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Article ; Online: Distribution of Pt single atom coordination environments on anatase TiO

Zang, Wenjie / Lee, Jaeha / Tieu, Peter / Yan, Xingxu / Graham, George W / Tran, Ich C / Wang, Peikui / Christopher, Phillip / Pan, Xiaoqing

Nature communications

2024 Volume 15, Issue 1, Page(s) 998

Abstract: Single-atom catalysts (SACs) offer efficient metal utilization and distinct reactivity compared to supported metal nanoparticles. Structure-function relationships for SACs often assume that active sites have uniform coordination environments at ... ...

Abstract	Single-atom catalysts (SACs) offer efficient metal utilization and distinct reactivity compared to supported metal nanoparticles. Structure-function relationships for SACs often assume that active sites have uniform coordination environments at particular binding sites on support surfaces. Here, we investigate the distribution of coordination environments of Pt SAs dispersed on shape-controlled anatase TiO
Language	English
Publishing date	2024-02-02
Publishing country	England
Document type	Journal Article
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-024-45367-z
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with in Situ TEM and IR

Avanesian, Talin / Christopher Phillip / Dai Sheng / Graham George W / Kale Matthew J / Pan Xiaoqing

Journal of the American Chemical Society. 2017 Mar. 29, v. 139, no. 12

2017

Abstract: Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal ... ...

Abstract	Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.
Keywords	adsorption ; carbon monoxide ; geometry ; image analysis ; infrared spectroscopy ; nanoparticles ; oxidation ; platinum ; prediction ; surface area ; temperature ; transmission electron microscopy
Language	English
Dates of publication	2017-0329
Size	p. 4551-4558.
Publishing place	American Chemical Society
Document type	Article
ZDB-ID	3155-0
ISSN	1520-5126 ; 0002-7863
ISSN (online)	1520-5126
ISSN	0002-7863
DOI	10.1021%2Fjacs.7b01081
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Article ; Online: Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with in Situ TEM and IR.

Avanesian, Talin / Dai, Sheng / Kale, Matthew J / Graham, George W / Pan, Xiaoqing / Christopher, Phillip

Journal of the American Chemical Society

2017 Volume 139, Issue 12, Page(s) 4551–4558

Abstract	Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.
Language	English
Publishing date	2017-03-29
Publishing country	United States
Document type	Journal Article
ZDB-ID	3155-0
ISSN	1520-5126 ; 0002-7863
ISSN (online)	1520-5126
ISSN	0002-7863
DOI	10.1021/jacs.7b01081
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Article ; Online: Rh single atoms on TiO

Tang, Yan / Asokan, Chithra / Xu, Mingjie / Graham, George W / Pan, Xiaoqing / Christopher, Phillip / Li, Jun / Sautet, Philippe

Nature communications

2019 Volume 10, Issue 1, Page(s) 4488

Abstract: Single-atom catalysts are widely investigated heterogeneous catalysts; however, the identification of the local environment of single atoms under experimental conditions, as well as operando characterization of their structural changes during catalytic ... ...

Abstract	Single-atom catalysts are widely investigated heterogeneous catalysts; however, the identification of the local environment of single atoms under experimental conditions, as well as operando characterization of their structural changes during catalytic reactions are still challenging. Here, the preferred local coordination of Rh single atoms is investigated on TiO
Language	English
Publishing date	2019-10-03
Publishing country	England
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S. ; Research Support, Non-U.S. Gov't
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-019-12461-6
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Article: New Atomic-Scale Insight into Self-Regeneration of Pt-CaTiO3 Catalysts: Incipient Redox-Induced Structures Revealed by a Small-Angle Tilting STEM Technique

Zhang, Shuyi / Dai Sheng / Du Xianfeng / Graham George W / Katz Michael B / Pan Xiaoqing / Zhang Kui

The Journal of Physical Chemistry C. 2017 Aug. 17, v. 121, no. 32

2017

Abstract: A small-angle tilting technique, applied to scanning transmission electron microscopy (STEM), was used together with multislice image simulation to reveal new atomic-scale information about the structural evolution of single-crystalline Pt-doped CaTiO3 ... ...

