Novel manganese oxide confined interweaved titania nanotubes for the low temperature Selective Catalytic Reduction (SCR) of NOx by NH3
Abstract 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 NH 3 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 degC. The existence of abundant surface Mn 4+ 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 MnO x over TNT SA catalyst occurs bare minimum because of the low specific surface area and low pore volume, and this leads to poor deNO x activity. The Mn 4+ /Mn 3+ fraction deduced by XPS found to be considerably high for the Mn(0.25)/TNT H catalyst (Mn 4+ /Mn 3+ 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 (TiO 2 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 TiO 2 (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 Mn 4+ /Ti and Mn 4+ /Mn 3+ as well as the existence of surface Mn 4+ species in the titania nanotube appear to be directly correlated with the deNO x performance of the catalysts.