Deactivation modes of Diesel Oxidation Catalysts
Rama Krishna Dadi, Cummins
Rama Krishna Dadi, Krishna Gunugunuri, Ashok Kumar, Hongmei An, Yuhui Zha, Anand Srinivasan, Michael Cunningham
Cummins Inc., 1900 McKinley Ave, Columbus, IN 47201, U.S.A.
Hydrothermal aging and chemical aging are the dominant modes of deactivation on Diesel Oxidation Catalysts. HCs are injected into DOC to generate exotherm during thermal events. We present data to show the importance of thermal gradients on hydrothermal deactivation. Heat loss and axial convection leads to decrease in catalyst temperature from front end to rear end of the catalyst, resulting in hotter catalyst temperatures than target DOC out temperature. Hydrothermal aging impacts PGM particle size, which in turn impacts oxidation of NO, HCs and PGM. A fresh catalyst is more susceptible to PGM oxidation than an aged catalyst because of its lower particle size. Degradation of NO oxidation due to PGM oxidation is reversible, with high temperature events resulting in the regeneration of PGM oxides to metallic PGM. Chemical aging involves degradation of oxidation performance due to S, and P. While S degradation is reversible, P contamination results in permanent loss of oxidation performance. We present data to show the relationship between oxidation performance and S and P loading on DOC. The presence of S on catalysts retards the oxidation rate of PGM, which reduces the extent of Time on Stream (ToS) deactivation of NO oxidation. We present a model framework that can capture all the above-mentioned physical phenomena involving degradation of DOC.