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

Abstract

The thermal deactivation of Pd/CeO2–ZrO2–Al2O3 (Pd/CZA) three-way catalysts (TWCs) was studied using a full-sized washcoated monolithic honeycomb after engine-bench aging at 600–1000 °C under a stoichiometric-lean-rich cycling gas condition. This was followed by chassis dynamometer driving tests. The nanoscale structure of these aged catalysts was characterized by gas adsorption, X-ray diffraction, and electron microscopy imaging to elucidate the thermal deactivation mechanism. Aging at high temperatures and for long periods facilitated the Pd particle growth via surface migration and coalescence, which caused a drop in the number of active sites and thus the catalytic activity. The detailed particle growth kinetics was analyzed using simulated laboratory-scale aging of Pd/CZA powder samples at different temperatures (700–1000 °C) and periods of time (0–40 h). The as-obtained Pd particle size vs time data were successfully fitted by applying the Finke–Watzky model with two-step agglomeration, which provided the rate constants for the initial slow growth and the subsequent faster growth. The temperature dependence of the as-obtained rate constants showed simple Arrhenius-type behavior, which was expressed using the optimized frequency factor and activation energy for the Pd particle growth. Furthermore, these results were roughly consistent with the data obtained by the engine-bench aging test for the monolithic honeycomb catalysts. The sintering kinetic model developed in the present study will be useful for the prediction of TWC deactivation and lifetime.