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Abstract: In this study, the γ-MnO2 catalyst modified with PEG exhibits outstanding low-temperature performances for NO oxidation, and in-situ DRIFTS experiments were used to systematically investigate the low-temperature NO oxidation mechanisms over γ-MnO2. These results demonstrated that NO was first adsorbed on the surface of γ-MnO2 to form the nitrosyls, which could be further oxidized to nitrates under the action of the chemisorbed oxygen or lattice oxygen, and afterwards the formed nitrates were decomposed into nitrogen dioxide. Moreover, the inhibitory mechanism of SO2 on γ-MnO2 was also studied, and SO2 severely inhibit the NO oxidation performance of γ-MnO2 through forming stable sulfates that could easily consume the active sites of the catalyst to hinder the formation of nitrates, resulting in the termination of oxidation of NO to NO2. Clarifying the mechanisms of NO oxidation and SO2 poison is very essential for developing better NO oxidation catalysts.Graphical Abstract: [ABSTRACT FROM AUTHOR]