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Two major deactivation mechanisms of automotive catalysts during road usage are: 1. thermal aging 2. poison accumulation of oil-derived poisons such as zinc and phosphorus. A dynamometer-based aging cycle, incorporating a high-temperature low-poison mode to account for thermal aging followed by a low-temperature high-poison mode to account for poison accumulation, has been developed to allow the examination of catalyst formulations after exposure to both a harsh thermal and chemical aging environment. This type of aging cycle results in dynamometer-aged catalysts that are physically much more similar to road-aged catalysts than thermally-based dynamometer cycles. Using this aging-cycle, Pd-only, Pd-Rh and Pt-Rh light-off catalysts were examined. The Pd-Rh catalyst gave the best overall performance, with equivalent HC light-off performance to the Pd-only catalyst and equivalent NOx performance to the Pt-Rh catalyst.

The relative NOx performance of Pd-only and Pd-Rh catalysts has been investigated under a series of operating conditions on a vehicle and in a laboratory reactor. The vehicle data indicates that the choice of Pd-only vs. Pd-Rh technology should be specific to the operating conditions found on that vehicle. Under low temperature conditions, Pd-Rh and Pd-only catalysts have similar NOx performance attributes. However, high temperature portions of the drive cycle accentuate the differences between Pd-only and Pd-Rh catalysts and lead to a large NOx performance advantage for the Pd-Rh catalyst. Laboratory reactor data indicates that these differences in activity are tied to the poisoning effects of reduced sulfur species on Pd, which become more severe as the temperature is increased and as the gas-phase stoichiometry becomes richer.

It has long been recognized that the key to achieving stringent emission standards such as ULEV is the control of cold-start hydrocarbons. This paper describes a new approach for achieving excellent cold-start hydrocarbon control. The most important component in the system is a catalyst that is highly active at ambient temperature for the exothermic CO oxidation reaction in an exhaust stream under net lean conditions. This catalyst has positive order kinetics with respect to CO for CO oxidation. Thus, as the concentration of CO in the exhaust is increased, the rate of this reaction is increased, resulting in a faster temperature rise over the catalyst.

The use of hydrocarbon traps to reduce cold-start emissions is one of the numerous methods that have been suggested to meet ULEV hydrocarbon emission requirements. To aid in our understanding of hydrocarbon traps and in the design of improved hydrocarbon trap systems, in-situ mass spectrometry has been used to speciate several hydrocarbons during the first 505 seconds of an FTP from the exhaust of a 2.0 L vehicle fitted with hydrocarbon traps in the after treatment system. This technique allows second-by-second engine-out and vehicle-out hydrocarbon speciation. The in-situ mass specrometry technique has shown that hydrocarbon traps are generally effective for trapping aromatics and C4+ alkanes and alkenes, but are ineffective in trapping methane, ethane, and ethene: Further improvements in the trapping performance for C3-C5 hydrocarbons can be made by placing a water trap in front of the hydrocarbon trap.