Although core-shell catalysts have been actively studied for their excellent stability at high temperatures, most studies have focused on the development of synthetic methods and not conducted actual catalytic reactions at conditions, under which particles severely agglomerate. Here, we prepare a model catalyst with a well-defined size and interface of a Pt core and a gas-permeable SiO2 shell via advanced colloidal synthesis, and evaluate the catalytic response to CO and CH4 oxidation, each representing low (<300 degrees C) and high (>500 degrees C) temperature reactions. Compared to typical SiO2 supported Pt, the core-shell configuration shows comparable activity at CO oxidation and a much higher activity and stability for CH4 oxidation. However, even for the core-shell, degradation is inevitable, and possible reasons for this are discussed. These practical results on high-temperature catalysis provide important evaluation criteria and design guidelines for sintering-resistant nanocatalysts.