Cu-SAPO-34催化剂用于 NH3-SCR去除 柴油车尾气 NOx
文献类型：学位论文
| 作者 | 牛璨 |
| 学位类别 | 博士 |
| 答辩日期 | 2016-05 |
| 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 | NH3-SCR，Cu-SAPO-34，一步水热合成法，水热稳定性，硫中毒 NH3-SCR，Cu-SAPO-34，One-pot hydrothermal synthesized method， hydrothermal stability, SO2 poisoning |
| 其他题名 | Cu-SAPO-34 Catalysts for NH3-SCR of NOx from Diesel Exhaust |
| 学位专业 | 环境科学 |
| 中文摘要 | 以 NH3为还原剂的选择性催化还原NOx技术（NH3-SCR）是目前最有效的柴油车尾气 NOx净化技术之一，该技术的核心是高性能 NH3-SCR催化剂的开发。具备 CHA（Chabazite）结构的小孔分子筛 Cu-SAPO-34呈现出优良的SCR催化活性、高温水热稳定性以及良好的抗碳氢中毒能力等优点，受到广泛关注。目前制备 Cu-SAPO-34催化剂大多采用SAPO-34载体与铜盐溶液进行液相离子交换的方法，涉及交换、过滤、洗涤等过程，制备过程较繁琐，且铜负载量难以准确控制。采用一步水热合成法合成 Cu-SAPO-34时，铜在分子筛骨架形成的同时原位引入，铜负载量可控，操作简便，更适于推广应用。目前一步水热合成法制备的 Cu-SAPO-34用于NH3-SCR反应净化 NOx的研究报道较少，本论文对此进行了系统深入的研究。 本论文采用一步水热合成法制备系列 Cu-SAPO-34催化剂。通过X射线衍射（XRD）、N2物理吸附、程序升温脱附（TPD）、H2程序升温还原（H2-TPR）、紫外可见漫反射光谱（UV-vis-DRS）和 X射线光电子能谱（XPS）等表征手段对Cu-SAPO-34的分子筛结构、化学组成、表面酸性、铜物种的分布以及氧化还原性质进行分析研究。 论文首先研究了模版剂种类、合成凝胶的组成、焙烧温度等关键因素对一步水热合成法制备的 Cu-SAPO-34催化剂结构、组成以及催化性能的影响。研究表明，模板剂种类主要影响 Cu-SAPO-34催化剂的结晶度；适宜的焙烧温度对Cu-SAPO-34的孔结构的形成非常重要；合成凝胶的组成影响催化剂的表面酸性、铜负载量及铜物种的分布。通过上述关键参数的优化，一步水热合成法制备了具有优良SCR催化活性和N2选择性的Cu-SAPO-34催化剂。 研究了 Cu-SAPO-34催化剂铜负载量对催化剂的高温水热稳定性的影响，分析了 Cu-SAPO-34的高温水热老化机制。高温水热老化后Cu-SAPO-34催化活性下降，主要是由于高温水热老化造成了分子筛结晶度下降、酸性位减少以及活性物种Cu关重要。铜含量较高的 Cu-SAPO-34催化剂的高温水热稳定性较差，高温水热老化（800C）后发生结构坍塌，催化剂完全失活。低温水热老化也造成了 Cu-SAPO-34催化剂结晶度下降，活性物种Cu2+向 CuO团簇迁移。适宜的铜含量对Cu-SAPO-34的高温水热稳定性至o2+向 CuO团簇的转化，并最终导致了NH3-Cu-SAPO-34催化剂用于NH3-SCR去除柴油车尾气NOxSCR催化活性的降低。 研究了Cu-SAPO-34催化剂的抗硫性能和硫中毒机理。硫中毒造成Cu-SAPO-34催化剂NH3-SCR的活性显著下降。硫中毒导致在SCR反应条件下Cu-SAPO-34催化剂表面生成硫酸铵盐堵塞孔道；同时硫酸铜的形成也减少了活性位点；此外，当 SO2共存于SCR反应气氛时，SO2与NO发生竞争吸附，抑制了催化剂表面硝酸盐的生成。 为了提高 Cu-SAPO-34催化剂的低温水热稳定性和抗硫性能，本论文通过一步合成法引入第二种金属元素组分对Cu-SAPO-34催化剂进行了改进，制备了CuCe-SAPO-34, CuNb-SAPO-34和CuTi-SAPO-34催化剂。Ce的添加优化了Cu-SAPO-34催化剂上铜物种的分布，减少了CuO团簇的生成，增加了活性物种Cu2+的比例，致使CuCe-SAPO-34较 Cu-SAPO-34表现出更好的抗水性能和催化活性。与 Cu-SAPO-34催化剂相比，CuNb-SAPO-34和CuTi-SAPO-34催化剂在SCR反应中的抗硫性能和硫中毒后再生的能力均有明显提高。尤其是CuTi-SAPO-34催化剂不但表现出优良的抗硫性能以及硫中毒后再生的能力，而且还具有较高的抗碳氢中毒的性能，在柴油车尾气 NOx控制领域具有很好的应用前景。 |
| 英文摘要 | The selective catalytic reduction of NOx with NH3 (NH3-SCR) is one of the most promising technologies for NOx emission control in diesel engine exhaust. Research and development on NH3-SCR catalysts is the key to this technology. Cu-SAPO-34 catalysts with the small-pore Chabazite zeolite structure have attracted much attention due to their high NH3-SCR activity, good hydrothermal stability and resistance to hydrocarbons. The aqueous solution ion exchange method involves a two-step exchange process, filtering, washing and calcining, the copper loading is difficult to control accurately. One-pot hydrothermal synthesis method used low-cost copper-tetraethylenepentamine (Cu-TEPA) as Cu source and template to prepare Cu-CHA directly which was much simpler to perform, and might be applicable at industrial scale. In this thesis, a series of Cu-SAPO-34 catalysts were prepared by a one-pot synthesis method. The zeolite structure, chemical composition, surface acidity,distribution of Cu species and redox behavior of Cu-SAPO-34 catalysts were investigated by XRD, N2 physisorption, H2-TPR, NH3-TPD, UV-vis-DRS and XPS etc. First, the effects of key factors, including the type of template, gel composition and calcination temperature, on the zeolite