Removal of nitrogen oxides from the exhaust of a lean-tune gasoline engine

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• 作者：Bö ; gner ; W. ; Krä ; mer ; M. ; Krutzsch ; B. ; Pischinger ; S. ; Voigtlä ; nder ; D. ; Wenninger ; G. ; et. al.
• 关键词：Lean-burn engines ; Platinum ; Rhodium ; NO_x storage ; Adsorber catalysts ; NO_x reduction
• 刊名：Applied Catalysis B ; Environmental
• 出版年：1995
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：December 7, 1995
• 卷：7
• 期：1-2
• 页码：153-171
• 文件大小：1.04 M

摘要

There is an increasing interest in running passenger car engines lean of the stoichiometric air to fuel ratio (A/F) to improve fuel economy. One method being considered by vehicle manufacturers is to operate lean A/F (excess air) during cruising and return to stoichiometric operation when more power is required. The challenge for the catalyst manufacturer is to supply a product for this vehicle which will reduce NO_x emissions from both lean and stoichiometric operating points to below probable EC tier III legislative limits. A technique has been developed where NO_x is stored on an adsorbing catalyst while the engine runs lean. Upon switching to a short rich biased stoichiometric excursion the adsorbed NO_x is released and reduced by precious metal components on the catalytic system. Selected adsorber catalysts were tested on both simulated exhaust gas and a standard bench engine with secondary air injection. The results suggest an adsorbing process whereby NO is oxidized to NO₂ on Pt under lean conditions and the latter is subsequently adsorbed on an adsorbent material as a surface nitrate species. Upon return to a stoichiometric A/F ratio this species decomposes and NO_x is released and subsequently reduced. The adsorber was also tested on a bench prototype lean tune engine. The results indicate an averaged NO_x conversion of more than 90%over a test cycle in which the A/F ratio is cycled between lean operation and a rich biased stoichiometry.