I och med nuvarande och kommande lagkrav för utsläpp från tunga lastbilar finns en efterfrågan på utvecklade strategier för utsläppsminskning. För att kontrollera utsläppen av kväveoxider (NOx) används katalytisk omvandling med AdBlue (vätskeblandning av urea och vatten).  AdBlue-dropparna förångas av avgaserna eller på en förångningsyta där en väggfilm kan skapas som i sin tur kan öka risken för utfällningar av urea. Därför finns ett behov av ett reglersystem för att minimera risken för utfällning,  Målet med detta examensarbete var att skapa en bättre förståelse för hur risken för utfällning av urea kan relateras till den nuvarande kalibreringen på Scania och föreslå hur det nuvarande reglersystemet kan förbättras. Tester uppdelat i två delar genomfördes i en provcell. Först testades ureadoseringen i pulser där doseringsmängden, förångningstiden och pulsfrekvensen varierades. Därefter testades varierat avgasflöde mellan två flöden genom att ändra ramptiden.  Genom visuella inspektioner visade det sig att pulserna med urea behöver längre förångningstid än vad den aktuella kalibreringen anger. Detta för att minska risken av utfällningar. Vid dosering av urea över den stationära förångningskapaciteten skapades väggfilmen längre bort från doseringsenheten. Detta leder till mindre effektiv användning av den doserade urean. För varierat avgasflöde med de valda ramptidena förändrades inte risken för utfällning. Därför skulle det nuvarande styrsystemet kunna förbättras genom att inkludera en längre tid för förångning mellan ureadoseringspulserna. / With current and upcoming emission legislation for heavy-duty transport, there is a demand for improved emission abatement strategies. To control nitrogen oxide (NOx) emissions, catalytic conversion with AdBlue (a liquid mixture of urea and water) is used. Droplets of AdBlue are evaporated by the exhaust gas or on an evaporation surface where a wall film can be created. A wall film increases the urea deposit risk which in turn causes problems. Consequently, there is a need for a control system to minimize the risk of urea deposits. The target of this thesis was to create a better understanding of how the urea deposit risk can be related to the current control calibration at Scania and to suggest how the current control system could be improved. Tests were performed in an engine testbed, in two parts. Firstly, varying of urea dosing was tested in pulses where the dosing amount, evaporation time and pulse frequency were varied. Secondly, the exhaust flow rate was varied between two flows by changing the ramp time. Through visual inspections, it was shown that the urea dosing pulses need longer evaporation time than the current control calibration states, to reduce the build-up of urea deposits. Furthermore, when dosing urea above the stationary evaporation capacity, the wall film was created further away from the dosing unit, thus, leading to less efficient use of the injected urea. For varying exhaust flow rate, the chosen ramp times did not change the urea deposit risk. Therefore, the current control system could be improved by including longer time for evaporation between the urea injection pulses.

No description available.

Στην παρούσα εργασία μελετάται η αντίδραση αναγωγής των οξειδίων του αζώτου με προπυλένιο σε ισχυρά οξειδωτικές συνθήκες με χρήση καταλυτών Rh υποστηριγμένων σε τροποποιημένους φορείς TiO2 με ιόντα διαφορετικού σθένους (W6+ ή Ca2+) από το μητρικό κατιόν (Ti4+). Η τροποποίηση του φορέα επιτεύχθηκε με την διάχυση των ενισχυτικών κατιόντων στο κρυσταλλικό πλέγμα του TiO2 σε υψηλές θερμοκρασίες. Στους φορείς που παρασκευάστηκαν πραγματοποιήθηκαν μετρήσεις ειδικής επιφάνειας (ΒΕΤ), κρυσταλλικής δομής (XRD), ειδικής αγωγιμότητας (AC-Impedance) καθώς και μετρήσεις επιφανειακής οξύτητας (TPD-MS). Σε γενικές γραμμές η ενίσχυση του φορέα TiO2 έχει σαν αποτέλεσμα την διατήρηση της ειδικής επιφάνειας, την αύξηση της επιφανειακής οξύτητας, και την αλλαγή της ειδικής αγωγιμότητας σε σχέση με τον μη ενισχυμένο φορέα. Οι υποστηριγμένοι καταλύτες Rh παρασκευάστηκαν με την μέθοδο του υγρού εμποτισμού από