Дисертації з теми "Catalyst aging"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Catalyst aging.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-30 дисертацій для дослідження на тему "Catalyst aging".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Li, Haitao. "Supercritical carbon dioxide aided preparation of nickel oxide/alumina aerogel catalyst." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001090.
Повний текст джерела
2
MOROSANU, EDUARD ALEXANDRU. "Catalytic processes for CO2 conversion into Synthetic Methane." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2841162.
Повний текст джерела
3
Kandilli, Nur. "Development Of A Three Way Catalytic Converter For Elimination Of Hydrocarbons, Carbon Monoxide And Nitric Oxide In Automotive Exhaust." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612546/index.pdf.
Повний текст джерелаАнотація:
In this work, slurries of powder catalysts are washcoated on 22 mm diameter
and 13 mm height cordierite monoliths. CeO2-ZrO2 (CZO) and CeO2-ZrO2-
Al2O3 (CZAO) mixed oxides are synthesized by co-precipitation and sol-gel
methods respectively, to be used as support materials of Pd and Rh metals.
Metal loaded CZO is mixed with gamma phase alumina. Powder catalysts
and their slurries are characterized by XRD, BET, ICP-MS and the monolithic
catalysts are imaged by SEM. Catalytic activities of monolithic catalysts are
tested in dynamic test system which is computerized and basically composed
of gas flow control and conditioning units, split furnace, quartz reactor, mass
spectrometer and CO analyzer. Gas mixture containing CO, C3H6, C3H8, NO,
H2, O2, CO2, SO2, H2O and N2 is used to simulate the exhaust gas of
gasoline vehicles. O2 is oscillated at 1 Hz frequency around the
stoichiometric condition. Monolithic catalyst in the reactor is heated and
cooled between 150 ºC and 600 º
C. Gas composition data from massspectrometer and CO analyzer and temperature data from thermocouple at the monolith entrance, are converted to conversion versus temperature graphs. Results of 26 activity tests are compared. Catalyst containing coimpregnated CZO support material with metals, showed the lowest loss of catalytic performance after exposure to SO2 during activity tests. Catalyst containing separately impregnated CZO support material, showed the highest resistance against thermal aging at 900 º
C and 1000 º
C, and even improved catalytic activity after aging. These catalysts showed higher resistances against the applied procedures than the commercial catalyst.
4
Birgersson, Henrik. "Development and Assessment of Regeneration Methods for Commercial Automotive Three-Way Catalysts." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3931.
Повний текст джерела
5
Panpranot, Joongjai. "Hydrothermal aging of zeolite-based catalysts." Morgantown, W. Va. : [West Virginia University Libraries], 1998. http://etd.wvu.edu/templates/showETD.cfm?recnum=274.
Повний текст джерелаАнотація:
Thesis (M.S.)--West Virginia University, 1998.Title from document title page. Document formatted into pages; contains xi, 84 p. : ill. Includes abstract. Includes bibliographical references (p. 64-67).
6
Blades, Luke Aubrey William. "Ageing mechanisms in automotive catalysts." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.695255.
Повний текст джерелаАнотація:
This study uses a number of laboratory testing and ageing methods in order to investigate how effectively they correlate to catalyst ageing on a vehicle. The activity testing of full size catalyst bricks was successfully conducted using the Catagen Labcat test system, and correlation with the light-off activity of cored catalyst samples in the Horiba SIGU 2000 examined using the QUB global catalyst model. Static ageing was conducted in the laboratory, using the BAT equation to calculate ageing times for ageing temperatures relating to a RAT-A cycle. The thermal reactivity coefficients for static ageing in different ageing atmospheres were calculated and compared to those recommended by the EPA for dynamic ageing. Finally, using the results achieved from these raboratory ageing methods, recommendations were made as to how ageing models reviewed in the literature could be improved. From experimental results alone, it was seen that no correlation existed between the light-off performance of cored catalyst samples and full size bricks. However, the QUB global catalyst model was able to consider variations in precious metal dispersion between samples, differences between inlet temperature and gas concentrations, and heat transfer characteristics of the two reactors. The simulations performed were able to show good correlation between the test methods. However, the two tests methods showed differently the activity rank of the samples, indicating the variation in precious metal loading and dispersion throughout each full size brick. In other results, static ageing of palladium loaded catalyst samples was found to show no ageing effects due to time for ageing temperatures below 1000 C. Static ageing methods were also shown to cause deactivation at a slower rate than dynamic methods. It was shown that the Toyota ageing expression would better predict catalyst deactivation if it incorporated an oxygen factor, to describe ageing when no oxygen is present.
7
Woods, Andrew John. "Ageing and characterisation of automotive catalysts." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486263.
Повний текст джерелаАнотація:
Catalytic converter technologies situated in the exhaust streams of vehicles are under continuing pressure to meet more stringent emissions standards that requires increasing longevity along with higher efficiencies. This investigation studied the fundamental factors known to contribute to catalyst deactivation, by developing the specific designs and by construction of ageing facilities that isolated the ageing factors under inspection. Various static ageing schedules were completed along with rapid ageing cycles with the aid of a custom built synthetic gas ageing machine named AutoCAS, (Automotive Catalyst Ageing System). Explicit characterisation techniques to help define the extent of catalyst degradation were also developed. These focused on use of scanning electron, microscopy and transmission electron microscopy to produce images of the catalyst which could then be analysed using image analysis software. The software program enabled statistical data to be collated, allowing conclusions to be drawn about the surface structure before and after ageing. Raman spectroscopy was used to probe the changes in catalyst substrate after the ageing process. Results uncovered that Platinum/Rhodium, (PtIRh), catalysts behave differently to Palladium, Pd, catalysts with respect to particle agglomeration. Pd loaded samples exhibited relationships with respect to ageing time and temperature whilst PtlRh catalysts were only susceptible to ageing temperature. Also, concluded was that PtlRh catalysts undergo agglomeration in an inert nitrogen environment which is in direct contradiction to mathematical expressions already published. Precious metal particle agglomeration was found to have a relatively insignificant role to play in overall catalyst deactivation. RATA ageing showed that the thermal stressing incurred by thermal cycling affected the catalyst activity more so than ageing at uniform temperature. Application ofthe current QUB catalyst model showed that there may be other factors contributing to deactivation rather than just washcoat sintering and precious metal agglomeration as measured in this research.
