催化学报 ›› 2016, Vol. 37 ›› Issue (8): 1340-1346.DOI: 10.1016/S1872-2067(15)61109-3

• 论文 • 上一篇    下一篇

Si改性对V2O5/WO3-TiO2催化剂NH3-SCR活性和热稳定性的影响

刘雪松a,b, 吴晓东a,b, 许腾飞a, 翁端a,b, 司知蠢b, 冉锐a   

  1. a. 清华大学材料学院, 先进材料教育部重点实验室, 北京 100084;
    b. 清华大学深圳研究生院, 新材料研究所, 广东 深圳 518055
  • 收稿日期:2016-02-04 修回日期:2016-04-14 出版日期:2016-07-29 发布日期:2016-08-01
  • 通讯作者: Xiaodong Wu, Duan Weng
  • 基金资助:

    国家自然科学基金(51372137);国家高技术研究发展计划(863计划,2015AA034603).

Effects of silica additive on the NH3-SCR activity and thermal stability of a V2O5/WO3-TiO2 catalyst

Xuesong Liua,b, Xiaodong Wua,b, Tengfei Xua, Duan Wenga,b, Zhichun Sib, Rui Rana   

  1. a. Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China;
    b. Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong, China
  • Received:2016-02-04 Revised:2016-04-14 Online:2016-07-29 Published:2016-08-01
  • Contact: Xiaodong Wu, Duan Weng
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (51372137) and the National High Technology Research and Development Program of China (863 Program, 2015AA034603).

摘要:

V2O5/WO3-TiO2是NH3-SCR领域应用最为广泛的商用脱硝催化剂,该催化剂具有良好的抗硫中毒性能;但其水热稳定性却相对较差,高温条件下运行会严重失活.这主要是由于锐钛型TiO2在高温下发生团聚或相变,生成比表面积较小的晶红石型TiO2,进而导致活性组分V2O5和WO3团聚或挥发.结局问题的关键是提高载体TiO2的水热稳定性,而添加Al,Zr和Si等元素对TiO2进行改性则被认为是最有效的方法之一.Si改性的V2O5/WO3-TiO2催化剂水热老化后仍然具有较高的比表面积、较多的酸性位和稳定晶体结构,但其作用机理仍不明确.本文分别考察了750oC水热老化处理24 h对V2O5/WO3-TiO2和V2O5/WO3-TiO2-SiO2催化剂结构和催化活性的影响,并采用X射线衍射(XRD)、氢气程序升温还原(H2-TPR)、拉曼光谱(Raman)和氨气程序升温脱附(NH3-TPD)等手段研究了Si改善V2O5/WO3-TiO2催化剂水热稳定性的原因.结果表明,水热老化后,Si改善的催化剂和载体的比表面积降幅较小.XRD结果表明,Si添加到TiO2中可形成Ti-O-Si固溶体,固溶体的形成使TiO2晶界能提高,可防止水热老化过程中TiO2的团聚和相变,进而提高其水热稳定性.负载V后,Si对载体的稳定作用则更加明显.这主要是因为低熔点的V2O5会加剧载体的团聚和相变.结合H2-TPR和Raman结果可知,V2O5/WO3-TiO2催化剂水热老化后发生TiO2团聚或相变,进而导致活性组分多聚态V2O5团聚生成V2O5晶粒或Ti-V-O固溶体,而后者对SCR反应活性的贡献非常低;同时,水热老化还使得助剂WO3从WO3-TiO2中脱离出来,因而导致催化剂活性和选择性下降.然而由于V2O5/WO3-TiO2-SiO2催化剂载体具有良好水热稳定性,经水热处理后仍保持着锐钛晶型和较小的晶粒,抑制了活性组分V2O5的严重团聚或形成固溶体;同时还使得高分散态V2O5轻微团聚形成主要活性组分多聚态V2O5,因此催化活性反而提高.另外,由于V2O5/WO3-TiO2-SiO2催化剂中形成了Ti-O-Si固溶体,进而产生更多的酸性位,水热处理后,其酸性位降低幅度较小;而V2O5/WO3-TiO2催化剂酸性位数量明显减少,这与其载体和活性组分的烧结和相变相关,这也是导致其失活的主要原因之一.

关键词: V2O5/WO3-TiO2, 硅, NH3-SCR, 水热稳定性, 多聚态钒, 脱硝

Abstract:

V2O5/WO3-TiO2 and V2O5/WO3-TiO2-SiO2 catalysts were prepared by a wetness impregnation method, and both the catalysts were hydrothermally aged at 750 ℃ in 10 vol% H2O/air for 24 h. The catalysts were evaluated for NOx conversion using NH3 as the reductant. Hydrothermal ageing decreased the NOx conversion of V2O5/WO3-TiO2 catalyst severely over the entire measured temperature range. Interestingly, the NH3-SCR activity of the silica-modified catalyst at 220-480 ℃ is enhanced after ageing. The catalysts were characterized by X-ray diffraction, nitrogen adsorption, X-ray fluorescence, Raman spectroscopy, H2 temperature-programmed reduction, and NH3 temperature-programmed desorption. The addition of silica inhibited the phase transition from anatase to rutile titania, growth of TiO2 crystallite size and shrinkage of catalyst surface area. Consequently, the vanadia species remained highly dispersed and the hydrothermal stability of the V2O5/WO3-TiO2 catalyst was significantly improved.

Key words: V2O5/WO3-TiO2, Silica, NH3-SCR, Hydrothermal stability, Polymeric vanadia, De-NOx