Nano-metrology of platinum-ruthenium bimetallic catalysts and the cluster-to-crystal transformation

We have used atomic number, Z-contrast, imaging, performed using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) to study bimetallic ruthenium-platinum nanoparticles anchored within silica nanopores, a system that shows great promise as a catalyst for single-step hydrogenation reactions. By exploiting the ultra-high spatial resolution obtained with aberration-corrected STEM, it is possible to study the internal structure of individual nanoparticles within the support, and to analyze their size distribution. Specimens examined before catalysis showed evidence for coalescence of the precursor units (12-atom clusters) during loading into the silica support. An indication of the stability of the system during catalysis is given by the similarity of pre- and post-catalysis size distributions, whilst the multimodal nature of each distribution suggests certain preferred ('magic') particle sizes. Some larger particles appear facetted, and exhibit image periodicity characteristic of crystalline structures