8
Rachele, Karen Gonçalves. "Estudo de catalisadores modelo à base de CeO2-ZrO2 dopado com cobre para controle de emissões de NOx." Universidade do Estado do Rio de Janeiro, 2012. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=5048.
Повний текст джерелаАнотація:
Fundação de Amparo à Pesquisa do Estado do Rio de JaneiroConvencionalmente, metais nobres são empregados como metais ativos em catalisadores automotivos, mas o uso de cobre vem sendo estudado pelo fato de promover sítios ativos para adsorção química e redução de NOx. Diante deste contexto, esta dissertação visa testar novas formulações de catalisadores, com foco em seu desempenho na reação de redução do NO pelo CO e sua seletividade a N2. Foram avaliados o método de adição de cobre no preparo e os teores de cobre utilizados na preparação. Os métodos de adição utilizados foram impregnação a seco (IS), reação em estado sólido (RS) e coprecipitação (CO). Os teores de cobre estudados ficaram entre 0,36 e 6,9% (m/m). Além disso, foi estudado o impacto no desempenho do catalisador após envelhecimento térmico a 950C por 12h. Foram empregadas as seguintes técnicas de caracterização textural e físico-química como espectrometria de absorção atômica, fisissorção de N2, difração de raios X, espectroscopia Raman e redução a temperatura programada. Os catalisadores também foram avaliados na reação de redução do NO pelo CO. A análise textural indicou que o método de coprecipitação levou a características texturais diferentes dos outros catalisadores. Análises de DRX mostraram a formação de CuO cristalino para teores iguais ou superiores a 3,3% (m/m) de cobre. As análises de Redução a Temperatura Programada (RTP) indicaram que ocorreu uma forte interação na interface entre o suporte e as espécies de cobre dispersas, acompanhada da diminuição da temperatura de redução do CuO e da redução parcial da céria em temperaturas mais baixas. Os testes catalíticos mostraram um melhor desempenho dos catalisadores (IS) que apresentaram conversões mais elevadas em menores temperaturas. Com relação ao envelhecimento, observou-se uma diminuição significativa da eficiência dos catalisadores. Uma comparação com catalisadores à base de metal nobre mostrou um bom desempenho dos catalisadores à base de cobre, com a vantagem destes apresentarem emissão de N2O restrita a baixas temperaturas
Conventionally, noble metals are used as active metals in automotive catalytic converters, but the use of copper has been studied because copper promote active sites for chemical adsorption and reduction of NOx. Thus, this work aims to test new formulations of automotive catalysts, focusing on their performance in catalytic reduction of NO by CO and its selectivity to N2. The method of copper addition and the copper contents used in the preparation were evaluated. The addition methods used were dry impregnation (IS), solid state reaction (RS) and coprecipitation (CO). The copper contents studied were between 0,36 e 6,9 wt%. In addition, the impact on catalyst performance after thermal aging at 950 C for 12h was also studied. Textural and physico-chemical caracterization techniques were employed, such as atomic absorption spectrometry, N2 physisorption, X-ray diffraction, Raman spectroscopy and temperature programmed reduction. Catalysts were evaluated in the reduction reaction of NO by CO. The textural analysis indicated that addition of copper by the coprecipitation method led to textural characteristics different from the other catalysts. XRD analysis showed the formation of crystalline CuO for contents equal to or greater than 3,3 wt% of copper. TPR analysis indicated that there was a strong interaction at the interface between the substrate and the copper species dispersed together with the lowering of the temperature reduction of CuO and the partial reduction of ceria at lower temperatures. The catalytic activity results showed a better performance of the (IS) catalysts, which showed higher conversions at lower temperatures. Concerning the aging process, there was a significant decrease in the efficiency of the catalysts. A comparison with catalysts doped with noble metal showed good performance of the catalysts doped with copper, with the advantage of these presenting N2O emission restricted to low temperatures
9
Casapu, Maria Cristina. "NOx storage-reduction catalysts : material aspects, thermal ageing and reactivation." kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:30178.
Повний текст джерела
10
Wang, Fagen. "Hydrogen production from steam reforming of ethanol over an Ir/ceria-based catalyst : catalyst ageing analysis and performance improvement upon ceria doping." Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00967128.
Повний текст джерелаАнотація:
The objective of the thesis was to analyze the ageing processes and the modifications of an Ir/CeO2catalyst for steam reforming of ethanol. Over a model Ir/CeO2 catalyst, the initial and fast deactivationwas ascribed to ceria surface restructuring and the build-up of intermediates monolayer (acetate,carbonate and hydroxyl groups). In parallel, a progressive and slow deactivation was found to come fromthe structural changes at the ceria/Ir interface linked to Ir sintering and ceria restructuring. Theencapsulating carbon, coming from C2 intermediates polymerization, did not seem too detrimental to theactivity in the investigated operating conditions. By doping ceria with PrOx, the oxygen storage capacityand thermal stability were greatly promoted, resulting in the enhanced activity and stability. The Ir/CeO2catalyst was then modified by changing the shape of ceria. It was found that the shape and therefore thestructure of ceria influenced the activity and stability significantly. A simplified modeling of theseprocesses has contributed to support the new proposals of this work.
11
Kniep, Benjamin-Louis. "Microstructural modifications of copper zinc oxide catalysts as a function of precipitate ageing." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975886851.
Повний текст джерела
12
Lassi, U. (Ulla). "Deactivation Correlations of Pd/Rh Three-way Catalysts Designed for Euro IV Emission Limits:effect of Ageing Atmosphere, Temperature and Time." Doctoral thesis, University of Oulu, 2003. http://urn.fi/urn:isbn:9514269543.
