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

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

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22466号 / 工博第4727号 / 新制||工||1738(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 庸裕, 教授 陰山 洋, 教授 佐藤 徹 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

A conventional exhaust gas after treatment system (EATS) for the Euro VI legislation contains four different catalyst. The first two (particulate filter system) remove particulates and the last two (SCR system) remove nitrogen oxides (NOx). The particulate filter system also optimizes the gas composition with respect to nitrogen monoxide (NO) and nitrogen dioxide (NO2). The performance of the SCR system has a strong dependency on the NO:NO2 ratio as the so called selective catalytic reduction (SCR) reaction is kinetically favored at a NO:NO2 ratio of 1:1. The diesel oxidation catalyst (DOC) is placed first in the EATS. Due to this placement, the DOC is subjected to a rough environment, e.g. high temperatures and oil/fuel impurities that with time will affect its performance, i.e. the catalyst ages. In this master thesis, the aging of the DOC has been empirically correlated to thermal load and sulfur exposure. The study shows that it is possible to predict how the NO oxidation performance decays as a function of thermal and sulfur exposure. The empirical relation was fitted against two aging cycles and validated against an additional four. The results show that the loss of catalytic activity can to a large extent be explained by the cycle it has been used on. / Ett konventionellt efterbehandlingssystem för Euro VI-standarden innehåller fyra olika katalysatorer. De första två rensar (partikelfiltersystemet) från partiklar och de två sista (SCR-systemet) tar bort kväveoxider (NOx). Partikelfiltersystemet reglerar även gassammansättningen med avseende på kvävemonoxid (NO) och kvävedioxid (NO2). Prestandan för SCR-systemet har ett starkt beroende på NO:NO2-förhållandet där ett förhållande på 1:1 är kinetiskt gynnat för den så kallade SCR-reaktionen (eng: Selective Catalytic Reduction). Oxidationskatalysatorn (DOC) sitter som ett första steg i efterbehandlingen. Placeringen medför att katalysatorn finns i en tuff miljö där den till exempel utsätts för hög temperatur och olje/bränsleföroreningar som över tiden påverkar dess prestanda. Detta brukar kallas att DOC:n åldras. I detta examensarbete har åldrandet av DOC:n korrelerats empiriskt till termisk belastning och svavelexponering. Studien visar att det är möjligt att förutsäga hur NO-oxidationsprestandan avtar som en funktion av termisk last och svavelexponering. Det empiriska modellen anpassades till två åldringscykler och validerades emot ytterligare fyra cykler. Resultaten visar att den kvarvarande katalytiska aktiviteten i stor utsträckning kan förklaras genom vilken cykel den har körts på.

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