催化学报

催化学报 ›› 2011, Vol. 32 ›› Issue (5): 736-745.DOI: 10.1016/S1872-2067(10)60230-6

• 研究论文 • 上一篇    下一篇

NOx Reduction on Fully Formulated Lean NOx Trap Catalysts Subjected to Simulated Road Aging: Insights from Steady-State Experiments

Jin WANG, Yaying JI, Uschi GRAHAM, Caio CESAR SPINDOLA DE OLIVEIRA, Mark CROCKER*   

  1. Center for Applied Energy Research, University of Kentucky, Lexington, KY 40511, USA
  • 收稿日期:2011-02-28 修回日期:2011-04-08 出版日期:2011-05-31 发布日期:2014-09-29

NOx Reduction on Fully Formulated Lean NOx Trap Catalysts Subjected to Simulated Road Aging: Insights from Steady-State Experiments

Jin WANG, Yaying JI, Uschi GRAHAM, Caio CESAR SPINDOLA DE OLIVEIRA, Mark CROCKER*   

  1. Center for Applied Energy Research, University of Kentucky, Lexington, KY 40511, USA
  • Received:2011-02-28 Revised:2011-04-08 Online:2011-05-31 Published:2014-09-29

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摘要： Fully formulated lean NOx trap (LNT) catalysts of the type Pt/Rh/BaO/Al2O3 were prepared with and without incorporation of CeO2-ZrO2 in the washcoat, and their NOx reduction behavior was evaluated in steady-state, continuous flow experiments. In the fresh state, CeO2-ZrO2 addition was found to exert little effect on NOx reduction activity using H2, CO, and NH3 as the reductants. However, after simulated road aging, NOx reduction activity was significantly impaired for the CeO2-ZrO2-free catalyst, whereas the performance of the CeO2-ZrO2-containing analog was affected to only a minor degree. These differences are explained on the basis of high-resolution transmission electron microscopy measurements showing that Pt supported on CeO2-ZrO2 remained highly dispersed after aging, whereas Pt supported on BaO/Al2O3 underwent significant sintering. In addition, the Pt/CeO2-ZrO2 component did not accumulate sulfur during aging, unlike Pt/BaO/Al2O3 for which significant sulfation of the Ba phase occurred. For both catalysts, selectivity to NH3 in NO and NO2 reduction by H2 increased after catalyst aging, indicative of a change in the relative surface coverages of N and H ad-atoms on the precious metal sites.

关键词: lean NOx trap, NOx storage-reduction catalyst, steady state, NOx reduction, ceria-zirconia, catalyst aging

Abstract: Fully formulated lean NOx trap (LNT) catalysts of the type Pt/Rh/BaO/Al2O3 were prepared with and without incorporation of CeO2-ZrO2 in the washcoat, and their NOx reduction behavior was evaluated in steady-state, continuous flow experiments. In the fresh state, CeO2-ZrO2 addition was found to exert little effect on NOx reduction activity using H2, CO, and NH3 as the reductants. However, after simulated road aging, NOx reduction activity was significantly impaired for the CeO2-ZrO2-free catalyst, whereas the performance of the CeO2-ZrO2-containing analog was affected to only a minor degree. These differences are explained on the basis of high-resolution transmission electron microscopy measurements showing that Pt supported on CeO2-ZrO2 remained highly dispersed after aging, whereas Pt supported on BaO/Al2O3 underwent significant sintering. In addition, the Pt/CeO2-ZrO2 component did not accumulate sulfur during aging, unlike Pt/BaO/Al2O3 for which significant sulfation of the Ba phase occurred. For both catalysts, selectivity to NH3 in NO and NO2 reduction by H2 increased after catalyst aging, indicative of a change in the relative surface coverages of N and H ad-atoms on the precious metal sites.

Key words: lean NOx trap, NOx storage-reduction catalyst, steady state, NOx reduction, ceria-zirconia, catalyst aging