Повний текст джерелаАнотація:
Abstract
The aim of this thesis is the knowledge of the most relevant deactivation mechanisms of Pd/Rh three-way catalysts under different ageing conditions, the deactivation correlation of laboratory scale ageing and engine bench/vehicle ageings, and the evaluation of the deactivation correlation. In the literature review, the phenomena involved in the three-way catalyst operation and its deactivation are considered. In the experimental section, ageing-induced phenomena in the catalyst are studied and deactivation correlations between laboratory scale and engine bench/vehicle ageings are presented, based on the results of several surface characterization techniques. The effects of ageing atmosphere and temperature, and time are considered in particular.
Fresh and aged catalysts used in this study were metallic monoliths designed for Euro IV emission limits. Thermal ageings were carried out in the reductive, oxidative and inert atmospheres in the temperature range of 800°C to 1200°C, and in the presence of water vapour (hydrothermal ageing). The engine ageing was carried out in the exhaust gas stream of a V8 engine during a 40 hour period. The ageing procedure composed of rich and stoichiometric air-to-fuel ratios carried out consecutively. The vehicle ageing was accomplished under real driving conditions (100 000 kilometres).
According to the results, deactivation of a Pd/Rh monolith is a combination of several ageing phenomena. The most important deactivation mechanisms are the sintering of active phase, the collapse in surface area and ageing-induced solid-solid phase transitions in the bulk washcoat. Furthermore, poisoning is a relevant deactivation mechanism of the vehicle-aged catalyst. High ageing temperature, gas phase composition and exposure time are essential variables to the deactivation of a Pd/Rh three-way catalyst.
This thesis presents an approach to discover the deactivation correlation between the laboratory scale ageing and under the vehicle's operation in an engine bench or on-road. Based on the characterization results, the accelerated laboratory scale air ageing does not correspond to the ageing-induced changes in the catalyst under the vehicle's operation. Therefore, there is a need for a modified ageing cycle and according to the results, a deactivation correlation between the laboratory scale ageing and the engine bench ageing can be presented as a function of ageing temperature and atmosphere, and time. Instead, after the vehicle operation, the deactivation correlation cannot be presented based solely on the studied variables because, after 100 000 kilometres of driving, the role of poisoning should be taken into account in the ageing cycle.
The results of this thesis can be utilized and applied in the development of laboratory scale ageing cycles, which corresponds closely to the ageing-induced changes in the catalyst during the vehicle operation. This enables a rather fast testing of the catalyst's performance and reduces the cost during the manufacturing of catalysts.
13
Van, Zandycke Sylvie. "The role of catalase and glutathione on replicative lifespan in Saccharomyces cerevisiae." Thesis, Oxford Brookes University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325260.
Повний текст джерела
14
Khudur, Ivan. "Aluminium alloys ability to catalyse the oxidation of biodiesel : Development of a procedure to test alloys." Thesis, KTH, Kraft- och värmeteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215060.
Повний текст джерелаАнотація:
Biodiesel is a renewable and biodegradable fuel that has the possibility to replace conventional diesel fuel and reduce the environmental pollution. Despite its environmental benefits, it has been shown to cause damage to the vehicle engines, due to its oxidative properties. Different metals, such as copper, zinc and aluminium are present in the vehicle fuel system and have been shown to catalyse the oxidation of biodiesel. Several studies have been performed to investigate the interaction between these metals and fuel. However, some reports concluded contradicting results when it comes to the oxidation of biodiesel in contact with aluminium alloys. This project aimed therefore to investigate and create a simple method for comparing the catalytic effect on oxidation for metals, and use this method to evaluate the degradation rate of biodiesel in contact with aluminium alloys. Different heating methods and coating materials were tested using the biodiesel RME to develop the testing procedure. When a test procedure was established, three filter houses made from cast aluminium alloy and three aluminium ingots with different amount of copper were immersed in RME and the stability was evaluated. The results showed that using an oven at 80 °C to investigate the stability provided the most repeatable results, and the spray paint Auto K billack spray Universal appeared to be compatible to use with RME. The inner untreated surface of the fuel filter houses did not seem to increase the oxidation rate of biodiesel. Aluminium alloys with higher copper content degraded RME more than aluminium alloys with little/no copper, if the surface had been treated mechanically, but not to a large extent. This concludes that aluminium alloys may reduce the stability of biodiesel if it contains much copper and if the surface of the alloy has been treated. However, the detected reduction on oxidation stability could depend on other factors, and therefore it is recommended to conduct further experiments on test the aluminium alloys.Biodiesel är ett förnybart och biologiskt nedbrytbart bränsle som har möjligheten att ersätta konventionell diesel och minska föroreningen av miljön. Trots dess fördelar så har det visats att bränslet skadar motorerna i fordon, vilket beror på dess oxidativa egenskaper. Olika metaller, såsom koppar, zink och aluminium förekommer i fordons bränslesystem, och dessa har påvisats katalysera oxidationen av biodiesel. Flera studier har genomförts där interaktionen mellan de tidigare nämnda metallerna och biodiesel har undersökts. En del av dessa studier har fått motsägelsefulla resultat när det kommer till interaktionen mellan aluminium legeringar ochbiodiesel. Detta projekt har därför haft som syfte att ta fram en enkelt metod att jämföra metallers katalystiska effekt på biodieslets oxidations stabilitet, samt använda denna metod för att bedöma nedbrytningen av biodiesel i kontakt med aluminium legeringar. Olika uppvärmningsmetoder och täckningsmaterial undersöktes med hjälp av biodiesel gjord på rapsolja, RME, för att ta fram mätmetoden. När ett tillvägagångssätt hade fastlagts, så sänktes bitar av tre olika bränslefilterhus tillverkade av aluminium legeringar, och tre olika aluminium tackor med olika kopparhalter i RME och bränslets stabilitet mättes. Användning av ugn vid 80 °C för att testa biodieslets oxidations stabilitet gav de mest upprepbara resultaten, och sprejfärgen Auto K billack spray Universal var mest kompatibel att använda som täckningsmaterial. Den inre, obehandlade ytan av bränslefilterhusen visade sig inte påverka oxidations stabiliteten på biodieslet. Aluminijm legeringar med en högre koppar halt bröt ned RME lite mer än aluminium legeringar med lite/ingen koppas, men endast om ytan hade blivit mekaniskt behandlad. Detta ger slutsatsen att aluminium legeringar kan minska biodieslets stabilitet om det innehåller mycket koppar och om legeringens yta har blivit behandlad. Däremot så kan den reduktionen av oxidations stabiliteten bero på andra faktorer och det rekommenderas därför att genomföra fler experiment med aluminum legeringar och biodiesel.
