Composition-Dependent Performance of CexZr1鈥?i>xO2 Mixed-Oxide-Supported WO3 Catalysts for the NOx Storage Reduction鈥揝elective

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• 作者：Fabien Can ; S茅bastien Berland ; S茅bastien Royer ; Xavier Courtois ; Daniel Duprez
• 刊名：ACS Catalysis
• 出版年：2013
• 出版时间：June 7, 2013
• 年：2013
• 卷：3
• 期：6
• 页码：1120-1132
• 全文大小：618K
• 年卷期：v.3,no.6(June 7, 2013)
• ISSN：2155-5435

文摘

WO₃/Ce_xZr_1鈥?i>xO₂ materials were evaluated as a possible NH₃-selective catalytic reduction (SCR) active catalyst in a NO_x storage reduction (NSR) + SCR combined system. The effect of the support composition was investigated at a constant WO₃ loading (9.1 wt % of WO₃). The impact of WO₃ promotion over textural, structural, acid鈥揵ase, and redox properties of SCR samples was characterized by means of nitrogen adsorption鈥揹esorption isotherms, XRD, NO_x storage capacity, NH₃ temperature programmed desporption, pyridine adsorption followed by FTIR, and H₂-TPR. Catalytic activities in NH₃-SCR and NH₃-SCO reactions as well as corresponding kinetics parameters are also discussed. All WO₃/Ce鈥揨r materials are active and fully selective in N₂ for NO_x reduction by NH₃ and ammonia oxidation by O₂. For the SCR reaction, the rate of NO conversion is found approximately half-order with respect to NO, and negative to nearly zero-order with respect to NH₃. Tungstated ceria鈥搝irconia materials were then associated downstream with a model Pt鈥揃a/Al NSR catalyst. Whatever the WO₃鈥揅e/Zr catalyst, the global NO_x conversion and N₂ yield are significantly enhanced by the addition of the SCR catalyst. Special attention is paid to the influence of the ceria content of the SCR catalyst on the ammonia reactivity in the combined NSR + SCR system. It is demonstrated that NH₃ produced during the regeneration step of Pt鈥揃a/Al catalyst can react either with NO_x (NH₃-SCR) or with O₂ (NH₃-SCO). This reactivity depends both on the Ce/Zr ratio of support and on the temperature. Finally, it is demonstrated that at high temperature (i.e., 400 掳C), the strength of the acid sites of the WO₃鈥揅e/Zr catalysts is not sufficient to ensure no ammonia slip.

Keywords:

NO_x; NH₃; SCR; NSR; tungsten; WO₃/Ce_xZr_1鈭?i>xO₂