structure, chemical composition and catalytic performance of the one-pot synthesized Cu-SAPO-34 catalysts were studied.The type of template was found to mainly influence the crystallinity of the final Cu-SAPO-34. An appropriate calcination temperature was important for the formation of the pore structure of Cu-SAPO-34. The gel composition affected the surface acidity, Cu loading and distribution of Cu species for Cu-SAPO-34. A Cu-SAPO-34 catalyst with very high activity and N2 selectivity was synthesized by an improved one-pot synthesis method. The effect of Cu loading on the high temperature hydrothermal stability of Cu-SAPO-34 catalysts and the mechanisms of hydrothermal aging at high temperatures were investigated and discussed. It was found that the hydrothermal aging of Cu-SAPO-34 catalysts at high temperatures resulted in a decrease in SCR activity, which was caused by a decrease in crystallinity and number of acid sites and the migration of active Cu2+ species to CuO clusters. The optimum Cu loading is important to obtain Cu-SAPO-34 catalysts with high hydrothermal stability. After hydrothermal aging at 800oC,collapse of the CHA framework could occur and result in complete deactivation of Cu-SAPO-34 catalyst with higher Cu loading. Low temperature hydrothermal aging of Cu-SAPO-34 could also result in decreased catalytic activity, due to the decrease of crystallinity and the migration of active Cu species. The impact of SO2 on the SCR2+ activity of Cu-SAPO-34 catalysts was investigated, and possible mechanisms for the deactivation induced by sulfur were clarified. The SCR activity of Cu-SAPO-34 catalysts was significantly decreased after SO2 poisoning. It was found that SO2 poisoning can result in the formation of ammonium sulfate species in the SCR reaction,which may block the zeolite pores, as well as decrease the number of active sites due to the formation of CuSO4. In addition, competitive adsorption between SO2 and NOx can occur, and the formation of nitrates on the catalyst surface can be suppressed in the SCR reaction in the presence of SO2. In order to improve the low temperature hydrothermal stability and the sulfur resistance of Cu-SAPO-34, additional metallic elements were added to Cu-SAPO-34 catalysts in this study. CuCe-SAPO-34, CuNb-SAPO-34 and CuTi-SAPO-34 catalysts were successfully prepared by the one-pot synthesis method. CuCe-SAPO-34 showed better low temperature hydrothermal stability and activity than Cu-SAPO-34. The addition of Ce suppressed the formation of CuO clusters and increased the amount of active Cu2+ , and could stabilize the framework structure and active Cu2+ ions under hydrothermal conditions. Compared to Cu-SAPO-34, CuNb-SAPO-34 and CuTi-SAPO-34 showed better SO2 tolerance in the SCR reaction and higher activity for poisoned samples after regeneration. In particular, CuTi-SAPO-34, which showed excellent SO2 tolerance and hydrocarbon resistance, should be a promising candidate for application in NH3-SCR systems in diesel exhaust. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/36948]  |
| 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 | 牛璨. Cu-SAPO-34催化剂用于 NH3-SCR去除 柴油车尾气 NOx[D]. 北京. 中国科学院研究生院. 2016. |
入库方式： OAI收割
来源：生态环境研究中心
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