15
Blasetti, Cecilia. "Extensive oxidation treatments: ageing effects on a catalytic model system studied in UHV by STM." Doctoral thesis, Università degli studi di Trieste, 2009. http://hdl.handle.net/10077/3096.
Повний текст джерелаАнотація:
2007/2008This thesis concerns a surface science approach for the investigation of the ageing process of a model catalyst. It combines extreme oxidation conditions with Ultra High Vacuum (UHV) compatible characterization techniques. Our model system was the surface oxide formed on Rh(110); to grow such oxide, we used three alternative oxygen sources, optimizing for each case the preparation recipe. When dosing molecular oxygen, pressures in the ∼ 10− 4 mbar range were used, therefore bridging, to some extent, the pressure gap. For characterization of the oxides we used mainly Scanning Tunneling Microscopy (STM) and Thermal Desorption Spectroscopy (TDS), providing atomic scale and desorption mechanism information, respectively. Low Energy Electron Microscopy (LEEM) and X-ray Photoelectron Specroscopy (XPS) complemented our measurements with large scale morphology and reactivity data and with chemically resolved results. To mimic real catalytic conditions, we setup an ageing protocol consisting of cycles of oxidation and annealing in UHV (up to more than ∼ 40), with each of the three oxygen sources. In this way, we were able to observe two different kinds of ageing: a “contaminant-driven” and an “intrinsic” one, caused by the iterative oxidation procedure. The latter is connected to the presence of a new species we detected on the (1 × 1) surface obtained after the oxide desorption, that we named “units” (or ageing fingerprints). By decreasing their number we were able to show that the intrinsic ageing is, at least partially, reversible. We could not uniquely determine the structure of the “units”, but plausible models are proposed. ------------------------------------------------
Questa tesi si occupa dello studio dell’invecchiamento artificiale di un catalizzatore modello, combinando condizioni di ossidazione estreme con le tecniche di caratterizzazione, compatibili con l’ultra-alto-vuoto (UHV), proprie della scienza delle superfici. Il nostro sistema modello era l’ossido superficiale formato sul Rh(110); per crescere questo ossido, abbiamo utilizzato tre sorgenti alternative di ossigeno, ed abbiamo ottimizzato la ricetta di preparazione nei singoli casi. Utilizzando l’ossigeno molecolare abbiamo dosato a pressioni dell’ordine di ca. 10− 4 mbar, ed in questo modo abbiamo in parte colmato la “pressure gap” che solitamente divide gli studi su sistemi modello da quelli di catalisi reale. Per caratterizzare gli ossidi abbiamo usato principalmente la microscopia a scansione ad effetto tunnel STM e la spettroscopia di desorbimento termico TDS, che ci hanno fornito rispettivamente informazioni su scala atomica e sul meccanismo di desorbimento. Le tecniche LEEM e XPS hanno contribuito in modo complementare alle nostre misure con dati di morfologia e reattività su larga scala, da un lato, e con dati risolti chimicamente, dall’altro. Per simulare le condizioni della catalisi reale, abbiamo sviluppato un protocollo di invecchiamento (“ageing”) composto da cicli di ossidazione e riscaldamento in ultra-alto-vuoto (fino a ca. 40), con ognuna delle tre sorgenti di ossigeno. Seguendo questa procedura, abbiamo osservato due diversi tipi di invecchiamento dell’ossido di rodio: un primo tipo dominato dalla presenza di contaminanti, ed un secondo invece che abbiamo chiamato “intrinseco”, causato cioè dalle ripetute ossidazioni. Quest’ultimo dipende dalla presenza di una nuova specie osservata sulla superficie (1 × 1) che si ottiene a seguito del desorbimento di ciascun ossido, che abbiamo chiamato “units” (o -ageing fingerprint-). Ri- ducendo la densità di questa specie siamo stati in grado di mostrare come l’invecchiamento intrinseco sia, almeno in parte, reversibile. Non abbiamo potuto determinare univocamente la struttura delle “units”, ma alcuni modelli possibili vengono proposti.
XXI Ciclo
1981
16
Easterling, Vencon G. "The Effects of Ceria Addition on Aging and Sulfation of Lean NOx Traps for Stand Alone and LNT-SCR Applications." UKnowledge, 2013. http://uknowledge.uky.edu/cme_etds/17.
Повний текст джерелаАнотація:
THE EFFECTS OF CERIA ADDITION ON AGING AND SULFATION OF LEAN NOx TRAPS FOR STAND ALONE AND LNT-SCR APPLICATIONS
Model powder and fully formulated monolithic lean NOx trap (LNT) catalysts were used to investigate the effect of ceria on desulfation behavior. Temperature-programmed reduction (TPR) experiments (model catalysts) showed each of the oxide phases present is able to store sulfur and possesses distinct behavior (temperature at which desulfation occurs). La-CeO2 or CeO2-ZrO2-containing samples (monoliths) showed a greater resistance to deactivation during sulfation and required lower temperatures to restore the NOx storage efficiency to its pre-sulfation value.
Fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging to elucidate the effect of washcoat composition on LNT aging. Elemental analysis revealed that residual sulfur, associated with the Ba phase, decreased catalyst NOx storage capacity and that sintering of the precious metals resulted in decreased contact between the Pt and Ba phases.
Spatially-resolved inlet capillary mass spectrometry (SpaciMS) was employed to understand the factors influencing the selectivity of NOx reduction in LNT catalysts degreened and thermally aged) containing Pt, Rh, BaO and Al2O3, and contained La-stabilized CeO2. Stretching of the NOx storage and reduction zone (NSR) zone resulted in increased selectivity to NH3 due to the fact that less catalyst was available to consume NH3 by either the NH3-NOx SCR reaction or the NH3-O2 reaction. Additionally, the loss of oxygen storage capacity (OSC) and NOx storage sites, along with the decreased rate of NOx diffusion to Pt/Rh sites, led to an increase in the rate of propagation of the reductant front after aging, in turn, resulting in increased H2:NOx ratios at the Pt/Rh sites and consequently increased selectivity to NH3.
