Abstract
The diesel emission after-treatment system, so-called 4-way diesel catalyst that combined oxidation catalyst with high temperature De-NOx catalyst was studied. Oxidation catalyst based on support composed of Al2O3 and TiO2 was optimized in respect of precious metal and additives. When platinum was impregnated, its optimum loading was 30g/ft 3 and effective additives for sulfate suppression were V2O5 and Cr2O3. Whereas, in palladium loaded catalyst, optimum loading was 70g/ft 3, and V2O5 and Pr6O11 were competent in sulfate suppression. NO conversion of precious metal ion exchanged high temperature zeolite catalyst was improved as the Si/Al molar ratio of raw zeolite decreased. Catalyst using hydrogen ion bonded raw zeolite had better NO conversion than that using sodium ion bonded zeolite. In combining oxidation and De-NOx catalyst for dual beds configuration, front De-NOx and rear oxidation catalysts array was advisable for high HC and NO conversion. Single layer catalyst that was wash-coated with uniform mixture of oxidation and De-NOx powder showed better HC and NO conversion than dual beds catalyst, but SO2 oxidation was also higher with single layer catalyst in spite of adding V2O5 for SO2 oxidation suppression.