improved performance in oxidation reaction extents. However, why this occurs and under what conditions an impact is expected are unknown. In order to demonstrate why these catalysts work better than their standard counterparts and how significant the improved performance is, the CO oxidation performance over a series of Pt−Pd/Al2O3 catalysts, each with a different distribution of precious metal down the length, while maintaining equivalent totals of precious metal, was modeled. Simulations with different flow rates, ramp rates, steady-state temperatures at the end of the ramp rate, different total precious metal loadings, and CO inlet values were compared. At conversions less than 50%, the most significant differences were noted when the temperature was ramped to just at the CO oxidation light-off point (a typical measure of 50% conversion/oxidation), with catalysts containing more precious metal at the downstream portions leading to better light-off conversion performance. However, in terms of cumulative emissions over a long period of time, a “front-loaded” design proved best. These results are readily explained by decreased CO poisoning and the propagation of the heat derived from the exotherm from the front to the rear of the catalyst. Also, although the trends were the same, regardless of change in the parameter, the impact of different distributions was more apparent under conditions where a catalyst would be challenged, i.e., at low temperature ramp rates, higher CO inlet concentrations, and lower amounts of total catalyst used. At higher ramp rates, the input heat from the entering gas stream played an increasingly important role, relative to conduction associated with the exotherm, dampening the effects of the catalyst distribution. Therefore, although catalysts that are zone-coated with precious metals, or any active sites, could prove better in terms of performance than homogeneously distributed active site catalysts, this improvement is only significant under certain reaction conditions. In a mixture of three reactants, CO, C3H6 and NO oxidation, it was found that a loading a larger amount of active sites in the catalyst middle, maintained better CO and C3H6 oxidation but not NO oxidation, which required the whole catalyst length. A faster light-off conversion was also related to higher amount of precious metal at the catalyst outlet. The CO conversion performance for a variety of distributed precious metal designs was evaluated as a function of exposure time to sulphur and the spatial accumulation profile of sulphur along the monolith length was predicted. The results illustrate that the sulphur accumulates near the catalyst inlet and decreases toward the outlet, resulting in shifting the reaction zones further toward the catalyst outlet. With sulfation, light-off temperatures (T50) increased and the time for back to front reaction propagation also increased. A back loaded catalyst resulted in the best light-off conversion compared to the other catalyst designs and a middle loaded catalyst maintained a higher overall conversion if sulphur poisoning takes place. These catalyst designs were also tested under thermal aging conditions by using a second order sintering model integrated with the CO oxidation reaction model. The spatial normalized dispersion profiles along the monolith showed that the catalyst outlet experienced significant damage relative to the inlet due to sintering. A front loaded catalyst design had the highest catalytic activity due its resistance to sintering.

Infra-Red thermography and spatially-resolved capillary inlet mass spectrometry (SpaciMS) have been used to characterize propylene oxidation along a Pt/Al2O3 monolith-supported catalyst, before and after heterogeneous deactivation. The combined techniques clearly show reaction location, and therefore catalyst use, and how these change with thermal and sulphur degradation. Following the heterogeneous thermal aging, the reaction zones at steady state were broader and located farther into the catalyst relative to those observed with the fresh catalyst. As well, the time for the temperature and concentration waves to travel through the catalyst during back-to-front ignition increased. These effects were more pronounced with 1500 ppm propylene relative to 4500 ppm propylene. Such trends could not be detected based on standard catalyst-outlet measurements. The light-off behaviour was also impacted by the aging, resulting in complex changes to the temperature front propagation, depending on the propylene concentration. With each sulphur exposure step, light-off temperatures increased and the time for back-to-front ignition during temperature programmed oxidation changed pattern. With 1500 ppm propylene fed, the reaction zones established during steady-state operation shifted farther into the catalyst and increased slightly in width following sulphur treatment; at very high temperature and for 4500 ppm propylene, the reaction zones were very close to the catalyst inlet and virtually indistinguishable between catalyst sulphation states. However, at lower steady-state temperatures for the higher propylene concentration, the catalyst did experience delays in reaction light-off and light-off position moved downstream in the catalyst with sulphur damage.

碩士
嘉南藥理科技大學
環境工程與科學系暨研究所
99
This study used biodiesel from waste cooking oil in different proportions, added to commercially available diesel fuel. Biodiesel is divided into three in the order of commercially available super-diesel (B2), 10% biodiesel (B10), 20% biodiesel (B20). The water-soluble ions in the diesel PM2.5 aerosol was acquired from diesel engine under the load conditions of 0%, 25%, 50%. Additionally, comparison with a variety of biodiesel in different loads, the tests of applying the diesel particulate filter (DPF) installation of catalytic oxidizer (DOC) of the exhaust emissions characteristics are carried out. The results show that the amount of waste cooking oil to add more to reduce emissions of water-soluble ions in PM2.5 aerosol particles. Based on B2 diesel at 0% load, total ion concentration of the exhaust PM2.5 under the installation of DPF with DOC has the reduction efficiency up to 95%. At 50% load, B10 diesel fuel with DPF plus DOC has reduction efficiencies of up to 92.2%. At 25 % load, B20 with DPF plus DOC has emission reduction efficiency of inorganic salts reached as high as 85.7%. Applying the same biodiesel, the higher the load the inorganic salts in PM2.5 particulate will be increased. The regenerated DPF with DOC using B2 diesel under different load has a good reduction efficiencies with about 24~48% decrease in inorganic salts. Regeneration of DPF will have to extend the life of the reduction effect. DPF with smaller aperture will reduce the aerosol particles in the water-soluble ion concentration, indicating the performance of reduction efficiency will increase. Contrastively, the longer length of DPF will reduce its effectiveness.