Mössbauer Spectroscopy in Heterogeneous Catalysis

Millet, J.M.M.

doi:10.1016/s0360-0564(06)51006-5

Cited by 37 publications

(9 citation statements)

References 190 publications

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“…, Fe, Sn, Au, Ru, Ir, etc .) in single-atom catalysts. , For example, using 57 Fe Mössbauer spectroscopy, Fe(III) and Fe(II) species can be clearly distinguished and the presence of Fe crystalline structures ( e.g. , α-Fe, γ-Fe, and Fe x C) can be assessed, as demonstrated for Fe/NC SACs. , …”

Section: Synthesis and Characterization Of Single-atom Catalystsmentioning

confidence: 99%

Single-Atom Catalysts across the Periodic Table

et al. 2020

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Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom−host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

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Section: Synthesis and Characterization Of Single-atom Catalystsmentioning

confidence: 99%

Single-Atom Catalysts across the Periodic Table

et al. 2020

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“…[66] To briefly review the key points of discussion, in D 4h symmetry the two lowest lying triplet states are 3 A 2g with a d-orbital occupation pattern of (xy) 2 (z 2 ) 2 (xz) 1 (yz) 1 (x 2 − y 2 ) 0 and 3 E g with degenerate (xy) 2 (z 2 ) 1 (xz) 2 (yz) 1 (x 2 − y 2 ) 0 or (xy) 2 (z 2 ) 1 (xz) 1 (yz) 2 (x 2 − y 2 ) 0 configurations. Additionally, there is a low-lying 5 A 2g state, and it is difficult to predict the energetic gap between the correct triplet ground state and the higher lying triplet and quintet states. However, for the purpose of estimating the uncertainty of Mössbauer parameter predictions, the key point here is not whether the energetic separation of triplet and quintet states is predicted with quantitative accuracy, but how good the quality of the predicted electron density for the specific triplet states is in comparison with experimental data and in relation to the calibration line.…”

Section: Complicated Electronic Structuresmentioning

confidence: 99%

“…Mössbauer spectroscopy is of central importance for studying the electronic structures of iron in diverse environments: from mononuclear coordination complexes in frozen solution, to inorganic cofactors in enzymes, to iron sites in bulk materials and catalytically active sites on surfaces or amorphous materials. [1][2][3][4][5][6][7][8][9] The experimental study of iron in such systems is often complemented with a computational analysis, chiefly via density functional theory (DFT). As a result, the oxidation and spin states of the iron ion, its coordination number, and the composition and symmetry of its immediate environment can be pinpointed.…”

Section: Introductionmentioning

confidence: 99%

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Gallenkamp

Kramm

Proppe

et al. 2020

Int J of Quantum Chemistry

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Single-atom catalysts with iron ions in the active site, known as FeNC catalysts, show high activity for the oxygen reduction reaction and hence hold promise for access to low-cost fuel cells. Because of the amorphous, multiphase structure of the FeNC catalysts, the iron environment and its electronic structure are poorly understood. While it is widely accepted that the catalytically active site contains an iron ion ligated by several nitrogen donors embedded in a graphene-like plane, the exact structural details, such as the presence or nature of axial ligands, are unknown. Computational chemistry in combination with Mössbauer spectroscopy can help unravel the geometric and electronic structures of the active sites. As a first step toward this goal, we present a calibration of computational Mössbauer spectroscopy for FeN 4-like environments. The uncertainty of both the isomer shift and the quadrupole splitting prediction is determined, from which trust regions for the Mössbauer parameter predictions of computational FeNC models are derived. We find that TPSSh, B3LYP, and PBE0 perform equally well; the trust regions with B3LYP are 0.13 mm s −1 for the isomer shift and 0.36 mm s −1 for the quadrupole splitting. The calibration data is made publicly available in an interactive notebook that provides predicted Mössbauer parameters with individual uncertainty estimates from computed contact densities and quadrupole splitting values. We show that a differentiation of common FeNC Mössbauer signals by a separate analysis of isomer shift and quadrupole splitting will most likely be insufficient, whereas their simultaneous evaluation will allow the assignment to adequate computational FeNC models.

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“…In general, the applications of MES on iron containing materials fall in one of the five categories, such as phase identification (iron oxides or iron carbides), determination of oxidation states, structure information, particle size determination, and kinetics of bulk transformations 24 . The hyperfine parameters extracted from spectral analysis can yield detailed local electronic, magnetic, structural, and chemical information on Fe atoms in samples 25 26 . For example, the Mössbauer spectrum of χ-Fe 5 C 2 is usually fitted with three sextets that correspond to the three crystallographic sites of the structure that may be occupied by the iron atoms, thus leading to a different atomic environment for each of them 27 .…”

mentioning

confidence: 99%

Mössbauer Spectroscopy of Iron Carbides: From Prediction to Experimental Confirmation

Liu

Zhao

Meng

et al. 2016

Sci Rep

110

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The Mössbauer spectroscopy of iron carbides (α-Fe, γ'-FeC, η-Fe2C, ζ-Fe2C, χ-Fe5C2, h-Fe7C3, θ-Fe3C, o-Fe7C3, γ'-Fe4C, γ''-Fe4C, and α'-Fe16C2) is predicted utilizing the all electron full-potential linearized augmented plane wave (FLAPW) approach across various functionals from LDA to GGA (PBE, PBEsol, and GGA + U) to meta-GGA to hybrid functionals. To validate the predicted MES from different functionals, the single-phase χ-Fe5C2 and θ-Fe3C are synthesized in experiment and their experimental MES under different temperature (from 13 K to 298 K) are determined. The result indicates that the GGA functional (especially, the PBEsol) shows remarkable success on the prediction of Mössbauer spectroscopy of α-Fe, χ-Fe5C2 and θ-Fe3C with delocalized d electrons. From the reliable simulations, we propose a linear relationship between Bhf and μB with a slope of 12.81 T/μB for iron carbide systems and that the proportionality constant may vary from structure to structure.

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Mössbauer Spectroscopy in Heterogeneous Catalysis

Cited by 37 publications

References 190 publications

Single-Atom Catalysts across the Periodic Table

Single-Atom Catalysts across the Periodic Table

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Mössbauer Spectroscopy of Iron Carbides: From Prediction to Experimental Confirmation

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