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Frontiers of Materials Science

Front. Mater. Sci.    2016, Vol. 10 Issue (2) : 211-223     DOI: 10.1007/s11706-016-0331-2
RESEARCH ARTICLE |
Study on the mechanism of NH3-selective catalytic reduction over CuCexZr1--<?Pub Caret?>x/TiO2
Xujuan CHEN1,Xiaoliang SUN1,Cairong GONG1,*(),Gang LV2,Chonglin SONG2
1. School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China
2. State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
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Abstract

Copper--cerium--zirconium catalysts loaded on TiO2 prepared by a wet impregnation method were investigated for NH3-selective catalytic reduction (SCR) of NOx. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH3 is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe0.25Zr0.75/TiO2 at high temperature, while Br?nsted acid sites are more important than Lewis acid sites at low temperature. For the NH3+NO+O2 co-adsorption, NH3 species occupy most of activity sites on CuCe0.25Zr0.75/TiO2 catalyst, and mainly exist in the forms of NH4+ (at low temperature) and NH3 coordinated (at high temperature), playing a crucial role in the NH3-SCR process. Two different reaction routes, the L-H mechanism at low temperature (<200°C) and the E-R mechanism at high temperature (>200°C), are presented for the SCR reaction over CuCe0.25Zr0.75/TiO2 catalyst.

Keywords CuCe0.25Zr0.75/TiO2      catalyst      selective catalytic reduction (SCR)      diffuse reflectance infrared transform spectroscopy (DRIFT)      reaction mechanism     
Corresponding Authors: Cairong GONG   
Issue Date: 11 May 2016
 Cite this article:   
Xujuan CHEN,Xiaoliang SUN,Cairong GONG, et al. Study on the mechanism of NH3-selective catalytic reduction over CuCexZr1--<?Pub Caret?>x/TiO2[J]. Front. Mater. Sci., 2016, 10(2): 211-223.
 URL:  
http://journal.hep.com.cn/foms/EN/10.1007/s11706-016-0331-2
http://journal.hep.com.cn/foms/EN/Y2016/V10/I2/211
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Xujuan CHEN
Xiaoliang SUN
Cairong GONG
Gang LV
Chonglin SONG
Fig.1  NH3-TPD curves of CuCexZr1-x/TiO2 catalysts.
Fig.2  NO-TPD curves of CuCexZr1-x/TiO2 catalysts.
Fig.3  DRIFT spectra of the CuCe0.25Zr0.75/TiO2 catalyst arising from NH3 adsorption at 50°C (a), 150°C (b), 200°C (c), 250°C (d), 300°C (e), 350°C (f), and 400°C (g).
Fig.4  DRIFT spectra of the CuCe0.25Zr0.75/TiO2 catalyst arising from the NO+O2 co-adsorption at 50°C (a), 150°C (b), 200°C (c), 250°C (d), 300°C (e), 350°C (f), and 400°C (g).
Fig.5  DRIFT spectra of the CuCe0.25Zr0.75/TiO2 catalyst pre-treated by exposure to NH3 followed by exposure to NO+O2 at (a) 170°C and (b) 375°C for various time.
Fig.6  DRIFT spectra of the CuCe0.25Zr0.75/TiO2 catalyst pre-treated by exposure to NO+O2 followed by exposure to NH3 at (a) 170°C and (b) 375°C for various time.
Fig.7  DRIFT spectra of the CuCe0.25Zr0.75/Ti catalyst arising from the NH3+NO+O2 co-adsorption at 50°C (a), 100°C (b), 150°C (c), 200°C (d), 250°C (e), 300°C (f), 350°C (g), and 400°C (h).
Fig.1  Catalytic activities for the NOx reduction by NH3 on CuCexZr1-x/TiO2 catalysts.
Fig.2  The yield of N2O as a function of reaction temperature for CuCexZr1-x/TiO2 catalysts.
Fig.1  

(a) The stability and effects of (b) SO2 and (c) H2O on the SCR of NOx with NH3 over CuCe0.25Zr0.75/TiO2 catalyst.

<?Pub Caret?>
Fig.1  TEM images and EDX analyses for the Cu/TiO2 catalyst and the CuCe0.25Zr0.75/TiO2 catalyst.
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