It has long been a challenge for activating O2 by transition‐metal nanocatalysts, which might lose activity due to strong tendency for oxidation. Herein, O2 could be activated by durable encapsulated cobalt nanoparticles (NPs) with N‐doped graphitic carbon shells (Co@N‐C), but not by encapsulated cobalt NPs with graphitic carbon, exposed cobalt NPs supported on activated carbon, or N‐doped carbon. Electron paramagnetic resonance, real‐time in situ FTIR spectroscopy, and mass spectrometry measurements demonstrated the generation of the highly active superoxide radical, O2.−. This unique ability enables Co@N‐C to afford an excellent catalytic performance in model aerobic oxidation of monomeric lignin‐derived alcohols. Further analysis elucidated that encapsulated cobalt and nitrogen‐doped graphitic carbon might contribute to the capacity through influencing the electronic properties of outer layers. Moreover, through isolation by N‐doped graphitic carbon shells, the inner metallic cobalt NPs are inaccessible in term of either alcohols or oxygenated products, and a distinctive resistance to leaching and agglomeration has been achieved.