νιτρική πρόδρομη ένωση. Οι καταλύτες που παρασκευάστηκαν χαρακτηρίστηκαν ως προς την διασπορά της ενεργού φάσης καθώς και του μέσου μεγέθους των κρυσταλλιτών του μετάλλου με χημορόφηση H2. Η σύγκριση των καταλυτών με βάση την ενεργότητα τους για την αναγωγή του ΝΟ καθώς και την εκλεκτικότητά τους σε Ν2, έδειξε δύο διαφορετικές δράσεις της ενίσχυσης. Ενίσχυση με ιόντα W6+, οδηγεί σε αύξηση της ενεργότητας με παράλληλη ελαφρά αύξηση της εκλεκτικότητας σε Ν2. Η ενίσχυση του καταλύτη με ιόντα Ca2+ οδηγεί σε αύξηση της ενεργότητας για την αναγωγή του ΝΟ με παράλληλη όμως, σημαντική μείωση της εκλεκτικότητας σε Ν2. Η συμπεριφορά αυτή ερμηνεύτηκε με βάση το θεωρητικό υπόβαθρο που περιγράφει τις τροποποιήσεις των ηλεκτρονιακών ιδιοτήτων του φορέα και είναι γνωστό ως φαινομένου DIMSI. Η βελτίωση των καταλυτικών ιδιοτήτων που παρουσιάζουν οι ενισχυμένοι καταλύτες έδωσε το ερέθισμα για την μελέτη του μηχανισμού της αντίδρασης για την αναγωγή του ΝΟ με προπυλένιο στους καταλύτες αυτούς καθώς και τις διαφορές που παρουσιάζουν σε σχέση με τον μη-ενισχυμένο καταλύτη. Η μελέτη του μηχανισμού πραγματοποιήθηκε με χρήση των τεχνικών υπέρυθρης φασματοσκοπίας (FTΙR) και φασματοσκοπίας μάζας (Mass Spectroscopy). Σε γενικές γραμμές τα αποτελέσματα δείχνουν ότι το ΝΟ ροφάται μοριακά σε κέντρα Rh. Παρουσία ανηγμένων κέντρων το ΝΟ διασπάται προς ατομικά ροφημένα είδη Ν και Ο. Ανα-συνδυασμένη εκρόφηση των ειδών Ν οδηγούν στον σχηματισμό Ν2 στην αέρια φάση, ενώ παραγωγή του Ν2Ο σχετίζεται με την δημιουργία του συμπλόκου είδους Rh(NO)2. Η αναγέννηση των ενεργών κέντρων επιτυγχάνεται με την μερική οξείδωση του προπυλενίου σε οξειδωμένα κέντρα Rh αρχικά προς ακρολεϊνη. Περαιτέρω οξείδωση της ακρολεϊνης οδηγεί στον σχηματισμό θραυσμάτων COO- και CHx με τον ενδιάμεσο σχηματισμό ειδών του τύπου του ακρυλικού οξέος. / In the present study, the catalytic reduction of NO with propylene in the presence of excess oxygen was examined, over Rh catalysts supported on doped TiO2 carriers with tungsten or calcium cations. Doped TiO2 carriers were prepared employing the solid state diffusion technique at elevated temperatures. Characterization of doped carriers consisted of specific surface (BET) area and crystalline mode (XRD) measurements as well as measurements of the specific conductivity (AC-Impedance) and surface acidity (TPD-MS). In general, doping TiO2 results in an increase of the surface acidity, in alterations of specific conductivity and in the preservation of the specific surface in a manner, which depends on dopant concentration and calcinations temperature. Supported Rh catalysts were prepared following the wet impregnation method using Rh(NO3)3 as the precursor metal compound. Characterization of the prepared catalysts consisted of dispersion and mean metal crystalline size measurements, employing hydrogen chemisorption at ambient temperature. Comparison of the doped catalysts, as far as the activity toward NO reduction and the selectivity to N2 is concerned, shows two different behaviors. Doping with W6+ cations results in higher NO reduction activity with a slightly increase of selectivity toward dinitrogen formation. Doping with Ca2+ leads to higher catalytic activity for the reduction of NO, while the selectivity was found to decrease upon increasing calcium content. The above observations are explained by the theory of dopant induced metal support interactions (DIMSI). The mechanistic pathways of the above mentioned reaction over Rh/TiO2 catalysts were studied employing infrared (IR) and mass spectroscopy (MS). The results showed, that NO is molecularly absorbed on the Rh. In the presence of reduced Rh sites NO dissociation occurs, resulting in N and O adspecies. Recombination of N species results in the production of dinitrogen in the gas phase. N2O formation is correlated with the presence of the dinitrosyl complex species on the catalytic surface. Reaction of the latter with NO from the gas phase leads to N2O production. Regeneration of oxidized Rh sites is achieved via oxidation of propylene to acrolein. Further oxidation of the latter leads to the formation of carboxylates.

