Diesel Soot Catalyzes the Selective Catalytic Reduction of NOx with NH3

The catalytic activity of soot samples for the selective catalytic reduction (SCR) of NO x with NH 3 was investigated in dependence of the NO 2 , NO and NH 3 concentration in the temperature range between 200 and 350 °C. The highest NO x reduction of up to 25 % was measured in the presence of both NO 2 and NO at a GHSV of 35,000 h −1 . Decreasing space velocities resulted in an increase of the SCR activity. In the absence of NO 2 , NO x reduction was not observed. Carbon oxidation and SCR reaction occurred in parallel due to the presence of NO 2 and O 2 , but hardly influenced each other, which suggested that in the NO x reduction on soot most probably physisorbed species were involved. The observed stoichiometries indicated the action of the fast SCR reaction in the presence of NO and the NO 2 SCR reaction in the absence of NO, while the observed gas phase and surface species pointed at reaction steps similar to those on classical SCR catalysts.