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A laboratory flow reactor test has been developed to examine hydrocarbon (HC) storage for diesel catalysts. Light-off testing alone has not been sufficient to rank diesel oxidation catalysts (DOCs) in agreement with vehicle HC conversions over the European driving cycle. HC emissions are important because of Stage II combined HC+NOx standard. During cold start and much of the ECE driving cycle, inlet catalyst temperatures on diesel passenger cars spend much time below 200°C. This is where more than half of the HC mass can be emitted. To be effective, DOCs must achieve sufficiently low HC light-off temperatures, or incorporate materials such as zeolites that trap HC until light-off is achieved. Consideration of both HC storage and light-off results together improve ranking of DOCs similar to vehicle ranking. Three supplier DOCs have been evaluated.

A simplified method was developed to obtain three-way catalyst performance data to be used for predicting vehicle CVS-H emissions. This method involves engine dynamometer aging of catalysts and characterization of their performance as a function of four variables, namely, redox potential, temperature, space velocity and a modulation parameter. In the process of reducing the number of variables, several simplifications were made. The simplifications, their limitations and the characteristic trends in the performance of a 11 Pt/Rh catalyst are discussed.

With the use of a simulated exhaust system, the sulfuric acid and sulfur dioxide emission from a monolith noble-metal oxidation catalyst (Engelhard IIB) is measured. It was found that the storage rate of sulfur onto an initially sulfur-free catalyst decreases to a few percent of the sulfur rejection rate within 3-4 h. The amount of sulfur on the catalyst when the catalyst is in equilibrium with 20 ppm sulfur in the gas phase varies between 0.3 weight percent of the catalyst at about 400°C to 0.1 weight percent at 600°C. The sulfur can readily desorb from the catalyst if the gas phase sulfur content is lowered or if the catalyst temperature is increased. It was found that the conversion of sulfur dioxide to sulfuric acid reaches thermodynamic equilibrium at temperatures of 400-500°C and space velocities of 30,000 h-1. These conditions correspond approximately to a small V8 engine at 20 mph cruise.