3D dynamic structure of a Pt nanoparticle on SrTiO₃ (001) during in-situ heating atomic-resolution ADF STEM imaging

Noble metal nanoparticles supported on semiconducting substrates have long been used in heterogeneous catalysis. A central objective in this field is to identify the active sites for catalysis, which requires precise determination of the 3D atomic structure of nanoparticles on substrates. Furthermore, it has widely accepted that catalytic active sites undergo dynamic structural changes under reaction conditions. However, direct observation of such 3D dynamic structures at the atomic scale, particularly under elevated temperatures and reducing environments, remains a challenge. Here, we present the 3D atomic structure of an epitaxially grown platinum nanoparticle, consisting of 263 Pt atomic sites, supported on an atomically flat SrTiO₃ (001) surface, using single-projection atomic-resolution scanning transmission electron microscopy (STEM) combined with quantitative statistical analysis. In-situ heating experiments under reduced atmosphere reveal that the Pt atoms with lower coordination numbers are mobile within the second-nearest-neighbor atomic sites, and we describe the 3D dynamic atomic structure of the Pt nanoparticle by the distribution of partial occupation of Pt atoms. Furthermore, we perform density functional theory calculations based on the experimentally reconstructed 3D atomic structure and find that excess negative charges accumulate at the lower CN atomic sites, which likely serve as catalytically active sites.