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Open AccessArticle

Mobility of NH3-Solvated CuII Ions in Cu-SSZ-13 and Cu-ZSM-5 NH3-SCR Catalysts: A Comparative Impedance Spectroscopy Study

1
Institute of Inorganic Chemistry (IAC), RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
2
Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
*
Authors to whom correspondence should be addressed.
Catalysts 2018, 8(4), 162; https://doi.org/10.3390/catal8040162
Received: 14 March 2018 / Revised: 8 April 2018 / Accepted: 9 April 2018 / Published: 18 April 2018
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
The mobility of NH3-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NOx with NH3 (NH3-SCR) over Cu-zeolite catalysts at low temperatures. Here, we utilize in situ impedance spectroscopy to explore the mobility of NH3-solvated CuII ions, i.e., CuII(NH3)n, in Cu-SSZ-13 and Cu-ZSM-5 zeolites with varied Cu ion exchange levels, and observed that both the zeolite framework (CHA or MFI) and the Cu exchange level influence the high-frequency dielectric relaxation processes that are associated with the short-range (local) motion of CuII(NH3)n. Our results suggest that the local motion of CuII(NH3)n species is favored within the CHA framework due to the unique cage structure, and thereby contribute to the overall ion conductivity at high frequencies, which, on the contrary, is not observed for ZSM-5, where NH3-solvated Cu2+ ions do not experience a comparable constrained space for local motion. This study sheds new light on the mobility of Cu active sites under NH3-SCR related reaction conditions and may contribute to an advanced understanding of the underlying mechanism. View Full-Text
Keywords: selective catalytic reduction of NOx; impedance spectroscopy; Cu-SSZ-13 zeolite; Cu-ZSM-5 zeolite selective catalytic reduction of NOx; impedance spectroscopy; Cu-SSZ-13 zeolite; Cu-ZSM-5 zeolite
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MDPI and ACS Style

Rizzotto, V.; Chen, P.; Simon, U. Mobility of NH3-Solvated CuII Ions in Cu-SSZ-13 and Cu-ZSM-5 NH3-SCR Catalysts: A Comparative Impedance Spectroscopy Study. Catalysts 2018, 8, 162.

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