Oxidation of Diesel Particulates by Catalyzed Wall-Flow Monolith Filters. 2. Regeneration Characteristics of Platinum, Lithium, and Platinum-Lithium Catalyzed Filters

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.