Patent ID: 7313911
Filing Date: 2008-01-01
Classification: B01D,F01N,Y02T

Abstract:
1. A method of removing nitrogen oxides from the exhaust gas of a lean-burn internal combustion engine by selective catalytic reduction (SCR) using ammonia, wherein the exhaust gas is routed first over a platinum-containing pre-catalyst and then over an SCR catalyst and the exhaust gas upstream of the pre-catalyst has an exhaust-gas temperature T E , wherein the platinum-containing pre-catalyst includes a filter function for the soot particles contained in the exhaust gas and wherein at an exhaust-gas temperature T E below a predetermined temperature T 1 , the ammonia is supplied to the exhaust gas either directly or in the form of a compound hydrolyzable to ammonia upstream of the pre-catalyst, and at an exhaust-gas temperature T E above T 1 , ammonia supply to the exhaust gas is changed from a supply upstream of the pre-catalyst to a supply between the pre-catalyst and the SCR catalyst, wherein when the filter needs to be regenerated, the filter function of the pre-catalyst is regenerated by ammonia being oxidized at the pre-catalyst at an exhaust-gas temperature T A above 300° C. and the temperature of the pre-catalyst being raised above the soot ignition temperature by the released heat of oxidation.