Diesel-Entstickung: Katalysierte Reduktion von NOx mittels NH3 an Metalloxid- und Perowskit-aktivierten Zeolith-Katalysatoren [Catalytic reduction of NOx with NH3 over metal oxide zeolites]

Abstract

Reduction of nitrogen oxides (NOx) in oxygen rich atmosphere requires a suitable reductant like ammonia. In diesel engine exhausts, ammonia can selectivly reduce NOx in presence o f excess oxygen with the help of a suitable catalyst. Zeolite ZSM-5 (Si/Al = 20) itself is a poor catalyst for the reduction of NOx with ammonia in presence of Oz, but when supported with metals like Cu, Fe, Cr and Ni behaves as active catalyst for NOx-reduction. Cu-ZSM-5 shows better activity then other metal- ZSM-5, both with and without water. Perovskites such as LaFeO3, LaCoO3 and LaNiO3 are prepared by coprecipitation method and are coated on cordierite honeycomb by sol-gel technique with ZSM-5 as supporting material. LaFeO3 shows good activity for NOx-reduction and low N2O formation, indicating high selectivity. It is observed that in presence of water the NOx-conversion has dropped. However, the selectivity of the reaction is better, the Cu-ZSM-5 is exception to this case.