A “Smart” Catalyst: Sinter‐Resistant Supported Iridium Clusters Visualized with Electron Microscopy

Aydin, Ceren; Lu, Jichang; Browning, Nigel D.; Gates, Bruce C.

doi:10.1002/ange.201201726

Cited by 21 publications

(8 citation statements)

References 49 publications

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“…Artifacts such as these including migration of metal atoms or small clusters occur under these imaging conditions as reported elsewhere 29. 30…”

supporting

confidence: 58%

Three‐Dimensional Structural Analysis of MgO‐Supported Osmium Clusters by Electron Microscopy with Single‐Atom Sensitivity

Aydin¹,

Kulkarni²,

Chi³

et al. 2013

Angew Chem Int Ed

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Supported metals are a widely applied class of industrial catalyst, [1] with properties depending on the size, shape, and structure of the metal species. [2,3] The sensitivity of the catalytic properties to the structure is maximized when the structures are smallest [4] and the interactions of the metal with the support maximized.[5] Consequently, attention has increasingly been focused on metal species in the size range between single-metal-atom (mononuclear) metal complexes [6] and clusters [7] that incorporate less than about 10 metal atoms. Work on such catalysts is now emerging from industrial laboratories, especially those concerned with supported platinum for hydrocarbon conversions. [8,9] Understanding of the properties of such highly dispersed metals is benefiting especially from the application of atomic-resolution scanning transmission electron microscopy (STEM). [10] Recent reports, including those from industry, [11] illustrate the power of this technique, especially when used in concert with spectroscopic methods.[12] Important next steps are determination of the nuclearities and three-dimensional structures of supported metal clusters present in mixtures typical of industrial catalysts.Three-dimensional structures can in prospect be determined by tomographic imaging techniques, but the methods require long sample exposures for imaging at multiple angles, [13] and beam-sensitive samples do not survive. Consequently, atomic-resolution tomography of small supported metal clusters has not yet been achieved with this technique.To acquire such information about highly dispersed supported metals, we took a different approach, pushing the limits of imaging by aberration-corrected STEM, characterizing small three-dimensional metal clusters by their twodimensional projections. Thus, we extracted 3D structures from atomic-resolution images acquired with short dwell times to minimize the influence of the electron beam on the samples-without significantly compromising the signal-tonoise ratios. We illustrate the approach with a characterization of MgO-supported osmium clusters having nuclearities of 10 and less in mixtures of planar (2D) and 3D structures.The metal was chosen to be osmium because oxidesupported osmium carbonyl clusters are catalysts for reactions including alkene isomerization [14] and hydrogenation, [15] carbon monoxide hydrogenation, [16] and alkane hydrogenolysis.[17] Osmium offers the further advantages of being a metal that is a) heavy, offering high contrast with supports consisting of light atoms in STEM imaging, b) synthesizable in the form of carbonyl clusters of various nuclearities, and c) relatively stable in the electron beam.[18] These clusters have been synthesized as osmium carbonylate ions in basic solutions and on basic supports. [19] MgO was chosen as the support because it is a) basic, facilitating the cluster syntheses, b) composed of light atoms, for contrast with osmium in STEM imaging, and c) present in the high-area powder form as highly crystalline particles that are s...

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“…Artifacts such as these including migration of metal atoms or small clusters occur under these imaging conditions as reported elsewhere 29. 30…”

supporting

confidence: 58%

Three‐Dimensional Structural Analysis of MgO‐Supported Osmium Clusters by Electron Microscopy with Single‐Atom Sensitivity

Aydin¹,

Kulkarni²,

Chi³

et al. 2013

Angew Chem Int Ed

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“…43 AC-STEM is capable of both high resolution and high sensitivity, but the electron doses conventionally used for atomic resolution imaging are high, approaching 10 6 e -/A 2 or more. These fluences can transfer significant energy to the adsorbed metals, such as iridium, leading to beam-induced sintering, 44 thereby complicating the interpretation of the native sizes of the metal-containing species. However, Ir-O-Ir species bound to α-Fe 2 O 3 surfaces (Figure 4) were shown to be stable under AC-STEM illumination for a minute or more.…”

