Substrate-supported noble metal single-atom catalysts (SACs) are widely used in many important chemical reactions for their high activity and selectivity. However, the fabrication of high concentration of single-atom catalysts (SACs) with long-term stability remains a challenge. For example, at the working conditions, usually calcination at a high temperature, the supported SACs migrate and coarsen (a process named Ostwald ripening), resulting in a decreased catalytic performance. Writing in Nature Communications, researchers from Dalian Institute of Chemical Physics (Chinese Academy of Sciences) and Tianjin University of Technology, found that the high- temperature calcination of Pt nanoparticles on reductive Fe 2 O 3 substrate in air is favorable for the formation of high concentrations of thermally stable Pt SACs, which is different from the traditional Ostwald ripening. By employing the Climate in situ gas & heating solution and HAADF-STEM imaging, they directly observed the disintegration of Pt nanoparticles at 800 °C under a flow of 1 bar O 2 . During the in- situ reaction process, they found particle disappearance occurs in the absence coalescence, implying the genesis of atomically-dispersed Pt entities. The in-situ results are in good agreement with the ex-situ characterizations and theoretical calculations. The new findings provide a new route to fabricate high-metal-loading and thermal stable SACs for a wide range of industrially important catalytic reactions.