Korrelation von integralen und lokalen Untersuchungsmethoden an Abgasnachbehandlungssystemen für Magermotoren
Schönebaum, Simon; Simon, Ulrich (Thesis advisor); Moos, Ralf (Thesis advisor)
Aachen (2019, 2020)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2019
In this work the use of DRIFT spectroscopy for the investigation of molecular processes on different catalytic converters for exhaust gases of lean burn engines was investigated. The results were correlated with the outcomes of different integral measurement methods. By that, a better understanding of underlying processes resulting in certain integral observations was approached. With the help of DRIFT spectroscopy, the interpretation of HF-IS measurements on a SCR converter was improved: The already known correlation of resonance frequency and the mobility of adsorbed NH3 species was sharpened by a precise definition of the kind of mobile species. In addition to that, the influence of highly mobile [CuI(NH3)2]+ complexes on the resonance frequency was proofed. During this work, initial experiments for the correlation of integral and local investigation methods on several, technically relevant LNTs were performed. First, detailed DRIFTS investigations were correlated with high-resolution methods for material analysis such as TEM-EDX to obtain detailed information about cross effects between the different compounds and their de- or increase by different converter architectures. The results were then correlated with catalytical tests. The correlation showed a critical impact of ceria as well as barium-containing components on the NOx storage behavior. Additionally, the time-resolved formation as well as decomposition of different reaction intermediates as well as products in dependence of different LNT compositions was investigated. By that, the interpretation of measurement results from laboratory gas test bench were improved: The observed high NOx storage of one investigated catalyst was traced back to very high precious metal dispersion over the active components. Also, the use of ceria as low temperature NOx-storage was found to be critical for the performance of the LNTs during regeneration as it increases the direct oxidation of hydrocarbons and by this lowers the regeneration performance of the LNT. Additionally, an optimal dispersion of precious metals and BaCO3 were identified to be crucial to the systems performance. In the last chapter of this work the desorption of 1-Octanol from a oxidation catalyst was investigated by TP-DRIFTS. With the help of these investigations, the formation of any liquid phase during adsorption was excluded and the decomposition processes of 1-Octanol during TPO experiments were confirmed with the help of observed intermediates.