The reaction mechanism for the selective catalytic reduction (SCR) of nitric oxide by ammonia on (010) V2O5 surface represented by a V2O9H8 cluster was simulated by density functional theory (DFT) calculations. The computations indicated that SCR reaction consisted of three main parts. In the first part ammonia activation on Br&oslash / nsted acidic V-OH site as NH4+ species by a nonactivated process takes place. The second part includes the interaction of NO with pre-adsorbed NH4 + species to eventually form nitrosamide (NH2NO). The rate limiting step for this part as well as for the total SCR reaction is identified as NH3NHO formation reaction. The last part consists of the decomposition of NH2NO on the cluster which takes advantage of a hydrogen transfer mechanism between the active V=O and V-OH groups. Water and ammonia adsorption and dissociation are investigated on (101) and (001) anatase surfaces both represented by totally fixed and partially relaxed Ti2O9H10 clusters. Adsorption of H2O and NH3 by H-bonding on previously H2O and NH3 dissociated systems are also considered. By use of a (001) relaxed Ti2O9H10 cluster, the role of anatase support on SCR reaction is investigated. Since NH2NO formation on Ti2O9H10 cluster requires lower activation barriers than on V2O5 surface, it is proposed that the role of titanium dioxide on SCR reaction could be forming NH2NO. The role of vanadium oxide is crucial in terms of dissociating this product into H2O and N2. Finally, NH3 adsorption is studied on a V2TiO14H14 cluster which represents a model for vanadia/titania surface.

The Master thesis deals with utilization possibilities of fly ash after selective non-catalytic reduction (SNCR) process for Portland cement preparation as a correction component to the raw material with regard to contaminated fly ash by ammonium sulphate or ammonium hydrogensulfate that is one of the products from SNCR process. Presented thesis was focused on behaviour of raw meal with ammonia hydrogensulfate contaminated fly ash after SNCR during burning of Portland clinker in simulated kiln conditions. The thesis deals with Portland clinker preparation from this kind of raw mix and it studies mainly clinker quality, clinker phases and structure. Quantitative phase composition of prepared samples of clinker was performed by optical microscopy measurements using point counting method and XRD analysis (Rietveld method). Hydration heat flow of prepared clinker was measured by Isothermal Calorimetry. TG-DTA analysis of prepared raw meal was studied due to better comparison of prepared samples and better understanding of processes during burning process.

