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类型 综合研究 预答辩日期 2018-03-12
开始(开题)日期 2015-09-11 论文结束日期 2018-01-17
地点 东南大学四牌楼校区动力楼422 论文选题来源 省(自治区、直辖市)项目    论文字数 9 (万字)
题目 过渡金属氧化物低温SCR催化剂脱硝性能及机理研究
主题词 低温SCR,过渡金属氧化物,铁氧化物,钒基催化剂,密度泛函理论
摘要 低温选择性催化剂还原(SCR)脱硝技术在降低固定源燃烧烟气氮氧化物排放方面具有广阔的应用前景。作为该技术的核心环节,低温SCR脱硝催化剂仍面临低温活性及抗硫性能差的问题,制约其工业化应用。本文从新型过渡金属氧化物催化剂开发和钒基脱硝催化剂改性两条路径出发,对过渡金属氧化物低温脱硝性能进行系统分析,筛选出满足工业应用环境的低温脱硝催化剂,并借助密度泛函(DFT)理论从分子层面对催化剂表面脱硝反应过程及硫水失活原因进行分析。 首先对比了常规新型过渡金属元素为活性组分的金属氧化物及硫酸盐催化剂脱硝性能。相同活性元素摩尔含量情况下,Mn、Ce金属氧化物催化剂表现出优异的中低温活性,但对应的硫酸盐催化剂只在较窄的高温区间表现出一定的脱硝活性。研究认为硫酸根对活性元素氧化还原性能的抑制是导致其低温活性减弱的主要原因。相比之下,硫酸根存在显著增加了Cu、Fe基催化剂的表面酸性,对其脱硝活性的影响较弱,其中铁基催化剂在中高温区域具有优异的脱硝性能。 从机理角度出发对铁氧化物催化剂的改性研究中,通过引入Cu、Co得到的负载型Cu-Fe/TiO2、Co-Fe/TiO2催化剂及体相掺杂型CuFeOx与CoFeOx复合氧化物催化剂低温脱硝活性均得到有效提升。负载改性铁基催化剂活性受高浓度水蒸汽影响显著,Cu-Fe/TiO2催化剂脱硝性能150~300℃范围都受到抑制,Co-Fe/TiO2催化剂温度窗口向高温区域迁移。催化剂表面吸附物种热稳定性及自身氧化还原性能的差异导致了有无水蒸汽环境下不同的SCR反应性能。SO2接触会造成体相掺杂催化剂低温活性的不可逆损失,活性组分硫酸盐化是造成催化剂硫中毒的主要原因。新型过渡金属氧化物脱硝催化剂虽在洁净气氛下具有优异的低温脱硝活性,但H2O和SO2引起的失活与中毒仍然是限制其实践应用的关键障碍。 钒基催化剂的改性研究发现,助剂MoO3和Nb2O5的添加均可以有效提高钒基催化剂低温脱硝性能。钒氧化物分散状态的改善与活性位点反应性能的提升是改性催化剂性能提升的主要因素。抗中毒性能研究表明,H2O与SO2对改性钒基催化剂的失活具有显著的协同加速效应。应用温度低于225℃时,表面硫酸铵盐的沉积会导致催化剂逐渐失活。表面硫酸铵盐的反应及热分解特性显示高于350℃的热处理可使得失活催化剂活性完全恢复。相比于颗粒催化剂,成型样品H2O与SO2环境下的失活速率变缓,225℃时3V6Nb/WTi催化剂可在H2O、SO2环境下长时间保持稳定的脱硝效率。 钒基催化剂理论计算结果显示:还原剂在表面L酸位点的吸附较弱,B酸位点的吸附更为稳定。不同活性位点反应途径的对比分析表明L酸位催化途径最大能垒较高,达到57.83kcal/mol,而B酸位催化过程的反应能垒较低。研究发现由于表面情况的差异,B酸位可能有不同的反应途径。计算结果从分子层面论证了B酸位点对脱硝反应的重要性。同时,理论计算研究表明高浓度的H2O在催化剂表面的竞争吸附导致的对活性位点占据、表面空间压缩是含水环境下催化剂活性下降的原因。SO2在催化剂表面的单独吸附很弱,而H2O、NH3与SO2共存时通过气相催化水解生成的亚硫酸盐团簇与催化剂表面V=O基团具有较强的结合能力,研究认为该水解过程是导致钒基催化剂H2O和SO2环境下加速失活的主要原因。
英文题目 The Study of Transition Metal Oxide Catalysts Low Temperature NH3-SCR Performance and Mechanism
英文主题词 Low-temperature SCR, transition metal oxide, iron oxide, vanadium based catalysts, density function theory
英文摘要 Low-temperature selective catalytic reduction (SCR) of NOx with NH3 is new technology with the broad application prospects in reducing the NOx emission of stationary sources. As the key element of this technology, the low-temperature SCR catalysts still face some obstacles such as the unsatisfactory low-temperature activity and SO2 resistance restricting its real application. The system investigations of transition metal oxide catalysts low temperature SCR performance are performed in this paper, combining two paths including the development of novel transition metal oxides catalysts and the modification of tranditional V-W-Ti catalysts, in order to obtain the practical catalyst under the real industrial condition. The density function theory (DFT) calculations were used to deepen the understanding of surface reaction process and the deactivation reasons of H2O and SO2 in the molecular level. The SCR activity and physical-chemical characterstics of different transition metal oxide and sulfate catalysts were compared firstly. Under the same molar content of active elements, the oxide catalysts of Mn and Ce exhibited the excellent SCR activity at the low and medium temperatures, while the corresponding sulfate catalysts only showed the deNOx effiency in the narrow high temperature range. The inhibition of active elements redox capacity by the existence of surface sulfate radical was concluded to be the main reason for the lost of low temperature activity. In comparison, the influence of sulfate radical on Fe\Cu based samples was weaker. The surface sulfate radical increased the surface acidities of these catalysts. Fe based catalysts showed the good SCR activity in the medium temperature range. The modification of iron oxide catalysts were carried out by introducing Cu and Co elements according to the reported reaction mechanism. The low-temperature SCR activities of the novel supported catalysts Cu-Fe/TiO2, Co-Fe/TiO2 and bulk phase doping catalysts CuFeOx, CoFeOx were all improved distinctly. However, the performance of supported catalysts was affected by high concentration water vapor. The SCR activity of Cu-Fe/TiO2 between 150℃ and 300℃ was inhibited seriously and the temperature window for Co-Fe/TiO2 shifted towards the higher temperature. The different thermal stability of surface adsorbed species and materials redox capacities leaded to the different SCR performance under the