METHOD AND CATALYST FOR REDUCING NITROGEN OXIDE CONTAINED IN LEAN EXHAUST GAS OF INTERNAL COMBUSTION ENGINE, AND METHOD FOR MANUFACTURING CATALYST THEREOF

摘要

PROBLEM TO BE SOLVED: To provide a method for reducing nitrogen oxide contained in lean exhaust gas using ammonia by selective contact reduction with a reduction catalyst, which is a SCR catalyst excellent in activity and long time stability and shows substantially decreased emission of a vanadium compound relatively to a conventionally known level or no emission of the vanadium compound at a high exhaust gas temperature.

SOLUTION: In a case of a method for reducing nitrogen oxide contained in lean exhaust gas of an internal combustion engine by selective contact reduction using ammonia with a reduction catalyst and at the same time oxidizing a portion of nitrogen monoxide contained in the exhaust gas to nitrogen dioxide and thereafter leading the exhaust gas together with ammonia to the reduction catalyst, the reduction catalyst contains a zeolite ion-exchanged with a transition metal and oxidation of nitrogen monoxide is carried out so that the exhaust gas contains 30 to 70 vol.% of nitrogen dioxide before contact with the reduction catalyst.

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