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The deactivation of noble metal oxidation catalysts by lead and halide lead scavengers was studied in engine and laboratory experiments. The halide scavengers caused rapid but completely reversible inhibition of the catalyst activity, which existed only as long as the halide was present. The effects of catalyst temperature and noble metal concentration indicated that the halide scavenger dissociated upon adsorption on the catalyst. Palladium and platinum-palladium catalysts were more susceptible to halide inhibition than were platinum catalysts. Lead alone or lead plus scavengers produced a persistent poisoning of the catalyst. Lead poisoning effects were increased by increased catalyst temperatures and fuel lead content. Tests with scavengers only, conducted in an engine previously operated on leaded fuel, showed that lead was transported to the catalyst causing lead poisoning even in the absence of lead in the fuel.

A new analytical method, absorption of tunable diode laser radiation, can detect small concentrations of gases with fast response. This technique has been applied to the detection of vehicle sulfate emissions in the form of sulfuric acid (H2SO4) vapor. Previously available methods for sulfate analysis required collecting samples for 10 min. or more. Our laser system has a response time of 2.4 s. This allowed tracking the sulfate emissions of a vehicle during a Highway Fuel Economy Test. The data suggests that catalyst temperature is the major parameter controlling sulfate emissions and that storage and release of sulfur occurs at low and high catalyst temperatures, respectively. The same method detected methane during both the Highway Fuel Economy Test and the Federal Test Procedure. It identified the conditions, and corresponding concentrations, for high methane emissions. A qualitative comparison with total hydrocarbon emissions uncovered significant differences during accelerations.