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University of Kentucky

1. Jones, Samantha. Ceria Based Catalysts for Low Temperature NOx Storage and Release.

Degree: 2016, University of Kentucky

Model ceria catalysts were evaluated for NOx storage and desorption performance under lean conditions. Three different storage temperatures (80 °C, 120 °C, and 160 °C) were utilized to evaluate NOx storage. Higher temperatures resulted in higher NOx storage. It was observed that storage of platinum promoted ceria resulted in higher NOx storage compared to promotion with palladium. NOx desorption behavior of platinum promoted ceria indicated that the majority of NOx is released at high temperatures (> 350 °C), comparatively palladium promotion released more of the stored NOx at lower temperatures. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) indicated that platinum promotion results in NOx storage as thermally stabile nitrates, while palladium promotion results in NOx storage as thermally labile nitrites. Doping ceria with trivalent rare earth oxides has been shown to improve NOx storage by generating lattice oxygen vacancies. Ceria doped with Pr, Y, La, Sm, and Nd at two different concentrations (5 and 20 mol%) and promoted with Pt were evaluated. Doping ceria with 5% Sm, Nd, and Pr improved the amount of NOx stored while the addition of Sm and La did not improve storage. Upon increasing dopant concentration, NOx storage decreased in all cases but Pr. However, increasing Pr concentration was found to increase NOx storage as well as low temperature NOx release. Ceria doped with Pr promoted with Pd increased the amount of NOx released at lower temperatures compared to Pt promotion, although palladium promotion resulted in lower storage. Similar DRIFTS spectra were obtained with Ce-Pr when promoted with Pt or Pd compared to model catalysts. Platinum promotion results in the storage of NOx at nitrates, which require high temperatures for removal. Comparatively, Pd promotion results in NOx stored at nitrites requiring lower temperatures for removal. Ceria doped with Pr proved to be promising, although not thermally stable when exposed to high temperatures as may be seen during a DPF clean up. Therefor, stabilizing Ce-Pr catalysts with Zr were evaluated. It was found that stabilizing Ce-Pr with Zr was not found to be beneficial to the catalyst performance.

Subjects/Keywords: NOx; Low temperature NOx storage; Passive NOx Adsorbers; PNA; DRIFTS; Ce-Pr; and doped ceria.; Chemistry; Inorganic Chemistry

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Jones, S. (2016). Ceria Based Catalysts for Low Temperature NOx Storage and Release. (Doctoral Dissertation). University of Kentucky. Retrieved from https://uknowledge.uky.edu/chemistry_etds/67

Chicago Manual of Style (16th Edition):

Jones, Samantha. “Ceria Based Catalysts for Low Temperature NOx Storage and Release.” 2016. Doctoral Dissertation, University of Kentucky. Accessed April 06, 2020. https://uknowledge.uky.edu/chemistry_etds/67.

MLA Handbook (7th Edition):

Jones, Samantha. “Ceria Based Catalysts for Low Temperature NOx Storage and Release.” 2016. Web. 06 Apr 2020.

Vancouver:

Jones S. Ceria Based Catalysts for Low Temperature NOx Storage and Release. [Internet] [Doctoral dissertation]. University of Kentucky; 2016. [cited 2020 Apr 06]. Available from: https://uknowledge.uky.edu/chemistry_etds/67.

Council of Science Editors:

Jones S. Ceria Based Catalysts for Low Temperature NOx Storage and Release. [Doctoral Dissertation]. University of Kentucky; 2016. Available from: https://uknowledge.uky.edu/chemistry_etds/67

2. Frizon, Vincent. Corrélation composition chimique-structure-propriétés de réductibilité / mobilité de l’oxygène / catalyse d’oxydation au sein d’oxydes à base de cérium, zirconium et de praséodyme : Correlation between chemical composition-structure-properties of reducibility and oxygen mobility with the oxidation of automotive pollutants by (Ce, Zr, Pr) mixed oxides.

Degree: Docteur es, Chimie, 2018, Lyon

Ces travaux de thèse ont pour vocation d'étudier des oxydes mixtes Ce1-x-yZrxPryO2-z afin de corréler composition chimique-structure avec les propriétés de réductibilité/mobilité ionique de l'oxygène associées aux performances catalytiques pour l'oxydation du CO et du propane, en conditions essence et Diesel. La connaissance de la quantité de terres rares au degré d'oxydation +4 a été déterminante. Notamment, plus le taux de Pr4+ est important, plus le composé est réductible et plus la mobilité de l'oxygène s'accroît. L'évaluation du coefficient de diffusion de l'oxygène D* a montré que sa valeur devenait élevée, rivalisant ainsi avec les meilleurs conducteurs ioniques de l'oxygène à basse température. Les échanges isotopiques de l'oxygène permettent de montrer que la vitesse d'échange croît quand le taux de Pr augmente. L'étude de la combustion du propane sur ces oxydes a montré qu'une bonne mobilité de l'oxygène permettait d'améliorer les performances catalytiques. Ainsi, l'oxyde de composition Ce0,45Zr0,1Pr0,45O2-x (CZP45) présente les meilleures propriétés pré-citées et l'activité catalytique la plus élevée. L'oxyde CZP45 a donc été imprégné de Pd afin d'être comparé à deux catalyseurs utilisés industriellement et à iso-teneur en Pd, dispersée sur ?-Al2O3 (Diesel) et Ce0,5Zr0,5O2-x (essence). En régime Diesel, Pd-CZP45, après une étape initiale de réduction, présente une meilleure activité catalytique à basse température que Pd-?-Al2O3 pour l'oxydation du propane. Nous avons expliqué ces excellentes performances par la présence de clusters de Pd2+/Pd° finement dispersés sur l'oxyde (CZP45) et par la capacité du catalyseur à adsorber et conduire l'oxygène