Made available in DSpace on 2015-05-14T13:21:13Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3269530 bytes, checksum: 966a88d9d616a8a7788293bac03f1bcd (MD5) Previous issue date: 2012-04-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work involved the synthesis of an oxide with perovskite structure (ABO3), the strontium stannate (SrSnO3), with orthorhombic structure, space group Pbnm, by the polymeric precursor method. This material has been applied as capacitor, sensor for gases as NO, CO, H2, humidity and it is actually being studied as a catalyst. At the beginning of this work, pure SrSnO3 and doped with 10 mol % of nickel (Sr0,9SnNi0,1O3, SrSn0,9Ni0,1O3, Sr0,95Sn0,95Ni0,1O3) were characterized by thermal analysis (TG / DTA), infrared spectroscopy (IR), Ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, X-ray diffraction and surface area by BET method. The catalytic activity of the non-supported material was evaluated in the reduction reaction of nitrogen monoxide (NO) by carbon monoxide (CO), followed by characterization by XRD, IR and Raman analysis. The material calcined at 800°C presented SrCO3 as secondary phase, with a reduction in its intensity when Ni2+ replaces Sr2+ in the lattice. Doping did not lead to a meaningful change in the long range order by increased the short range order. The system best catalytic performance (SrSn0,9Ni0,1O3) achieved approximately 90% of conversion of CO into CO2 and 85% of NO into N2. In the second part of the work catalysts were supported (10% mass, the active phase /support) on anatase, gamma alumina, ceria and zirconia, using the resin obtained by the polymeric precursor method, with characterization as described before. This procedure aimed at evaluating the effect of the support in the activity of perovskite for the same reaction conditions. It was possible to confirm the catalyst deposition on all supports, in spite of the difficulty in the characterization as a film was formed on the powder surface, leading to superposition of peaks/bands. / Este trabalho envolveu a síntese de um óxido com a estrutura perovskita (ABO3), o estanato de estrôncio (SrSnO3), com estrutura ortorrômbica com grupo espacial Pbnm, usando o método dos precursores poliméricos. Este material apresenta aplicações como capacitores, sensores de gases como o CO, NOx, H2, umidade e atualmente vem sendo estudado como catalisador. No início deste trabalho, o SrSnO3 puro e dopado com 10 % em mol de níquel (Sr0,9SnNi0,1O3, SrSn0,9Ni0,1O3, Sr0,95Sn0,95Ni0,1O3) foi caracterizado, fazendo uso da análise térmica (TG/DTA), espectroscopia de infravermelho (IV), espectroscopia na região do Ultra-violeta - visível, espectroscopia RAMAN, Difração de Raios-X (DRX) e área superficial pelo método de BET. A atividade catalítica dos materiais não suportados foi avaliada na reação de redução do monóxido de nitrogênio (NO) com monóxido de carbono (CO) seguida de caracterização por DRX, IV e Raman. O material calcinado a 800°C, apresenta o SrCO3 como fase secundária, sendo que a substituição do Sr2+ pelo Ni2+ reduz a formação de carbonato. A dopagem não alterou significativamente a ordem a longo alcance mas aumentou a desordem a ordem curto alcance. O sistema com melhor desempenho catalítico (SrSn0,9Ni0,1O3) obteve conversões de aproximadamente 90% de CO a CO2 e 85% de NO a N2. Na segunda parte do trabalho os catalisadores foram suportados (10% em massa, fase ativa/suporte), na anatase, gama alumina, céria e zircônia, a partir da resina obtida pelo método dos precursores poliméricos, com caracterização pelas técnicas descritas anteriormente. Buscou-se, dessa forma, avaliar o efeito do suporte na atividade desta perovskita nas mesmas condições reacionais. Foi possível confirmar a deposição do catalisador sobre todos os suportes, sendo a análise dificultada por se tratar de um filme na superfície do pó, às vezes com sobreposição de picos/bandas.

