Determination of the Redox Processes in FeBEA Catalysts in NH<sub>3</sub>−SCR Reaction by Mössbauer and X-ray Absorption Spectroscopy

Maier, Sarah; Jentys, Andreas; Metwalli, Ezzeldin; Müller‐Buschbaum, Peter; Lercher, Johannes A.

doi:10.1021/jz200313c

Cited by 25 publications

(51 citation statements)

References 40 publications

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Section: Selected Operando Methodsmentioning

confidence: 99%

“…Prime examples of operando applications encompass reforming, hydrodesulfurization (HDS), hydrogenation, selective oxidation, and automotive catalysis, covering a wide range of materials (e.g., zeolites, sulfides, oxides, supported transition and noble metal clusters/ nanoparticles). [51][52][53][54][55]85,[126][127][128][129][130][131] In XAS, the X-ray energy is tuned over an absorption edge and the photoelectron (wave) created at an atom scatters at neighboring atom(s), with the interference modulating the absorption cross-section above the excitation threshold. While XANES (X-ray Absorption Near-Edge Structure; near-edge region up to ≈100 eV post-edge) provides information on phases, atomic/electronic structure and oxidation states, EXAFS (Extended X-ray Absorption Fine Structure; ≈100-800 eV postedge) indicates exact bond lengths and coordination numbers (as a limitation, adsorbed molecules cannot be detected, though).…”

Section: X-ray Absorption Spectroscopy (Xas: Xanes and Exafs)mentioning

confidence: 99%

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Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Rupprechter

2021

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described as metal dispersion (number of metal surface atoms relative to the total number of metal atoms in the catalyst), whereas the support is characterized by the specific surface area (m 2 g −1). For hemispherical metal particles of ≈1.5, 2, 5, and 10 nm diameter, the dispersion is about 0.8, 0.6, 0.3, and 0.1, respectively, illustrating why the nanoscale is required not to waste precious metal inside the particles. The ultimate dispersion is, of course, provided by single metal atoms and this concept is followed in "single atom catalysis" or "single site catalysis". [10-17] However, the adsorption and reaction steps of a catalytic reaction do typically not occur on isolated single atoms, but also involve neighboring sites, for example, of the oxide support [18] or of a metal matrix (for bimetallic nanoparticles, active metal atoms may be embedded in an inert or less-active metal matrix [11,19-23]). The so-called site isolation of active atoms may prevent CC bond cleavage (coking), which requires at least two neighboring active metals. In any case, the stability of the single atoms is the key challenge, as atoms may diffuse and sinter. Furthermore, for example, Pt, Pd, Cu, or Au atoms are mobilized by CO, [24-28] forming CO-M 1 units that may eventually sinter into larger clusters. Herein, we define metal clusters as entities with less than ≈100 atoms, characterizing the so-called "non-scalable" regime (Figure 1a). [29] Their atomic and electronic structure is significantly different from that of bulk metals, for example, with respect to atom positions (icosahedral vs face centered cubic fcc), distances (lattice contraction or expansion), and band structure (semiconductor vs metal). Clearly, these properties are size-dependent ("each atom counts" [30,31]), with pronounced impact on adsorption and reaction properties. [5,32] Accordingly, nanoparticles with more than ≈100 atoms are in the "scalableregime" and start to have or exhibit bulk atomic and electronic structure. [6,32-34] Nevertheless, the relative contributions of corner, edge, step, terrace and phase boundary sites on the surface of a nanoparticle (Figure 1b,c) are still size-dependent. [35,36] Meso-scale ("black") powders of metals are clearly bulk-like and have very low dispersion (Figure 1d), but the µm-sized aggregates still consist of adjoining nanocrystals with structured surfaces, comparable to that of true nanoparticles. Operando characterization of working catalysts, requiring per definitionem the simultaneous measurement of catalytic performance, is crucial to identify the relevant catalyst structure, composition and adsorbed species. Frequently applied operando techniques are discussed, including X-ray absorption spectroscopy, near ambient pressure X-ray photoelectron spectroscopy and infrared spectroscopy. In contrast to these area-averaging spectroscopies, operando surface microscopy by photoemission electron microscopy delivers spatially-resolved data, directly visualizing catalyst heterogeneity. For thorough interpretation, the exper...