This work describes characterizations of Ce1-x-yZrxPryO2-z mixed oxides to link their chemical composition-structure with their reducibility/oxygen mobility. These latter properties were correlated with their catalytic activity for the oxidation of CO and propane, both in stoichiometric (gasoline) and lean-burn (Diesel) conditions. The determination of the quantity of rare earth at the +4 oxidation degree, especially for Pr4+, has been of paramount importance. Actually, the higher the Pr4+ rate, the more reducible is the oxide and the better is the oxygen mobility. The evaluation of the diffusion coefficient of the oxygen D* highlighted high values, similar to those of the best reported oxygen ionic conductors at low temperature. Isotopic exchanges showed that the oxygen exchange rate increases with the Pr loading in the oxide. The catalytic activity for propane combustion of these oxides increases with their oxygen mobility. Finally, CZP45 (Ce0,45Zr0,1Pr0,45O2-x) exhibits the best pre-quoted properties as well as the highest catalytic activity. Therefore, CZP45 has been impregnated with Pd. The activity of Pd-CZP45 catalyst was compared with two industrially catalysts containing the same Pd content supported either on ?-Al2O3 (Diesel) or Ce0,5Zr0,5O2-x (gasoline). In Diesel conditions, Pd-CZP45 shows a better low-temperature catalytic activity than Pd-?-Al2O3…

Advisors/Committee Members: Vernoux, Philippe (thesis director), Demourgues, Alain (thesis director).

Subjects/Keywords: Oxydes mixtes à base de Ce Zr Pr; Mesures magnétiques; Propriétés de réductibilité; Échange isotopique; Conductivité ionique/électronique; Mobilité de l’oxygène; Oxydation du propane; Catalyse automobile (TWC, DOC); Rare earths based mixed oxides; Magnetic measurements; Reducibility properties; Isotopic exchange; Ionic/electronic conductivity; Oxygen mobility; Propane oxidation; Automotive catalysis (TWC, DOC); 541.395

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Frizon, V. (2018). Corrélation composition chimique-structure-propriétés de réductibilité / mobilité de l’oxygène / catalyse d’oxydation au sein d’oxydes à base de cérium, zirconium et de praséodyme : Correlation between chemical composition-structure-properties of reducibility and oxygen mobility with the oxidation of automotive pollutants by (Ce, Zr, Pr) mixed oxides. (Doctoral Dissertation). Lyon. Retrieved from http://www.theses.fr/2018LYSE1030

Chicago Manual of Style (16th Edition):

Frizon, Vincent. “Corrélation composition chimique-structure-propriétés de réductibilité / mobilité de l’oxygène / catalyse d’oxydation au sein d’oxydes à base de cérium, zirconium et de praséodyme : Correlation between chemical composition-structure-properties of reducibility and oxygen mobility with the oxidation of automotive pollutants by (Ce, Zr, Pr) mixed oxides.” 2018. Doctoral Dissertation, Lyon. Accessed April 06, 2020. http://www.theses.fr/2018LYSE1030.

MLA Handbook (7th Edition):

Frizon, Vincent. “Corrélation composition chimique-structure-propriétés de réductibilité / mobilité de l’oxygène / catalyse d’oxydation au sein d’oxydes à base de cérium, zirconium et de praséodyme : Correlation between chemical composition-structure-properties of reducibility and oxygen mobility with the oxidation of automotive pollutants by (Ce, Zr, Pr) mixed oxides.” 2018. Web. 06 Apr 2020.

Vancouver:

Frizon V. Corrélation composition chimique-structure-propriétés de réductibilité / mobilité de l’oxygène / catalyse d’oxydation au sein d’oxydes à base de cérium, zirconium et de praséodyme : Correlation between chemical composition-structure-properties of reducibility and oxygen mobility with the oxidation of automotive pollutants by (Ce, Zr, Pr) mixed oxides. [Internet] [Doctoral dissertation]. Lyon; 2018. [cited 2020 Apr 06]. Available from: http://www.theses.fr/2018LYSE1030.

Council of Science Editors:

Frizon V. Corrélation composition chimique-structure-propriétés de réductibilité / mobilité de l’oxygène / catalyse d’oxydation au sein d’oxydes à base de cérium, zirconium et de praséodyme : Correlation between chemical composition-structure-properties of reducibility and oxygen mobility with the oxidation of automotive pollutants by (Ce, Zr, Pr) mixed oxides. [Doctoral Dissertation]. Lyon; 2018. Available from: http://www.theses.fr/2018LYSE1030

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