Reverse Micelle Strategy for the Synthesis of MnO -TiO Active Catalysts for NH-Selective Catalytic Reduction of NO at Both Low Temperature and Low Mn Content.

MnO -TiO catalysts (0, 1, 5, and 10 wt % Mn nominal content) for NH-SCR (selective catalytic reduction) of NO have been synthesized by the reverse micelle-assisted sol-gel procedure, with the aim of improving the dispersion of the active phase, usually poor when obtained by other synthesis methods (e.g., impregnation) and thereby lowering its amount. For comparison, a sample at nominal 10 wt % Mn was obtained by impregnation of the (undoped) TiO sample. The catalysts were characterized by using an integrated multitechnique approach, encompassing X-ray diffraction followed by Rietveld refinement, micro-Raman spectroscopy, N isotherm measurement at -196 °C, energy-dispersive X-ray analysis, diffuse reflectance UV-vis spectroscopy, temperature-programmed reduction technique, and X-ray photoelectron spectroscopy. The obtained results prove that the reverse micelle sol-gel approach allowed for enhancing the catalytic activity, in that the catalysts were active in a broad temperature range at a substantially low Mn loading, as compared to the impregnated catalyst. Particularly, the 5 wt % Mn catalyst showed the best NH-SCR activity in terms of both NO conversion (ca. 90%) and the amount of produced NO (ca. 50 ppm) in the 200-250 °C temperature range.