A study of sulfur dioxide poisoning on ceria based three way catalysts

This thesis work aims to better understand the various aspects in automotive emission control catalysis. First part focuses on the sulfur poisoning issues in ceria based three-way catalysts employed in gasoline engines. Second part concentrates on the efficiency of NOx storage phase in BaO-Al2O 3 catalysts for the lean burn diesel engines. Species formed upon SO2 poisoning on ceria and zirconia modified ceria were characterized theoretically and experimentally under different poisoning conditions. Surface and bulk Ce2(SO4) 3, Ce(SO4)2, Ce2O2S could form depending on poisoning temperature and SO2/O2 fugacity. Their influence on the Oxygen Storage Capacity (OSC) of the catalysts and the related deactivation mechanism for Water Gas Shift (WGS) reaction have also been investigated thoroughly in a simulated pulse reactor. Basically, the redox (reduce-oxidize) cycle of the TWC was blocked by the formation of Ce2O2S under reducing condition, which is hard to be reoxidized by either H2O or CO2. Additionally, the influence of various BaO*Al2O3 structures on the NOx trapping capacity was studied using XRD, TPD and FTIR techniques. Different than pure barium oxide, the BaAl2O4 shows interesting NO2 trapping properties by blocking the formation of carbonate in the catalysts