dry and wet conditions. The contact of SO2 resulted in the deactivation of bulk phase doping catalysts at low temperatures irreversibly.The deep research concluded that the sulfation of active species was the main reason accounting for the catalysts poisoning. Even though these novel transition metal oxide catalysts own the excellent SCR activity at low temperatures, the deactivation and poisoning caused by H2O and SO2 is still the obvisou obstacle for their real application. The study of vanadium based catalysts found that the modification by MoO3 and Nb2O5 could improve the SCR activity of vanadium based catalysts at low temperatures. The adjustment of vanadium oxide dispersed state and the enhancement of active species reactivity accouted for the performance elevation. The synergy effect of H2O and SO2 on accelerating the catalyst deactivation was found during the SO2 resistance test. The deposition of ammonium sulfate species on catalysts surface was proved to be the main reason of catalysts deactivation below 225℃. The decomposition and reactivity investigation of surface ammonium sulfate species indicated that the thermal treatment above 350℃ could regenerate the deactivated catalysts totally. Compared with the particle sample, the H2O and SO2 deactivation rate of monolith catalyst decreased. 3V6Nb/WTi honeycombed catalyst showed the stable NOx conversion during the long time test at 225℃ in the presence of H2O and SO2. The density functional theory (DFT) calculation of vanadium based catalyst showed the adsorption of NH3 on Br?nsted acid sites was more stable than that on Lewis acid sites. Similarly, the energy barrier of Br?nsted acid site reaction paths was smaller than that of Lewis acid site reaction path. Due to the diversity of surface condtions, there might be different Br?nsted acid site reaction paths. The calculation result proved the importance of Br?nsted acid sites for the SCR reaction of vanadium based catalysts. The occupancy of active species and surface reaction space by competitive adsorption of high concentration water vapor could explain the activity decline phonemonen under the wet condition. The adsorption of SO2 alone on the catalyst surface was very weak. But the sulfurous acid salt clusters formed through gas phase catalytic reaction with the coexistence of NH3, H2O and SO2 have strong binding capacity with the surface V=O structure. This behavior was deduced to lead to the synergy deactivation of H2O and SO2 for vanadium based catalysts.
学术讨论
主办单位时间地点报告人报告主题
东南大学能源与环境学院 2017.10.16 东南院102 王如竹 YongTae Kang 能源与环境研究前沿与人才培养
仲兆平课题组 2015.8.11 热能所会议室 朱林 Progress report on Low and Medium Temperature SCR Catalysts
仲兆平课题组 2015.12.28 热能所会议室 朱林 2015第4季度研究进展报告
仲兆平课题组 2016.12.19 热能所会议室 朱林 2016研究进展总结报告
仲兆平课题组 2017.9.29 热能所会议室 朱林 2017理论计算化学研究进展报告
仲兆平课题组 2017.11.6 热能所会议室 朱林 2017第4季度研究总结报告
东南大学能源与环境学院 2016.4.18 东南院102 孙建中 How to give an effective and scientific presentation: The A to Z of PowerPoint
东南大学能源与环境学院 2017.9.28 东南院102 陈标华 Selective Transformation of Various Nitrogen-containing Exhaust Gases towards N2 over Zeolite Catalysts
东南大学能源与环境学院; 江苏省制冷学会 2017.9.5 中山院301 Kuanrong Qiu Advanced Organic Rankine Cycle:its theory, applications and new development in building distributed and smart energy systems
     
学术会议
会议名称时间地点本人报告本人报告题目
11th China-Korea Clean Energy Workshop 2016.9.20-23 江苏南京 DeNOx performance and characteristic study for transition metals doped iron based catalysts prepared by citric method
2017年中国工程热物理学会燃烧学学术会议 2017.10.13-15 江苏南京 燃煤电厂SCR脱硝装置导流及氨混合系统数值模拟研究
     
代表作
论文名称
Comparison study of Cu-Fe-Ti and Co-Fe-Ti oxide catalysts for selective catalytic reduction of NO
NH3-SCR performance of Mn-Fe/TiO2 catalysts at low temperature in the absence and presence of water
A comparative study of metal oxide and sulfate catalysts for selective catalytic reduction of NO
DeNOx performance and characteristic study for transition metals doped iron based catalysts
Effect of MoO3 on vanadium based catalysts for the selective catalytic reduction of NOx with NH3
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
张靖周 正高 教授 博导 南京航空航天大学
杨宏旻 正高 教授 博导 南京师范大学
袁竹林 正高 教授 博导 东南大学
陈晓平 正高 教授 博导 东南大学
张军 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
王沛 其他 讲师 东南大学