Study on the NO2 production pathways and the role of NO2 in fast selective catalytic reduction DeNOx at low-temperature over MnOx/TiO2 catalyst

Selective catalytic reduction of NO by NH 3 (SCR) at low temperature usually considered to be the combination of NO oxidation and “Fast SCR” process. However, the NO oxidation mechanism and the role of NO 2 over “Fast SCR” process are controversial. Focusing on these problems, the in-deep studies were performed over the typical MnO x /TiO 2 catalysts. Combining in-situ DRIFT, TPD-MS and DFT calculation results, an integrated NO oxidation mechanism was proposed based on an “Nitro-assisted oxygen activation” concept where the activation and transformation of O 2 is linked with the transformation of nitro species. The O O bond of O 2 can be weakened by generating a variation of bidentate nitrates, which can promote the break of O O bond and the formation of NO 2 . The formation of the variation of bidentate nitrates was the rate-determining step over NO oxidation. Additionally, we further reveal that the crucial role of NO 2 over “Fast SCR” process lies in participating the hydrogen abstraction from coordinated NH 3 and promoting the production of NH 2 active species which can direct react with NO to generate N 2 and H 2 O. The removability of NO 2 can coupling the MnO 2 (NO oxidation active component) and TiO 2 support (“Fast SCR” active component) together. Our findings provide insight into the design and improvement of catalysts or reaction pathways over the low-temperature SCR process.