The MnO x /TiO2 catalysts have been proved very active in the catalytic oxidation of NO to NO2, but the mechanism of this heterogeneous reaction was still not clear. In this study, through a systematic in situ diffuse reflectance infrared Fourier transform spectroscopy investigation, the main pathway of NO oxidation over MnO x /TiO2 was revealed. Experimental results indicated that the NO was first coordinated to Mn sites, forming nitrosyls, which were readily oxidized to nitrates by lattice oxygen, and then the nitrates were decomposed to NO2 at high temperatures. However, when SO2 was present, the formation of nitrates was significantly hindered because the SO2 would permanently occupy the active Mn sites as sulfates. We believe that this revealed the mechanism of NO oxidation and SO2 deactivation would provide useful guidance for the development of better catalysts toward fast selective catalytic reduction, NO x storage-reduction, continuously regenerating trap, and NO x wet scrubbing.

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