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Section: Selected Operando Methodsmentioning

confidence: 99%

Section: X-ray Absorption Spectroscopy (Xas: Xanes and Exafs)mentioning

confidence: 99%

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Rupprechter

2021

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“…Variogram-based pre-edge analysis will be in general a valuable approach in XAS studies, e.g. those reported by Høj et al (2009), Klukowski et al (2009), Maier et al (2011), Bordiga et al (2013), Liu et al (2013Liu et al ( , 2014, Tepluchin et al (2014) and Doronkin et al (2014b), providing further information about oxidation state and geometry also under operando conditions.…”

Section: Evolution Of Fe Species In 1% Fe/al 2 O 3 and 05% Fe/bea Camentioning

confidence: 99%

“…Another established method is the use of the edge position (Berry et al, 2003;Maier et al, 2011), as this is directly affected by the oxidation state. This method has its advantages when pre-edge analysis becomes difficult due to the low intensity of the pre-edge peak occurring for octahedrally coordinated Fe and a high noise level (Maier et al, 2011). In fact, the pre-edge method suffers when analysing low-intensity pre-edge spectra due to distortions in the preedge variogram (Fig.…”

Section: Evolution Of Fe Species In 1% Fe/al 2 O 3 and 05% Fe/bea Camentioning

confidence: 99%

Identification of the iron oxidation state and coordination geometry in iron oxide- and zeolite-based catalysts using pre-edge XAS analysis

et al. 2015

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Analysis of the oxidation state and coordination geometry using pre-edge analysis is attractive for heterogeneous catalysis and materials science, especially for in situ and time-resolved studies or highly diluted systems. In the present study, focus is laid on iron-based catalysts. First a systematic investigation of the pre-edge region of the Fe K-edge using staurolite, FePO4, FeO and α-Fe2O3 as reference compounds for tetrahedral Fe(2+), tetrahedral Fe(3+), octahedral Fe(2+) and octahedral Fe(3+), respectively, is reported. In particular, high-resolution and conventional X-ray absorption spectra are compared, considering that in heterogeneous catalysis and material science a compromise between high-quality spectroscopic data acquisition and simultaneous analysis of functional properties is required. Results, which were obtained from reference spectra acquired with different resolution and quality, demonstrate that this analysis is also applicable to conventionally recorded pre-edge data. For this purpose, subtraction of the edge onset is preferentially carried out using an arctangent and a first-degree polynomial, independent of the resolution and quality of the data. For both standard and high-resolution data, multiplet analysis of pre-edge features has limitations due to weak transitions that cannot be identified. On the other hand, an arbitrary empirical peak fitting assists the analysis in that non-local transitions can be isolated. The analysis of the oxidation state and coordination geometry of the Fe sites using a variogram-based method is shown to be effective for standard-resolution data and leads to the same results as for high-resolution spectra. This method, validated by analysing spectra of reference compounds and their well defined mixtures, is finally applied to track structural changes in a 1% Fe/Al2O3 and a 0.5% Fe/BEA zeolite catalyst during reduction in 5% H2/He. The results, hardly accessible by other techniques, show that Fe(3+) is transformed into Fe(2+), while the local Fe-O coordination number of 4-5 is maintained, suggesting that the reduction involves a rearrangement of the oxygen neighbours rather than their removal. In conclusion, the variogram-based analysis of Fe K-edge spectra proves to be very useful in catalysis research.

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“…Fe-containing zeolites (e.g., Fe-ZSM-5) are very useful as catalysts for a variety of reactions, including selective oxidation of methane to methanol [1][2][3], selective oxidation of benzene to phenol by N 2 O [4][5][6][7][8], oxidative dehydrogenation of alkanes [9][10][11], Fenton oxidation [12,13], selective reduction of NO x by hydrocarbons [14][15][16][17] or NH 3 [18][19][20][21], and decomposition of N 2 O [22][23][24][25][26][27][28][29][30][31]. The catalytic decomposition of N 2 O is important, because N 2 O is a potent greenhouse gas with a global warming potential 310 times that of CO 2 , and it also contributes to ozone layer depletion [32,33].…”

Section: Introductionmentioning

confidence: 99%

Catalytic decomposition of N2O over Fe-ZSM-11 catalysts prepared by different methods: Nature of active Fe species

Xie

Luo

Ma³

et al. 2015

Journal of Catalysis

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Determination of the Redox Processes in FeBEA Catalysts in NH₃−SCR Reaction by Mössbauer and X-ray Absorption Spectroscopy

Cited by 25 publications

References 40 publications

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Identification of the iron oxidation state and coordination geometry in iron oxide- and zeolite-based catalysts using pre-edge XAS analysis

Catalytic decomposition of N2O over Fe-ZSM-11 catalysts prepared by different methods: Nature of active Fe species

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Determination of the Redox Processes in FeBEA Catalysts in NH3−SCR Reaction by Mössbauer and X-ray Absorption Spectroscopy

Cited by 25 publications

References 40 publications

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Identification of the iron oxidation state and coordination geometry in iron oxide- and zeolite-based catalysts using pre-edge XAS analysis

Catalytic decomposition of N2O over Fe-ZSM-11 catalysts prepared by different methods: Nature of active Fe species

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Determination of the Redox Processes in FeBEA Catalysts in NH₃−SCR Reaction by Mössbauer and X-ray Absorption Spectroscopy