Mechanism of NOx storage in ceria containing storage reduction catalyst materials

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Despite the success of the first generation of NOx storage reduction catalysts (Pt/BaO/Al2O3) further developments of NOx storage reduction catalyst technology are urgently needed to improve the efficiency and durability as well as to meet future NOx emission standards. These include the development of more efficient storage and support materials countering a reduction in long term stability by thermal degradation and sulfur poisoning. As described in the literature, the presence of ceria in NOx storage reduction catalysts (Pt/BaO/CeO2/Al2O3) leads to an increase in NOx storage capacity at temperatures up to 300°C as well as to improved stability. However, a fundamental understanding of the mode of operation of such ceria containing NOx storage reduction catalysts is still missing. Thus the goal of this project is to elucidate the influence of ceria on the NOx storage mechanism and the properties of the storage component at temperatures up to 300°C using barium oxide/ceria mixed systems.Barium oxide/ceria mixed systems will first be investigated without and then with support (Al2O3) and nobel metal (Pt) component. To elucidate the NOx storage mechanism for the different ceria containing materials, the in situ Raman/FTIR methodology developed in the first founding period will be employed. This approach combines the potential of in situ Raman spectroscopy with quantitative FTIR gas phase analysis at the outlet of the in situ Raman cell. These studies include the determination of the corresponding NOx storage capacities. Due to the complexity of ceria containing NOx storage reduction catalysts the in situ Raman characterization will be supported by detailed studies using X-ray photoelectron spectroscopy (XPS) partly in combination with Raman and und UV-Vis spectroscopy.As the stability of NOx storage reduction catalysts is strongly related to their susceptibility to sulfur poisoning one focus of the project is to investigate the influence of sulfur (as SO2). Besides, the influence of other components with large volume fractions in the exhaust gas (CO2, H2O) will be studied. Their presence may significantly influence the NOx storage mechanism as demonstrated for H2O during the first funding period.