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Chen Z, Walsh AG, Zhang P. Structural Analysis of Single-Atom Catalysts by X-ray Absorption Spectroscopy. Acc Chem Res 2024. [PMID: 38334075 DOI: 10.1021/acs.accounts.3c00693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
ConspectusMetal nanoparticles (NPs) are one of the most frequently used heterogeneous catalysts. However, only the surface atoms in the NPs can participate in catalytic reactions. To maximize the atomic efficiency, the active sites can be reduced to single atoms. Generally, catalysts that have isolated metal atoms on the surface of a support are called single-atom catalysts (SACs). Many techniques have been developed and applied to probe the structures of SACs. Nevertheless, the structural characterization of SACs is still challenging as it requires the analysis of their structure and properties with atomic and sometimes even subatomic resolution. X-ray absorption spectroscopy (XAS) is a powerful tool in investigating the local coordination environment of SACs since it is element-specific and can provide accurate structural information at the subatomic level (∼0.01 Å).In this Account, we present our perspectives on the structural analysis of SACs from some unique features in the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). We first highlight the importance of the XANES peak features in the sensitive analysis of SAC structures. Such analysis is illustrated to be even more useful in the joint applications of experimental and theoretical XAS. The inspection of the metal-metal (M-M) peak in Fourier transformed EXAFS (FT-EXAFS) spectra is a widely used method to identify the single-atom structure, but this method is not always reliable. Thus, we point out the importance of fitting EXAFS and the thorough interpretation of structural parameters such as coordination numbers (CNs, the number of neighboring atoms next to a chosen atom), bond distances, and the Debye-Waller factor (σ2). The small FT-EXAFS peak for the M-M shell is often ignored in the structural analysis of SACs. Here, it is demonstrated that a careful analysis of these small peaks could help more reliably analyze the SAC structure, and it would be particularly useful in the analysis of a single-atom alloy (SAA). Next, the usefulness of bond distance and σ2 analysis is highlighted, and such analysis is shown to be particularly helpful for the analysis of SAAs, which is rarely discussed in the literature. Given the advantage that XAS data can be collected under various conditions, we show that in situ XAS can provide important information about the catalytic mechanism of the SAC catalyst. In particular, we emphasize the significance of using an advanced in situ technique to extract detailed structural information that is difficult to obtain from regular XAS experiments. Finally, we highlight the importance of jointly using XAS with other complementary methods in a more complete understanding of the structure and properties of SACs. It is anticipated that with further development of XAS techniques and improved data analysis, XAS will become even more powerful in providing insights into the structure-property relationships of SACs, which can advance their practical applications.
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Affiliation(s)
- Ziyi Chen
- Department of Chemistry, Dalhousie University, 6274 Coburg Road, Halifax, Nova Scotia B3H 4R2, Canada
| | - Andrew G Walsh
- Department of Chemistry, Dalhousie University, 6274 Coburg Road, Halifax, Nova Scotia B3H 4R2, Canada
| | - Peng Zhang
- Department of Chemistry, Dalhousie University, 6274 Coburg Road, Halifax, Nova Scotia B3H 4R2, Canada
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Wittkämper H, Hock R, Weißer M, Dallmann J, Vogel C, Raman N, Tacardi N, Haumann M, Wasserscheid P, Hsieh TE, Maisel S, Moritz M, Wichmann C, Frisch J, Gorgoi M, Wilks RG, Bär M, Wu M, Spiecker E, Görling A, Unruh T, Steinrück HP, Papp C. Isolated Rh atoms in dehydrogenation catalysis. Sci Rep 2023; 13:4458. [PMID: 36932106 PMCID: PMC10023779 DOI: 10.1038/s41598-023-31157-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 03/07/2023] [Indexed: 03/19/2023] Open
Abstract
Isolated active sites have great potential to be highly efficient and stable in heterogeneous catalysis, while enabling low costs due to the low transition metal content. Herein, we present results on the synthesis, first catalytic trials, and characterization of the Ga9Rh2 phase and the hitherto not-studied Ga3Rh phase. We used XRD and TEM for structural characterization, and with XPS, EDX we accessed the chemical composition and electronic structure of the intermetallic compounds. In combination with catalytic tests of these phases in the challenging propane dehydrogenation and by DFT calculations, we obtain a comprehensive picture of these novel catalyst materials. Their specific crystallographic structure leads to isolated Rhodium sites, which is proposed to be the decisive factor for the catalytic properties of the systems.
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Affiliation(s)
- Haiko Wittkämper
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Rainer Hock
- Lehrstuhl für Kristallographie und Strukturphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstr. 3, 91058, Erlangen, Germany
| | - Matthias Weißer
- Lehrstuhl für Kristallographie und Strukturphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstr. 3, 91058, Erlangen, Germany.
