物理化学学报 >> 2015, Vol. 31 >> Issue (9): 1761-1770.doi: 10.3866/PKU.WHXB201507291

催化和表面科学 上一篇    下一篇

铜负载量对LNT催化剂CuO-K2CO3/TiO2结构与性能的影响

范丰奇1,孟明1,*(),田野1,*(),郑黎荣2,张静2,胡天斗2   

  1. 1 天津大学化工学院,天津化学化工协同创新中心,天津市应用催化科学与工程重点实验室,天津300072
    2 中国科学院高能物理研究所,北京100049
  • 收稿日期:2015-04-17 发布日期:2015-09-06
  • 通讯作者: 孟明,田野 E-mail:mengm@tju.edu.cn;tianye@tju.edu.cn
  • 基金资助:
    国家自然科学基金(21276184, U1332102, 21476160);高等学校博士学科点专项科研基金(20120032110014);天津市自然科学基金(12JCYBJC14000, 15JCZDJC37400);中国大学学科人才引进计划(B06006)

Effect of Cu Loading on the Structure and Catalytic Performance of the LNT Catalyst CuO-K2CO3/TiO2

Feng-Qi. FAN1,Ming. MENG1,*(),Ye. TIAN1,*(),Li-Rong. ZHENG2,Jing. ZHANG2,Tian-Dou. HU2   

  1. 1 Collaborative Innovation Center of Chemical Science and Engineering Tianjin, Tianjin Key Laboratory of Applied Catalysis Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China
    2 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2015-04-17 Published:2015-09-06
  • Contact: Ming. MENG,Ye. TIAN E-mail:mengm@tju.edu.cn;tianye@tju.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21276184, U1332102, 21476160);Specialized Research Fund forthe Doctoral Program of Higher Education of China(20120032110014);Natural Science Foundation of Tianjin, China(12JCYBJC14000, 15JCZDJC37400);Program for Introducing Talents of Discipline to Universities of China(B06006)

摘要:

采用连续浸渍法制备了一系列非贵金属稀燃NOx阱(LNT)催化剂CuO-K2CO3/TiO2,考察了Cu负载量对催化剂结构和NOx储存还原性能的影响.发现8% (w) CuO-K2CO3/TiO2催化剂的催化性能最佳,其对NOx的储存量达到1.559 mmol·g-1,对NOx的还原效率高达99%,且在NOx还原过程中无副产物N2O产生.应用粉末X射线衍射(XRD),高分辩透射电子显微镜(HR-TEM), CO2程序升温脱附(CO2-TPD),扩展X射线吸收精细结构(EXAFS),氢气程序升温还原(H2-TPR)和原位漫反射红外光谱(in-situ DRIFTS)等技术详细表征了催化剂的结构.结果表明,不同Cu负载量的催化剂中,铜物种均主要以CuO相存在.铜的负载量直接影响铜物种、钾物种的存在状态,高分散的CuO相与表面K2CO3之间存在较强相互作用,这种相互作用不仅有利于NOx的储存,而且有利于增强催化剂的稳定性. in-situ DRIFTS结果表明, NOx储存过程中产生的两个负峰(1436和1563 cm-1)缘于碳酸盐的分解,这间接证明了碳酸盐作为储存介质参与到NOx储存反应中. EXAFS结果表明,经过15个稀燃/富燃循环测试,催化剂中的CuO相仍保持稳定.基于以上表征结果,提出了CuO和K2CO3在催化剂表面的分布模型,并探讨了NOx储存还原的可能机理.

关键词: NOx, 储存, 还原, 氧化铜, 碳酸钾

Abstract:

A series of non-platinic lean NOx trap (LNT) CuO-K2CO3/TiO2 catalysts with different Cu loadings were prepared by sequential impregnation, and they showed relatively good performance for lean NOx storage and reduction. The catalyst containing 8% (w) CuO showed not only the largest NOx storage capacity of 1.559 mmol·g-1 under lean conditions, but also the highest NOx reduction percentage of 99% in cyclic lean/rich atmospheres. Additionally, zero selectivity of NOx to N2O was achieved over this catalyst during NOx reduction. Multiple techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed desorption of CO2 (CO2-TPD), extended X-ray absorption fine structure (EXAFS), temperature-programmed reduction of H2 (H2-TPR), and in-situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS), were used for catalyst characterization. The results indicate that highly dispersed CuO is the main active phase for oxidation of NO to NO2 and reduction of NOx to N2. The strong interaction between K2CO3 and CuO was clearly revealed, which favors NOx adsorption and storage. The appearance of negative bands at around 1436 and 1563 cm-1, corresponding to CO2 asymmetric stretching in bicarbonates and -C=O stretching in bidentate carbonates, showed the involvement of carbonates in NOx storage. After using the catalysts for 15 cycles of NOx storage and reduction in alternative lean/rich atmospheres, the CuO species in the catalysts showed little change, indicating high catalytic stability. Based on the results of in-situ DRIFTS and the other characterizations, a model describing the NOx storage processes and the distribution of CuO and K2CO3 species is proposed.

Key words: NOx, Storage, Reduction, Copper oxide, Potassium carbonate

MSC2000: 

  • O643