3. Catalyst Location. The position of a catalyst within the exhaust system is an important factor in the degree of sulfur inhibition. Pd-based TWC catalysts have more high temperature resistance and are often located very close to the exhaust manifold in order to function quickly after the engine is started. In this position, the Pd-based catalyst operates at higher exhaust temperatures. Sulfur inhibition is greatest at temperatures below 400-425°C and Pd-based catalysts located in the manifold position experience temperatures from 500°C to 1050°C, where inhibition is considerably lower. Pd-only catalysts located in positions where they are exposed to lower temperatures would be more greatly affected by sulfur. Pd is of increased importance for meeting future California LEV III or EPA Tier 3 vehicle standards due to its unique application in the close-coupled converter location required for vehicles certifying to very stringent emission standards. Pd is required in closed-coupled catalysts due to its resistance to high temperature thermal sintering. Sulfur removal from Pd requires rich operation at higher temperatures than required for sulfur removal from other PGM catalysts (18). A catalyst system with underfloor catalysts experience cooler temperatures and sulfur inhibition is greater. In addition, the underfloor position makes it more difficult to regenerate and recover lost performance due to sulfur.
4 . Vehicle Use. Vehicles operate under a wide range of conditions of speed and load. Vehicles that operate at low speed and low load will have lower exhaust gas temperatures than those that operate at high speed and high load. As noted above, exhaust temperature is an important factor for sulfur inhibition. Sulfur inhibition is strongest at temperatures below 425°C and less strong at temperatures above 425°C. Therefore, vehicles which operate at low speed and load will experience greater sulfur inhibition and have fewer opportunities for regeneration. The type of vehicle, i.e. passenger car, sport/utility vehicle, or light/medium duty truck, will also be impacted differently for the same reasons detailed above.
3. Catalyst Location. The position of a catalyst within the exhaust system is an important factor in the degree of sulfur inhibition. Pd-based TWC catalysts have more high temperature resistance and are often located very close to the exhaust manifold in order to function quickly after the engine is started. In this position, the Pd-based catalyst operates at higher exhaust temperatures. Sulfur inhibition is greatest at temperatures below 400-425°C and Pd-based catalysts located in the manifold position experience temperatures from 500°C to 1050°C, where inhibition is considerably lower. Pd-only catalysts located in positions where they are exposed to lower temperatures would be more greatly affected by sulfur. Pd is of increased importance for meeting future California LEV III or EPA Tier 3 vehicle standards due to its unique application in the close-coupled converter location required for vehicles certifying to very stringent emission standards. Pd is required in closed-coupled catalysts due to its resistance to high temperature thermal sintering. Sulfur removal from Pd requires rich operation at higher temperatures than required for sulfur removal from other PGM catalysts (18). A catalyst system with underfloor catalysts experience cooler temperatures and sulfur inhibition is greater. In addition, the underfloor position makes it more difficult to regenerate and recover lost performance due to sulfur.
4 . Vehicle Use. Vehicles operate under a wide range of conditions of speed and load. Vehicles that operate at low speed and low load will have lower exhaust gas temperatures than those that operate at high speed and high load. As noted above, exhaust temperature is an important factor for sulfur inhibition. Sulfur inhibition is strongest at temperatures below 425°C and less strong at temperatures above 425°C. Therefore, vehicles which operate at low speed and load will experience greater sulfur inhibition and have fewer opportunities for regeneration. The type of vehicle, i.e. passenger car, sport/utility vehicle, or light/medium duty truck, will also be impacted differently for the same reasons detailed above.
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