Finally, a crystallite scale model was used to predict selectivity to NH3 from the LNT catalysts during rich conditions after a fixed amount of NOx was stored during lean conditions. Both the experimental and model predicted data showed that the production of NH3 is limited by the rate of diffusion from the Ba storage sites to the Pt particles at 200 °C. At 300 °C, the process is limited by the rate at which H2 is fed to the reactor.
17
Mehsein, Kawsar. "Degradation mechanisms study of NOx after-treatment SCR system using urea on a Diesel Particulate Filter catalyst." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2017. http://www.theses.fr/2017ENCM0012.
Повний текст джерелаАнотація:
La Reduction Catalytique Sélective (SCR) par l’ammoniac est un procédé qui est commercialement utilisé pour l’élimination des oxydes d’azote (NOx) issus des moteurs Diesel afin de répondre aux exigences des normes européennes concernant les émissions. Pour pouvoir mieux traiter les NOx, surtout à froid, la combinaison du catalyseur SCR à base de zéolithe échangée au Cu (Cu-Zéolithe) et le filtre à particules (SCRF) représente un avantage à son rapprochement du moteur. Néanmoins, la combinaison peut avoir aussi des inconvénients, lors de la régénération en continue du filtre à particules, le catalyseur SCRF sera soumis à de multiples occurrences thermiques et à de possible empoisonnement par le carburant et l’huile moteur durant toute la vie du système de post-traitement en véhicule. Etant donné que la législation européenne exige que le système de post-traitement soit opérationnel et efficace jusqu’à 160.000km, il est donc important de comprendre les phénomènes engendrés par le vieillissement hydrothermal du SCRF afin de pouvoir l’améliorer. Dans le cadre de ce travail, des simulations du vieillissement hydrothermal dans un four de laboratoire et en parallèle un vieillissement réel d’environ 120.000km d’une ligne de post-traitement comprenant le SCRF ont été réalisés. Les différents résultats ont permis de comprendre le mécanisme de dégradation de la performance du catalyseur à base de Cu-Zéolithe lié au traitement hydrothermal et de pouvoir corréler un vieillissement réel en véhicule à un vieillissement accéléré au four. De plus, des techniques rapides de caractérisation permettant de détecter l’état de vieillissement d’un catalyseur SCRF ont été sélectionnées. Finalement, un modèle mathématique basé sur les résultats expérimentaux a permis de décrire la dégradation de la capacité de stockage de l’ammoniac du catalyseur SCRF avec le traitement hydrothermalThe selective catalytic reduction (SCR) by urea or ammonia is a well-known method to meet the European emission regulation requirements concerning the reduction of nitrogen oxides (NOx) emissions from Diesel engines. In order to optimize the NOx reduction activity at all temperature range, a copper-exchanged zeolite (Cu-Zeolite) SCR catalyst is combined to a Diesel Particulate Filter (SCRF). However, during the continuous regeneration of the particulate filter, the SCRF catalyst will go through numerous constraints such as variable high temperature, poisoning compounds from Diesel fuel and engine oil, during the entire vehicle life of the after-treatment line. Moreover, the European legislation requires a durability of the after-treatment line for about 160,000km. Understanding the degradation of the SCRF catalyst by the hydrothermal ageing is of interest to apprehend the deactivation mechanism in order to develop a stable material. In the present work, accelerated hydrothermal ageing in laboratory oven and also a real driving ageing of an SCRF catalyst, included in an after-treatment line for about 120,000km, were performed. The different results obtained help to apprehend the degradation mechanism of a Cu-Zeolite SCRF catalyst performance and also to find a correlation between a 120,000km real driving ageing and an equivalence oven aged SCRF catalysts. Moreover, rapid characterization methods, to detect the hydrothermal ageing status of an SCRF catalyst, have been selected. Finally, a mathematical model, based on experimental results, has allowed to describe the degradation of the ammonia storage capacity of the SCRF catalyst with the hydrothermal ageing
18
Jelena, Kiurski. "Mehanizmi starenja katalizatora za hidrodesulfurizaciju." Phd thesis, Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, 1997. https://www.cris.uns.ac.rs/record.jsf?recordId=71439&source=NDLTD&language=en.