Section: Experimental Structure Characterizationmentioning

confidence: 99%

Supported Metal Pair-Site Catalysts

et al. 2020

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Complexes with neighboring metal centers and their analogues on surfaces are drawing increasing attention as catalysts. These include molecular homogeneous catalysts incorporating various ligands; enzymes; and solids that include pairs of metal atoms mounted on supports.Catalysts in this broad class are active for numerous reactions and offer unexplored opportunities to address challenging reactions, such as oxidation of methane and oxidation of water in artificial photosynthesis. The subject of supported metal pair-site catalysts is in its infancy, facing challenges in (a) precise synthesis, (b) structure determination at the atomic scale, and (c) stabilization in reactive atmospheres. In this Perspective, we summarize key characteristics of molecular and enzymatic catalysts that incorporate neighboring metal centers and build on this foundation to assess the emerging literature of metal pair-site catalysts on various supports. The supported catalysts include those synthesized by anchoring molecular dinuclear precursors to support surfaces and those synthesized by selective formation of dinuclear surface species from mononuclear surface species. Examples of metals in this class are rhodium and iridium, and

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“…For example, single-atom Ir supported on MgO was found to be intrinsically resistive to sintering, while Pt and Au supported on the same support material tended to sinter when they were treated in H 2 and the electron beam. [229] This phenomenon indicates the effect of the nature of metals themselves. Similarly, Campbell et al reported that Ag nanoparticles supported on reduced CeO 2 (111) have much higher stability than those supported on MgO (100), suggesting the effects of supports and metal-support interactions on the stability of SACs.…”

Section: Pyrolysis -Affordable In General Laboratoriesmentioning

confidence: 99%

“…The nature of metals, supports, and metal‐support interactions are the key factors affecting the stability of SACs. For example, single‐atom Ir supported on MgO was found to be intrinsically resistive to sintering, while Pt and Au supported on the same support material tended to sinter when they were treated in H 2 and the electron beam [229] . This phenomenon indicates the effect of the nature of metals themselves.…”

Section: Conclusion and Outlooksmentioning

confidence: 99%

Race on High‐loading Metal Single Atoms and Successful Preparation Strategies

et al. 2021

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Although single-atom catalysts (SACs) show significantly higher catalytic performance compared to conventional and nanoparticle-based catalysts (NPs) at the same amount of metal loading, their overall catalytic performance may still be unable to compete with the NPs in many applications due to the limited active sites. Generally, trace amounts of metal (less than 1 wt%) can be successfully loaded onto supports in an atomically-dispersed feature, and higher metal loading usually results in aggregation of the metal atoms. Hence, it is very important to further increase the density of isolated metal atoms in these rising-star SACs to pave the ways for widespread applications or even to replace the NPs. On the other hand, it is well known that this is one of the most challenging topics on SACs research. In this review, the advanced strategies to overcome this challenge and achieve high loading of isolated metal atoms on various supports will be extensively discussed together with the examples showing the research efforts to enrich the metal active sites from the pioneer works with metal loading below 0.2 wt% to the recently-reported SACs with metal loading over 20 wt%. Besides, there are still plenty of rooms to further improve the quantity and quality of metal loading on different supports, and outlooks of this scope is provided. We hope that this comprehensive review aids in the development of synthesis techniques for the new-generation SACs with richer active sites.

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A “Smart” Catalyst: Sinter‐Resistant Supported Iridium Clusters Visualized with Electron Microscopy

Cited by 21 publications

References 49 publications

Three‐Dimensional Structural Analysis of MgO‐Supported Osmium Clusters by Electron Microscopy with Single‐Atom Sensitivity

Three‐Dimensional Structural Analysis of MgO‐Supported Osmium Clusters by Electron Microscopy with Single‐Atom Sensitivity

Supported Metal Pair-Site Catalysts

Race on High‐loading Metal Single Atoms and Successful Preparation Strategies

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