【作者】 姚燕；

【导师】 沈伯雄；

【作者基本信息】 南开大学 ， 环境工程， 2012， 博士

【摘要】 以NH₃为还原剂选择性催化还原（SCR）去除烟气中氮氧化物（NO_x）是烟气脱硝技术中最为有效的控制措施之一。作为脱硝技术的核心，开发高活性以及抗毒性能好的催化剂一直是研究的热点。烟气除尘之后仍可能含有超细飞灰，而脱硫之后也存在二氧化硫残留以及水含量高等问题，因此，中毒就成为催化剂应用过程中不可避免的问题。低温NO_x-SCR技术因其能耗低而成为国内外研究的热点，然而对于催化剂运行过程中的中毒问题缺乏系统性的研究。以此为背景，本文以价格低廉的柱撑粘土为载体，就其低温负载锰铈活性成分的低温NO_x-SCR脱硝性能和中毒特性进行了系统研究。本文以锆基柱撑粘土（pillared clays，PILC）为载体负载MnO_x活性成份，发现粘土基催化剂表现出良好的低温NO_x-SCR性能；Ce的添加增强了MnO_x的分散性、催化剂储氧能力和表面NH₃吸附量，使得Mn-Ce/ZrO2-PILC在180-240℃温度范围的NO_x转化率达到90%以上。同时，对氨氮比、氧含量等操作参数对催化剂脱硝活性的影响进行了考察。在此基础上，本文采用浸渍法分别研究了碱金属（K2O/Na2O）以及钾盐（K₂SO₄、KCl）对Mn-Ce/ZrO2-PILC催化剂脱硝活性的影响。研究发现，NO_x转化率的降低主要归结于K/Na在催化剂沉积，造成催化剂比表面积的下降、表面NH₃吸附能力以及氧化还原特性的降低，而且K的抑制作用要强于Na。K₂SO₄以及KCl也对催化剂也产生了严重的中毒作用，催化剂失活的机理主要体现在与碱金属氧化物中毒机理相同。采用水洗和酸洗对各中毒催化剂进行了再生处理，水洗对中毒量较低的中毒催化剂再生效果良好，而对于失活严重的催化剂则基本无作用。0.1M H₂SO₄酸洗可以有效去除有毒物质，而且增强了NH₃吸附能力，其再生效果要好于水洗再生。对催化剂的碱土金属中毒研究表明，Ca/Mg沉积在催化剂表面，降低催化剂比表面积、影响催化剂氧化还原性和表面酸性，也可造成催化剂的严重失活。对Ca中毒催化剂的再生发现。酸洗再生效果要优于水洗，而且不同酸洗溶液对再生的效果有所不同。硫酸洗涤再生增强了催化剂的表面吸附NH₃的能力，比硝酸的再生效果好。此外，本文系统研究了H₂O含量、反应温度等不同操作参数下H₂O对催化剂脱硝活性的影响，发现H₂O对催化剂产生可逆性的抑制作用，而且低反应温度以及高H₂O含量对催化剂活性的不利影响越明显。反应系统中SO2对此类柱撑粘土负载锰铈催化剂的毒化作用非常严重，表面硫铵盐的沉积以及活性成分的硫酸化是催化剂活性降低的主要原因。本实验对SO2中毒催化剂热处理后，发现仅可恢复10%左右的脱硝活性；而水洗再生可使催化剂活性基本完全恢复。更多还原

【Abstract】 The selective catalytic reduction （SCR） of NO_xwith NH₃as reductant hasproven to be a promising technology to reduce the NO_xemission in the flue gas.Catalysts are critical to selective catalytic reduction of NO_x. Much attention ispresently focused on developing catalysts with high activity and good resistant topoison. Since most of the flue gases contain some amounts of ultra-fine particles,sulfur and water after desulfurization and dedust equipment, deactivation of catalystsis inevitable in the using process. Recently, low-temperature SCR has attracted moreand more interests for its low energy consumption. However, the poisoning effects ofsulfur and ash in flue gas has not invested systemly in the low-temperature SCR. Inthis dissertation, pillared clays were prepared and used as catalyst support. Thelab-scale investigations of activity performance and potential deactivation of MnO_xbased catalysts were investigated for low-temperature NO_x-SCR.The catalysts of Zr-pillared calys （ZrO2-PILC） supported MnO_xshowed highDeNO_xperformance in the low-temperature （80-240℃） SCR. It was found that theintroduction of Ce could improve the dispersion of MnO_x, enhance the oxygenstorage capacity and the adsoroption of NH₃, which is beneficial to NO_x-SCR. Theresults showed that NO_xconversion would be more than90%in the range of180-240℃. The operating parameters, such as NH₃concentration and O2concentration on theDeNO_xwere also investigated.The comprehensive study of the effects of alkali metals oxides （K2O/Na2O） anddifferent species of potassium （K₂SO₄, KCl） were conducted over theMn-Ce/ZrO2-PILC catalyst. Activity assessments of poisoned samples indicated thatcatalyst deactivation involves decrease of BET surface area, restraint of adsorptioncapacity of NH₃and reduction features of the catalysts. It also showed that Kexhibited greater poisoning effect than Na. Potassium in the form of chloride andsulfate is also a strong poison for the catalyst, and the resultes indicated that thepoisoning mechanism of potassium salt is similar to that of alkali metal oxides. Regeneration of deactivated catalysts were conducted by washing with water anddiluted sulphuric acid. Water washing was a promising method to the catalystsdeactivated with lower molar ratio of poison to Mn, except for the heavily deactivatedcatalyst. Washing with0.1mol/L H₂SO₄solution could increase the adsorption ofNH₃and the catalyst activity was even higher than the fresh one.Alkaline-earth metals could also induce serious deactivation to the NO_x-SCRcatalysts. The deposition of poison resulted in pore plugging and decrease of surfaceacidity and low-temperature reducibility. Washing with diluted acid solution, such assulphuric acid and nitric acid, presented to be more effective than water washing.Washing with sulphuric acid could create new acid sites and enhance the adsorptionof NH₃, which is beneficial to the NO_x-SCR.The effects of H₂O and SO2were also investigated in the research. H₂O wouldinhibit the catalytic activity, and the effect relateed with vapor content and thereaction temperature. However, the activity restored quickly to its original level aftercutting off of H₂O. While the catalyst was sensitive to the SO2in the gas, andpoisoning effect was irreversible. The deposition of ammonium salts on catalystsurface and sulfation of catalyst active phase were found to be the main reasons forthe deactivation of catalysts. Furthermore, thermal treatment and water-washing wereapplied for the regeneration of the SO2-deacivited catalysts. It was found that washingwith water could recover the most catalyst activity, thermal treatment, in contrast, dolittle to the regeneration.更多还原