Made available in DSpace on 2015-05-14T13:21:14Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3299520 bytes, checksum: 187bb191b68b3815838de32a36c06f36 (MD5) Previous issue date: 2011-12-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Strontium stannate (SrSnO3) is a perovskita with orthorhombic structure (Pbnm), which has been extensively studied due to its potential technological applications, such as: thermally stable capacitors, sensors for various gases, including CO, NOx, Cl2, H2 and humidity. Nowadays, it has been studied as a promising material to be used as a catalyst. In this work, Sr1-xSnCuxO3, SrSn1-yCuyO3, Sr1-xSn1-yCux+yO3 (x, y ou x+y = 0; 1; 5 e 10% mol the copper) powders were synthesized by the polymeric precursor method and characterized by thermogravimetric analysis (TG/DTA), X-ray diffraction (XRD), infrared (IR) and ultraviolet-visible (UV-Vis) spectroscopy, Raman spectroscopy, specific surface area (BET) and then powders were evaluated in the catalytic reduction of NO with CO. The powders (SrSnO3:Cu) had orthorhombic perovskite structure at 700 oC, with SrCO3 and SnO2 as secondary phases. The introduction of copper in the structure leads to a higher short range disorder, as evidenced by the infrared and Raman spectra. In the Infrared spectra, the splitting of the 3 band (500-700 cm-1) was observed, which can be associated to the presence of two types of symmetry around the tin. In UV-Vis spectra bands related to d-d transitions of Cu2+ ions were observed besides related to forbiden transitions of Cu+ ions for higher calcination temperatures and copper amounts. The catalytic activities of SrSnO3 was improved by copper addition into the structure, whereas samples with 5 % of copper presented the highest conversions, reaching 100 % of NO into N2 and 100 % of CO into CO2 at 550 oC. This result is as good or even better than lanthanium based catalysts. The surface area was not a determining factor for NO reduction and CO oxidation. Other factors were more important for a high catalytic performance, as defects, that lead to more active sites for NO and CO adsorption, besides the presence of Cu+ and redox reaction (Cu+/Cu2+) that improve adsorption and NO reduction by CO. / O estanato de estrôncio (SrSnO3) é uma perovskita com estrutura ortorrômbica (Pbnm), que tem sido bastante estudado devido a aplicações tecnológicas potenciais, tais como: capacitores termicamente estáveis, sensores de vários gases, incluindo CO, NOx, Cl2, H2 e umidade. Atualmente vem sendo estudado como material promissor na área de catálise. Neste trabalho, materiais Sr1-xSnCuxO3, SrSn1-yCuyO3, Sr1-xSn1-yCux+yO3 (x, y ou x+y = 0; 1; 5 e 10 % em mol de cobre) foram sintetizados pelo método dos precursores poliméricos e caracterizados por análise termogravimétrica (TG/DTA), difração de raios-X (DRX), espectroscopia na região do infravermelho (IR), na região do Ultravioleta-visível, espectroscopia Raman, área superficial especifica (BET) e em seguida os materiais foram avaliados no processo catalítico para a redução de NO com CO. Os materiais obtidos apresentaram estrutura perovskita ortorrômbica a 700 ºC, com SrCO3 e SnO2 como fases secundárias. A introdução do cobre na estrutura tornou os materiais mais desorganizados a curto alcance, conforme espectróscopias de infravermelho e Raman. Nos espectros de infravermelho foi observado o desdobramento da banda 3 (500 700 cm-1), podendo ser associado à presença de dois tipos de simetria em torno do estanho. Nos espectros de UV-Vis podem ser observadas bandas referentes às transições d-d dos íons Cu2+ e com o aumento da temperatura de calcinação e da quantidade do cobre foram observadas bandas referentes a transições proibidas dos íons Cu+. A atividade catalítica do SrSnO3 foi melhorada com a inserção do cobre na estrutura, sendo as amostras com 5% de cobre as que apresentaram as melhores conversões, chegando até 100% de NO a N2 e 100% de CO a CO2 a 550 ºC. Este resultado foi tão bom quanto, ou melhor, que os catalisadores à base de lantânio. A área superficial não foi o único parâmetro determinante para a redução do NO e oxidação do CO. Outros fatores foram mais importantes para o bom desempenho catalítico, como os defeitos, que proporcionam mais sítios ativos para a adsorção de NO e CO, como também a existência de íons Cu+ e a reação redox (Cu+/ Cu2+) que beneficiam a adsorção e a redução de NO com CO.

