Paired redox-acid sites on metal oxide surface with synergistic effect for NH3-SCR of NOx

Fudong  Liu, University of Central Florida

Paired redox-acid sites on metal oxide surface with synergistic effect for NH₃-SCR of NO_x

Ge Song, Shaohua Xie, Fudong Liu*

 Department of Civil, Environmental, and Construction Engineering, Catalysis Cluster for Renewable Energy and Chemical Transformations (REACT), NanoScience Technology Center (NSTC), University of Central Florida, Orlando, Florida 32816, United States

*Corresponding author: fudong.liu@ucf.edu (F. Liu)

 

Selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) is a well-established technology for NO_x removal from industrial flue gas and diesel engine exhaust [1, 2]. Previous studies have reported that metal oxides containing redox species and acid components, such as Fe₂O₃-WO₃, CeO₂-WO₃ and CeO₂-Nb₂O₅, showed remarkably outstanding NH₃-SCR performance, which was ascribed to formation of redox sites and acid sites on catalysts arising from local mixed oxides [3-6]. However, the interaction between redox sites and acid sites especially on the NH₃-SCR catalyst surface has not been investigated systematically. In this study, the synergistic effect between redox sites and acid sites on NH₃-SCR activity of serial catalysts was quantitatively studied.

Herein, the role of redox-acid pair sites was systematically investigated on supported binary oxide catalysts (i.e. CeO₂/WO₃, WO₃/CeO₂, Fe₂O₃/WO₃, WO₃/Fe₂O₃, CeO₂/Nb₂O₅, Nb₂O₅/CeO₂, Fe₂O₃/Nb₂O₅, Nb₂O₅/Fe₂O₃). Catalysts containing different amounts of redox-acid pair sites on the surface were prepared by incipient wet impregnation with fine-tuned loading of acid components or redox components, in which the redox components were loaded onto acid supports or vice versa. Catalysts were characterized by XRD, Raman spectra, H₂-TPR, NH₃/NO_x-TPD, and in situ DRIFTS to quantitatively clarify the effect of surface redox-acid pair sites on catalytic performance. Results indicated a positive correlation between NH₃-SCR and redox-acid pair sites. Based on this research, a comprehensive mechanism contributing to high deNO_x performance in NH₃-SCR resulting from desired redox-acid pair sites is elucidated, providing theoretical guidance to the design of highly efficient non-zeolitic NH₃-SCR catalytic systems.

 

References

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