Patent ID: 6713030
Filing Date: 2004-03-30
Classification: B01D,F01N,Y02A,Y02T

Abstract:
A method of reducing the content of nitrogen oxides (NOx) in the exhaust gas of a diesel engine operating in a substantially continuously lean burn mode, which method comprises:passing the exhaust gases over a selective catalytic reduction catalyst comprising zeolite which both releasably adsorbs ammonia and catalyses the reduction of NOx to nitrogen by ammonia during an engine cycle; supplying ammonia to the catalyst during the engine cycle from a source of ammonia, when the catalyst temperature is above a first pre-determined temperature; adsorbing ammonia to the catalyst during ammonia supply; discontinuing the ammonia supply when the catalyst is below a second pre-determined temperature; and reacting ammonia absorbed on the catalyst with NOx when the catalyst is below a second pre-determined temperature.