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题名	新型钒铈氧化物催化剂用于NH3选择性 催化还原NOx的研究
作者	连志华
学位类别	博士
答辩日期	2015-05
授予单位	中国科学院研究生院
授予地点	北京
导师	贺泓
关键词	选择性催化还原，钒铈氧化物催化剂，NOx催化去除，低温活性,selective catalytic reduction, vanadium-cerium oxides catalysts, catalytic abatement of NOx, low temperature activity
其他题名	Selective Catalytic Reduction of NOx with NH3 over Novel V-Ce Oxides Catalysts
学位专业	环境科学
中文摘要	以NH3为还原剂在催化剂的作用下选择性还原NOx(NH3-SCR)生成无毒无害的N2，是去除固定源和移动源中NOx应用最广且最为有效的技术之一。目前应用最多的NH3-SCR催化剂体系是V2O5-WO3(MoO3)/TiO2，虽然已经工业应用多年，但是仍存在一些问题，例如操作温度高、活性温度窗口窄、高温时N2O大量生成等，因此开发高效稳定的新型NH3-SCR催化剂体系成为众多科学工作者研究的热点。     本论文开发了新型的钒铈氧化物催化剂用于NH3选择性催化还原NOx研究。多种制备方法用于合成VOx/CeO2催化剂，包括均匀沉淀法、传统浸渍法、初湿浸渍法以及溶胶凝胶法，其中均匀沉淀法制备的VOx/CeO2(P)催化剂NH3-SCR活性最高，并且具有更高的抗水抗硫性能，而溶胶凝胶法制备的VOx/CeO2(S)催化剂的活性最低。VOx/CeO2(P)催化剂表面CeO2结晶度较低，表面钒物种得到更好的分散，表面钒含量更高，进而产生更多的酸性位，能够更好地吸附和活化NH3物种。这些因素均有助于催化剂获得更高的SCR活性和抗硫性能。采用均匀沉淀法对VOx/CeO2催化剂进行第三种过渡金属氧化物的掺杂，其中Nb的添加能够显著提高其低温催化性能。30 wt.% Nb-1VOx/CeO2催化剂具有最高的SCR活性与抗水抗硫性能，并且优于3V2O5-WO3/TiO2催化剂，具有很好的工业应用前景。     在含有SO2的SCR气氛中长时间反应后，VOx/CeO2催化剂表面形成了大量硫酸盐物种，比表面积和孔容积显著下降，酸性位减少；但是Nb-VOx/CeO2催化剂上基本没有发现硫酸根的存在，仍保持较高的比表面积，具有较高的抗硫中毒性能。两种催化剂硫中毒的机理类似，主要表现为表面硝酸盐的形成受到强烈抑制，阻断了NH3吸附物种与NOx吸附物种反应的L-H路径，只能与气相NO或弱吸附的NO通过E-R路径发生反应，使得低温催化活性有所下降。     由于钒具有一定的生物毒性，我们还进一步开发了非钒催化剂(Mn-Nb复合氧化物)用于低温NH3-SCR研究。Mn2Nb1Ox催化剂具有比MnOx和NbOx催化剂更高的NH3-SCR活性以及N2生成选择性。MnOx催化剂具有高的氧化还原性能，高温时NH3发生非选择性氧化，导致NOx转化率和N2生成选择性降低。Nb的添加不仅降低其氧化还原性能，提高高温N2选择性；还能够提高MnOx的酸性，特别是Brønsted酸性位的增多，有利于提高低温催化性能。强氧化性的MnOx与强酸性的NbOx结合能够得到优秀的低温NH3-SCR催化剂。
英文摘要	Selective catalytic reduction of NOx with NH3 (NH3-SCR) is a well-proven technique for the removal of NOx from stationary and mobile sources. The most widely used catalyst system is V2O5-WO3(MoO3)/TiO2 which still shows some inevitable problems in practical use, including low activity below 300 oC, narrow operation temperature window, and N2O formation at high temperatures. Therefore, many researchers continue to focus on the development of novel, highly efficient and stable NH3-SCR catalysts.     In this study, we prepared novel vandium-cerium catalysts for selective catalytic reduction of NOx with NH3. Among different preparation methods, including homogeneous precipitation, rotary evaporation impregnation, incipient wetness impregnation and sol-gel methods, the VOx/CeO2(P) catalyst prepared by homogeneous precipitation method exhibited the best NH3-SCR activity and the strongest resistance to H2O and SO2. At the same time, VOx/CeO2(S) prepared by sol-gel methods showed poor catalytic performance. Lower CeO2 crystallinity on the surface, better dispersion of vanadium species, and higher surface concentration of vanadium species together with more acid sites all played a role in the higher SCR activity over VOx/CeO2(P).     A superior Nb-VOx/CeO2 catalyst was prepared by doping Nb into the VOx/CeO2 catalyst. The addition of Nb was able to significantly promote the SCR activity of the VOx/CeO2 catalyst, especially in the low temperature range. 30 wt.% Nb-1VOx/CeO2 catalyst exhibited higher NH3-SCR activity than 3V2O5-WO3/TiO2. The lower crystallinity, stronger redox capability and more Brønsted acid sites of the Nb-VOx/CeO2 catalyst were all responsible for its more excellent NH3-SCR performance.     After sulfur poisoning experiments, sulfate species formed on the VOx/CeO2 catalyst, and the specific surface area and pore volume decreased evidently, thus the amount of acid sites decreased. For the Nb-VOx/CeO2 catalyst, little sulfate species were detected. Nb-VOx/CeO2 showed a large specific surface area and strong resistance against to SO2. The formation of nitrate species was inhibited and the L-H pathway between NH3 and NOx adsorbed species was cut off, leading to SCR activity loss at low temperature.     Due to the toxicity of vanadium, a series of Mn-Nb oxides catalyst was also prepared by homogeneous precipitation methods for NH3-SCR at low temperatures. Mn2Nb1Ox calcined at 500 oC exhibited the best catalytic activity. MnOx had strong redox capability, resulting in low N2 selectivity due to the unselective oxidation of NH3 at relatively high temperatures. The addition of Nb to MnOx enhanced the acidity, especially the Brønsted acidity, which is responsible for the low temperature SCR activity. The combination of MnOx with strong redox capability and NbOx with high acidity simultaneously led to high NOx conversion and N2 selectivity over the Mn2Nb1Ox catalyst.
内容类型	学位论文
源URL	[http://ir.rcees.ac.cn/handle/311016/34344]
专题	生态环境研究中心_大气污染控制中心
推荐引用方式 GB/T 7714	连志华. 新型钒铈氧化物催化剂用于NH3选择性 催化还原NOx的研究[D]. 北京. 中国科学院研究生院. 2015.

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