Simultaneous conversion of nitrogen oxides and soot into nitrogen and carbon dioxide over iron containing oxide catalysts in diesel exhaust gas

Abstract

This paper deals with the simultaneous catalytic conversion of NOx and soot into N2 and CO2 in diesel exhaust gas. Several iron containing oxide catalysts were partially modified by the alkali metal potassium and were used for NOx–soot reaction in a model exhaust gas. Fe1.9K0.1O3 has shown highest catalytic performance for N2 formation in the so far investigated catalysts. Further studies have shown that Fe1.9K0.1O3 was deactivated in a substantial way after about 20 TPR experiments due to the agglomeration of the promoter potassium. Experiments carried out over the aged Fe1.9K0.1O3 catalyst have shown that NOx–soot reaction was suppressed at higher O2 concentration, since O2–soot conversion was kinetically favored. In contrast to that, the catalytic activity was increased in presence of NO2 and H2O. Mechanistic examinations suggest that (CO) intermediates, formed at the soot surface, are the reactive sites in the NOx–soot reaction. Higher catalytic performance in presence of NO2 could be explained by the enhanced formation of these (CO) species. Moreover, nitrate species formed at the catalyst surface might also play an important role in NOx–soot conversion.