Abstract
The readjustment of kinetic parameters in models of automotive catalytic converters due to catalyst aging calls for a better understanding of the correlation between model parameters and easily accessible quantitative catalyst properties. It is shown by means of CO light-off and CO chemisorption measurements that the catalytic activity of a commercial Pt/Al2O3 diesel oxidation catalyst can be successfully correlated to the catalytic surface area. This correlation exhibits the same trend for all investigated aging temperatures, aging times and lean aging atmospheres. However, no distinct correlation between catalytic activity and catalytic surface area is found for aging treatment in N2. The mechanism of noble metal sintering seems to depend on the oxygen content of the aging atmosphere and aging in N2 leads to a particle size distribution which is more beneficial to the catalyst activity, as compared to the particle sizes arising from lean aging conditions. This observation also implies that CO oxidation over platinum is structure sensitive. Furthermore, a refined microkinetic model for the platinum catalyzed oxidation of CO is developed which comprises two different paths for CO2 formation. The experimentally found correlation between catalytic activity and catalytic active surface area is successfully used for simulation of the activity change caused by lean hydrothermal aging. Spatially resolved gas phase concentration profiles of CO and CO2 during CO oxidation at full conversion are measured for further validation of the model.
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