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Palladium-rhodium catalyst technologies have been investigated to establish the relationship between emission performance and their oxygen storage capacity (OSC) or other physical properties. Catalyst performance was evaluated using stand dynamometer and FTP testing after both oven air aging and engine aging. Monolith catalysts were characterized for aged surface area and precious metal dispersion. Various components of the washcoat supports were characterized by surface area and X-ray diffraction (XRD) analysis for phase composition and CeO2-ZrO2 solid solution crystallite size. The correlation between OSC delay times and tailpipe emissions for NMHC, CO and NOx was highly nonlinear in these studies. Addition of CeO2-ZrO2 solid solution components to the washcoat significantly improved steady state activity after aging, but did not significantly affect the correlation between emissions and OSC.

Both laboratory and engine dynamometer testing were used to characterize the relative activity of Pt, Pd and Rh supported on Ce and/or La stabilized supports. In the laboratory studies performance was measured after laboratory aging under conditions designed to simulate severe engine aging. The impact of Pt-Rh and Pd-Rh alloying on performance was examined as well as the cumulative effect of both metals on overall activity. The performance of laboratory aged non-alloyed Pt-Rh and Pd-Rh catalysts was dominated by the Rh function. For Pt-Rh the overall performance features for CO and NOx conversion were very similar over the Rh-only, Pt + Rh (separated metals) and alloyed Pt-Rh catalysts. Pt-Rh alloying was found to have a detrimental impact on high temperature HC performance.

In studying H2S emissions, it is desirable to have an analytical technique which is rapid, continuous, accurate and easy to use in a laboratory or vehicle exhaust environment. Typically, H2S has been measured using the EPA impinger method with collection times on the order of 1 to 2 minutes. Other techniques have been developed with significantly shorter response times. However, it has been shown that the major release of H2S occurs in less than 20 seconds after a vehicle changes from rich to lean operation. Therefore, it is highly desirable to have an H2S analytical technique with a response time of less than 10 seconds. In this paper, the benefits of use of a chemical ionization mass spectrometer (CIMS) to continuously monitor H2S and SO2, emissions are reported. Using the CIMS technique, the effects of several operating parameters on the release of H2S and SO2 from automotive catalysts were studied.

A brief review of a variety of Inspection/Maintenance programs is provided. The costs and benefits of several of these programs are discussed. The effects of vehicle operating parameters on the performance of the catalyst in the exhaust system of the vehicle are discussed in detail. Key variables for catalyst performance are light-off performance and exhaust temperature and air/fuel ratio. The relative effects of common causes of catalyst deactivation on control of HC, CO and NOx are also discussed.

On a global basis there is a resurgence of interest in the use of palladium in automotive emission control catalysts because of cost, availability and performance advan­tages under certain operating con­ditions relative to more expensive noble metals. This paper reviews a variety of potential vehicle applic­ations for the use of palladium containing catalysts. Included in the study are for the replacement of platinum by palladium in conventional platinum/rhodium systems, palladium-only three-way catalysts, palladium-only dual bed catalysts and two-stroke and lean-burn engine applications.

An H2S odor problem has appeared for certain vehicles fitted with modern three-way catalysts. A sulfur storage/H2s release mechanism is proposed as a source of the odor problem. The effects of various operating parameters on the release of H2S are presented. Two methods of modifying three-way catalysts to minimize H2S release while maintaining good catalyst performance and high temperature durability are demonstrated.