1
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Sarma BB, Maurer F, Doronkin DE, Grunwaldt JD. Design of Single-Atom Catalysts and Tracking Their Fate Using Operando and Advanced X-ray Spectroscopic Tools. Chem Rev 2022; 123:379-444. [PMID: 36418229 PMCID: PMC9837826 DOI: 10.1021/acs.chemrev.2c00495] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The potential of operando X-ray techniques for following the structure, fate, and active site of single-atom catalysts (SACs) is highlighted with emphasis on a synergetic approach of both topics. X-ray absorption spectroscopy (XAS) and related X-ray techniques have become fascinating tools to characterize solids and they can be applied to almost all the transition metals deriving information about the symmetry, oxidation state, local coordination, and many more structural and electronic properties. SACs, a newly coined concept, recently gained much attention in the field of heterogeneous catalysis. In this way, one can achieve a minimum use of the metal, theoretically highest efficiency, and the design of only one active site-so-called single site catalysts. While single sites are not easy to characterize especially under operating conditions, XAS as local probe together with complementary methods (infrared spectroscopy, electron microscopy) is ideal in this research area to prove the structure of these sites and the dynamic changes during reaction. In this review, starting from their fundamentals, various techniques related to conventional XAS and X-ray photon in/out techniques applied to single sites are discussed with detailed mechanistic and in situ/operando studies. We systematically summarize the design strategies of SACs and outline their exploration with XAS supported by density functional theory (DFT) calculations and recent machine learning tools.
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Affiliation(s)
- Bidyut Bikash Sarma
- Institute
for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, Engesserstraße 20, 76131 Karlsruhe, Germany,Institute
of Catalysis Research and Technology, Karlsruhe
Institute of Technology, Hermann-von-Helmholtz Platz 1, Eggenstein-Leopoldshafen, 76344 Karlsruhe, Germany,
| | - Florian Maurer
- Institute
for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, Engesserstraße 20, 76131 Karlsruhe, Germany
| | - Dmitry E. Doronkin
- Institute
for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, Engesserstraße 20, 76131 Karlsruhe, Germany,Institute
of Catalysis Research and Technology, Karlsruhe
Institute of Technology, Hermann-von-Helmholtz Platz 1, Eggenstein-Leopoldshafen, 76344 Karlsruhe, Germany
| | - Jan-Dierk Grunwaldt
- Institute
for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, Engesserstraße 20, 76131 Karlsruhe, Germany,Institute
of Catalysis Research and Technology, Karlsruhe
Institute of Technology, Hermann-von-Helmholtz Platz 1, Eggenstein-Leopoldshafen, 76344 Karlsruhe, Germany,
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2
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Pacchioni G, Rahman TS. Defect engineering of oxide surfaces: dream or reality? JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:291501. [PMID: 35504272 DOI: 10.1088/1361-648x/ac6c6d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Accepted: 05/03/2022] [Indexed: 06/14/2023]
Abstract
In this brief perspective we analyze the present status of the field of defect engineering of oxide surfaces. In particular we discuss the tools and techniques available to generate, identify, quantify, and characterize point defects at oxide surfaces and the main areas where these centers play a role in practical applications.
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Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via R. Cozzi 55, 202125, Milano, Italy
| | - Talat S Rahman
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
- Renewable Energy and Chemical Transformation Cluster, University of Central Florida, Orlando, FL 32816, United States of America
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3
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Chiesa M, Giamello E. On the Role and Applications of Electron Magnetic Resonance Techniques in Surface Chemistry and Heterogeneous Catalysis. Catal Letters 2021. [DOI: 10.1007/s10562-021-03576-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Abstract
Some relevant aspects of Electron Paramagnetic Resonance (EPR) applied to the fields of surface chemistry and heterogeneous catalysis are illustrated in this perspective paper that aims to show the potential of these techniques in describing critical features of surface structures and reactivity. Selected examples are employed covering distinct aspects of catalytic science from morphological analysis of surfaces to detailed descriptions of chemical bonding and catalytic sites topology. In conclusions the pros and cons related to the acquisition of EPR instrumentations in an advanced laboratory of surface chemistry and heterogeneous catalysis are briefly considered.
