Novel manganese oxide confined interweaved titania nanotubes for the low-temperature Selective Catalytic Reduction (SCR) of NOx by NH₃

ECO PHYSICS CLD 70S

A series of manganese confined titania nanotubes (Mn/TNT) prepared by alkaline hydrothermal synthesis technique and were investigated for the Selective Catalytic Reduction (SCR) of NO_X with NH₃ in the presence of excess (10 vol.%) oxygen. Remarkably, the surface texture and tubular morphology of Mn/TNT-H catalyst greatly promote the NO_X conversions in the temperature regime of 100–300°C. The existence of abundant surface Mn⁴+ species apparently contributes to the remarkable low-temperature SCR activity, and additionally the increased surface area, high dispersion and numerous Lewis acid sites distribution contribute to broaden temperature window over Mn/TNT-H catalyst with 0.25 Mn/Ti atomic ratio. The impregnation of MnOx over TNT-SA catalyst occurs bare minimum because of the low specific surface area and low pore volume, and this leads to poor deNOx activity. The Mn⁴+/Mn³+ fraction deduced by XPS found to be considerably high for the Mn(0.25)/TNT-H catalyst (Mn⁴+/Mn³+ = 2.15) while in other catalysts the fraction is typically in the range of 0.36–1.34. Raman scattering reveals a redshift of 13 cm−1 from 640 cm−1 (TiO₂-Hombikat) to 627 cm−1 in Mn/TNTs-H sample, which indicates the formation of a new phase or structural difference. In comparison with the Mn supported on TiO₂ (Hombikat) nanoparticles, the Mn species on the developed tubular Mn/TNT-H were less pronounced to coagulate under the reaction temperatures. It is interesting to note that the relative atomic ratios of Mn⁴+/Ti and Mn⁴+/Mn³+ as well as the existence of surface Mn⁴+ species in the titania nanotube appear to be directly correlated with the deNOx performance of the catalysts.

http://www.sciencedirect.com/science/article/pii/S0021951715003772?via%3Dihub