Soot Combustion Activity and Potassium Mobility in Diesel Particulate Filters Coated with a K-Ca-Si-O Glass Catalyst

Potassium volatility and activity in a novel K-Ca-Si-O glass catalyst was investigated over extended periods of soot oxidation. Soot was continuously deposited and oxidized by maintaining a glass catalyst-coated filter at temperatures above the oxidation balance point to provide a soot mass equivalent to 100 000 miles of engine operation. Testing revealed the 52-SiO2, 35-K2O, and 13-CaO wt % glass catalysts show a significant improvement in soot oxidation performance over a Pt catalyst. The glass catalyst retains soot oxidation catalytic activity even after testing equivalent to 100 000 miles of use. Migration of potassium in the catalyzed filter from the inlet to the outlet channels was observed. Although potassium was detected on an uncoated downstream core after 50 h of testing, showing that some volatilization of K occurs, the catalyst retains remarkable activity. Surface analysis characterization shows K enrichment of the catalytic glass surface relative to the bulk, which supports the proposed mechanism that water vapor in the diesel exhaust draws K+ ions to the glass surface. The studies demonstrate that a glass designed to allow the catalyst surface to be replenished with K ions on a continuous basis can overcome previous concerns about the durability of soot catalysts relying on alkali metals.