Shigeru Nojima

121 Selective reduction of NOx over Ir/metallosilicate catalyst for a lean burn gasoline engine

Publisher Summary Several catalysts capable of reducing NOx with hydrocarbons contained in the exhaust gases of lean burn gasoline engines have been proposed in the recent years. However, these catalysts suffer deterioration problems due to heat, water vapor, and sulfur dioxide in the exhaust gas. Several efforts have been made to overcome the disadvantages of prior art catalysts and have found that iridium catalysts supported on MFI-type metallosilicate with activation treatment have had high NOx reduction activity and have deteriorated very little even in an atmosphere of high temperatures. This chapter focuses on catalytic performance and durability of NOx reduction activity for a lean burn gasoline engine exhaust gas. The NOx reduction experiment was conducted in a flow reactor system with a gas mixture which simulated a lean burn gasoline engine exhaust gas. The chapter examines the effect of O2 concentration on the catalytic performance of the three De–NOx catalysts for the HC–SCR reaction. The O2 concentration was changed from 0.48% to 8% under model gas conditions. The three-way catalyst showed high NOx reduction activity in only 0.48% (stoichiometry) of O2 concentration and showed low NOx reduction activity in an excessive oxygen atmosphere.