Abstract	A small-angle tilting technique, applied to scanning transmission electron microscopy (STEM), was used together with multislice image simulation to reveal new atomic-scale information about the structural evolution of single-crystalline Pt-doped CaTiO3 thin films, grown by pulsed laser deposition, that occurs in response to reduction and reoxidation treatments. Specifically, we were able to confirm that Pt atoms are randomly dispersed throughout the as-grown film, most often occupying Ti sites, show that the smallest (∼1 nm) Pt-rich clusters embedded within CaTiO3 after reduction have a structure consistent with metallic Pt, and demonstrate that the Pt atoms from these clusters occupy mainly Ca sites, in the form of ordered Pt-atom arrays, after reoxidation.
Keywords	calcium ; catalysts ; physical chemistry ; transmission electron microscopy
Language	English
Dates of publication	2017-0817
Size	p. 17348-17353.
Publishing place	American Chemical Society
Document type	Article
ISSN	1932-7455
DOI	10.1021%2Facs.jpcc.7b05200
Database	NAL-Catalogue (AGRICOLA)

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Article: Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2

DeRita, Leo / Christopher Phillip / Dai Sheng / Graham George W / Lopez-Zepeda Kimberly / Pan Xiaoqing / Pham Nicholas

Journal of the American Chemical Society. 2017 Oct. 11, v. 139, no. 40

2017

Abstract: Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically ... ...

Abstract	Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO2. In these structures, isolated Pt atoms, Ptiso, remain stable through various conditions, and spectroscopic evidence suggests Ptiso species exist in homogeneous local environments. Comparing Ptiso to ∼1 nm preoxidized (Ptox) and prereduced (Ptmetal) Pt clusters on TiO2, we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Ptiso ≪ Ptmetal < Ptox. Ptiso species exhibited a 2-fold greater turnover frequency for CO oxidation than 1 nm Ptmetal clusters but share an identical reaction mechanism. We propose the active catalytic sites are cationic interfacial Pt atoms bonded to TiO2 and that Ptiso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO2. This approach should be generally useful for studying the behavior of supported precious metal atoms.
Keywords	active sites ; adsorption ; carbon monoxide ; catalysts ; catalytic activity ; dispersions ; energy ; geometry ; image analysis ; infrared spectroscopy ; nanoparticles ; oxidation ; protocols ; reaction mechanisms ; spectral analysis ; titanium dioxide ; transmission electron microscopy
Language	English
Dates of publication	2017-1011
Size	p. 14150-14165.
Publishing place	American Chemical Society
Document type	Article
ZDB-ID	3155-0
ISSN	1520-5126 ; 0002-7863
ISSN (online)	1520-5126
ISSN	0002-7863
DOI	10.1021%2Fjacs.7b07093
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Smart Pd Catalyst with Improved Thermal Stability Supported on High-Surface-Area LaFeO

Onn, Tzia Ming / Monai, Matteo / Dai, Sheng / Fonda, Emiliano / Montini, Tiziano / Pan, Xiaoqing / Graham, George W / Fornasiero, Paolo / Gorte, Raymond J

Journal of the American Chemical Society

2018 Volume 140, Issue 14, Page(s) 4841–4848

Abstract: The concept of self-regenerating or "smart" catalysts, developed to mitigate the problem of supported metal particle coarsening in high-temperature applications, involves redispersing large metal particles by incorporating them into a perovskite- ... ...

