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SCR Catalyst Systems Optimized for Lightoff and Steady-State Performance
ISSN: 1946-3952, e-ISSN: 1946-3960
Published April 20, 2009 by SAE International in United States
Citation: Theis, J., "SCR Catalyst Systems Optimized for Lightoff and Steady-State Performance," SAE Int. J. Fuels Lubr. 2(1):332-341, 2009, https://doi.org/10.4271/2009-01-0901.
A laboratory study was performed to optimize a zoned configuration of an iron (Fe) SCR catalyst and a copper (Cu) SCR catalyst in order to provide high NOx conversion at lean A/F ratios over a broad range of temperature for diesel and lean-burn gasoline applications. With an optimized space velocity of 8,300 hr-1, a 67% (by volume) Fe section followed by a 33% Cu section provided at least 80% NOx conversion from approximately 230°C to 640°C when evaluated with 500 ppm NO and NH3. To improve the lean lightoff performance of the SCR catalyst system during a cold start, a Cu SCR catalyst that was 1/4 as long as the rear Cu SCR catalyst was placed in front of the Fe SCR catalyst. When evaluated with an excess of NH3 (NH3/NO ratio of 2.2), the Cu+Fe+Cu SCR system had significantly improved lightoff performance relative to the Fe+Cu SCR system, although the front Cu SCR catalyst did decrease the NOx conversion at temperatures above 475°C by oxidizing some of the NH3 to N2 or NO.
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