MnOx/CeO2–TiO2 mixed oxide catalysts for the selective catalytic reduction of NO with NH3 at low temperature

Abstract

A series of CeO2–TiO2 supported manganese oxides on CeO2 and TiO2 were prepared with differing CeO2/TiO2 ratios by wet impregnation and used for low-temperature selective catalytic reduction (SCR) of NO with NH3. The properties of the catalysts were examined using X-ray diffraction, Brunauer–Emmett–Teller (BET) surface area, temperature-programmed desorption (TPD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The activity of a Mn–TiO2 catalyst was greatly enhanced by the addition of a small amount of CeO2 in the low temperature range (120–160°C); Mn(20)/Ce(4)–TiO2 catalyst exhibited the highest catalytic activity. With increasing CeO2 loading, the surface area of the catalysts decreased, and the peaks corresponding to crystallite CeO2 grew sharply. As determined by BET and XRD studies, the manganese oxides existed in either highly dispersed or amorphous phases; crystallite structures were not observed. The XPS and TEM imaging results revealed that the Mn(20)/Ce(4)–TiO2 catalyst had the highest concentrations of surface Mn atoms and possessed an abundant amount of Mn4+. The NH3-TPD studies confirmed that this catalyst also had the highest NH3 adsorption intensity. These studies concluded that an optimal TiO2/CeO2 catalyst support ratio enhanced both the catalytic activity in the SCR reaction and the Mn dispersion.