Significantly Improving N2 Selectivity and H2O Resistance by Confining Mn into TiO2 Nanotubes for Low-Temperature Selective Catalytic Reduction of NO with NH3

The narrow active window, low N2 selectivity, and poor resistance to H2O and SO2 restrict Mn-based catalyst industrial application for selective catalytic reduction of NOx with NH3. Given that TiO2 nanotubes are considered an ideal support for manganese-based low-temperature denitrification catalysts due to various favorable properties, confined structure Mn–TiO2 nanotubes (MnTiOx-NT) were prepared by the sol gel method combined with the alkaline hydrothermal method. Characterization results indicated that the specific surface area, chemisorbed oxygen, Lewis acid sites, and Mn4+ content increased as the Mn added amount is raised from 5% to 15%. Accordingly, the catalytic activity of catalysts increased, and 0.15MnTiOx-NT catalyst exhibited the most exceptional reaction performance with NO conversion rates exceeding 97% and 100% N2 selectivity within a broad temperature range spanning from 160 to 360 °C at 30000 h–1. DFT calculations demonstrated that surface oxygen vacancies play a crucial role in resisting water, inhibiting the overoxidation of NH3, and promoting the generation of NO2. In situ DRIFTS revealed that NH3 absorbed on Lewis acid sites, NO2, and chelating nitrites were the main reactive intermediate species in the NH3-SCR reaction over 0.15MnTiOx-NT catalyst. Fast-SCR and Langmuir–Hinshelwood (L–H) reaction mechanisms coexisted in the NH3-SCR reaction. The confinement structure of catalysts provides a research idea for designing catalysts that can significantly improve nitrogen selectivity and water resistance in the future.