N atoms were selectively doped at substitutional or interstitial sites in the MnO2 lattice using N2 plasma. This research provides a site-selective N-doping method and a deep insight into the different effects of doping sites.

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Formaldehyde (HCHO) is a priority pollutant in the indoor environment, which is irritative and carcinogenic to humans. The non-noble metal oxides have a wide application prospect in the decomposition of HCHO. Defects in metal oxides have been widely accepted as active sites in heterogeneous catalysis. Compared with the extensive study of oxygen defects, the effect of cation defects has not been clearly addressed. Herein, Mn defect-rich Mn 3 O 4 was synthesized by pyrolysis of Ce-doped MnCO 3 . It is found for the first time that the content of Mn defects in Mn 3 O 4 can be adjusted by introducing Ce. The introduction of Ce resulted in the higher contents of Mn defects, which significantly enhances the HCHO decomposition. Moreover, Mn defect can effectively narrow the half-metallic gap of Mn 3 O 4 , regulate the electronic structure and coordination environment of surrounding oxygen, and further improve the activity and mobility of neighboring oxygen atoms. Importantly, Mn defects are not only beneficial to the generation of neighboring oxygen vacancy but also conducive to enhancing the activation ability of oxygen vacancy for O 2 . The advantages resulting from Mn defects significantly enhance the HCHO decomposition. This research proposes a strategy to adjust cation defects and deepens the comprehension of the function of cation defects.