Ostwald-ripening sintering kinetics of Pd-based three-way catalyst: Importance of initial particle size of Pd

The sintering rates of commercial and lab-prepared Pd three-way catalysts (TWCs) as a function of the catalyst mileage were examined by CO chemisorption, XRD and TEM. Interestingly, the sintering rates of the Pd catalysts with a larger initial particle size were slower than those with a smaller initial particle size. This moderation of the growth rate of Pd with increasing initial particle sizes was consistent with the Ostwald-ripening mechanism, attributable mainly to the combination of the decrease of the surface tension of the Pd crystallite and the increase of the evaporating activation energy of Pd. Moreover, the variation of the Pd particle size distribution (PSD) observed in the TEM analysis was well predicted by the Ostwald-ripening sintering model in which the sintering kinetic parameter was a unique function of the initial particle size of Pd.