The Preparation And Performance Study Of NO Catalytic Oxidation Catalyst

The technology of NO selective catalytic oxidation (SCO) is of great impotance in the field of flus gas purification.Using this technique, the NO can be partial catalytic oxidated to NO2by excess oxygen in flue gas, and then the NOx is absorbed by desulfurizer and translate into nitrates. This technology can be used to transform existing device conveniently coveniently, save investment, and to realize the goal of desulfizaton and desulfization simultaneously. What’s more, increasing the oxidation degree of NOx(NO2/NOx) can effectively improve the reaction efficiency and the rate of the low-temperature SCR technology. In the SCO technology, the preparetion and perforance of catalysts is the key point. At present, MnOx catalysts exert the advantage of high denitrification activity, selectivity, et.al, and show high commercial value. But, the mechanism of NO oxidation reaction has not been in agree. Additionally, MnOx catalysts are obviously poisoed by SO2in flus gas. So the preparation of effective SCO catalysts and the study of reaction mechanism and SO2influence on catalysts play an important theorentical guiding significance for the development of flue gas cleaning in our country.In this paper, A series of ZrO2supported manganese oxides catalysts (MnOx/ZrO2) were prepared by loading of manganese oxides on ZrO2supporter for the selective catalytic oxidation (SCO) of flue gas NO to NO2. The effect of preparation conditions (calcination temperation, metal loading, precursor and loading method, avtive component) and reantion condition (reaction temperation, oxygen concentration, space velocity) on the catalytic conversion of NO was investigated. The structures and properties of catalysts were characterized by N2adsorption, scanning electron microscope (SEM), X-Ray Diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS). The MnOx/ZrO2catalyst containing8wt%manganese prepared by volumetric impregnation shows the highest catalytic activity for NO conversion. The highly dispersed MnO2is proved to be the active species for SCO. The mechanism of catalytic conversion of NO is studied by NO isothermal adsorption and temperature programed desorption (TPD) accompanied by temperature programed surface reaction (TPSR). Results show that the oxidation of NO is induced by NO adsorption and the oxidation rate of NO adsorbed on the catalytic surface is far higher than that of NO2desorption. Also the peak temperature of NO2desorption is in accordance with the best SCO temperature. Thus the rate controlling step for NO conversion process is the desorption of NO2rather than the oxidation of surface NO.Furthermore, the influence of SO2on Mn/ZrO2was studed through activity test experiment. In addition, The catalysts were characterized by SO2transient response, TPD, BET surface area, fourier transform infrared spectroscopy (FT-IR), XRD and XPS to investigate the chemical essence of SO2poisoned catalysts. The results indicated that SO2in flue gas inhibited the catalytic activity for NO oxidation obviously. SO2was oxided to SO3and then reacted with supporter to form zirconium sulfate, which could lead to the destroy of catalysts’ structure, occupy the active site and influence the adsorption form of NO on the catalysts’ surface, cause the inactivation of catalysts.At the end, to further improve the SCO activity and sulfur tolerance of Mn/ZrO2catalysts, other metal oxides were addied as auxiliaries to modify catalysts. Results indicated that the addition of Ce, La, Ce oxides improved Mn/ZrO2catalysts’ activity for NO oxidation at lower temperature to some extend and suspended the deactivity of catalysts by SO2poisoning, but the modified catalysts were still short of anti-sulfur property, SO2in flue gas can cause irreversible deactivity on modified catalysts as before. The Cr, Fe, Mo modified Mn/ZrO2catalysts deduced catalysts’ avtivity for NO oxidation on the whole.