| | - Johannes Dallmann
- Lehrstuhl für Kristallographie und Strukturphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstr. 3, 91058, Erlangen, Germany
| | - Carola Vogel
- Lehrstuhl für Kristallographie und Strukturphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstr. 3, 91058, Erlangen, Germany
| | - Narayanan Raman
- Lehrstuhl für Chemische Reaktionstechnik (CRT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Nicola Tacardi
- Lehrstuhl für Chemische Reaktionstechnik (CRT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Marco Haumann
- Lehrstuhl für Chemische Reaktionstechnik (CRT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Peter Wasserscheid
- Lehrstuhl für Chemische Reaktionstechnik (CRT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany.,Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Tzung-En Hsieh
- Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 12489, Berlin, Germany.,Energy Materials In-Situ Laboratory Berlin (EMIL), HZB, 12489, Berlin, Germany
| | - Sven Maisel
- Lehrstuhl für Theoretische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Michael Moritz
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Christoph Wichmann
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Johannes Frisch
- Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 12489, Berlin, Germany.,Energy Materials In-Situ Laboratory Berlin (EMIL), HZB, 12489, Berlin, Germany
| | - Mihaela Gorgoi
- Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 12489, Berlin, Germany.,Energy Materials In-Situ Laboratory Berlin (EMIL), HZB, 12489, Berlin, Germany
| | - Regan G Wilks
- Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 12489, Berlin, Germany.,Energy Materials In-Situ Laboratory Berlin (EMIL), HZB, 12489, Berlin, Germany
| | - Marcus Bär
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany.,Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 12489, Berlin, Germany.,Energy Materials In-Situ Laboratory Berlin (EMIL), HZB, 12489, Berlin, Germany.,Department X-Ray Spectroscopy at Interfaces of Thin Films, Helmholtz Institute for Renewable Energy (HI ERN), 12489, Berlin, Germany
| | - Mingjian Wu
- Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung), Cauerstraße 3, 91058, Erlangen, Germany
| | - Erdmann Spiecker
- Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung), Cauerstraße 3, 91058, Erlangen, Germany
| | - Andreas Görling
- Lehrstuhl für Theoretische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Tobias Unruh
- Lehrstuhl für Kristallographie und Strukturphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstr. 3, 91058, Erlangen, Germany
| | - Hans-Peter Steinrück
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany
| | - Christian Papp
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstr. 3, 91058, Erlangen, Germany. .,Physikalische und Theoretische Chemie, Freie Universität Berlin, Arnimallee 22, 14195, Berlin, Germany.
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Zhang W, Fu Q, Luo Q, Sheng L, Yang J. Understanding Single-Atom Catalysis in View of Theory. JACS AU 2021; 1:2130-2145. [PMID: 34977885 PMCID: PMC8715482 DOI: 10.1021/jacsau.1c00384] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Indexed: 05/20/2023]
Abstract
In the past decade, isolated single atoms have been successfully dispersed on various substrates, with their potential applications being intensively investigated in different reactions. While the essential target of research in single-atom catalysis is the precise synthesis of stable single-atom catalysts (SACs) with clear configurations and impressive catalytic performance, theoretical investigations have also played important roles in identifying active sites, revealing catalytic mechanisms, and establishing structure-activity relationships. Nevertheless, special attention should still be paid in theoretical works to the particularity of SACs. In this Perspective, we will summarize the theoretical progress made on the understanding of the rich phenomena in single-atom catalysis. We focus on the determination of local structures of SACs via comparison between experiments and simulations, the discovery of distinctive catalytic mechanisms induced by multiadsorption, synergetic effects, and dynamic evolutions, to name a few, the proposal of criteria for theoretically designing SACs, and the extension of original concepts of single-atom catalysis. We hope that this Perspective will inspire more in-depth thinking on future theoretical studies of SACs.
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Affiliation(s)
- Wenhua Zhang
- Hefei
National Laboratory for Physical Sciences at the Microscale, Synergetic
Innovation Centre of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- Department
of Material Science and Technology of China, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qiang Fu
- Hefei
National Laboratory for Physical Sciences at the Microscale, Synergetic
Innovation Centre of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qiquan Luo
- Institutes
of Physical Science and Information Technology, Anhui University, Hefei, Anhui 230601, China
| | - Li Sheng
- Department
of Chemical Physics, University of Science
and Technology, Hefei, Anhui 230026, China
| | - Jinlong Yang
- Hefei
National Laboratory for Physical Sciences at the Microscale, Synergetic
Innovation Centre of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- Department
of Chemical Physics, University of Science
and Technology, Hefei, Anhui 230026, China
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Hartwig C, Schweinar K, Nicholls R, Beeg S, Schlögl R, Greiner M. Surface composition of AgPd single-atom alloy catalyst in an oxidative environment. J Chem Phys 2021; 154:174708. [PMID: 34241061 DOI: 10.1063/5.0045999] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Single-atom alloys (SAAs) have recently gained considerable attention in the field of heterogeneous catalysis research due to their potential for novel catalytic properties. While SAAs are often examined in reactions of reductive atmospheres, such as hydrogenation reactions, in the present work, we change the focus to AgPd SAAs in oxidative environments since Pd has the highest catalytic activity of all metals for oxidative reactions. Here, we examine how the chemical reactivity of AgPd SAAs differs from its constituent Pd in an oxidative atmosphere. For this purpose, electronic structure changes in an Ag0.98Pd0.02 SAA foil in 1 mbar of O2 were studied by in situ x-ray photoemission spectroscopy and compared with the electronic structure of a Pd foil under the same conditions. When heated in an oxidative atmosphere, Pd in Ag0.98Pd0.02 partly oxidizes and forms a metastable PdOx surface oxide. By using a peak area modeling procedure, we conclude that PdOx on Ag0.98Pd0.02 is present as thin, possibly monolayer thick, PdOx islands on the surface. In comparison to the PdO formed on the Pd foil, the PdOx formed on AgPd is substantially less thermodynamically stable, decomposing at temperatures about 270 °C lower than the native oxide on Pd. Such behavior is an interesting property of oxides formed on dilute alloys, which could be potentially utilized in catalytic oxidative reactions such as methane oxidation.
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Affiliation(s)
- Caroline Hartwig
- Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
| | - Kevin Schweinar
- Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany
| | - Rachel Nicholls
- Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
| | - Sebastian Beeg
- Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
| | - Robert Schlögl
- Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
| | - Mark Greiner
- Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
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