Nitrogen oxides are harmful byproducts of combustion processes. One possible way for abatement of these is the selective catalytic reduction with ammonia (NH3-SCR). Currently applied catalytic systems reach good NOx-conversion and N2-selectivity at temperatures above 300°C. At lower reaction temperatures, which are especially important for mobile NOx-sources, present catalytic systems do show satisfactory performances. One possible catalytic system for those applications are modified cerium oxides. The modifications of CeO2 is mostly done by doping the crystal structure with hetero-ions or impregnating the catalyst with vanadium oxide.
The dissertation on hand concerns itself with the impact of three-valent dopants on the catalytic activity of cerium oxides with and without V-impregnation. Fe3+, Y3+, Co3+, Sb3+ and Bi3+ were chosen as doping elements in varying concentration. The obtained mixed oxides and solid solutions of the type Ce(1-x)MxO(2-d) were catalytically tested and thoroughly characterized. To understand the structure of the catalysts under reaction conditions, operando EPR, DRIFTS and in situ XANES were applied.
The investigations have shown that for the supports of the type Ce(1-x)MxO(2-d) a direct link between available surface oxygen and catalytic activity was found. Fe- and Sb-doping had a positive effect on the NOx-conversion, whereby Y- and Bi-doping effected the conversion negatively.
For V-impregnated systems, it was shown, that redoxactive dopants could impact the catalytically important V4+/V4+-cycle and thereby decrease catalytic activity. This was especially visibly in Fe-doped systems. The most active sample was V-impregnated, Sb-doped ceria, due to its improved amount of available surface oxygen and its active V4+/V5+-shuttle.