Low-Temperature Selective Catalytic Reduction of NO sub(x) with NH sub(3) over Novel Mn-Zr Mixed Oxide Catalysts

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