Research in the field of NOX abatement has grown significantly in the past two decades. The general trend has been to develop new catalysts with complex materials in order to meet the stringent environmental regulations. The master’s thesis deals with the cleaning flue gases through a filter element which is from porous ceramics. There is catalyst implemented for NOx reduction throug the method of selective catalytic reduction in the filter element. There is also description of experimental unit for flue gas cleaning. Part of the thesis is creation of prediction model which allows to predict efficiency reduction in the filtration device operating conditions with some accuracy.

<p>Zeolites contain distinct Brønsted acid site (H⁺) ensembles that arise from differences in the arrangement of framework Al atoms (Al−O(−Si−O)x−Al) between isolated (x ≥3) and paired (x=1,2) configurations, the latter defined by their ability to exchange certain divalent cations (e.g., Cu²⁺, Co²⁺). Manipulation of the synthesis conditions used to prepare MFI zeolites has been proposed to influence the proximity of framework Al atoms, but in a manner that is neither determined randomly nor by any simple predictive rules. Moreover, the effects of proton proximity have been studied for hydrocarbon catalysis in MFI zeolites, but interpretations of catalytic phenomena are convoluted by effects of the distribution of framework Al atoms among different crystallographic tetrahedral sites (T-sites) and diverse pore environments (i.e., confining environments) present in MFI. This work instead focuses on the chabazite (CHA) framework, which contains a single crystallographically-distinct lattice tetrahedral site (T-site) that allows clarifying how synthesis conditions influence Al proximity, and in turn, how H⁺ site proximity influences catalysis independent of T-site location. </p> <p> Selective quantification of the number and type of H⁺ site ensembles present in a given zeolite allows for more rigorous normalization of reaction rates by the number of active sites, but also for probing the number and identity of active sites on bifunctional catalysts that contain mixtures of Brønsted and Lewis acid sites. Gaseous NH₃ titrations can be used to count the total number of protons on small-pore CHA zeolites, which are inaccessible to larger amine titrants (e.g., pyridine, alkylamines), and can be used to quantify the exchange stoichiometry of extraframework metal cations (e.g., Cu²⁺, [CuOH]⁺) that are stabilized at different framework Al arrangements. Additionally, paired Al sites in CHA zeolites can be titrated selectively by divalent Co²⁺ cations, whose sole presence is validated by measuring UV-Visible spectra, counting residual protons after Co²⁺ exchange, and titration of paired Al with other divalent cations (e.g., Cu²⁺). These different titration procedures enabled reliable and reproducible quantification of different Al arrangements, and recognition of the effects of different synthetic methods on the resulting arrangement of framework Al atoms in CHA zeolites. </p> <p>Upon the advent of this suite of characterization and titration tools, different synthetic methods were developed to crystallize CHA zeolites at constant composition (e.g., Si/Al = 15) but with systematic variation in their paired Al content. The substitution of N,N,N-trimethyl-1-adamantylammonium (TMAda⁺) cations for Na⁺ in the synthesis media (Na⁺/TMAda⁺<2), while holding all other synthetic variables constant, resulted in CHA zeolites of similar composition (Si/Al = 15) and organic content (ca. 1 TMAda⁺ per cage), but with percentages of paired Al (0-44%) that increased with the total amount of sodium retained on the zeolite product. This result suggests that sodium atoms are occluded near the ammonium group of TMAda⁺ leading to the formation of a paired Al site. Replacement of Na⁺ by other alkali cations in the synthesis media allowed for the crystallization of CHA (Si/Al = 15) at higher ratios of alkali to TMAda⁺than accessible by Na⁺, likely due to the ability of different alkali cations to favor (or inhibit) crystallization of other zeolite phases. Incorporation of different alkali cations during CHA crystallization influences the formation of paired Al sites in different ways, likely reflecting the nature of different alkali to preferentially occupy different positions within the CHA framework. <i>Ab initio</i> molecular dynamics simulations were used to assess the stability of various Al-Al arrangements in the presence of combinations of alkali and TMAda⁺ cations, and provide thermodynamic insight into electrostatic interactions between cationic structure-directing agents that stabilize paired Al sites in CHA. </p> <p> Using these synthetic procedures to prepare CHA zeolites of similar composition, but with varied arrangements of framework Al, the catalytic consequences of framework Al arrangement were investigated using acid and redox catalysis. The low-temperature (473 K) selective catalytic reduction of NOx with NH₃ (NH₃-SCR) was investigated over Cu-exchanged CHA zeolites containing various Al arrangements. Cu cations exchange as both divalent Cu²⁺ and monovalent [CuOH]⁺ complexes, which exchange at paired and isolated Al sites, respectively, and turnover with similar SCR rates (473 K). <i>In situ</i> and <i>operando</i> X-ray absorption spectroscopy (XAS) were used to monitor the oxidation state and coordination environment of Cu as a function of time and environmental conditions. Rationalization of these experimental observations by first-principles thermodynamics and <i>ab initio</i> molecular dynamics simulations revealed that both Cu²⁺ and [CuOH]⁺ complexes are solvated by NH₃ and undergo reduction to Cu⁺ upon oxidation of NO with NH₃. Cu⁺ cations become mobilized by coordination with NH₃ under reaction conditions (473 K, equimolar NO and NH₃ feed), and activate O₂ through a dicopper complex formed dynamically during reaction. These results implicate the spatial density of nominally site-isolated Cu cations and, in turn, the arrangement of anionic framework Al atoms that anchor such cationic Cu complexes, influence the kinetics of O₂ activation in selective oxidation reactions, manifested as SCR rates (per 1000 A³) that depend quadratically on Cu density (per 1000 A³) and become rate-limiting processes in practice at low temperatures.</p> <p>Furthermore, first-order and zero-order rate constants (415 K, per H⁺) of methanol dehydration, a probe reaction of acid strength and confinement effects in solid Brønsted acids, are nearly one order of magnitude larger on paired than on isolated protons in CHA zeolites, reflecting differences in prevalent mechanisms and apparent enthalpic and entropic barriers at these different active site ensembles. Yet, these differences in rate constants and activation parameters at isolated and paired protons do not persist within larger pore zeolites (e.g., MFI). <i>In situ </i>IR spectra measured during steady-state methanol dehydration catalysis (415 K, 0.05-22 kPa CH₃OH) reveal that surface methoxy species are present in CHA zeolites containing paired protons, but not in CHA zeolites containing only isolated protons or MFI zeolites, providing evidence that sequential dehydration pathways via methoxy intermediates become accessible on paired protons in CHA. Density functional theory is used to provide atomistic detail of confined intermediates and transition states at isolated and paired protons in CHA and MFI zeolites, indicating that paired protons in CHA preferentially stabilize dehydration transition states that are partially-confined within the 8-membered ring (8-MR) of CHA. These findings provide evidence that catalytic diversity for the same stoichiometric reaction among zeolites of fixed structure and composition, even for frameworks containing a single T-site, can be introduced deliberately through synthetic control of the atomic arrangement of matter. </p>

