Process and apparatus for reducing the nitrogen oxide content in exhaust gases by the controlled addition of NH3
AssigneeJohnson Matthey Public Limited Company
InventorsGuy Richard Chandler, Raj Rao Rajaram, Claus Friedrich Goersmann, Valerie Anne Self
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Abstract
In the reduction of quantities of Nox in the exhaust gases of lean bum engines such as diesel engines, using a selective reduction catalyst and a source of ammonia, the present invention improves overall conversion by supplying ammonia or a precursor intermittently so that it is adsorbed and desorbed during the engine operating cycle.
Claims14
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.
An apparatus for reducing the content of nitrogen oxides (NOx) in the exhaust gas of a diesel engine operating in a substantially continuously lean burn mode comprising:
- (a) an exhaust apparatus capable of allowing exhaust gas to flow therethrough;
- (b) a selective catalytic reduction catalyst comprising zeolite located in the flow-path of the exhaust gas and being capable of both catalyzing the reduction of NOx in the exhaust gas to nitrogen and releasably adsorbing ammonia during the engine cycle;
- (c) means for supplying ammonia from an ammonia source to the catalyst;
- and
- (d) switching means for controlling the supply of ammonia during an engine cycle such that ammonia supply is switched on when the catalyst temperature rises above a first pre-determined temperature at which ammonia is adsorbed on the catalyst and the ammonia supply is switched off when the catalyst temperature falls below a second pre-determined temperature, whereby adsorbed ammonia is available to react with NOx when the catalyst is below the first pre-determined temperature.
Dependencies are inferred from the claim text.