Повний текст джерелаАнотація:
Apstrakt je obrađen tehnologijama za optičko prepoznavanje teksta (OCR).U ovom radu izvršena su ispitivanja deaktivacije katalizatora za hidrodesulfurizaciju (HDS), uz simulaciju starenja u laboratorijskim uslovima i paralelna ispitivanja katalizatora iz realnog industrijskog postrojenja. Širok interval uslova u laboratorijskoj simulaciji (temperatura, vreme tretmana, oksidacione i inertne atmosfere) pružio je osnov za ocenu uticaja različitih parametara na brzinu starenja katalizatora i definisanje kritičnih uslova, posebno pri regeneraciji katalizatora. Ispitivanja dva tipa HDS katalizatora, NiO-MoO3/y-Al2O3 i CoO- MoO3/y-Al2O3 i binarnih modelnih sistema NiO/ Al2O3, uz primenu komplementamih metoda za ispitivanje stukture i teksture čvrstih poroznih materijala, omogućila su uvid u mehanizme starenja u ovim složenim katalitičkim sistemima. Utvrđeno je da je oksidaciona atmosfera, posebno vodena para, kritičan faktor u kinetici stukturnih i teksturalnih promena u katalitičkom sistemu. Segregacija aktivne faze, interakcija sa nosačem, sinterovanje i gubitak aktivne faze iz sistema simultani su procesi koji dovode do trajne deaktivacije katalizatora. Visina radne temperature i moguća lokalna pregrevanja u sloju katalizatora, podstaknuta promenama difuzionih karakteristika kataličkog zrna, ključni su za destrukciju aktivne faze katalizatora, uz segregaciju prekursora oksidne faze molibdena, čiji je uticaj izrazit u fazi regeneracije. Intermedijarno prisustvo tečne faze oksida molidena, koja obliva površinu nosača, uslovljavajući intenzivno sinterovanje i ubrzanu interakciju izmedju ostalih faza u sistemu, predstavlja osnovni mehanizam u starenju katalizatora za HDS.Abstract was processed by technology for Optical character recognition (OCR).Deactivation studies of hydrodesulphurization catalysts were performed, based on both aging simulation in laboratory conditions and investigation of catalysts from an industrial HDS plant. Broad interval of conditions applied in laboratory simulation (temperature, treatment duration, oxidation and inert atmospheres) was the basis for evaluating the effect of different parameters on catalyst aging kinetics and defining critical conditions, with emphasis on regeneration procedure. The investigations of two catalyst types, NiO-MoO3/y-Al2O3 and C0O-MoO3/y-Al2O3, and NiO/Al2O3 binary model systems, using complementary methods for structural and textural investigations of porous solid systems, enabled the insight in aging mechanisms of these complex catalytic systems. The oxidation atmosphere, especially water vapor, is critical for the rate of structural and textural changes in the catalysts. Segregation in active phase, interaction with the support, sintering and loss of active component from the catalyst are the simultaneous processes bringing about the irreversible deactivation of the catalyst. The temperature gradient in working conditions and possible formation of hot spots in catalyst reactor bed, affected also by changes of diffusion characteristics of catalyst grain, are crucial factors for segregation of molybdenum oxide precursor, which effect is pronounced during regeneration. The mechanism of HDS catalyst aging is based on intermediary presence of moIybdenum oxide liquid phase on the support surface, facilitating intensive sintering and interactions of other phases of catalytic system.
19
Xia, Yuzhen. "Carbone fonctionnalisé pour une meilleure performance des piles à combustible." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0116/document.
Повний текст джерелаАнотація:
Dans le contenu de l’amélioration des performances des piles à combustible, des catalyseurs Pt/Vulcan ont été greffés soit avec du polystyrène sulfonate (PSSA) soit avec de l'acide 4-phenysulfonique (PSA). L'influence du ratio du greffage, de la couche de diffusion de gaz et de la qualité de Nafion, sur les performances électrochimiques ont été étudiées en demi-pile et en assemblage membrane-électrodes (AME). La surface électrochimique du catalyseur a été améliorée en présence de la couche microporeuse sur le papier carboné en tant que couche de diffusion de gaz, aussi une densité de courant supérieure et une résistance de transfert de charge inférieure ont été observées. Pt/Vulcan catalyseurs ont été greffés des chaines PSSA avec 5, 10 et 20 wt.% 4-styrènesulfonate de sodium. Les résultats en demi-pile et en pile ont montré que des taux de sulfonation de 5 à 10 wt.% étaient optimaux. La sulfonation des catalyseurs a aussi été effectuée avec 5.8, 11.6, 18.0 et 23.3 wt.% PSA. Des résultats meilleurs ont été obtenus par la sulfonation. L'AME ayant 18.0 wt.% PSA a présenté une excellente stabilité pendant 3000 cycles de test de vieillissement accéléré. Moins de Nafion a entraîné une plus faible performance des demi-piles, aussi des AMEs ayant catalyseurs des greffé de 5 wt.% PSSA ou PSA. Cependant, celles contenant 10 et 20 wt.% de PSSA, ont montré un une densité de puissance élevé lors que la quantité de Nafion a diminué de 0.50 à 0.25 mg•cm-2In the development of the performances of PEM fuel cell, sulfonated Pt/Vulcan catalysts were prepared by grafting with either polystyrene sulfonate (PSSA) or with 4-phenysulfonic acid (PSA). The influences of the graft ratio, the amount of Nafion and the gas diffusion layer, on the electrochemical performances were studied in a half-cell and membrane electrode assembage (MEA). Larger electrochemical surface area of the catalyst was obtained in the presence of microporous layer on the carbon paper, as well as higher ORR current and lower charge transfer resistance. PSSA was grafted onto Pt/Vulcan catalysts by in-situ radical polymerization with 5, 10 and 20 wt.% sodium styrene sulfonate. It was presented in the half-cell tests and fuel cell tests that the catalysts grafted with 5 and 10 wt.% sulfonated groups performed improved properties. Pt/Vulcan catalysts were also grafted with 5.8, 11.6 18.0 and 23.3 wt.% PSA. Compared with non-functionalized catalysts, significant developments were achieved because of the sulfonation. The MEA with 18.0 wt.% PSA was studied in accelerated durability tests and showed excellent durability after 3000 cycles. For half-cells and MEAs with catalysts grafted with 5wt.% PSSA or PSA groups, low Nafion addition resulted in to lower performances. However, the MEAs with 10 and 20 wt.% PSSA exhibited an enhanced performance than the counterparts with 0.50 mg•cm-2 Nafion
20
Havil, Patrick. "Influence du vieillissement thermique sur les proprietes physico-chimiques et la reactivite des catalyseurs mono et bimetalliques a base de platine et/ou rhodium sur alumine ou sur cerine." Paris 6, 1988. http://www.theses.fr/1988PA066291.
Повний текст джерелаАнотація:
Une etude systematique de la stabilite des catalyseurs de post-combustion mono et bimetalliques, platine-rhodium, supportes sur alumine et cerine a ete realisee pour un vieillissement thermique a des temperatures variant de 600 a 1100**(o)c. Les catalyseurs ont ete ensuite testes avec un melange de gaz synthetique simulant les conditions reelles. Le vieillissement a lieu principalement en milieu oxydant. Il est du soit au frittage de la phase metallique par grossissement des particules de 1 a 30 nm soit a l'encapsulation ou a la migration des ions platine et rhodium dans le support
21
Saïd, Hassane Charifat. "Valorisation chimique et biotechnologique de la biodiversité marine de l’Archipel des Comores : recherche de molécules naturelles anti-âge." Thesis, La Réunion, 2020. https://elgebar.univ-reunion.fr/login?url=http://thesesenligne.univ.run/20_16_C_SaidHassane_Diff.pdf.