No description available.

The selective catalytic reduction by ammonia (NH3-SCR) of nitrogen oxides (NOx) is a promising technology that is applied to eliminate NOx pollutants from combustion sources like diesel engines. Mn-based oxides are considered a promising catalyst for this process and many efforts were exerted by scholars to make improvements, including addition of other elements to the catalyst framework. The present study investigates the reaction mechanism and pathways using in-situ DRIFTS FTIR analysis for three Mn-based catalysts: a) mixed metal oxide MnCeTiOx, b) Mn impregnated on mesoporous titanium silicate-1 Mn/MesoTS1, and c) Mn/MesoTS1 after protection by secondary growth of silicalite-1 abbreviated as SG-Mn/MesoTS1. Various experiments were carried out on all the catalysts involving pre adsorbing NH3 then introducing NO+O2 to react with the pre adsorbed species and vice versa. It was found that the mixed metal oxide, MnCeTiOx, exhibited higher activity due to variation of different metals and higher metal content compared to the Mn-zeolite catalysts, approximately 29 Wt% Mn vs 4 Wt %, respectively. However, from comparing the two Mn-zeolite catalysts, each containing roughly 5 Wt% Mn, the catalyst after protection by secondary growth, SG-Mn/MesoTS1, showed improvement in the adsorption capability enhancing the overall performance due to the higher amount of acid sites than Mn/MesoTS1, explained by the presence of additional Brønsted and Lewis acid sites. From DRIFTS experiments, both E-R and L-H mechanism could be coexisting and taking place at 150C for all three catalysts. However, it was concluded that although both mechanisms could take place during the reaction, the acid sites on the catalyst surface for all three samples mostly favor the adsorption of NH3 species over NOx species making the E-R mechanism more assertive at 150C.

