The recognition of the negative impact of NOx resulted in increasingly tighter automotive emission regulations. Companies are under pressure to develop methods, which can meet the legislative demands. After treatment solutions, and especially Selective Catalytic Reduction, became the focus of research and have shown so far promising results. However, more in depth understanding of the SCR process under different conditions is needed. This thesis describes an investigation of the SCR performance using gas and urea injections under steady state and transient conditions undertaken on a light duty diesel engine using a 1D exhaust system designed for uniform flow across the catalyst. Under steady state conditions, the SCR performance was examined for low and high temperature conditions. Ammonia was supplied either as 5% ammonia gas or in form of urea injection. The engine was operating at 1500 rpm and 6 and 8 bar BMEP to provide an exhaust gas temperature of 210 °C and 265 °C respectively. Also, the effect of SCR brick length on the NOx conversion was investigated using SCR catalysts of length 30, 45 and 75 mm. To measure the influence of NO2:NOx ratio on the SCR performance, different sizes of standard DOC were used. NH3:NOx dosage levels included; α~0.5 - deficient ammonia, α~1.0 - stoichiometric ammonia, α~1.25 - excess ammonia. Gas emissions were measured before and after the SCR catalysts with a Horiba FTIR analyser during steady state and long transient tests. It was found that conditions such as temperature and NO2:NOx had the biggest impact on the SCR performance. During the steady state engine conditions, at α~1.0 ammonia dosing and NO2:NOx ratio of 0, only 17% of NO was converted in the first 30 mm of the SCR brick length. The conversion was improved at high temperature (263 °C) to 31%. A fast response CLD analyser was used during short transient testing to sample emissions with a high resolution. The short transient test with standard 0.5 and 1 DOC, and fixed ammonia dosing, showed that NOx conversion was reduced during the ramp event due to deficient ammonia and a drop in the supplied NO2:NOx ratio. During urea injection experiments, urea was injected either through an oblique pipe arrangement with a mixer device placed downstream or directly into a mixing can. In this case the mixer device was replaced with a straight pipe. A 75mm SCR was fitted and to ensure that supplied NO2:NOx ratio was zero, a palladium only DOC was used post a DPF. It was found that a large proportion of urea decomposition and hydrolysis was occurring on the surface of the SCR catalyst. Comparing NOx performance between urea injection and ammonia gas dosing experiment, more NO was converted for a given NH3:NOx ratio when ammonia was supplied in the form of gas. That was true for low and high temperature tests. For most studies, a long 10 degree diffuser was used in front of the SCR to provide uniform gas distribution across the catalyst. In addition SCR performance was investigated with a 180 degree sudden expansion diffuser in order to measure the influence of temperature and velocity profiles. During this study, a 45 mm SCR catalyst was used to provide a moderate amount of NO conversion and ammonia slip. The results showed that the flow and temperature distribution upstream of the SCR catalyst will have an effect on the NOx conversion, and that gas velocity has bigger impact on NOx conversion than gas temperature.

