Mechanistic Studies of Catalytic Reduction of Nitrogen Oxides from Diesel Engine Exhaust over Manganese and Cerium Oxide Based Catalysts

Abstract

Finding a catalyst system that is effective and consistent for the selective reduction of NOx during lean exhaust conditions has been a predominant challenge to both industrial and research institutions, despite the large number of reported catalysts tested. The selective catalytic reduction of NO + NO2 (NOx) with CO and C3 hydrocarbons at low temperatures (175-225 oC) is investigated over manganese and cerium catalysts with and without the presence of a precious metal. 1% Pt/Mn/Al catalysts show promising results for the reaction, with continuous NOx conversions well more than 35% in the period extending beyond 170 hours. The synthesis technique of the catalyst and the reaction temperature greatly effects the reaction. There is no evidence of the presence of other nitrogen oxides in the products except for a very small quantity of N2O only at the beginning of the reaction. Mechanistic studies reveal manganese to be the major catalytic sites, while the platinum plays a secondary role. Mn/Ce/Al also show continuous deNOx activity with NOx conversions of 28-35%.