Повний текст джерелаАнотація:
Le vieillissement du corps humain crée un terrain propice au développement de certaines pathologies. Afin de ralentir ou retarder l’apparition des effets physiologiques normaux ou pathologiques liés à l’âge, différentes stratégies de recherche peuvent être développées. Aussi, dans le cadre de cette thèse, plusieurs éponges marines, collectées à Mayotte, ont été évaluées pour leur capacité à produire des métabolites aux propriétés anti-âge. L’évaluation des activités biologiques a été menée sur les cibles suivantes : élastase et tyrosinase (vieillissement cutané), CDK7 et protéasome (cancers), Fyn kinase (maladie d’Alzheimer), catalase (stress oxydant) et sirtuine 1 (différentes fonctions biologiques). Les éponges Lendenfeldia sp. et Scopalina hapalia, en raison de leurs activités biologiques, ont été sélectionnées pour des études chimiques. L'extraction, l'isolement et l'identification de leurs métabolites ont été entrepris par différentes techniques chromatographiques (CLMP, CLHP…) et spectroscopiques (SMHR, RMN 1D et 2D). Vingt métabolites appartenant aux classes chimiques des alkylglycérols, des buténolides, des dicétopipérazines, des épidioxystérols, des phospholipides ainsi que des polybromodiphényléthers ont été isolés de ces deux éponges. Il est à noter que quatre métabolites de structures nouvelles ont été isolés de S. hapalia dont la composition chimique n’avait été jusqu’à ce jour que très peu étudiée. Par ailleurs, peu d’études portant sur la caractérisation et le potentiel de production de métabolites d’intérêts de la communauté microbienne associée à S. hapalia ont été retrouvées dans la littérature. Dans cette thèse, la communauté bactérienne de cette éponge a été caractérisée, par une approche de métagénomique ciblée. Cette étude a mis en lumière une communauté majoritairement dominée par les Protéobactéries suivis par les Cyanobactéries, les Bacteroidetes, les Planctomycètes ainsi que les Actinobactéries. L’étude de la diversité microbienne cultivable a permis l’isolement de microorganismes appartenant aux genres Bacillus, Micromonospora, Salinispora, Rhodococcus, Aspergillus, Chaetomium et Nigrospora. Enfin, trente microorganismes ont été caractérisés pour leur capacité à produire des molécules bioactives en mettant en œuvre les techniques de culture classique couplées à une récupération in situ des molécules produites par les microorganismes. L’évaluation des activités anti-âge des extraits produits a été réalisée par un criblage sur les sept cibles biologique étudiées. Quinze souches différentes ont été identifiées comme prometteuses pour la recherche de métabolites aux différentes propriétés anti-âgeHuman aging creates a breeding grounds for the development of conditions that get more common as we get older. In order to slow or delay the onset of physiological or pathological effects of aging process, different research strategies can be developed. Thus, in the context of this PhD work, several marine sponges collected in Mayotte, were evaluated for their capacity to produce metabolites with anti-aging properties. The evaluation of biological activities was carried out on the following biological targets: elastase and tyrosinase (skin aging), CDK7 and proteasome (cancers), Fyn kinase (Alzheimer's disease), catalase (oxidative stress) and sirtuin 1 (different biological functions). Because of their biological activities, the marine sponges Lendenfeldia sp. and Scopalina hapalia were selected for chemical studies. The extraction, isolation and identification were undertaken by various chromatographic (MPLC, HPLC ...) and spectroscopic (HRMS, 1D and 2D NMR) techniques. Twenty metabolites belonging to the chemical classes of alkylglycerols, butenolides, diketopiperazines, epidioxysterols, phospholipids and polybromodiphenyl ethers were isolated from these sponges. It should be noted that four new metabolites of new structures were isolated from S. hapalia whose chemical composition has been little studied up until now. Furthermore, there is a paucity of information on its microbial community and its potential for bioactive metabolites production. The bacterial community associated with S. hapalia was therefore characterized by a targeted metagenomic approach. This study shed light on a diverse community highly dominated by Proteobacteria followed by Cyanobacteria, Bacteroidetes, Planctomycetes as well as Actinobacteria. The use of cultivation approach allowed the isolation of microorganisms affiliated to genera Bacillus, Micromonospora, Salinispora, Rhodococcus, Aspergillus, Chaetomium and Nigrospora. Finally, the potential of isolated microorganisms to produce bioactive molecules was investigated in two steps: 1) by implementing conventional culture techniques coupled with in situ recovery of the molecules produced by the microorganisms, 2) by screening the produced crude extracts from thirty isolates for anti-aging activities. The results highlighted fifteen promising microorganisms producing bioactive metabolites with various anti-aging activities
22
Anguita, Paola. "Impact des biocarburants sur le système d’oxydation catalytique des véhicules diesel." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1181.
Повний текст джерелаАнотація:
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 catalytiquesThe 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
23
Foster, Adam Lamar. "Accelerated thermal aging of iron-zeolite SCR catalyst on an engine bench." 2008. http://etd.utk.edu/2008/December2008MastersTheses/FosterAdamLamar.pdf.
Повний текст джерела
24
Ottinger, Nathan Andrew. "Effects of high temperature cyclic aging on a fully-formulated lean NO[subscript x] trap catalyst." 2008. http://etd.utk.edu/August2008MastersTheses/OttingerNathanAndrew.pdf.
Повний текст джерела
25
Furtado, Nélida Sofia Tavares. "Ageing on commercial automotive catalysts, a structure reactivity study." Master's thesis, 2014. http://hdl.handle.net/10362/13934.
Повний текст джерелаАнотація:
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.
26
Foster, Adam Lamar. "Accelerated Thermal Aging of Fe-Zeolite SCR Catalysts on an Engine Bench." 2008. http://trace.tennessee.edu/utk_gradthes/375.
