Promotional effect of ion-exchanged K on the low-temperature hydrothermal stability of Cu/SAPO-34 and its synergic application with Fe/Beta catalysts

doi:10.1007/s11783-020-1322-1

Front. Environ. Sci. Eng.

2021, Vol. 15

Issue (2) : 30 https://doi.org/10.1007/s11783-020-1322-1

RESEARCH ARTICLE

Promotional effect of ion-exchanged K on the low-temperature hydrothermal stability of Cu/SAPO-34 and its synergic application with Fe/Beta catalysts

Chen Wang^1,², Jun Wang¹, Jianqiang Wang¹, Meiqing Shen¹(

)

¹. School of Chemical Engineering & Technology, Key Laboratory for Green Chemical Technology of State Education Ministry, Tianjin University, Tianjin 300072, China
². School of Environment and Safety Engineering, North University of China, Taiyuan 030051, China

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Abstract

• K⁺ hinder the structural degradation of Cu/SAPO-34 under humid condition<100°C.

• K⁺ on Cu/SAPO-34 brings lower acidity and inferior SCR activity at high temperature.

• Fe/Beta was used to compensate the low activity of Cu/SAPO-34 at high temperature.

• The hybrid catalysts with KCu/SAPO-34 and Fe/Beta show a great potential for using.

K ions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging. The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction (SCR) activity. For the fresh Cu/SAPO-34 catalysts, K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites. After hydrothermal aging, the structural integrity and amount of active sites decreased on pure Cu/SAPO-34. While the K-loaded catalysts showed improved chabazite structure, acidity, and active site conservation with increasing K loading. However, although the 0.7 wt% K catalyst maintained the same crystallinity, active site abundance, and low-temperature SCR activity as the fresh catalyst upon aging, an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Brönsted acid sites. To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature, Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34, and a wide active temperature window of SCR activity was obtained. Thus, our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NO_x in real-world applications.

Keywords Selective catalytic reduction Cu/SAPO-34 catalyst Ion-exchanged K Low-temperature hydrothermal stability Fe/Beta catalyst

Corresponding Author(s): Meiqing Shen

Issue Date: 08 September 2020

Cite this article:

Chen Wang,Jun Wang,Jianqiang Wang, et al. Promotional effect of ion-exchanged K on the low-temperature hydrothermal stability of Cu/SAPO-34 and its synergic application with Fe/Beta catalysts[J]. Front. Environ. Sci. Eng., 2021, 15(2): 30.

URL:

https://academic.hep.com.cn/fese/EN/10.1007/s11783-020-1322-1
https://academic.hep.com.cn/fese/EN/Y2021/V15/I2/30

Tab.1 Specific surface areas and K contents over pure and K loaded samples before and after low-temperature hydrothermal aging

Tab.2 Cu and K contents over pure and K loaded samples ^a)

Fig.1 (a) XRD pattern of pure and K contained catalysts before (solid line) and after (dash line) aging and (b) the relative crystallinity from XRD patterns.

Fig.2 The ex-situ DRIFTs results of pure and K loaded catalysts before (solid line) and after (dash line) hydrothermal aging. (a) units in absorbance and (b) Kubelka-Munk.

Fig.3 ²⁷Al (a), ³¹P (b) and ²⁹Si (c) NMR results of pure and K contained catalysts before (solid line) and after (dash line) aging.

Fig.4 (a) NH₃-TPD results of pure and K contained catalysts before (solid line) and after (dash line) aging; (b) the relative acidity from NH₃-TPD results.

Fig.5 (a) The H₂-TPR profiles and (b) qualitative data of pure and K contained catalysts before (solid line) and after (dash line) aging.

Fig.6 (a) The EPR results of pure and K contained catalysts before (solid line) and after (dash line) aging and (b) the quantitative results from EPR results.

Fig.7 NO_x conversion during standard SCR reaction over pure and K contained catalysts before (solid line) and after (dash line) aging.

Fig.8 (a) The conservation of SCR activity as a function of Cu²⁺ preservation at 200°C; (b) The conservation of SCR activity as a function of acidity preservation at 200°C; (c) The conservation of SCR activity as a function of Cu²⁺ preservation at 500°C; (d) The conservation of SCR activity as a function of acidity preservation at 500°C.

Fig.9 Conversion of NO_x during standard SCR reaction over the monolith catalysts.

Fig.10 Conversion of NO_x during standard SCR reaction over hybrid catalysts.

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