Les systèmes de post-traitement qui combinent diverses fonctionnalités dans un même dispositif catalytique sont considérées comme une solution efficace pour réussir l’objectif définie par les restrictives futures normes qui régulent les émissions de l'industrie automobile. Ils permettent non seulement de réduire les coûts intrinsèques dus à l’encombrement mais aussi, dans certains cas, de favoriser les réactions catalytiques par des effets thermiques ou synergiques. Ce concept est particulièrement étudié pour les moteurs Diesel dont la ligne d'échappement peut comprendre jusqu'à quatre éléments. La réduction des NOx peut être réalisée par réduction catalytique sélective de l'ammoniac sur filtre (NH3-SCRF) en utilisant des catalyseurs à base de zéolite échangée par Cu ou Fe. Ce filtre à suie catalysé assume simultanément deux fonctions: l'élimination des particules et la réduction des espèces de NOx vers N2 et de l’eau. En ce qui concerne les catalyseurs SCR, la couche active est classiquement déposée sur les parois d'un substrat de grande porosité dont les canaux sont bloqués à des extrémités alternatives. Une porosité accrue du substrat du filtre (tel que la cordiérite ou SiC) est nécessaire pour permettre le dépôt de la quantité de phase de catalyseur nécessaire pour le traitement des émissions gazeuses en assurant une filtration efficace et sans produire un effet de contre-pression du system. En plus, il est nécessaire de remarquer que des nouvelles réactions se produiront dans ce système puisque la suie Diesel, le NOx et l'agent réducteur sont présents dans la même unité pour la première fois. Selon la littérature actuellement disponible, les polluants et la suie peuvent interagir de trois manières principales: 1) la suie bloque l'accessibilité du flux gazeux aux sites actifs «classiques» du catalyseur; 2) possibilité de réduction des NOx sur les particules de suie; et enfin, 3) la présence de suie affecte les performances des réactions SCR ou, au contraire, les réactions SCR affectent le processus d'oxydation des particules jusqu'à ce que la compétition pour le NO2 soit produite / Aftertreatment systems that combine various functionalities into the same catalytic device are considered to be an efficient solution to reach the target defined by the restrictive future emission standards that regulate the automotive industry emissions. They are able not only to reduce the intrinsic costs due to the packaging but also, in some cases, to promote catalytic reactions by thermal or synergistic effects. This concept is being particularly explored for Diesel engines whose exhaust line may comprise up to four separate elements. NOx abatement can be accomplished by ammonia selective catalytic reduction on filter (NH3-SCRF) using Cu or Fe-exchanged zeolite-based as catalysts. This catalysed soot filter assumes two functions, simultaneously: removal of particles and reduction of NOx species towards N2. Regarding the SCR catalysts, the active layer is conventionally deposited onto the walls of a high porosity substrate whose channels are blocked at alternative ends. An increased porosity of the filter (such as cordierite or SiC) substrate is required to allow the deposition of the amount of catalyst phase needed for the treatment of gaseous emissions while efficient filtration and without producing a backpressure effect. Furthermore, it is necessary to remark that new reactions will occur in this system as Diesel soot, NOx and the reductant agent are present in the same unit for the first time. Accordingly to the literature currently available, there are three main ways that NOx pollutants and soot may interact: 1) soot blocking the accessibility of gas flow to “classic” active sites of the catalyst; 2) possibility of NOx reduction takes place over the soot particles; and finally, 3) soot presence affects SCR reactions performance or, contrarily, SCR reactions affects PM oxidation process as far as competition for NO2 will be produced

The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.

The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.

La Réduction Catalytique Sélective (SCR) par l'ammoniac, ou l'urée, est un procédé connu de post-traitement permettant de réduire efficacement les oxydes d'azote émis par les motorisations Diesel, en azote et en eau. Les zéolithes échangées au cuivre sont parmi les meilleures formulations pour une application sur véhicules légers, puisque efficaces sur une large zone de température. Le but de cette thèse était d'étudier la stabilité hydrothermale de ce type de catalyseur. L'approche utilisée au cours de ce travail repose sur l'étude des différentes fonctionnalités d'un catalyseur commercial de NH3-SCR présent sous forme de monolithe, à l'état frais et pour différentes conditions de vieillissement, au Banc Gaz Synthétique couplée à une analyse physico-chimique précise de la phase active du catalyseur. Ceci nous a permis de comprendre les phénomènes de désactivation intervenant au cours d'un vieillissement hydrothermal et de mesurer leur impact sur l'activité et la sélectivité de ce type de catalyseur. Après traitement hydrothermal, on assiste à une désalumination plus ou moins importante de la zéolithe, pouvant conduire à l'effondrement de sa structure, ainsi que d'importantes modifications au niveau du cuivre dès les plus faibles températures de vieillissements. Les résultats ont montré l'importance de maintenir une teneur minimal de cuivre en position d'échange, afin de conserver une capacité de stockage en ammoniac suffisante, mais surtout pour garantir une bonne efficacité à basse température en SCR du NO. Le maintien de la structure de la zéolithe semble essentiel pour que le catalyseur conserve une bonne efficacité et sélectivité au cours du temps. / The Selective Catalytic Reduction (SCR) by ammonia, or urea, is a well-known after-treatment process used for converting efficiently the nitrogen oxides, emitted by Diesel engines, into nitrogen and water. Copper-exchanged zeolites are among the most efficient formulations for light-duty applications, since effective over a wide temperature-range. The aim of this thesis is to study the hydrothermal stability of this type of catalyst. The approach used is this work is based on the study of the catalytic properties of a fresh commercial monolith catalyst for NH3-SCR in fresh and after different ageing conditions, at synthetic gas test bench, coupled with a comprehensive physicochemical analysis of the catalyst active phase. This allowed us to understand the deactivation phenomena occurring during a hydrothermal ageing and the impact on the catalyst activity and selectivity. A hydrothermal treatment induces a dealumination of the zeolite, into a more or less significant extent, which can lead to its collapse, as well as important modifications of the copper sites, even at low ageing. The results showed the importance to maintain a minimal copper content into exchanged sites, in order to retain a sufficient ammonia storage capacity, and especially to provide a good efficiency for the SCR of NO at low temperature. The preservation of the zeolite structure seems to be essential in order to maintain the catalyst efficiency and selectivity over time.