Exploiting automatic image processing and in-situ transmission electron microscopy to understand the stability of supported nanoparticles

The activity and lifetime of heterogeneous catalysts are linked with their structural stability in reactive environments. Atmospheric pressure electron microscopy is used to understand how a model catalyst – Pt/Pd nanoparticles supported on Al2O3 – responds to reduction and oxidation.  Significant metal vaporization and diffusion were observed at temperatures above 600 °C, in oxygen and air. This behavior implies that material transport through the vapor during typical catalyst aging processes can play a significant role in catalyst evolution. We developed and exploited data analysis tools to track the temporal evolution of Au nanoparticles deposited on SiN as a model system to understand this process. We describe how a systematic investigation of dataset preparation, neural network architecture, and accuracy evaluation lead to a tool for determining the size and shape of nanoparticles in high pixel resolution TEM images. We use this algorithm to generate data regarding the complexities of nanoparticle coarsening, ripening, and evaporation. We have developed an analytical model that describes this process, showing how local and long-range particle interactions through diffusive transport affect evaporation. The extensive data allows us to determine physically reasonable values for the model parameters, quantify the particle size at which Gibbs-Thompson pressure accelerates the evaporation process, and explore how individual particle interactions deviate from mean field behavior.