【作者】 张晓鹏；

【导师】 沈伯雄；

【作者基本信息】 南开大学 ， 环境工程， 2013， 博士

【摘要】 NH3-SCR脱硝工艺因其经济性、高效性,成为脱除电站锅炉烟气中NO的主流工艺。传统商业催化剂V2O5-WO3(MoO3)/TiO2脱硝温度窗口为300-400℃,为了避免重复加热烟气,SCR反应器必须安装在脱硫、除尘装置的上游,而该烟气段高浓度的烟尘会影响催化剂脱硝性能,降低催化剂使用寿命。低温NH3-SCR脱硝工艺有希望使SCR反应器布置在静电除尘器之后,降低粉尘冲蚀对催化剂的影响,使该工艺备受关注。但是,多数烟气在通过脱硫装置后仍含有少量的S02,在低温条件下SO2对SCR催化剂有很强的毒化作用,并且在烟气中含有H20的情况下,SO2的毒化作用更强。因此,低温SCR催化剂的抗SO2、抗H20性能是研究的核心。以此为背景,本文以Mn/Ce-ZrO2催化剂为研究对象,对其进行了低温脱硝性能,特别是抗H20、抗SO2性能的研究。对Mn/Ce-ZrO2与传统的低温脱硝催化剂Mn／P25和Mn/Al2O3进行了低温SCR脱硝活性及抗H20、抗SO2性能的对比。结果表明,Mn/Ce-ZrO2具有更高的低温活性,这与其氧化还原性质有关。H2-TPR显示,Mn/Ce-ZrO2更容易发生氧化还原反应。Mn/Ce-ZrO2的抗H20、抗SO2性能最好,可能的原因是Mn/Ce-ZrO2具有较多的表面酸位点,且表面生成的硫铵盐不稳定。为了进一步揭示Mn/Ce-ZrO2脱硝性能更好的原因,对比了Mn/Ce-ZrO2, Mn/CeO2和Mn/ZrO26勺低温SCR脱硝活性及抗H20、抗SO2性能。结果发现,较高的MnO。分散度,较强的氧化还原能力,更多的表面吸附氧是Mn/Ce-ZrO2具有高低温脱硝活性的原因。抗H20、抗S02实验之后催化剂表面生成的水合物较少,且硫酸化程度低是Mn/Ce-ZrO2具有强抗H20、抗S02性能的原因。对Mn/Ce-ZrO2进行加Co改性发现,Co改性载体所制备的催化剂Mn/Co-Ce-ZrO2具有更高的MnOx分散度,更强的表面酸性和氧化还原能力,更多的表面吸附氧和Mn4＋,因此其脱硝活性更高,在180℃脱硝效率达97.1%。同时Mn/Co-Ce-ZrO2具有更强的抗H20、抗SO2性能。通入H2O+SO2后,脱硝活性虽略有下降,但能稳定维持在91%,切断H2O+SO2后,其活性完全恢复。XPS表明,抗H2O+SO2实验中Mn/Co-Ce-ZrO2表面几乎没有硫酸盐的累积。对Mn/Co-Ce-ZrO2催化剂进行系统研究,发现在不同条件下Mn/Co-Ce-ZrO2均展现出较高的SCR脱硝活性及抗H20、抗SO2性能。动力学研究发现,Mn/Co-Ce-ZrO2的SCR反应活化能E=17543.3J-mol-1。较低的反应活化能是Mn/Co-Ce-ZrO2具有较高的低温SCR脱硝活性的原因。为了降低催化剂成本,采用堇青石和沸石分子筛涂覆的方式制备催化剂。两种方式制备的催化剂都具有较高的催化活性,但沸石分子筛涂覆制备的催化剂抗H2O+SO2性能更强。载体用硫酸处理后抗H2O+SO2性能进一步提高。更多还原

【Abstract】 Selective catalytic reduction (SCR) of NO with NH3is widely used to reduce NO producing in combustion processes because of the low cost and high efficiency. V2O5-WO3(MOO3)/TiO2is the most commonly adopted commercialized catalyst system with high activity in the temperature range of300-400℃. However, the deactivation of catalysts caused by dust and SO2is serious because the unit for SCR catalysts has to be located upstream of the desulfurizer and the electrostatic precipitator when the reaction temperature is considered. In order to avoid reheating the flue gas, the unit of SCR catalysts has to be located upstream of the desulfurizer and electrostatic precipitator. However, the high concentration of dust reduces the performance and longevity of catalysts. Therefore, it’s necessary to develop low-temperature SCR catalysts which can be located downstream of the desulfurizer and electrostatic precipitator. Most of the flue gas contains a few amounts of SO2even after the desulfurizer. Catalysts for low-temperature SCR are generally very sensitive to SO2and the deactivated action of SO2will be more intense when H2O is present. Therefore, the resistance to SO2and H2O is the core of low-temperature SCR study. Base on these facts, we researched the performance of NO removal and the resistance to SO2and H2O of Mn/Ce-ZrO2.A contrastive study was made on Mn/Ce-ZrO2, Mn/P25and Mn/Al2O3. The results showed that Mn/Ce-ZrO2had a better activity at lower temperature. This corresponded to the redox character of the catalysts. The results of H2-TPR showed that Mn/Ce-ZrO2was more easily to initiate reduction reaction. Mn/Ce-ZrO2had the best resistance to SO2and H2O which might due to more acid sites and the instability of ammonia sulfate on the surface of Mn/Ce-ZrO2.A contrastive study was made on Mn/Ce-ZrO2, Mn/CeO2and Mn/ZrO2to study the reason for the good performance of NO removal and the good resistance to SO2and H2O of Mn/Ce-ZrO2. Mn/Ce-ZrO2had higher dispersion of manganese oxides, better redox property and more weakly adsorbed oxygen species, which resulted in the higher activity of Mn/Ce-ZrO2. In addition, Mn/Ce-ZrO2showed a good resistance to SO2and H2O which was due to the weak water absorption and weak sulfation process on the surface of the catalyst.Co was used as a modifier for Mn/Ce-ZrO2and Mn/Co-Ce-ZrO2with Co as a modifier for the support had a higher dispersion of manganese oxides, a better redox property and more surface adsorbed oxygen species and Mn4+. These facts caused a better low-temperature activity for Mn/Co-Ce-ZrO2. In addition, Mn/Co-Ce-ZrO2showed an excellent resistance to SO2and H2O and presented91%NO conversion under SO2and H2O and the activity of Mn/Co-Ce-Zr02totally recovered after cutting off the injection of SO2and H2O. XPS results indicated that the introduction of cobalt as a modifier for the support of catalysts decreased the formation of sulfate salts and hydroxyls on the surface of Mn/Co-Ce-ZrO2.A systematic study was made on Mn/Co-Ce-ZrO2and it showed an excellent performance of NO removal and the resistance to SO2and H2O at different conditions. The results of kinetic study showed that the active energy of Mn/Co-Ce-ZrO2was17543.3J·mol-1and the lower active energy is the reason for the good performance of NO removal for Mn/Co-Ce-ZrO2. To reduce costs, Mn/Co-Ce-ZrO2was coated on cordierite and zeolites. Both catalysts coated on cordierite and zeolites had good performance of NO removal. And the catalyst coated on zeolites had better resistance to SO2and H2O. The treatment with H2SO4for zeolites improved the resistance to SO2and H2O of the catalyst.更多还原