With increasing legislative demands to remove nitrogen oxides (NOx) from automotive diesel exhaust, new catalyst systems are investigated and intensely studied in industry as well in academia. The most prevailing catalytic method of choice is the selective catalytic reduction (SCR) where non-toxic urea is used as a reductant for practical reasons. Usually urea is stored in a separate tank and once injected into the exhaust system it hydrolyses into the more aggressive reductant NH3 and CO2. 4 NH3 + 4 NO + O2 -> 4 N2 + 6 H2O (NH3-SCR reaction) In regions where vanadium is not banned cost effective V2O5/WO3/TiO2 NH3-SCR catalyst systems can be used. Vanadium based are well understood, but they do however not provide stability above ca. 550 °C for longer periods of time. In exhaust treatment systems where the temperature is either high or where high temperature excursions are experienced from e.g. regeneration of particulate filters, zeolite based catalysts are therefore today the most promising candidates as high-temperature stable and non-toxic catalysts for the NH3-SCR reaction. Among the most promising candidates are the Cu- and Fe-based zeolites. Usually Fe based zeolites show good performance in the temperature range 250-500 °C and reasonable stability, whereas Cu-based zeolites show good low-temperature activity in the 180-400 °C range. The presence of copper does however also lead to a lower stability of the catalyst material. Since the low-temperature activity is of paramount importance it is necessary to improve this behavior. Therefore the purpose of this project is to investigate: - The deactivation mechanism of copper based zeolites - The influence of the zeolite framework on stability and activity These investigations should mostly be carried out on model systems such as Cu-ZSM-5 and Cu-IM-5. Recently it was found that zeolite materials with the CHA-type structure show increased hydrothermal stability, most likely originating from the small 8-MR window openings in the structure. Part of the project should therefore also include investigations on this type and other similar structures, and therefore entail: - Synthesis, in-depth characterization and catalytic testing of Cu-SSZ-13 and Cu-SAPO-34 (both structures having the CHA-type framework) - Theoretical DFT calculations on relevant parameters found by the in-depth investigation of the afore-mentioned materials - Synthesis and testing of similar materials with 8-MR windows to elucidate the influence of the zeolite sub-structure i.e. if different ring sizes in the structure influences the catalytic performance Relevant characterization techniques include, besides conventional methods, in situ methods such as: high resolution (transmission) electron microscopy, infrared (and raman) spectroscopy together with X-ray absorption spectroscopy. These are all techniques that will complement each other to produce invaluable results. Zeolites are today applied in many and diverse applications both within automotive and environmental catalysis, but also within the petrochemical and renewable chemistry. The findings of this project are therefore also believed to contribute to a more comprehensive understanding of this class of materials, relevant to many areas of heterogeneous catalysis, and therefore have the potential, to create research and business with very high impact. / Vennestrom, PNR. (2014). Selective catalytic reduction of nitrogen oxides with ammonia over microporous zeolite catalysts [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43217

While the car fleet becomes increasingly larger it is important to lower the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from high NOx emissions and particulates, in the case when diesel is utilized, and emissions at cold start from gasoline engines. One way of treating the high NOx levels is to introduce ammonia in the diesel exhausts and let it react with the NOx to form nitrogen gas and water, which is called SCR (Selective Catalytic Reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose. This thesis presents the efforts made to test the SiC-based field effect transistor (SiC-FET) sensor technology both as an ammonia sensor for SCR systems and as a cold start lambda sensor. The SiC-FET sensor has been shown to be highly sensitive to ammonia both in laboratory and engine measurements. As a lambda sensor it has proven to be both sensitive and selective, and its properties have been studied in lambda stairs both in engine exhausts and in the laboratory. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application. / <p>On the day of the public defence of the doctoral thesis, the status of article III was: in press. Report code: LiU-Tek-Lic-2003:50.</p>

