Low-Temperature Selective Catalytic Reduction of NO_<i>x</i> with NH₃ over Novel Mn–Zr Mixed Oxide Catalysts

Abstract

Novel Mn–Zr mixed oxide catalysts have been prepared by the citric acid method for the low-temperature selective catalytic reduction (SCR) of NO x with ammonia in the presence of excess oxygen. They have been characterized by a series of techniques, specifically N 2 adsorption–desorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). It was found that an Mn(0.5)–ZrO x -450 (Mn/(Mn + Zr) mole ratio of 0.5) catalyst showed the highest activity, giving 100% NO x conversion at 100 °C with a space velocity of 30 000 h –1 . XRD results suggested that an Mn–Zr solid solution was formed in the Mn(0.5)–ZrO x -450 catalyst, with highly dispersed MnO x . TPR data indicated a strong interaction between the zirconium oxide and manganese oxide, which improved the reduction ability of the MnO x . The TPD results indicated that an appropriate NH 3 adsorption ability was beneficial for the low-temperature SCR. The catalyst showed a certain level of sulfur tolerance and water resistance. The effect of H 2 O could be quickly eliminated after its removal, whereas deactivation by SO 2 proved to be irreversible.