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Eckelt F, Rothweiler P, Braun F, Voss L, Šarić A, Vrankić M, Lützenkirchen-Hecht D. In Situ Observation of ZnO Nanoparticle Formation by a Combination of Time-Resolved X-ray Absorption Spectroscopy and X-ray Diffraction. Materials (Basel) 2022; 15:8186. [PMID: 36431670 PMCID: PMC9699227 DOI: 10.3390/ma15228186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 11/07/2022] [Accepted: 11/15/2022] [Indexed: 06/16/2023]
Abstract
The formation of ZnO nanomaterials from different Zn acetylacetonate precursor solutions was studied in situ by employing simultaneous, time-resolved X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS) at the Zn K-edge. The precursor solutions were heated from room temperature to the desired reaction temperatures in a hermetically sealed cell dedicated to X-ray experiments. In general, the first indications for the formation of hexagonal ZnO were found for elevated temperatures of about 80 °C both by XRD and EXAFS, and the contributions increase with temperature and time. However, no reaction intermediates could be proved in addition to the Zn precursors and the formed hexagonal ZnO materials. Furthermore, the results show that the efficiency of the reaction, i.e., the conversion of the precursor material to the ZnO product, strongly depends on the solvent used and the reaction temperature. ZnO formation is accelerated by an increased temperature of 165 °C and the use of 1-octanol, with a conversion to ZnO of more than 80% after only a ca. 35 min reaction time according to a detailed analysis of the EXAFS data. For comparison, an identical concentration of Zn acetylacetonate in water or dilute alkaline NaOH solutions and a reaction temperature of around 90 °C leads to a smaller conversion of approximately 50% only, even after several hours of reaction. The particle size determined from XRD for different orientations shows a preferred orientation along the c-direction of the hexagonal crystal system, as well in accordance with scanning electron microscopy. The LaMer model explained this highly non-uniform growth of needle-like ZnO crystallites.
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Affiliation(s)
- Franz Eckelt
- Faculty of Natural Sciences, University of Wuppertal, Gauss-Str. 20, 42119 Wuppertal, Germany
| | - Patrick Rothweiler
- Faculty of Natural Sciences, University of Wuppertal, Gauss-Str. 20, 42119 Wuppertal, Germany
| | - Frederic Braun
- Faculty of Natural Sciences, University of Wuppertal, Gauss-Str. 20, 42119 Wuppertal, Germany
| | - Lukas Voss
- Faculty of Natural Sciences, University of Wuppertal, Gauss-Str. 20, 42119 Wuppertal, Germany
| | - Ankica Šarić
- Centre of Excellence for Advanced Materials and Sensing Devices, Division of Materials Physics, Ruđer Bošković Institute, HR-10002 Zagreb, Croatia
| | - Martina Vrankić
- Centre of Excellence for Advanced Materials and Sensing Devices, Division of Materials Physics, Ruđer Bošković Institute, HR-10002 Zagreb, Croatia
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Liu Y, Halder A, Seifert S, Marcella N, Vajda S, Frenkel AI. Probing Active Sites in Cu xPd y Cluster Catalysts by Machine-Learning-Assisted X-ray Absorption Spectroscopy. ACS Appl Mater Interfaces 2021; 13:53363-53374. [PMID: 34255469 DOI: 10.1021/acsami.1c06714] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Size-selected clusters are important model catalysts because of their narrow size and compositional distributions, as well as enhanced activity and selectivity in many reactions. Still, their structure-activity relationships are, in general, elusive. The main reason is the difficulty in identifying and quantitatively characterizing the catalytic active site in the clusters when it is confined within subnanometric dimensions and under the continuous structural changes the clusters can undergo in reaction conditions. Using machine learning approaches for analysis of the operando X-ray absorption near-edge structure spectra, we obtained accurate speciation of the CuxPdy cluster types during the propane oxidation reaction and the structural information about each type. As a result, we elucidated the information about active species and relative roles of Cu and Pd in the clusters.
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Affiliation(s)
- Yang Liu
- Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York 11794, United States
| | - Avik Halder
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States
| | - Soenke Seifert
- X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States
| | - Nicholas Marcella
- Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York 11794, United States
| | - Stefan Vajda
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States
- Institute for Molecular Engineering, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, United States
- Department of Nanocatalysis, J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Prague 8 18223, Czech Republic
| | - Anatoly I Frenkel
- Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York 11794, United States
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973, United States
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Terrill NJ, Dent AJ, Dobson B, Beale AM, Allen L, Bras W. Past, present and future-sample environments for materials research studies in scattering and spectroscopy; a UK perspective. J Phys Condens Matter 2021; 33:483002. [PMID: 34479225 DOI: 10.1088/1361-648x/ac2389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 09/03/2021] [Indexed: 06/13/2023]
Abstract
Small angle x-ray scattering and x-ray absorption fine structure are two techniques that have been employed at synchrotron sources ever since their inception. Over the course of the development of the techniques, the introduction of sample environments for added value experiments has grown dramatically. This article reviews past successes, current developments and an exploration of future possibilities for these two x-ray techniques with an emphasis on the developments in the United Kingdom between 1980-2020.