Graphic Abstract
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4
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de Souza EF, Pacheco HP, Miyake N, Davis RJ, Toniolo FS. Computational and Experimental Mechanistic Insights into the Ethanol-to-Butanol Upgrading Reaction over MgO. ACS Catal 2020. [DOI: 10.1021/acscatal.0c04616] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Eugenio F. de Souza
- Chemical Engineering Program of COPPE/UFRJ, Federal University of Rio de Janeiro, P.O. Box 68502, CEP 21941-972 Rio de Janeiro, Brazil
| | - Henrique P. Pacheco
- Chemical Engineering Program of COPPE/UFRJ, Federal University of Rio de Janeiro, P.O. Box 68502, CEP 21941-972 Rio de Janeiro, Brazil
| | - Naomi Miyake
- Department of Chemical Engineering, University of Virginia, 102 Engineer’s Way, Charlottesville, 22904-4741 Virginia, United States
| | - Robert J. Davis
- Department of Chemical Engineering, University of Virginia, 102 Engineer’s Way, Charlottesville, 22904-4741 Virginia, United States
| | - Fabio S. Toniolo
- Chemical Engineering Program of COPPE/UFRJ, Federal University of Rio de Janeiro, P.O. Box 68502, CEP 21941-972 Rio de Janeiro, Brazil
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5
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Merkel DG, Lengyel A, Nagy DL, Németh A, Horváth ZE, Bogdán C, Gracheva MA, Hegedűs G, Sajti S, Radnóczi GZ, Szilágyi E. Reversible control of magnetism in FeRh thin films. Sci Rep 2020; 10:13923. [PMID: 32811888 PMCID: PMC7435192 DOI: 10.1038/s41598-020-70899-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Accepted: 08/03/2020] [Indexed: 11/22/2022] Open
Abstract
The multilayer of approximate structure MgO(100)/[nFe51Rh49(63 Å)/57Fe51Rh49(46 Å)]10 deposited at 200 °C is primarily of paramagnetic A1 phase and is fully converted to the magnetic B2 phase by annealing at 300 °C for 60 min. Subsequent irradiation by 120 keV Ne+ ions turns the thin film completely to the paramagnetic A1 phase. Repeated annealing at 300 °C for 60 min results in 100% magnetic B2 phase, i.e. a process that appears to be reversible at least twice. The A1 → B2 transformation takes place without any plane-perpendicular diffusion while Ne+ irradiation results in significant interlayer mixing.
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Affiliation(s)
- Dániel G Merkel
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary.
- Centre for Energy Research, P.O.B. 49, 1525, Budapest, Hungary.
| | - Attila Lengyel
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
| | - Dénes L Nagy
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
| | - Attila Németh
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
| | - Zsolt E Horváth
- Centre for Energy Research, P.O.B. 49, 1525, Budapest, Hungary
| | - Csilla Bogdán
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
| | - Maria A Gracheva
- Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117, Budapest, Hungary
| | - Gergő Hegedűs
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
| | - Szilárd Sajti
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
| | | | - Edit Szilágyi
- Wigner Research Centre for Physics, P.O.B. 49, 1525, Budapest, Hungary
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6
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Eggert B, Schmeink A, Lill J, Liedke MO, Kentsch U, Butterling M, Wagner A, Pascarelli S, Potzger K, Lindner J, Thomson T, Fassbender J, Ollefs K, Keune W, Bali R, Wende H. Magnetic response of FeRh to static and dynamic disorder. RSC Adv 2020; 10:14386-14395. [PMID: 35498452 PMCID: PMC9051944 DOI: 10.1039/d0ra01410a] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 03/16/2020] [Indexed: 11/21/2022] Open
Abstract
This study shows the similarity of the thermally-driven (dynamic disorder) and structural disorder-driven (static disorder) magnetic phase transition in B2-FeRh.
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7
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Zhang Y, Afzal N, Pan L, Zhang X, Zou J. Structure-Activity Relationship of Defective Metal-Based Photocatalysts for Water Splitting: Experimental and Theoretical Perspectives. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2019; 6:1900053. [PMID: 31131201 PMCID: PMC6524102 DOI: 10.1002/advs.201900053] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 02/26/2019] [Indexed: 05/05/2023]
Abstract
Photocatalytic water splitting is promising for hydrogen energy production using solar energy and developing highly efficient photocatalysts is challenging. Defect engineering is proved to be a very useful strategy to promote the photocatalytic performance of metal-based photocatalysts, however, the vital role of defects is still ambiguous. This work comprehensively reviews point defective metal-based photocatalysts for water splitting, focusing on understanding the defects' disorder effect on optical adsorption, charge separation and migration, and surface reaction. The controllable synthesis and tuning strategies of defective structure to improve the photocatalytic performance are summarized, then the characterization techniques and density functional theory calculations are discussed to unveil the defect structure, and analyze the defects induced electronic structure change of catalysts and its ultimate effect on the photocatalytic activity at the molecular level. Finally, the challenge in developing more efficient defective metal-based photocatalysts is outlined. This work may help further the understanding of the fundamental role of defect structure in the photocatalytic reaction process and guide the rational design and fabrication of highly efficient and low-cost photocatalysts.
