A New Approach to Describe Thermal Aging of Automotive Catalysts Containing Precious Metal Alloys

Regarding thermal real-world aging of automotive catalysts, no deeply developed model or correlation is yet available. Therefore, a new method is developed. A diesel oxidation catalyst (DOC) is aged in the oven and indicated a systematic crystallite growth. Additionally, catalytic deactivation is only dependent on the crystallite size. The crystallite size acts as an indicator for the precious group metal (PGM) surface. This determines a quantitative correlation between the temperature stress, the crystallite size, and, finally, the catalytic activity for oven-aged samples of a DOC. On the basis of this result, the method for the description of oven aging is worked out. It is a physical model that gets as input parameters the aging temperature and aging time for oven aging. This information can be used to calculate the crystallite growth. Further, the corresponding catalytic activity for all species (NO, CO, HC) can also get calculated. All results are achieved with DOCs containing a platinum (Pt) palladium (Pd) alloy washcoat. An idea for an enhancement for the description of thermal real-world aging is also introduced. The background of the enhanced model is that also crystallite growth by real-world aging and the corresponding catalytic activity could get calculated for every moment in time of a temperature run.