<p>While the car fleet becomes increasingly larger it is important to lower the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from high NO_x emissions and particulates, in the case when diesel is utilized, and emissions at cold start from gasoline engines. One way of treating the high NO_x levels is to introduce ammonia in the diesel exhausts and let it react with the NO_x to form nitrogen gas and water, which is called SCR (Selective Catalytic Reduction). However, in order to make this system reduce NO_x efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NO_x or ammonia sensor is needed. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose.</p><p>This thesis presents the efforts made to test the SiC-based field effect transistor (SiC-FET) sensor technology both as an ammonia sensor for SCR systems and as a cold start lambda sensor. The SiC-FET sensor has been shown to be highly sensitive to ammonia both in laboratory and engine measurements. As a lambda sensor it has proven to be both sensitive and selective, and its properties have been studied in lambda stairs both in engine exhausts and in the laboratory. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.</p> / On the day of the public defence of the doctoral thesis, the status of article III was: in press. Report code: LiU-Tek-Lic-2003:50.

The increasing size of the car fleet makes it important to find ways of lowering the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from emissions at cold start, in the case when gasoline is utilized, and high NOx emissions and particulates from diesel engines. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose. One way of treating the high NOx levels from diesel engines is to introduce ammonia in the exhausts and let it react with the NOx in a special catalytic converter to form nitrogen gas and water, which is called SCR (selective catalytic reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed. This thesis presents the efforts made to test the SiC-based field effect sensor device both as a cold start lambda sensor for gasoline engines and as an NH3 sensor for SCR systems in diesel engines. The MISiC (metal insulator silicon carbide) lambda sensor has proven to be both sensitive and selective to lambda, and its properties have been studied in lambda stairs both in gasoline engine exhausts and in the laboratory. There is, however, a small cross-sensitivity to CO. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The metal tends to form islands by time, which decreases the catalytic activity and thereby gives the sensor, which is binary when fresh, a linear behavior. Successful attempts to prevent the restructuring through depositing a protective layer of insulator on top of the metal were made. The influence of increasing the catalytic activity in the measurement cell was also studied. It was concluded that the location of the binary switch point of MISiC lambda sensors could be moved towards the stoichiometric value if the consumption of gases in the measurement cell was increased. The MISiC NH3 sensor for SCR systems has been shown to be highly sensitive to ammonia both in laboratory and diesel engine measurements. The influence of other diesel exhaust gas components, such as NOx, water or N2O has been found to be low. In order to make the ammonia sensor more long-term stable experiments on samples with different types of co-sputtered Pt or Ir/SiO2 gas-sensitive layers were performed. These samples turned out to be sensitive to NH3 even though they were dense and NH3 detection normally requires porous films. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application. / On the day of the ublic defence of the doctoral thesis, the status of article IV was: accepted, article V was: submitted and article VII was: manuscript.

The stringent regulations of emission levels from heavy duty vehicles create a demand for new methods for reducing harmful emissions from diesel engines. This thesis deals with the modelling of the nitrogen oxide (NOx) emissions from heavy duty vehicles using a selective catalyst as an aftertreatment system, utilising ammonia (NH3) for its reduction. The process of the selective catalytic reduction (SCR) is nonlinear, since the result of the chemical reactions involved depends on the load operating point and the temperature. The purpose of this thesis is to investigate different methods for nonlinear system identification of SCR systems with control applications in mind. The main focus of the thesis is on finding suitable techniques for effective NOx reduction without the need of over dosage of ammonia. By using data collected from a simulator together with real measured data, new black-box identification techniques are developed. Scaling and convergence properties of the proposed algorithms are analysed theoretically. Some of the resulting models are used for controller development using e.g. feedback linearisation techniques, followed by validation in a simulator environment. The benefits of nonlinear modelling and control of the SCR system are highlighted in a comparison with control based on linear models of the system. Further, a multiple model approach is investigated for simultaneous control of NOx and tailpipe ammonia. The results indicate an improvement in terms of ammonia slip reduction in comparison with models that do not take the ammonia slip into account. Another approach to NOx reduction is achieved by controlling the SCR temperature using techniques developed for LPV systems. The results indicate a reduction of the accumulated NOx.