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Affiliation(s)
- Yong‐Chao Zhang
- Key Laboratory for Green Chemical Technology of Ministry of EducationSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin300072China
- Collaborative Innovative Center of Chemical Science and Engineering (Tianjin)Tianjin300072China
| | - Nisha Afzal
- Key Laboratory for Green Chemical Technology of Ministry of EducationSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin300072China
- Collaborative Innovative Center of Chemical Science and Engineering (Tianjin)Tianjin300072China
| | - Lun Pan
- Key Laboratory for Green Chemical Technology of Ministry of EducationSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin300072China
- Collaborative Innovative Center of Chemical Science and Engineering (Tianjin)Tianjin300072China
| | - Xiangwen Zhang
- Key Laboratory for Green Chemical Technology of Ministry of EducationSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin300072China
- Collaborative Innovative Center of Chemical Science and Engineering (Tianjin)Tianjin300072China
| | - Ji‐Jun Zou
- Key Laboratory for Green Chemical Technology of Ministry of EducationSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin300072China
- Collaborative Innovative Center of Chemical Science and Engineering (Tianjin)Tianjin300072China
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8
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Pacchioni G, Freund HJ. Controlling the charge state of supported nanoparticles in catalysis: lessons from model systems. Chem Soc Rev 2018; 47:8474-8502. [DOI: 10.1039/c8cs00152a] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Model systems are very important to identify the working principles of real catalysts, and to develop concepts that can be used in the design of new catalytic materials.
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Affiliation(s)
| | - Hans-Joachim Freund
- Fritz-Haber-Institut der Max-Planck-Gesellschaft
- Department of Chemical Physics
- 14195 Berlin
- Germany
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9
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Hemmingson SL, Feeley GM, Miyake NJ, Campbell CT. Energetics of 2D and 3D Gold Nanoparticles on MgO(100): Influence of Particle Size and Defects on Gold Adsorption and Adhesion Energies. ACS Catal 2017. [DOI: 10.1021/acscatal.6b03173] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Stephanie L. Hemmingson
- Department of Chemistry, University of Washington, Campus Box
351700 Seattle, Washington 98189-1700, United States
| | - Gabriel M. Feeley
- Department of Chemistry, University of Washington, Campus Box
351700 Seattle, Washington 98189-1700, United States
| | - Naomi J. Miyake
- Department of Chemistry, University of Washington, Campus Box
351700 Seattle, Washington 98189-1700, United States
| | - Charles T. Campbell
- Department of Chemistry, University of Washington, Campus Box
351700 Seattle, Washington 98189-1700, United States
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10
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Jiménez JM, Bourret GR, Berger T, McKenna KP. Modification of Charge Trapping at Particle/Particle Interfaces by Electrochemical Hydrogen Doping of Nanocrystalline TiO 2. J Am Chem Soc 2016; 138:15956-15964. [PMID: 27960341 PMCID: PMC5193466 DOI: 10.1021/jacs.6b08636] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
Particle/particle
interfaces play a crucial role in the functionality
and performance of nanocrystalline materials such as mesoporous metal
oxide electrodes. Defects at these interfaces are known to impede
charge separation via slow-down of transport and increase of charge
recombination, but can be passivated via electrochemical doping (i.e.,
incorporation of electron/proton pairs), leading to transient but
large enhancement of photoelectrode performance. Although this process
is technologically very relevant, it is still poorly understood. Here
we report on the electrochemical characterization and the theoretical
modeling of electron traps in nanocrystalline rutile TiO2 films. Significant changes in the electrochemical response of porous
films consisting of a random network of TiO2 particles
are observed upon the electrochemical accumulation of electron/proton
pairs. The reversible shift of a capacitive peak in the voltammetric
profile of the electrode is assigned to an energetic modification
of trap states at particle/particle interfaces. This hypothesis is
supported by first-principles theoretical calculations on a TiO2 grain boundary, providing a simple model for particle/particle
interfaces. In particular, it is shown how protons readily segregate
to the grain boundary (being up to 0.6 eV more stable than in the
TiO2 bulk), modifying its structure and electron-trapping
properties. The presence of hydrogen at the grain boundary increases
the average depth of traps while at the same time reducing their number
compared to the undoped situation. This provides an explanation for
the transient enhancement of the photoelectrocatalytic activity toward
methanol photooxidation which is observed following electrochemical
hydrogen doping of rutile TiO2 nanoparticle electrodes.
