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Palladium-rhodium three-way catalysts (Pd/Rh TWCs) demonstrate the most versatile capability in achieving California LEV/ULEV emission standards for various applications ranging from thermally severe high-temperature close-coupled locations to thermally limited cooler underfloor environments. Engine aged dual-brick converters consisting of front Pd catalysts followed by rear Pd/Rh TWCs met ULEV emission standards for a high-temperature close-coupled 4.3L medium-duty truck and LEV standards for a much cooler underfloor 3. IL passenger car location, as well as intermediate environments experienced by a 3.8L vehicle. The Pd + Pd/Rh TWC systems have performance advantages and are more cost effective compared to Pd-only or trimetal (Pt/Pd/Rh) systems. For thermally limited systems such as the 3. IL system, addition of air to the Pd + Pd/Rh system was necessary.

During combustion, organosulfur compounds typically contained in gasoline are converted to SO2. Over automotive emission control catalysts, the SO2 can be converted to other sulfur compounds such as H2S,COS, and H2SO4. The chemistry of sulfur over catalysts is a function of A/F as well as catalyst composition. Exhaust emission control catalysts are also poisoned by exhaust SO2. The present study probes the extent of poisoning as a function of A/F, fuel sulfur levels and noble metal composition. The effect of fuel sulfur levels (14-6000 ppm) during aging and evaluation of platinum/rhodium, palladium/rhodium and palladium-only three-way control catalysts was evaluated. Performance measurements are reported for both engine dynamometer and vehicle systems.

A key element of diesel emission control is reduction of the particulate or soot that is emitted by diesel engines. These particulates are made up of a carbonaceous fraction, a volatile organic fraction, and a sulfate fraction. In this study, the role of flow-through oxidation catalysts on the control of each of these fractions is reported. Laboratory and vehicle studies were made to investigate the importance of catalyst washcoat and noble metal composition as well as vehicle operating conditions on the control of the various soot fractions. The effects of exposure of catalysts to high levels of sulfur were also examined. An optimized catalyst was found to provide good control of the volatile organic fraction and sulfate fraction of diesel particulate emissions. For control of sulfates, silica is preferred over alumina as the washcoat and palladium is preferred over platinum as the noble metal. At higher temperatures, release of sulfate is thermodynamically controlled to low levels.

Strict mobile source emission legislation in many countries throughout the world are motivating research and development efforts to bring forth advanced formulations. Steep rises in the price of rhodium during the past couple of years is resulting in intense efforts to control the costs of the new catalyst technologies being developed. This paper examines some catalyst development strategies being explored to accomplish the above objectives.