Abstract	The concept of self-regenerating or "smart" catalysts, developed to mitigate the problem of supported metal particle coarsening in high-temperature applications, involves redispersing large metal particles by incorporating them into a perovskite-structured support under oxidizing conditions and then exsolving them as small metal particles under reducing conditions. Unfortunately, the redispersion process does not appear to work in practice because the surface areas of the perovskite supports are too low and the diffusion lengths for the metal ions within the bulk perovskite too short. Here, we demonstrate reversible activation upon redox cycling for CH
Language	English
Publishing date	2018--11
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	3155-0
ISSN	1520-5126 ; 0002-7863
ISSN (online)	1520-5126
ISSN	0002-7863
DOI	10.1021/jacs.7b12900
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO

DeRita, Leo / Dai, Sheng / Lopez-Zepeda, Kimberly / Pham, Nicholas / Graham, George W / Pan, Xiaoqing / Christopher, Phillip

Journal of the American Chemical Society

2017 Volume 139, Issue 40, Page(s) 14150–14165

Abstract	Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO
Language	English
Publishing date	2017-10-11
Publishing country	United States
Document type	Journal Article
ZDB-ID	3155-0
ISSN	1520-5126 ; 0002-7863
ISSN (online)	1520-5126
ISSN	0002-7863
DOI	10.1021/jacs.7b07093
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: In situ atomic-scale observation of oxygen-driven core-shell formation in Pt

Dai, Sheng / You, Yuan / Zhang, Shuyi / Cai, Wei / Xu, Mingjie / Xie, Lin / Wu, Ruqian / Graham, George W / Pan, Xiaoqing

Nature communications

2017 Volume 8, Issue 1, Page(s) 204

Abstract: The catalytic performance of core-shell platinum alloy nanoparticles is typically superior to that of pure platinum nanoparticles for the oxygen reduction reaction in fuel cell cathodes. Thorough understanding of core-shell formation is critical for ... ...

Abstract	The catalytic performance of core-shell platinum alloy nanoparticles is typically superior to that of pure platinum nanoparticles for the oxygen reduction reaction in fuel cell cathodes. Thorough understanding of core-shell formation is critical for atomic-scale design and control of the platinum shell, which is known to be the structural feature responsible for the enhancement. Here we reveal details of a counter-intuitive core-shell formation process in platinum-cobalt nanoparticles at elevated temperature under oxygen at atmospheric pressure, by using advanced in situ electron microscopy. Initial segregation of a thin platinum, rather than cobalt oxide, surface layer occurs concurrently with ordering of the intermetallic core, followed by the layer-by-layer growth of a platinum shell via Ostwald ripening during the oxygen annealing treatment. Calculations based on density functional theory demonstrate that this process follows an energetically favourable path. These findings are expected to be useful for the future design of structured platinum alloy nanocatalysts.Core-shell platinum alloy nanoparticles are promising catalysts for oxygen reduction, however a deeper understanding of core-shell formation is still required. Here the authors report oxygen-driven formation of core-shell Pt
Language	English
Publishing date	2017-08-07
Publishing country	England
Document type	Journal Article
ISSN	2041-1723
ISSN (online)	2041-1723
DOI	10.1038/s41467-017-00161-y
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Adsorbate-mediated strong metal-support interactions in oxide-supported Rh catalysts.

Matsubu, John C / Zhang, Shuyi / DeRita, Leo / Marinkovic, Nebojsa S / Chen, Jingguang G / Graham, George W / Pan, Xiaoqing / Christopher, Phillip

Nature chemistry

2017 Volume 9, Issue 2, Page(s) 120–127

Abstract: The optimization of supported metal catalysts predominantly focuses on engineering the metal site, for which physical insights based on extensive theoretical and experimental contributions have enabled the rational design of active sites. Although it is ... ...

Abstract	The optimization of supported metal catalysts predominantly focuses on engineering the metal site, for which physical insights based on extensive theoretical and experimental contributions have enabled the rational design of active sites. Although it is well known that supports can influence the catalytic properties of metals, insights into how metal-support interactions can be exploited to optimize metal active-site properties are lacking. Here we utilize in situ spectroscopy and microscopy to identify and characterize a support effect in oxide-supported heterogeneous Rh catalysts. This effect is characterized by strongly bound adsorbates (HCO
Language	English
Publishing date	2017-02
Publishing country	England
Document type	Journal Article
ZDB-ID	2464596-5
ISSN	1755-4349 ; 1755-4330
ISSN (online)	1755-4349
ISSN	1755-4330
DOI	10.1038/nchem.2607
Database	MEDical Literature Analysis and Retrieval System OnLINE

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