Metal Loading Affects the Proton Transport Properties and the Reaction Monitoring Performance of Fe-ZSM-5 and Cu-ZSM-5 in NH₃-SCR

Titelangaben

Chen, Peirong ; Moos, Ralf ; Simon, Ulrich:
Metal Loading Affects the Proton Transport Properties and the Reaction Monitoring Performance of Fe-ZSM-5 and Cu-ZSM-5 in NH₃-SCR.
In: The Journal of Physical Chemistry C. Bd. 120 (2016) Heft 44 . - S. 25361-25370.
ISSN 1932-7455
DOI: https://doi.org/10.1021/acs.jpcc.6b07353

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Abstract

Metal-promoted zeolites are widely applied as catalysts for the selective catalytic reduction of nitrogen oxide by NH3 (NH3-SCR). Here, we describe a systematic study on the proton transport properties of Fe-ZSM-5 and Cu-ZSM-5 NH3-SCR catalysts with different metal loadings. By means of in situ impedance spectroscopy (IS), we revealed the different influence of exchanged Fe and Cu on the NH3-supported proton transport in different atmospheres (N2 and NO/O2) and, consequently, on the monitoring of the NH3-SCR reaction using the zeolite catalysts directly as sensors. On the one hand, the mobility of adsorbed NH3 species as proton carriers, determined by the NH3–zeolite interaction, was influenced differently by Fe and Cu and their loadings. While the increase of Fe loading weakened slightly the NH3–zeolite interaction, a higher Cu loading enhanced significantly the NH3–zeolite interaction. On the other hand, highly proton-conducting ammonium ion (NH4+) intermediates, as unveiled by IS combined with DRIFTS, formed on Cu-ZSM-5 due to NO–NH3 coadsorption and influenced the proton transport properties significantly in a complex manner. This systematic study thus not only clarifies several mechanistic aspects for NH3-SCR monitoring using zeolite catalyst directly as sensor but also provides new perspectives to understand mechanistically the NH3-SCR reaction over Fe– and Cu–zeolite catalysts.