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Affiliation(s)
| | - Andrew J Dent
- Diamond Light Source, Didcot, Oxfordshire, OX11 0DE, United Kingdom
| | - Barry Dobson
- Sagentia Ltd, Harston Mill, Harston Mill, CB22 7GG, United Kingdom
| | - Andrew M Beale
- Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, United Kingdom
- The Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire, OX11 0FA, United Kingdom
| | - Lisa Allen
- Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, United Kingdom
- The Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire, OX11 0FA, United Kingdom
| | - Wim Bras
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, One Bethel Valley Road TN 37831, United States of America
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Rupprechter G. Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso-Scale Aggregates. Small 2021; 17:e2004289. [PMID: 33694320 DOI: 10.1002/smll.202004289] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 02/16/2021] [Indexed: 05/16/2023]
Abstract
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 experimental results should be complemented by density functional theory. The operando approach enables to identify changes of cluster/nanoparticle structure and composition during ongoing catalytic reactions and reveal how molecules interact with surfaces and interfaces. The case studies cover the length-scales from clusters via nanoparticles to meso-scale aggregates, and demonstrate the benefits of specific operando methods. Restructuring, ligand/atom mobility, and surface composition alterations during the reaction may have pronounced effects on activity and selectivity. The nanoscale metal/oxide interface steers catalytic performance via a long ranging effect. Combining operando spectroscopy with switching gas feeds or concentration-modulation provides further mechanistic insights. The obtained fundamental understanding is a prerequisite for improving catalytic performance and for rational design.
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Affiliation(s)
- Günther Rupprechter
- Institute of Materials Chemistry, Technische Universität Wien, Getreidemarkt 9/BC/01, Vienna, 1060, Austria
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Dolcet P, Maurer F, Casapu M, Grunwaldt J. Insights into the Structural Dynamics of Pt/CeO2 Single-Site Catalysts during CO Oxidation. Catalysts 2021; 11:617. [DOI: 10.3390/catal11050617] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Despite their high atomic dispersion, single site catalysts with Pt supported on CeO2 were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO2 single site catalyst under more complex gas mixtures, including CO, C3H6 and CO/C3H6 oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt4+ to Pt2+ due to the increase of temperature, CO adsorbs and reduces Pt2+ to Ptδ+ and assists its migration with final formation of PtxΔ+ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria.
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Martini A, Borfecchia E. Spectral Decomposition of X-ray Absorption Spectroscopy Datasets: Methods and Applications. Crystals 2020; 10:664. [DOI: 10.3390/cryst10080664] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
X-ray absorption spectroscopy (XAS) today represents a widespread and powerful technique, able to monitor complex systems under in situ and operando conditions, while external variables, such us sampling time, sample temperature or even beam position over the analysed sample, are varied. X-ray absorption spectroscopy is an element-selective but bulk-averaging technique. Each measured XAS spectrum can be seen as an average signal arising from all the absorber-containing species/configurations present in the sample under study. The acquired XAS data are thus represented by a spectroscopic mixture composed of superimposed spectral profiles associated to well-defined components, characterised by concentration values evolving in the course of the experiment. The decomposition of an experimental XAS dataset in a set of pure spectral and concentration values is a typical example of an inverse problem and it goes, usually, under the name of multivariate curve resolution (MCR). In the present work, we present an overview on the major techniques developed to realize the MCR decomposition together with a selection of related results, with an emphasis on applications in catalysis. Therein, we will highlight the great potential of these methods which are imposing as an essential tool for quantitative analysis of large XAS datasets as well as the directions for further development in synergy with the continuous instrumental progresses at synchrotron sources.
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Rabeah J, Briois V, Adomeit S, La Fontaine C, Bentrup U, Brückner A. Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions. Chemistry 2020; 26:7395-7404. [PMID: 32118340 PMCID: PMC7317854 DOI: 10.1002/chem.202000436] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Indexed: 01/12/2023]
Abstract
Operando EPR, XANES/EXAFS, UV‐Vis and ATR‐IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least‐squares fitting (MCR‐ALS) of simultaneously recorded XAS and UV‐Vis data sets, it was found that an initially formed (bpy)(NMI)CuI‐ complex (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole ) is converted to two different CuII species, a mononuclear (bpy)(NMI)(CH3CN)CuII‐OOH species detectable by EPR and ESI‐MS, and an EPR‐silent dinuclear (CH3CN)(bpy)(NMI)CuII(μ‐OH)2⋅CuII (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)CuII‐TEMPO monomers that are also EPR‐silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non‐reducible CuII leads to slight deactivation at extended reaction times.
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Affiliation(s)
- Jabor Rabeah
- Leibniz-Institut für Katalyse an der Universität Rostock, Albert-Einstein-Str. 29a, 18059, Rostock, Germany
| | - Valérie Briois
- Synchrotron SOLEIL, L'Orme des Merisiers, BP48, Saint-Aubin, 91192 Gif-sur Yvette, France
| | - Sven Adomeit
- Leibniz-Institut für Katalyse an der Universität Rostock, Albert-Einstein-Str. 29a, 18059, Rostock, Germany
| | - Camille La Fontaine
- Synchrotron SOLEIL, L'Orme des Merisiers, BP48, Saint-Aubin, 91192 Gif-sur Yvette, France
| | - Ursula Bentrup
- Leibniz-Institut für Katalyse an der Universität Rostock, Albert-Einstein-Str. 29a, 18059, Rostock, Germany
| | - Angelika Brückner
- Leibniz-Institut für Katalyse an der Universität Rostock, Albert-Einstein-Str. 29a, 18059, Rostock, Germany
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