Transient Bimodal Particle Size Distributions during Pt Sintering on Alumina and Silica

Sintering of Pt nanoparticles dispersed on alumina and two types of silica supports has been investigated under oxidizing conditions by use of transmission electron microscopy. Particle size distributions have been measured and analyzed as a function of time (up to 24 h) and temperature (500, 550, and 600 \ub0C). The measurements reveal transient bimodal and (sometimes) multimodal size distributions as the particles grow from 3 nm to about 10 nm. The likely role of support surface heterogeneity in the formation of bimodal size distributions has been analyzed theoretically. The experiments and the theoretical analysis stress limitations of conventional sintering models that operate with a mean particle size and a uniform support surface. Furthermore, the results underline the difficulties in deducing the dominant sintering mechanism from particle size distributions