Повний текст джерелаАнотація:
Selective catalytic reduction (SCR) of NOx with urea/NH3 is a leading candidate to the impending more stringent emissions regulations for diesel engines. Currently, there is no consensus on the durability and the deactivation mechanisms associated with zeolite-based SCR catalysts, nor is there an established protocol for rapidly aging zeolite-based SCR catalysts that replicates the catalyst deactivation associated with field service. A 517 cc single-cylinder, naturally-aspirated direct injection (NA/DI) diesel engine is used to perform accelerated thermal aging on Fe-zeolite SCR catalysts. The engine is fitted with an exhaust aftertreatment system consisting of a DOC, a SCR catalyst and a DPF. Accelerated aging protocol established for the SCR catalyst utilizes high temperature exhaust gases during the active regeneration of the DPF. Accelerated aging is carried out at exhaust gas temperatures of 650, 750 and 850°C at the SCR inlet and at a gas hourly space velocity (GHSV) of approximately 40,000 h-1. The engine is maintained at 1500 rpm and supplemental fuel is injected upstream of the DOC to alter the temperature of the aftertreatment system. The aged Fe-zeolite SCR catalysts are evaluated for NOx performance in a bench-flow reactor and characterized by multiple surface characterization techniques for materials changes.
The NOx performance of the front sections of the engine-aged catalysts is severely degraded. BET surface area measurements of the engine-aged catalyst indicate a severe reduction of catalyst surface area in the front sections of the catalysts aged at 750 and 850°C. However, the catalyst aged at 650°C has a catalyst surface area similar to that of a fresh catalyst; thereby ruling out reduction of catalyst surface area as the sole cause of the catalyst deactivation seen in the front sections of the engine-aged catalysts. The similar shape of the NOx conversion profiles observed with these catalyst sections even at different aging temperatures indicates some type of catalyst poisoning; however, the cause of catalyst degradation in these catalyst sections is not identified in this investigation.
There is a good relationship between the NOx performance and catalyst aging temperature for the rear sections of the engine-aged catalysts – NOx performance decreases with increasing aging temperature. XRD patterns and NO oxidation experiments reveal evidence of zeolite dealumination in the engine-aged catalysts. BET surface area measurements show that catalyst surface area decreases with increasing aging temperature, which further supports the suggestion of zeolite dealumination as the cause of catalyst deactivation in the rear sections of the engine-aged catalysts.
A comparison between the engine-aged and field-aged catalysts is conducted to assess the validity of the implemented accelerated thermal aging protocol in replicating the aging conditions observed in the field-aged catalyst. Bench-flow reactor evaluation is used to determine the NOx performance of the engine-aged and field-aged catalysts, and in depth surface studies are used to determine the deactivation mechanisms associated with each type of catalyst aging. SEM micrographs and BET surface area measurements of the aged catalysts show that the deactivation mechanism associated with catalyst aging is primarily physical damage to the zeolite washcoat for both the field-aged and engine-aged catalysts. Furthermore, X-ray diffraction and NO oxidation experiments identify zeolite dealumination as the underlying cause of the washcoat degradation. Finally, BFR evaluation shows that the NOx performance of the catalyst aged at 750°C for approximately 50 hours compares very well to that of the field-aged catalyst with a service life of 3 years. It is concluded that accelerated thermal aging on the engine bench is successful in bringing about similar catalyst changes to those seen with the field-aged catalyst.
27
Cheng, Ching-Li, and 鄭敬俐. "An immunohistochemical study of Mn-SOD and catalase changes during aging." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/05381558969115114959.
Повний текст джерела
28
Kauser, Sobia, Gillian E. Westgate, M. R. Green, and Desmond J. Tobin. "Human Hair Follicle and Epidermal Melanocytes Exhibit Striking Differences in Their Aging Profile which Involves Catalase." 2011. http://hdl.handle.net/10454/7453.
Повний текст джерелаАнотація:
noCanities or senile hair graying, a universally recognized sign of aging, remains unresolved in terms of physiological causes, although a strong genetic contribution is understood (Gunn et al., 2009). As the hair fiber continues to grow long after melanin production ceases, we suggest that melanocytes in the hair follicle may be more sensitive to the impact of chronological aging than are keratinocytes. Moreover, follicular melanocytes also age more markedly than those in the overlying epidermis. The hair follicle provides a unique opportunity to decouple the impact of age on two hair follicular tissue functions: hair formation and hair pigmentation. ... This study provides analysis of race, age, and anatomically matched cultures of adult human epidermal and hair follicle melanocytes (HFMs).
29
Kniep, Benjamin-Louis [Verfasser]. "Microstructural modifications of copper zinc oxide catalysts as a function of precipitate ageing / vorgelegt von Benjamin-Louis Kniep." 2005. http://d-nb.info/975886851/34.
Повний текст джерела
30
Wood, John M., H. Decker, H. Hartmann, Bhavan Chavan, Hartmut Rokos, J. D. Spencer, Sybille Hasse, et al. "Senile hair graying: H2O2-mediated oxidative stress affects human hair color by blunting methionine sulfoxide repair." 2009. http://hdl.handle.net/10454/6241.
Повний текст джерелаАнотація:
Senile graying of human hair has been the subject of intense research since ancient times. Reactive oxygen species have been implicated in hair follicle melanocyte apoptosis and DNA damage. Here we show for the first time by FT-Raman spectroscopy in vivo that human gray/white scalp hair shafts accumulate hydrogen peroxide (H(2)O(2)) in millimolar concentrations. Moreover, we demonstrate almost absent catalase and methionine sulfoxide reductase A and B protein expression via immunofluorescence and Western blot in association with a functional loss of methionine sulfoxide (Met-S=O) repair in the entire gray hair follicle. Accordingly, Met-S=O formation of Met residues, including Met 374 in the active site of tyrosinase, the key enzyme in melanogenesis, limits enzyme functionality, as evidenced by FT-Raman spectroscopy, computer simulation, and enzyme kinetics, which leads to gradual loss of hair color. Notably, under in vitro conditions, Met oxidation can be prevented by L-methionine. In summary, our data feed the long-voiced, but insufficiently proven, concept of H(2)O(2)-induced oxidative damage in the entire human hair follicle, inclusive of the hair shaft, as a key element in senile hair graying, which does not exclusively affect follicle melanocytes. This new insight could open new strategies for intervention and reversal of the hair graying process.