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Nanostructured sulphur traps for the protection of high performance nox storage/reduction catalysts in low emission engine applications


Developed sulphur traps were investigated on a diesel vehicle regarding the protection of a NOx storage/reduction catalyst. Durability tests of SOx traps and NOx trap in combination with state-of-the-art and the two new developed SOx traps were performed. For the bench-scale tests a 1.9l 74kW VW TDI Touran was used. In the bench-scale tests the vehicle is operated for 15.000 to 20.000km in a dynamic cycle at the velocities of 50, 70 and 100km/h. Experiments at 10ppm and 30ppm S fuel were made, but in the first case the deactivation was too slow.
The identification of the single spectra out of a large datasets obtained e.g. from time resolved experiments can be analyzed by the combination of the 2D correlation analysis and Principal Component Analysis. As a first step the dataset is analyzed by means of Moving window 2D correlation analysis with an appropriate size of the window as described in literature to obtain the spectral position of interest. This is especially interesting on cyclic perturbations in experiments. Afterwards to identify the spectra of the pure components as well as the concentration profile of these on the dataset the advanced least square fitting procedure is applied. The input concentration matrix is determined by mean of Sample-Sample correlation, which gives a suitable concentration profile to identify the species. Furthermore the resolving of complex spectra with respect to the unsynchronized behaviour (which species is formed prior or precede compared to each other).
It was discovered for the first time that the presence of water in the feed can significantly promote the SOx storage of novel S-traps, probably facilitating via capillary condensation in the micropores and formation of sulphuric acid, the bulk transport of SOx species. The results were first evidenced in screening tests and confirmed under high space velocity conditions, low concentration of SO2 and presence of CO2, e.g. under reaction conditions simulating practical conditions of application. The results allow a different design of S-traps and to significant improve the performances especially at low reaction temperatures and in the presence of emissions from diesel engines.
Novel S-traps not containing noble metals, but instead non-transition metals such as Cu, Ce, Mn in a structured or ordered oxide-type matrix have been developed and tested both under screening test conditions and under more realistic conditions simulating those of diesel car emissions. The performances of these materials depend considerably on the method of preparation, but using suitable preparation procedures in order to tailor the pore structure and the catalyst-sorbent composition it is possible to obtain high performances equivalent to those of samples containing noble metals to promote the oxidation of SO2 to SO3.
Metal impregnated metal organic framework materials were prepared as self destructing compounds for storage of SOx in a oxygen rich atmosphere. The destruction could be caused by sulfation or thermal decomposition (at temperatures above 300 °C). Metal organic framework (MOF) materials with copper as central metal and benzoetricarboxylixacid as organic linker were impregnated with bariumchloride to obtain a material with SOx storage capacity at temperatures below 300 °C. By optimization of the central metal (oxidation component), crystallinity and storage metal the material offer a good storage material for temperatures below 300°C. The final material is obtained by impregnation of a Cu- MOF with BaCl2. The MOF is obtained with hydrothermal treatment at 110° for 12 h of a metal salt + alcohol/water mixture. The obtained materials were characterized by standard techniques like BET, XRD, AAS, IR and SEM. The total SO2 uptake capacity was determined with 50ppm SO2 in 12%O2.
We have developed a new technique for the monitoring of SOx(g) (SOx(g) = SO2 + SO3) in the presence of large O2 excess (typical flue and exhaust gas conditions) in an essentially continuous manner that requires only a standard SO2 analyser and a high temperature furnace. The system is based on the thermodynamic equilibrium between SO2, SO3 and O2, the concentration of O2 being essentially constant in the present case. The gas feed containing the SOx-species is passed over a (sulfur-saturated) catalyst at a known temperature that yields an effluent containing a mixture of SO2 and SO3, whose concentration ratio is known and given by a thermodynamic plot or a calibration curve. The SO2 concentration is then measured with a standard SO2 analyser and the SO3 concentration is thereafter calculated derived.