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Affiliation(s)
- Juan M Jiménez
- Department of Chemistry and Physics of Materials, University of Salzburg , Hellbrunner Straße 34/III, A-5020 Salzburg, Austria
| | - Gilles R Bourret
- Department of Chemistry and Physics of Materials, University of Salzburg , Hellbrunner Straße 34/III, A-5020 Salzburg, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, University of Salzburg , Hellbrunner Straße 34/III, A-5020 Salzburg, Austria
| | - Keith P McKenna
- Department of Physics, University of York , Heslington, York YO10 5DD, United Kingdom
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11
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Copéret C, Estes DP, Larmier K, Searles K. Isolated Surface Hydrides: Formation, Structure, and Reactivity. Chem Rev 2016; 116:8463-505. [DOI: 10.1021/acs.chemrev.6b00082] [Citation(s) in RCA: 107] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Christophe Copéret
- Department of Chemistry and
Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland
| | - Deven P. Estes
- Department of Chemistry and
Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland
| | - Kim Larmier
- Department of Chemistry and
Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland
| | - Keith Searles
- Department of Chemistry and
Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland
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12
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Kumar G, Lau SLJ, Krcha MD, Janik MJ. Correlation of Methane Activation and Oxide Catalyst Reducibility and Its Implications for Oxidative Coupling. ACS Catal 2016. [DOI: 10.1021/acscatal.5b02657] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Gaurav Kumar
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Sai Lap Jacky Lau
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Matthew D. Krcha
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Michael J. Janik
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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13
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14
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McKenna KP. Electronic and chemical properties of a surface-terminated screw dislocation in MgO. J Am Chem Soc 2013; 135:18859-65. [PMID: 24279391 PMCID: PMC3892727 DOI: 10.1021/ja408342z] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Dislocations represent an important and ubiquitous class of topological defect found at the surfaces of metal oxide materials. They are thought to influence processes as diverse as crystal growth, corrosion, charge trapping, luminescence, molecular adsorption, and catalytic activity; however, their electronic and chemical properties remain poorly understood. Here, through a detailed first-principles investigation into the properties of a surface-terminated screw dislocation in MgO we provide atomistic insight into these issues. We show that surface dislocations can exhibit intriguing electron trapping properties which are important for understanding the chemical and electronic characteristics of oxide surfaces. The results presented in this article taken together with recent experimental reports show that surface dislocations can be equally as important as more commonly considered surface defects, such as steps, kinks, and vacancies, but are now just beginning to be understood.
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Affiliation(s)
- Keith P McKenna
- Department of Physics, University of York , Heslington, York YO10 5DD, United Kingdom
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15
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Gonchar A, Risse T. Characterisation of paramagnetic Mo impurities on MgO(100) single-crystalline films grown on Mo(100). Mol Phys 2013. [DOI: 10.1080/00268976.2013.811305] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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16
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Pacchioni G. Electronic interactions and charge transfers of metal atoms and clusters on oxide surfaces. Phys Chem Chem Phys 2013; 15:1737-57. [DOI: 10.1039/c2cp43731g] [Citation(s) in RCA: 175] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Sousa C, Tosoni S, Illas F. Theoretical Approaches to Excited-State-Related Phenomena in Oxide Surfaces. Chem Rev 2012. [DOI: 10.1021/cr300228z] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Carmen Sousa
- Departament de Química
Física and Institut de Química Teòrica i Computacional
(IQTCUB), Universitat de Barcelona, C/Martí
i Franquès 1, 08028 Barcelona, Spain
| | - Sergio Tosoni
- Departament de Química
Física and Institut de Química Teòrica i Computacional
(IQTCUB), Universitat de Barcelona, C/Martí
i Franquès 1, 08028 Barcelona, Spain
- Departamento de Química, Universidad de Las Palmas de Gran Canaria, Campus Universitario
de Tafira, 35017 Las Palmas de Gran Canaria, Spain
| | - Francesc Illas
- Departament de Química
Física and Institut de Química Teòrica i Computacional
(IQTCUB), Universitat de Barcelona, C/Martí
i Franquès 1, 08028 Barcelona, Spain
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18
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Pacchioni G, Freund H. Electron Transfer at Oxide Surfaces. The MgO Paradigm: from Defects to Ultrathin Films. Chem Rev 2012; 113:4035-72. [DOI: 10.1021/cr3002017] [Citation(s) in RCA: 241] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei
Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53−20125,
Milano, Italy
| | - Hajo Freund
- Fritz-Haber-Insitut
der MPG,
Department of Chemical Physics, Faradayweg 4-6, 14195 Berlin, Germany
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19
