Abstract: A series of WO₃-modified MnO_x/TiO₂ catalysts were prepared by three different impregnation methods and were investigated by specific surface area measurement, X-ray diffraction, laser Raman spectroscopy, H₂ temperature-programmed reduction, high-resolution transmission electron microscopy, and in situ Fourier transform infrared spectroscopy. The three-component catalysts obtained with the one-step impregnation exhibited the best catalytic activity. The characterization data revealed that a synergism between tungsten and manganese oxide existed in the catalysts when tungsten was loaded either prior to or simultaneously with manganese, which made the active components better dispersed and blocked the transformation of TiO₂ from the anatase to rutile structure. The manganese oxide existed in the form of Mn₂O₃ on all the samples but was accompanied by a small amount of MnO₂ for 15%MnO_x-5%WO₃/TiO₂. WO₃ improved the reducibility and enhanced the amount and strength of the surface acid sites, especially the Brönsted acid sites and promoted the formation of the active intermediate (-NH₂). Lewis acid sites had the major role in the low temperature selective catalytic reduction reaction while surface -NH₂ was an important intermediate species.

Key words: tungsten oxide, modification, manganese oxide, low-temperature selective catalytic reduction, surface acidity, active intermediate