Approaches and Advances to the challenges of treating emissions at low temperatures

Todd  Toops, Oak Ridge National Laboratory

Removing the harmful pollutants in automotive exhaust has been an intense focus of the automotive industry over the last several decades. Current state-of-the-art catalysts achieve 90% conversion of pollutants between 200 °C and 350 °C and consequently, more than 50% of the emissions occur in the first 2-3 minutes under “cold-start” or idling conditions. While such performance enables meeting current emission standards, as emissions regulations become more stringent meeting the emission regulations will require increased activity during this warm-up period. To further complicate matters, the increased Corporate Average Fuel Economy (CAFE) standards that will be implemented over the next decade will result in the introduction of more fuel-efficient engines. This will result in lower exhaust temperatures, which further necessitates the need for increased emissions control activity at low temperatures. These low temperature issues are expected to affect a wide range of powertrain options to meet the fuel economy standards including diesel vehicles, gasoline-powered vehicles, and hybrid electric vehicles.

With these challenges in mind the USDRIVE Advanced Combustion and Emission Control Technology Team has set a goal of achieving 90% conversion of CO/HC/NOx at 150 °C. Increasing the platinum group metal (PGM) content commonly found in the emissions control devices may help to improve the catalytic efficiency, but such methods are too expensive for long term success. Other options to meet the emissions standards include hydrocarbon/NOx absorbers; however, while this pathway would help mitigate cold-start emissions, the lowering of the average exhaust temperature suggests this approach alone will be insufficient and ultimately a more complete solution will be necessary.

This presentation will outline three categorical approaches being pursued to address these challenges and discuss how they can be employed together for maximum benefit. The first area that will be discussed is the study of improvements of conventional PGM-based oxidation catalysts with a focus on the how modifying the support can lead to improved activity, durability and tolerance to sulfur. The second approach discussed will be the investigation of novel catalytic materials that are not currently being commonly used in emissions control catalysts, with an emphasis on non-PGM materials. The third system will briefly touch on trap materials and what temperatures a family of materials is active for hydrocarbons and NOx. Finally, a discussion on how these systems can work together to meet emissions standards cost effectively will be presented.

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