Structural snapshots of the SCR reaction mechanism on Cu-SSZ-13

Günter, T.; Carvalho, Hudson Wallace Pereira de; Doronkin, Dmitry E.; Sheppard, Thomas L.; Glatzel, Pieter; Atkins, Andrew; Rudolph, Julian; Jacob, Christoph R.; Casapu, Maria; Grunwaldt, Jan‐Dierk

doi:10.1039/c5cc01758k

Cited by 111 publications

(176 citation statements)

References 41 publications

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“…XANES data had earlier shown that NO and NH 3 together are able to reduce Cu 2+ to Cu + at 200 °C [8], confirming earlier findings [9,[59][60][61]. The reduction is reflected in the loss of intensity of the Cu 2+ EPR signal during the same treatment, step…”

Section: In-situ Epr Of Cu-cha In the Scr Reactionsupporting

confidence: 77%

Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

et al. 2016

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Recent quantitative electron paramagnetic resonance spectroscopy (EPR) data on different copper species present in copper exchanged in CHA zeolites are presented and put into context with the literature on other copper zeolites. The information were obtained using ex-situ and in-situ EPR on copper ion exchanged into a CHA zeolite with Si/Al = 14±1 to obtain Cu/Al = 0.46 ±0.02. The results shed light on the identity of different copper species present after activation in air. Since the EPR signal is quantifiable, the content of the different EPR active species has been elucidated and Cu 2+ in 2Al positions in the 6-membered rings (6mr) of the CHA structure has been characterized. sites of the CHA structure under the applied conditions.

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Section: In-situ Epr Of Cu-cha In the Scr Reactionsupporting

confidence: 77%

Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

et al. 2016

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“…These observations indicate a Fe 3+ ↔Fe 2+ redox cycle in Fe-ZSM-5 catalysts similar as the widely accepted Cu 2+ ↔Cu + redox cycle in Cu-SSZ-13 catalysts (Figure 11a) [3,10,11,44,45,54]. More interestingly, the formed NH 4 + intermediates were found to largely determine the NH 3 -SCR activity of Fe-ZSM-5 catalysts at low temperatures ( Figure 11b).…”

Section: Zeolite Framework Typesupporting

confidence: 49%

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

Chen

Simon

2016

Catalysts

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Proton transport is an elementary process in the selective catalytic reduction of nitrogen oxides by ammonia (DeNO x by NH 3 -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 NH 3 -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 NH 3 -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 NH 3 -zeolite interaction, NO-zeolite interaction in the presence of adsorbed NH 3 , or formation of NH 4 + 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 NH 3 -SCR on zeolite catalysts.

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“…Three reference spectra are given in Figure 1, showing the effect on the Cu sites of oxygen, ammonia and their combination. As discussed in more detail earlier [13], Cu is fully oxidized under oxygen flow, but becomes reduced in the presence of ammonia, as the decreased pre-edge feature (specific for Cu 2+ , 3d 9 ) confirms. The intense feature in the rising edge at 8982.7 eV is related to Cu + in linear coordination [7] and is even more pronounced without oxygen.…”

Section: Resultsmentioning

confidence: 67%

“…Gases were dosed with individual mass flow controllers to obtain a gas mixture of 0-1000 ppm NO, 0-1000 ppm NH 3 , 10% O 2 and ~1.5% H 2 O in He and analysed by an FTIR spectrometer (MKS 2030). Further experimental details are given elsewhere [13].…”

Section: Methodsmentioning

confidence: 99%

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HERFD-XANES and XES as complementaryoperandotools for monitoring the structure of Cu-based zeolite catalysts during NO_x-removal by ammonia SCR

Günter

Doronkin

Carvalho

et al. 2016

J. Phys.: Conf. Ser.

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Abstract. In this article, we demonstrate the potential of hard X-ray techniques to characterize catalysts under working conditions. Operando high energy resolution fluorescence detected (HERFD) XANES and valence to core (vtc) X-ray emission spectroscopy (XES) have been used in a spatially-resolved manner to study Cu-zeolite catalysts during the standard-SCR reaction and related model conditions. The results show a gradient in Cu oxidation state and coordination along the catalyst bed as the reactants are consumed. Vtc-XES gives complementary information on the direct adsorption of ammonia at the Cu sites. The structural information on the catalyst shows the suitability of X-ray techniques to understand catalytic reactions and to facilitate catalyst optimization. IntroductionOver the past years, X-ray absorption spectroscopy (XAS) has been successfully applied to elucidate the structure of metal sites in a variety of solid compounds and liquid phase complexes. The application of high energy resolution fluorescence detected -X-ray Absorption Near Edge Structure (HERFD-XANES) spectroscopy offers the possibility to unravel additional spectral features and thus more information on the sample compared to conventional XAS [1,2]. This high resolution is achieved by measuring the fluorescence signal of the Kß-line (3p  1s). The 3p orbitals interact more with the valence 3d and 4p orbitals and therefore show a stronger influence on the environment than the less pronounced mixing of 2p and 3d orbitals, which results in the Kα-line [3]. By selecting a Kß-line as a single fluorescence channel, a higher energy resolution is achieved as the core-hole life-time during the X-ray absorption process can be circumvented [4]. An additional technique to characterize metal sites is X-ray emission spectroscopy (XES), where electrons from an occupied higher orbital are transferred to an empty lower orbital. Information on occupied states is therefore gained by XES, whereas XANES is a long established complementary technique that provides information on the electron transfer to unoccupied states [5]. Particularly the transfer of electrons from valence orbitals provides new insights into the interaction between metal

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Structural snapshots of the SCR reaction mechanism on Cu-SSZ-13

Cited by 111 publications

References 41 publications

Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

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

HERFD-XANES and XES as complementaryoperandotools for monitoring the structure of Cu-based zeolite catalysts during NO_x-removal by ammonia SCR

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Structural snapshots of the SCR reaction mechanism on Cu-SSZ-13

Cited by 111 publications

References 41 publications

Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

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

HERFD-XANES and XES as complementaryoperandotools for monitoring the structure of Cu-based zeolite catalysts during NOx-removal by ammonia SCR

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HERFD-XANES and XES as complementaryoperandotools for monitoring the structure of Cu-based zeolite catalysts during NO_x-removal by ammonia SCR