Acta Phys. -Chim. Sin. ›› 2014, Vol. 30 ›› Issue (8): 1559-1566.doi: 10.3866/PKU.WHXB201405283

• CATALYSIS AND SURFACE SCIENCE • Previous Articles     Next Articles

Effects of Two Different CeO2 Materials on Lean NOx Trap Performance below 300 ℃

ZHU Jin-Xin1, SHEN Mei-Qing1,2, Lü Liang-Fang1, WANG Jun1, WANG Jian-Qiang1   

  1. 1. Key Laboratory for Green Chemical Technology of State Education Ministry, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, P. R. China;
    2. State Key Laboratory of Engines, Tianjin University, Tianjin 300072, P. R. China
  • Received:2014-04-08 Revised:2014-05-26 Published:2014-07-18
  • Contact: WANG Jun, WANG Jian-Qiang E-mail:wangjun@tju.edu.cn;jianqiangwang@tju.edu.cn
  • Supported by:

    The project was supported by the National High-Tech Research and Development Program of China (863) (2011AA03A405).

Abstract:

The present work investigated the effects of two types of CeO2 materials on the lean NOx trap (LNT) performance over NOx storage reduction (NSR) catalysts below 300 ℃. These materials were obtained by mechanical mixing of 2% (w) Pt/Al2O3 (PA) with CeO2-X (X=S, I). X-ray diffraction (XRD), BET surface area measurements, and scanning electron microscopy (SEM) were used to characterize the physical structures of the catalysts, while X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR) were employed to identify and quantify the surface Ce3+ concentrations and the amounts of surface-active oxygen. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) was applied to analyze the surface adsorbed NOx species. Compared with CeO2-I, CeO2-S presented superior physico-chemical properties, including higher surface area, richer porous texture, stronger aging-resistance, and higher surface Ce3+ concentration. As a result, the PA+CeO2-S sample also exhibited outstanding NOx trapping capacity. Furthermore, interaction between Pt and CeO2 was observed in the PA+CeO2-X mixtures, which facilitates NO oxidation and the NOx trapping process owing to the accompanying increase in the activity of surface active oxygen on the CeO2. This interaction was stronger in the case of the PA+CeO2-S sample as compared with the PA+CeO2-I. The Ce3+ content and presence of active oxygen species on the CeO2 surface both play critical roles in the NOx trapping process and hydrothermal treatment of the CeO2 significantly decreased the NOx trapping capacity of both PA+CeO2 samples. It was also determined that the interaction between Pt and aged CeO2 is weakened and that the NOx trapping capacity of aged CeO2 is enhanced after loading a small amount of Pt, which is attributed to the promotion of nitrate formation by increased surface oxygen activity.

Key words: NOx storage and reduction catalyst, Ceria material, Pt metal, Lean NOx trap capacity, Physical-chemical property, Surface-active oxygen, Interaction

MSC2000: 

  • O643