Recent Progress in the Phase-Controlled Synthesis of Ruthenium Nanocrystals for Catalytic Applications.

Metal nanocrystals in metastable phases have received increasing attention owing to their unique physicochemical properties and potential catalytic applications. Bulk Ru crystallizes in the hexagonal close-packed (hcp) phase, but colloidal methods have enabled the synthesis of Ru nanocrystals in the metastable face-centered cubic (fcc) phase. In this report, we highlight recent progress in engineering the phase of Ru nanocrystals, with a focus on methods based on the seed-templating effect, such as facet symmetry matching, and kinetic control over the reduction pathway. We also discuss the thermal stability of metastable fcc-Ru nanocrystals, as well as their catalytic applications. We further summarize how hcp-Ru nanocrystals can serve as templates to direct the synthesis of Pd and Rh nanocrystals in the metastable hcp phase. Finally, we offer perspectives on quantitative kinetic control, scalable synthesis, and stabilization of nanocrystals in metastable phases.