Ces travaux de thèse ont porté sur l'étude approfondie de catalyseurs à base d'argent et d'or dans la réduction catalytique sélective des NOx par C3H6. Pour le système Ag/Al2O3, nous avons réussi à fournir une explication rationnelle de l'origine de l'existence d'un optimum d'activité pour une teneur en Ag de l'ordre de 2 %pds reporté à plusieurs reprises. La caractérisation par NOx-TPD des catalyseurs Ag/Al2O3 a permis d'attribuer l'origine de cet optimum à la teneur maximale en Ag pour laquelle la dispersion quasi-atomique de l'argent est préservée. Nous avons aussi démontré pour la première fois que l'activité des catalyseurs Ag/Al2O3 dans la réduction des NOx par C3H6 en présence de H2 augmentait lorsque la densité surfacique en Ag diminuait. Ceci a été expliqué par l'augmentation du nombre de sites du support pouvant adsorber les NOx lorsque la teneur en Ag diminue. Le système catalytique Au/Al2O3 a été également étudié. En diminuant le nombre de sites d'or dans le réacteur, un effet promoteur de H2 a été mis en évidence pour la première fois pour ce système dans la réduction des NOx par C3H6. Cet effet promoteur était plus important lorsque la teneur en Au diminue. L'activité catalytique du système Au/Al2O3 a été optimisée par la cérine, le catalyseur présentant 1%pds en CeO2 et 0,5%pds en Au a montré la meilleure conversion des NOx. L'activité catalytique d'un système Au-Ag/Al2O3 a également été examinée mais trouvée moins intéressante que celles des systèmes monométalliques. La conversion des NOx en N2 en présence de H2 sur un catalyseur Ag/Al2O3 a pu être améliorée de prés de 30 % en déposant l'argent sur un support prétraité hydrothermalement. / This work provides further insights into C3H6-SCR on alumina supported silver and gold catalysts. The origin of the optimum loading of 2 wt% of Ag on Al2O3 in the C3H6-SCR of NOx was elucidated with the help of an original characterization method (NOx-TPD). The optimum loading was attributed to the maximum loading of silver on Al2O3 for which highly dispersed Ag species are preserved. Our study highlights for the first time that the H2-C3H6-SCR catalytic performance of Ag/Al2O3 samples improved in the 150-550 °C temperature domain as the Ag loading decreased well below 2 wt%. A detailed kinetic study of H2-C3H6-SCR was performed and led us to conclude that the unexpected higher catalytic performance of the Ag samples with the lower Ag surface densities was attributed to the higher concentration of active sites on the Al2O3 supporting oxide able to chemisorb NOx species. Regarding Au/Al2O3 catalysts, our work provides the first experimental evidence of an H2 effect in C3H6-SCR over Au/Al2O3 catalysts. This effect could only be observed when the number of Au catalytic sites in the reactor was decreased. The influence of the Au loading on the H2-C3H6-SCR was investigated. Au/CeO2-Al2O3 system was optimized with addition of ceria. Among the Au/CeO2-Al2O3 catalysts evaluated, the sample containing 0.5 wt% Au and 1 wt% CeO2 exhibited the best NOx conversion in C3H6-SCR at low temperature (from 150 °C). The catalytic activity of bimetallic Au-Ag /Al2O3 catalysts was investigated in C3H6-SCR and H2-C3H6-SCR. Finally, NOx conversion to N2 on Ag/Al2O3 in H2-C3H6-SCR could be improved substantially by nearly 30 % when silver is added on hydrothermally pretreated Al2O3 support.