【作者】 姜烨；

【导师】 高翔； 王勤辉； 岑可法；

【作者基本信息】 浙江大学 ， 工程热物理， 2010， 博士

【摘要】 氮氧化物是世界各国公认的大气污染物之一。以NH3为还原剂的选择性催化还原(SCR)烟气脱硝技术是目前脱除烟气中NOx最有效的技术。催化剂是SCR烟气脱硝技术的核心,它是影响整个SCR系统脱硝效果和经济性的主要因素。中毒是SCR催化剂实际应用过程中不可避免的问题,它与燃料的特性密切相关。我国燃料(煤和废弃物)成分复杂,煤中硫分灰分含量高,废弃物中水分高。因此,研究催化剂对我国燃烧烟气的适应性具有重要的实际意义。本文依托于国家高技术研究发展计划(863计划)资助项目(No.2007AA061802)和国家自然科学基金资助项目(No.50776079),针对钛基SCR催化剂,就制备参数和操作参数对其NO还原特性的影响,钾和铅对V2O5/TiO2催化剂的作用机理进行了系统的研究,得到以下主要结果：1.研究了制备参数与钛基SCR催化剂脱硝性能之间的内在联系。详细分析了载体TiO2的性质、煅烧条件和V2O5担载量对V2O5/TiO2催化剂脱硝性能的影响,发现载体TiO2的比表面积越大,结晶度越弱,越有利于V2O5/TiO2催化剂上的SCR反应；在煅烧温度为500℃和煅烧时间为5h的条件下制备的1wt.% V2O5/TiO2催化剂具有最高的脱硝活性,在典型的SCR反应温度范围(300-400℃),NO转化率达到92.7-98.8%；随着催化剂上V2O5担载量的增加,有序的V2O5晶体随之增加,反应温度的升高将导致N2O生成量的增多,降低了催化剂的选择性。对于CeO2/TiO2催化剂,采用一步溶胶-凝胶法制备的催化剂脱硝活性最高；CeO2与TiO2的最佳配比(质量比)为0.6；最佳煅烧温度是500℃。在该条件制备的催化剂,在典型的SCR反应温度范围(300-400℃),NO转化率可达98.6%,选择性达到100%(空速50,000h-1)。2.研究了操作参数对钛基SCR催化剂脱硝性能的影响。在实际应用的条件下,在V2O5/TiO2催化剂上,SCR反应与O2成零级反应,与NO成一级反应,在n(NH3)/n(NO)大于等于1时与NH3成零级反应；H2O对V2O5/TiO2催化剂上的SCR反应具有一定抑制作用,但是同时能够抑制N2O的生成；反应气氛中的SO2在干烟气条件和湿烟气条件下对V2O5/TiO2催化剂上NO还原活性影响不大。对于CeO2/TiO2催化剂,在12,000-100,000 h-1的空速范围内该催化剂均表现出良好的适应性；O2在SCR反应中起重要作用。当O2浓度高于1%时,NO转化率将不再受到O2浓度的抑制,趋于一个恒定值；H2O和SO2对CeO2/TiO2催化剂的影响与其浓度和反应温度密切相关。3.阐明了不同形态的钾(KCl和K2SO4)和不同形态的铅(PbCl2和PbO)对V2O5/TiO2催化剂的作用机理。不同形态的钾或铅沉积在V2O5/TiO2催化剂表面,导致催化剂的比表面积和孔结构发生不同的变化；载体TiO2的结晶度发生变化；催化剂表面V原子的价态发生改变；催化剂表面活性位数量减少。钾或铅使V2O5/TiO2催化剂失活的主要原因是钾或铅中和了Br(?)nsted酸性位的酸性,使其NH3质子化的能力丧失,而Br(?)nsted酸性位对SCR反应过程中NH3的吸附和活化起重要作用。提出了不同形态的钾和不同形态的铅使V2O5/TiO2催化剂失活可能发生的路径。4.基于催化剂颗粒中毒的渐进壳模型,对颗粒状催化剂的中毒动力学进行了研究,建立了催化剂中毒动力学方程。以活性保留分率为桥梁,利用模型预测值和实验值建立了催化剂上钾负载量或铅负载量与反应时间的关系；当空速在15,000-60,000 h-1范围内、催化剂颗粒平均粒径在137-335μm范围内以及反应器管径在4-20 mm范围内对活性保留分率几乎没有影响；模拟了毒物浓度和中毒反应速率常数的耦合对活性保留分率的影响,模型结果与文献中报道的催化剂实际运行结果相符合。更多还原

