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

Abstract

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.