Kinetics-Based Prediction for Sintering of Pd/CeO2-ZrO2-Al2O3 Three-Way Catalysts during Engine-Bench Aging

The thermal deactivation of Pd/CeO2-ZrO2-Al2O3 (Pd/CZA) three-way catalysts(TWCs) was studied using a full-sized washcoated monolithic honeycombafter engine-bench aging at 600-1000 degrees C under a stoichiometric-lean-richcycling gas condition. This was followed by chassis dynamometer drivingtests. The nanoscale structure of these aged catalysts was characterizedby gas adsorption, X-ray diffraction, and electron microscopy imagingto elucidate the thermal deactivation mechanism. Aging at high temperaturesand for long periods facilitated the Pd particle growth via surfacemigration and coalescence, which caused a drop in the number of activesites and thus the catalytic activity. The detailed particle growthkinetics was analyzed using simulated laboratory-scale aging of Pd/CZApowder samples at different temperatures (700-1000 degrees C)and periods of time (0-40 h). The as-obtained Pd particle sizevs time data were successfully fitted by applying the Finke-Watzkymodel with two-step agglomeration, which provided the rate constantsfor the initial slow growth and the subsequent faster growth. Thetemperature dependence of the as-obtained rate constants showed simpleArrhenius-type behavior, which was expressed using the optimized frequencyfactor and activation energy for the Pd particle growth. Furthermore,these results were roughly consistent with the data obtained by theengine-bench aging test for the monolithic honeycomb catalysts. Thesintering kinetic model developed in the present study will be usefulfor the prediction of TWC deactivation and lifetime.

Automated summary

The thermal deactivation mechanism of Pd/CeO2-ZrO2-Al2O3 three-way catalysts (TWCs) was investigated through engine-bench aging and driving tests. The results showed that high temperature and prolonged aging promoted the growth of Pd particles, leading to a decrease in catalytic activity. A sintering kinetic model was developed to predict TWC deactivation and lifetime based on the analysis of particle growth kinetics.