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Catalysts 2016, 6(12), 204; doi:10.3390/catal6120204

In Situ Spectroscopic Studies of Proton Transport in Zeolite Catalysts for NH3-SCR

Institute of Inorganic Chemistry and Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52074 Aachen, Germany
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Academic Editor: Juan J. Bravo-Suarez
Received: 26 October 2016 / Revised: 8 December 2016 / Accepted: 9 December 2016 / Published: 14 December 2016
(This article belongs to the Special Issue In Situ and Operando Characterization in Catalysis)
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Abstract

Proton transport is an elementary process in the selective catalytic reduction of nitrogen oxides by ammonia (DeNOx by NH3-SCR) using metal-exchanged zeolites as catalysts. This review summarizes recent advancements in the study of proton transport in zeolite catalysts using in situ electrical impedance spectroscopy (IS) under NH3-SCR reaction conditions. Different factors, such as the metal cation type, metal exchange level, zeolite framework type, or formation of intermediates, were found to influence the proton transport properties of zeolite NH3-SCR catalysts. A combination of IS with diffuse reflection infrared Fourier transformation spectroscopy in situ (in situ IS-DRIFTS) allowed to achieve a molecular understanding of the proton transport processes. Several mechanistic aspects, such as the NH3-zeolite interaction, NO-zeolite interaction in the presence of adsorbed NH3, or formation of NH4+ intermediates, have been revealed. These achievements indicate that IS-based in situ methods as complementary tools for conventional techniques (e.g., in situ X-ray absorption spectroscopy) are able to provide new perspectives for the understanding of NH3-SCR on zeolite catalysts. View Full-Text
Keywords: proton transport; impedance spectroscopy; DRIFTS; reaction mechanism; NOx emission control; NH4+ intermediates proton transport; impedance spectroscopy; DRIFTS; reaction mechanism; NOx emission control; NH4+ intermediates
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Chen, P.; Simon, U. In Situ Spectroscopic Studies of Proton Transport in Zeolite Catalysts for NH3-SCR. Catalysts 2016, 6, 204.

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