Compared with conventional nanoparticle-sized catalytic systems, isolated atoms or atomic-layered clusters anchored on dedicatedly-designed nanostructures can not only dramatically increase the atom utilization rate of expensive noble metals but also enormously improve their catalytic activity and selectivity. In situ scanning transmission electron microscopy (STEM) with single-atom-analysis capabilities is recognized to be a powerful and straightforward approach for studying the underlying mechanisms of thermal or chemical stability and enhanced catalytic performance of heterogeneous catalysts. Using the aberration-corrected STEM equipped with in-situ gas-cell or heating holders (i.e. Protochips Atmosphere and Fusion systems), we recently observed different forms of atomic distribution of platinum atoms (e.g. single atoms and atomic-thin layered clusters) stabilized on a unique diamond-graphene core-shell nanostructure and explored their thermal behaviors under reaction-relevant chemical atmosphere, through which their robust sintering-resistance in contrast to platinum catalysts supported on commercial alumina powders was directly demonstrated. Therefore, this carbon-supported catalyst possesses promising industrial application potential for low-temperature direct dehydrogenation of n-butane. We also found that its catalytic performance is highly correlated to the tunable hybrid level (i.e. graphene-layer numbers) and surface defect status of such core-shell carbon supports, which offers a novel platform for in-situ TEM investigation into the microscopic mechanisms of the strong metal-support interactions.