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Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store. Nat Chem 2012; 4:934-40. [DOI: 10.1038/nchem.1476] [Citation(s) in RCA: 864] [Impact Index Per Article: 72.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Accepted: 09/06/2012] [Indexed: 11/08/2022]
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20
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Aziz MAA, Kamarudin NHN, Setiabudi HD, Hamdan H, Jalil AA, Triwahyono S. Negative effect of Ni on PtHY in n-pentane isomerization evidenced by IR and ESR studies. ACTA ACUST UNITED AC 2012. [DOI: 10.1016/s1003-9953(11)60329-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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21
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Sushko PV, Shluger AL, Toda Y, Hirano M, Hosono H. Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al
2
O
3. Proc Math Phys Eng Sci 2011. [DOI: 10.1098/rspa.2010.0560] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Surface structures of stoichiometric and oxygen-deficient complex subnanoporous oxide 12CaO·7Al
2
O
3
(C12A7) are generated by simulating lattice rupture under the influence of an external strain. Extra-framework anions are found to serve as buffers, maintaining stability of the lattice cages in both elastic and inelastic stretching regimes. Modification of the local atomic structure in the near-surface region reduces the band gap in stoichiometric insulating C12A7. On the contrary, the band gap appears in the oxygen-deficient form of C12A7, which is metallic in the bulk. This is due to formation of the surface electron traps, which differ both in the type of the local atomic structure and stability of the electronic states. The implications of this electronic structure for the surface chemical and electron emission properties are discussed.
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Affiliation(s)
- Peter V. Sushko
- Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, UK
- WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
| | - Alexander L. Shluger
- Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, UK
- WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
| | - Yoshitake Toda
- Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Masahiro Hirano
- Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Hideo Hosono
- Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
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22
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Lamberti C, Zecchina A, Groppo E, Bordiga S. Probing the surfaces of heterogeneous catalysts by in situ IR spectroscopy. Chem Soc Rev 2010; 39:4951-5001. [PMID: 21038053 DOI: 10.1039/c0cs00117a] [Citation(s) in RCA: 358] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
This critical review describes the reactivity of heterogeneous catalysts from the point of view of four simple, but essential for Chemistry, molecules (namely dihydrogen, carbon monoxide, nitrogen monoxide and ethylene) that are considered as probes or as reactants in combination with "in situ" controlled temperature and pressure Infrared spectroscopy. The fundamental properties of H(2), CO, NO and C(2)H(4) are shortly described in order to justify their different behaviour in respect of isolated sites in different environments, extended surfaces, clusters, crystalline or amorphous materials. The description is given by considering some "key studies" and trying to evidence similarities and differences among surfaces and probes (572 references).
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Affiliation(s)
- Carlo Lamberti
- Department of Inorganic, Physical and Materials Chemistry, NIS Centre of Excellence, University of Turin. Via P. Giuria 7, 10125 Torino, Italy
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23
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Affiliation(s)
- Peter V. Sushko
- Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom, WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan, and Department of Physics, St. Petersburg State University, St. Petersburg 198504, Russia
| | - Igor V. Abarenkov
- Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom, WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan, and Department of Physics, St. Petersburg State University, St. Petersburg 198504, Russia
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24
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Gonchar A, Risse T, Giamello E, Freund HJ. Additive coloring of thin, single crystalline MgO(001) films. Phys Chem Chem Phys 2010; 12:12520-4. [DOI: 10.1039/c0cp00197j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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25
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Chiesa M, Giamello E, Van Doorslaer S. Ammoniated electrons stabilized at the surface of MgO. J Am Chem Soc 2009; 131:12664-70. [PMID: 19673518 DOI: 10.1021/ja903179b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The reaction of excess electrons at the surface of MgO with ammonia leads to surface ammoniated electrons analogous to those formed when alkali metals are dissolved in anhydrous ammonia. Surface excess electrons are found to be solvated by up to three ammonia molecules, and well-resolved CW and pulsed EPR spectra allow for a precise description of the unpaired electron spin density distribution over the solvent molecules. The large majority of the electron spin density resides in the first-shell nitrogen fragments. HYSCORE spectra allow obtaining for the first time the full hyperfine interaction of the solvated electron with the ammonia protons, which is consistent with a small and negative spin density in the (1)H 1s orbital. Furthermore, the hyperfine and nuclear quadrupole tenors of the second-shell nitrogens could be unravelled.
