Mechanistic study of Ce-modified MnO x /TiO2 catalysts with high NH3-SCR performance and SO2 resistance at low temperatures

A series of Ce-MnO (x) /TiO2 catalysts were prepared using a novel sol-gel template method and investigated for low-temperature selective catalytic reduction (SCR) of NO with NH3 at temperatures ranging from 353 to 473 K. The 0.07Ce-MnO (x) /TiO2 catalyst showed the highest activity and best resistance to SO2 poisoning. The structure and properties of the catalysts were characterized using X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), thermogravimetry (TG)-differential scanning calorimetry (DSC)-mass spectroscopy (MS), high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller (BET) measurements, H-2-temperature-programmed reduction (TPR), and NH3-temperature-programmed desorption (TPD). The superior catalytic activity of the 0.07Ce-MnO (x) /TiO2 catalyst was probably due to a change in the active components, an increase in surface active oxygen and surface acid sites, and lower crystallinity and larger surface area with Ce doping. Furthermore, the reduction ability also became stronger. The SO2 poisoning resistance of the 0.07Ce-MnO (x) /TiO2 catalyst improved because doping with Ce can effectively decrease the formation of ammonium salt on the catalyst surface and the sulfation of MnO (x) . In situ diffuse-reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments indicated that addition of Ce could promote adsorption of NH3 and inhibit generation of some nitryl species. The SCR reactions over the catalysts mainly followed the Eley-Rideal mechanism accompanied with a partial Langmuir-Hinshelwood mechanism.