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Ag/Al2O3 was studied as a HC-SCR (Hydrocarbon - Selective Catalytic Reduction) catalyst for diesel application[1, 2 and 3]. Performance required of (or from) this catalyst is high NOx conversion with high thermal durability and sulfur resistance. Also low HC slip is desired. The Ag/Al2O3 system was improved by addition of additives. In the diesel 13-mode (Japan) evaluation, improved Ag/Al2O3 catalyst showed higher de-NOx activity (>50%) compared to the original when fresh. Improved Al2O3 catalyst showed smaller hysteresis of de-NOx activity between ramping up and down the temperature and smaller amount of HC slip. To study the improvement effect, interactions between the HC and catalyst were investigated by TG/DTA-MS (define) and FT-IR (define). TG/DTA measurement results showed that HC/O2 reaction was restrained in the improved catalyst. These results suggest that there was sufficient of HC for NOx reduction on the improved catalyst.

Soot (here, total particulate matter; TPM) accumulation in a diesel particulate filter (DPF) was characterized for two different engine conditions (high speed / high load and low speed / low load). Soot weight distribution within the filter was different in two engine conditions the accumulated PM layer was thicker when the engine conditions were low speed / low load even though the accumulated soot amounts were almost equivalent. Flow field conditions in a DPF were calculated and soot accumulation conditions were assumed from the solution. In the axial direction (with gas flow) uniform soot accumulation was suggested. However, in the radial direction (from center to side), non-uniform accumulation was suggested from the flow field solution and this result was experimentally confirmed. Temperature distribution in the DPF during uncontrolled soot regeneration was also calculated. The simulation suggested that the highest temperature would be observed in the back middle area of DPF.