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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).