Le problème étudié dans cette thèse est la commande en boucle fermée d'un système SCR (Réduction Sélective Catalytique) par l'urée tel qu'utilisé dans les systèmes de dépollution des gaz d'échappement des moteurs diesel automobiles. Une première contribution du manuscrit est en un modèle détaillé de la SCR, soulignant de la nature distribuée (1D) du système considéré, et plusieurs réductions successives de ce modèle de simulation conduisant à un modèle plus simple, utilisable à des fins de synthèse de contrôleur. Une seconde contribution consiste à prendre en compte la sensibilité au NH3 du capteur de NOx utilisé pour la rétroaction lors du développement d'algorithmes de commande (observateur d'état, boucle de rétroaction, séquencement de gain, interprétation du signal capteur). L'observateur-contrôleur présenté possède plusieurs points d'équilibre dues à la sensibilité du capteur de sortie. On montre que seul le point d'intérêt pratique est asymptotiquement stable, les autres étant instables naturellement, rendus instables par une implémentation spécifique ou aisémentdétectés comme indésirables. Ces deux contributions ont été testées expérimentalement et validées. En résumé, la méthode de contrôle proposée dans cette thèse permet, à partir d'un moteur conforme aux exigences Euro 5 et avec une procédure de pré-conditionnement du catalyseur, de satisfaire la norme Euro 6. / The problem studied in this thesis is the closed-loop control of a urea-SCR (urea Selective Catalytic Reduction) as used in aftertreatment systems of diesel vehicles. A first contribution of the thesis is a detailed model for the SCR, highlighting the distributed (1D) nature of the considered system, and several successive reductions of this simulation model leading to a simpler one, better-suited for control design purposes. A second contribution consists in considering the sensitivity to NH3 of the NOx sensor used in a feedback loop, in the development of the control algorithms (state observer, feedback, gain scheduling, measurement interpretation). The ambiguity of the output measurement could be detrimental to the closed loop response, as it generates multiple equilibrium points (artefacts), besides the point of practical interest. A study of the closed-loop dynamics is performed in the vicinity of each point, which shows that the closed loop system naturally converges to the point of interest not to the artefacts. Both contributions have been tested and validated experimentally. In summary, the method proposed in this thesis might allow an engine equipped with Euro 5 hardware to satisfy Euro 6 standard using a preconditioning procedure of the catalyst.

This master‘s thesis deals with denitrification of brown coal-fired boiler of electric power plant. First chapters describe technical characteristics of the boiler and possible measurements which would lead to lowering NOx emissions. In order for boiler to meet emission standards valid from 1.1.2016 flue gas treatment by selective catalytic reduction is proposed. Main part of the thesis is thermal calculation of the boiler with modifications necessary in order to apply SCR. The aim of calculation is to determine flue gas exit temperature and temperature at catalyst area in order to assess the suitability of proposed modifications.

The effect of soot on the catalytic properties of a diesel particulate filter coated with a catalyst for the selective catalytic reduction of NOx with ammonia (SDPF) was studied by means of model-gas experiments. After loading of the SDPF with model soot from 0 to 10 g l-1, the NH3 storage as well as the catalytic DeNOx behavior of the standard SCR reaction was investigated. The model soot present in the filter was shown to have an NH3 storage capacity. The soot deposit inside the SDPF filter wall lead to a decreased NO conversion in SCR experiments of up to 20 %. The NH3 breakthrough was found to be shifted towards earlier time-on-stream during NH3 adsorption on soot loaded SDPF samples. Both effects could be attributed to a diffusive mass transport limitation of the gas species through the soot to reach at the chemically active sites inside SDPF filter wall. The self-diffusion coefficient of NH3 probe molecules within a soot layer could be measured using Pulsed Field Gradient-NMR technique. The unit collector model is capable of describing the backpressure upon soot loading with a depth filtered (inside filter wall) soot amount of 1 g l-1 and 0.36 g l-1, respectively, for both SDPF types under investigation. Based on Scanning Electron Microscopy (SEM) investigation a 1-D microscopic soot filter wall-model was set up. The model implies soot as diffusion barrier for mass transport. It was calibrated based on experimental observations and allows to conclude on the distribution of the soot within the filter wall. Thus, a high soot-coverage of the porous filter wall close to the inlet channel, a slightly covered middle part and a soot free zone close to the outlet explains the observed reduction in NO conversion as well as the NH3 breakthrough at earlier time-on-stream during NH3 adsorption experiments for SDPF samples loaded with soot. A modelled homogeneous soot distribution (0.6 µm soot layer on top of washcoat) within the whole SDPF was shown to result in NO conversion drop up to 45 %.