Aggregation of CeO₂ particles with aligned grains drives sintering of Pt single atoms in Pt/CeO₂ catalysts

Understanding the sintering mechanism of platinum-group-metals (PGMs) supported on reducible oxides, such as CeO₂, is of fundamental and practical importance for the development of durable catalysts. It has been reported that the sintering of PGM nanoparticles occurs simultaneously with the aggregation of CeO₂ nanostructures during high temperature thermal treatment. However, mechanistic insights into the coupled sintering processes are insufficient, due to the lack of direct in situ observations of the atomic scale reconstruction processes. Here, we utilize in situ and ex situ transmission electron microscopy measurements to examine the processes of Pt and CeO₂ sintering in model catalytic materials consisting of Pt on isolated CeO₂ particles and Pt on aggregated CeO₂ particles with varying grain boundary alignment. CeO₂ particle aggregation is observed to occur most facilely at particle contacts with well aligned grain boundaries and in turn these contacts serve as locations of the most significant Pt sintering. Our results suggest that the surface reconstruction during CeO₂ aggregation provides the driving force for Pt sintering and provides new understanding of the sintering mechanism of PGM catalysts.