【Abstract】 Nitrogen oxides (NOx) are recognized as a major source of air pollution in the world. The selective catalytic reduction of NOx with NH3 as reductant is most efficient among the technologies abating NOx in flue gas at present. Catalysts are critical to selective catalytic reduction of NOx. They are the main factor affecting the NOx removal and economical efficiency of the whole SCR system. Poisoning is inevitable for SCR catalysts in their using process and relates with the fuel characteristics intimately. The fuel composition is complex in our country. The content of sulfur and ash in coal as well as the water content in waste is high. Therefore, the study on the adaptability of SCR catalysts to the firing flue gas in our country is important and meaningful. With the financial support from the National High Technology Research and Development of China (863 Program) (No. 2007AA061802) and National Science Foundation of China (No.50776079), the systemic studies were carrird out on the effect of preparation and operating parameters on the NO reduction of titania-based catalysts, as well as the V2O5/TiO2 catalysts’poisoning mechanism by potassium and lead. The main results are shown as following:1. The correlation between preparation parameters and the DeNOx performance of titania-based SCR catalysts was studies. The effect of the TiO2 property, calcination condition and V2O5 loadings on the DeNOx performance of V2O5/TiO2 catalysts were analyzed in detail. Large surface area and weak TiO2 crystallinity are advantageous to SCR reaction over the catalysts. When the 1 wt.% V2O5/TiO2 catalysts were calcinated at 500℃for 5 h, their DeNOx activity was highest and the NO conversion reached 92.7～98.8% at the typical SCR reaction temperature (300～400℃). The increase in orderly V2O5 crystallites and reaction temperature would lead to the N2O formation, thereby decreasing the selectivity of the catalysts. The CeO2/TiO2 cayalysts prepared by a single sol-gel mothod have the best SCR activity. The most active catalysts were obtained with a Ce loading of 0.6. The optimal calcination temperature was 500℃. At the typical SCR reaction temperature,98.6% of NO conversion and 100% of N2 selectivity were obtained at the gas hourly space velocity (GHSV) of 50,000 h-1 over the catalysts.2. The effect of operating parameters on the DeNOx performance of titania-based SCR catalysts was studied. In the actual operating condition, the SCR reaction over V2O5/TiO2 catalysts is zero-order for O2, first-order for NO and zero-order for NH3 when the molar ratio of NH3 to NO is higher than or equal to 1. H2O has an inhibiting effect on SCR reaction, while reduce the formation of N2O over V2O5/TiO2 catalysts.The presence of SO2 has no large impact on NO reduction activity over V2O5/TiO2 catalysts in dry or wet simulated flue gas. The best CeO2/TiO2 catalysts were effective for NO removal within a wide range of GHSV from 12,000 h-1 to 100,000 h-1. The presence of oxygen played an essential role in NO reduction, and the activity of the Ce(0.6)Ti catalyst was not depressed when oxygen concentration was higher than 1%. The effect of SO2 and H2O on the activity of the Ce(0.6)Ti catalyst was bound up with the reaction temperature.3. Action mechanism of different species of potassium or lead on V2O5/TiO2 catalysts was clarified. Different species of potassium or lead resulted in the change of specific surface area and porosity of the catalysts, the change of V valence and the decrease in the numbers of active sites at the surface of the catalysts. The main reason of the catalyst deactivation by K and Pb is that K or Pb coordinates to Br(?)nsted acid sites on the catalysts’surfaces and neutralizes the acidity of them. However, Br(?)nsted acid sites are important for the absorption and activation of NH3 in SCR reaction. According to the catalyst characterization results, the possible path in which the species of potassium or lead cause the deactivation of V2O5/TiO2 catalysts was proposed.4. Based on a model for the "shell-progressive" poisioning of a single catalyst particle in a catalytic reactor, the poisonsing kinetics was studied and the poisonsing kinetic equation was established. Combining the activity retention of the model simulation with that of the experimental values, the relation of the K or Pb loadings over the catalysts with the reaction time was established. The GHSV (15,000～60,000 h-1), mean catalyst particle diameter (137～335μm) and reactor diameter (4-20 mm) have almost no effect on the activity retention. The combined effect of the poison concentration and poisoning reaction rate constant on the activity retention was simulated based on the established model. The simulated results accord with the catalyst operating results reported in a published paper.更多还原