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 NOx with ammonia in the presence of excess oxygen. They have been characterized by a series of techniques, specifically N2 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)–ZrOx-450 (Mn/(Mn + Zr) mole ratio of 0.5) catalyst showed the highest activity, giving 100% NOx 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)–ZrOx-450 catalyst, with highly dispersed MnOx. TPR data indicated a strong interaction between the zirconium oxide and manganese oxide, which improved the reduction ability of the MnOx. The TPD results indicated that an appropriate NH3 adsorption ability was beneficial for the low-temperature SCR. The catalyst showed a certain level of sulfur tolerance and water resistance. The effect of H2O could be quickly eliminated after its removal, whereas deactivation by SO2 proved to be irreversible.