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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.

A study was undertaken to evaluate the feasibility of using the catalyst exotherm to diagnose the emission performance of the catalytic converter. The exotherm was evaluated as a potential diagnostic for large volume underfloor converters as well as for small volume warmup converters. Emphasis was placed on the ability to properly diagnose the emission performance of the converters while the vehicle was driven under a variety of transient driving schedules. For this study, type K thermocouples were used for measuring the temperatures. To minimize the variability of the exotherm data during transient driving, the exotherm needs to be sampled under fairly stable exhaust flow conditions. If a transient maneuver such as an acceleration occurs, a stabilization time is required before the exotherm can be sampled. The steady-state HC conversion of underfloor catalytic converters correlated well with the exotherm measured at the rear of the catalyst over a large range of conversions.

Ceria has become an increasingly important component in automotive exhaust catalysts over the past decade. Recently, with the proposal that measurements of oxygen storage be used for the on-board evaluation of catalyst performance for both low emission vehicles (LEV) and non-LEV vehicles, understanding the role of ceria and its deterioration with catalyst aging has become even more important. It is well established that ceria in an alumina support promotes oxygen storage/release by automotive catalysts under cycled air/fuel conditions, which in turn promotes the catalyst's conversion performance under those conditions. Another benefit of ceria is its enhancement of the catalytic activity for other reactions, such as the water-gas shift reaction under rich conditions. In addition, ceria may help catalyst durability by promoting precious metal dispersion and playing some role as a stabilizer of the support.