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Emission studies were carried out on clear-fueled and MMT®-fueled 100,000-mile Escort vehicles from the Alliance study [SAE 2002-01-2894]. Alliance testing had revealed substantially higher emissions from the MMT-fueled vehicle, and the present study involved swapping the engine cylinder heads, spark plugs, oxygen sensors, and catalysts between the two vehicles to identify the specific components responsible for the emissions increase. Within 90% confidence limits, all of the emissions differences between the MMT- and Clear-vehicles could be accounted for by the selected components. NMHC emission increases were primarily attributed to the effects of the MMT cylinder head and spark plugs on both engine-out and tailpipe emissions. CO emission increases were largely traced to the MMT cylinder head and its effect on tailpipe emissions. NOx emission increases were linked to the MMT catalyst.

Advances in fuel control strategy, emission system architecture, and catalyst technology have led to dramatic decreases in exhaust emissions in recent years. To continue this trend, especially at high mileages, the impact of engine oil derived contaminants will need to be minimized. In this study, the deactivating effects of oil-derived contaminants on advanced catalyst technologies was assessed using an oxalic acid washing technique to remove phosphorus and other oil-derived contaminants from fleet-aged automotive three-way exhaust catalysts. Acid washing removed most of the phosphorus on the catalyst (chief poison associated with decomposition of the engine oil antiwear additive ZDDP) without significantly affecting other catalyst properties. Catalysts from eight high-mileage vehicles were analyzed, representing four vehicle families.

Automotive three-way catalysts (TWC) were characterized using temperature-programmed reduction (TPR), x-ray diffraction (XRD), Raman spectroscopy, chemisorption measurements and laboratory activity measurements. Capabilities and limitations of these standard analytical techniques for the characterization of production-type automotive catalysts are pointed out. With the exception of chemisorption techniques, all appear to have general utility for analyzing exhaust catalysts. The techniques were used to show that the noble metals and ceria in fresh Pt/Rh and Pd/Rh catalysts are initially highly dispersed and contain a mixture of interacting and non-interacting species. Thermal aging of these catalysts (in the reactor or vehicle) caused both precious metal and ceria particles to sinter, thereby decreasing the interaction between the two.

Regeneration characteristics of Pt, Li, and Pt-Li catalyzed wall-flow monolith (WFM) filters were examined in a reactor mounted in the exhaust from a GM 4.3 L diesel engine. Regeneration rates were measured over a range of exhaust temperatures corresponding to various engine speeds and torques. A fresh 0.2 wt% Pt - 0.2 wt% Li filter regenerated much more rapidly than filters containing 0.2 wt% Pt, 0.4 wt% Pt, or 0.2 wt% Li. The data suggest that both Pt and Li operate as soot oxidation catalysts, with the Li following a redox mechanism proposed by McKee and Chatterji (Carbon 13, 381, 1975). Significant oxidation activity was observed with the fresh Pt-Li filter at temperatures as low as 350°C, thus demonstrating activity at temperatures nearly within the normal operating range of light-duty GM diesel vehicles. The Pt-Li filter deactivated with time on stream due to reaction of lithium with SO2 in the exhaust.

The fresh catalytic activities of both a production Pt-Pd catalyst and a GMR Pd-promoted Ag catalyst were evaluated in back-to-back emissions tests on an experimental Detroit Diesel Allison (DDA) 6V-92TA methanol-fueled engine. Both the 13-mode steady-state and transient heavy-duty diesel engine Federal Test Procedures were employed. The production catalyst was characterized by relatively high conversions (70-90%) of unburned methanol and carbon monoxide in both the transient and 13-mode tests. However, the production catalyst promoted the partial oxidation of unburned methanol to formaldehyde, as indicated by large negative apparent conversions of formaldehyde in both the transient and steady-state tests (-77% transient; -188% 13-mode).