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Affiliation(s)
- Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I - 10125 Torino, Italy.
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26
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Preda G, Pacchioni G, Chiesa M, Giamello E. The reactivity of CO2 with K atoms adsorbed on MgO powders. Phys Chem Chem Phys 2009; 11:8156-64. [DOI: 10.1039/b906192d] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Adsorption of the first row of transition metals on the perfect and defective MgO(100) surface. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.08.053] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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28
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Moreira IDP, Wojdeł JC, Illas F, Chiesa M, Giamello E. Evidence of magnetic ordering of paramagnetic surface defects on partially hydroxylated MgO nanocrystals. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.07.060] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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29
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Trionfetti C, Babich IV, Seshan K, Lefferts L. Presence of lithium ions in MgO lattice: surface characterization by infrared spectroscopy and reactivity towards oxidative conversion of propane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:8220-8228. [PMID: 18597504 DOI: 10.1021/la8006316] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The surface morphology of Li-promoted MgO catalysts prepared using the sol-gel method (sg) and wet impregnation procedure (imp), respectively, has been studied by low-temperature infrared spectroscopy of adsorbed CO molecules. The results show that step sites, as unselective catalytic centers, are the major features existing on the surface of pure MgO, and those are active toward the oxidative conversion of propane. However, the concentration of these sites is drastically reduced by the incorporation of lithium ions in the MgO lattice. In fact, the incorporated Li (+) ions tend to move into the surface region and occupy sites associated with lower coordination number (e.g., step sites). Li/MgO-sg catalysts are characterized by a higher concentration of incorporation of lithium compared to Li/MgO-imp. In the case of oxidative dehydrogenation/cracking of propane, Li/MgO-sg catalysts show higher activity and selectivity to olefins compared to materials prepared using wet impregnation. Catalytic performance differs strongly regarding (i) the amount of olefins formed, and (ii) the ratio of C(3)H(6)/C(2)H(4). It is shown that high density of active sites is essential for further oxidative dehydrogenation of propyl radicals to propylene and suppression of cracking reactions pathway.
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Affiliation(s)
- Cristiano Trionfetti
- Catalytic Processes and Materials Group, Faculty of Science and Technology, IMPACT, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
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30
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Pacchioni G, Sicolo S, Valentin CD, Chiesa M, Giamello E. A Route toward the Generation of Thermally Stable Au Cluster Anions Supported on the MgO Surface. J Am Chem Soc 2008; 130:8690-5. [DOI: 10.1021/ja710969t] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Sabrina Sicolo
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Cristiana Di Valentin
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Mario Chiesa
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Elio Giamello
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
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31
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Finazzi E, Di Valentin C, Pacchioni G, Chiesa M, Giamello E, Gao H, Lian J, Risse T, Freund HJ. Properties of Alkali Metal Atoms Deposited on a MgO Surface: A Systematic Experimental and Theoretical Study. Chemistry 2008; 14:4404-14. [DOI: 10.1002/chem.200702012] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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32
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Ruszak M, Witkowski S, Sojka Z. EPR and Raman investigations into anionic redox chemistry of nanoporous 12CaO·7Al2O3 interacting with O2, H2 and N2O. RESEARCH ON CHEMICAL INTERMEDIATES 2007. [DOI: 10.1163/156856707782169435] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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33
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Sterrer M, Berger T, Diwald O, Knözinger E, Allouche A. Ozonide ions on the surface of MgO nanocrystals. Top Catal 2007. [DOI: 10.1007/s11244-007-0321-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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34
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Napoli F, Chiesa M, Giamello E, Finazzi E, Valentin CD, Pacchioni G. Partially Hydroxylated Polycrystalline Ionic Oxides: A New Route toward Electron-Rich Surfaces. J Am Chem Soc 2007; 129:10575-81. [PMID: 17685526 DOI: 10.1021/ja073114k] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Charge traps at the surface of oxide materials play a fundamental role in various chemical processes, such as the activation of supported metal clusters. In this study, combining electron paramagnetic resonance with cluster model DFT calculations, we show that excess electrons at the surface of MgO, CaO, and SrO polycrystalline materials can be generated by preparing weakly hydroxylated surfaces followed by deposition of small amounts of alkali metals. The residual OH groups present on specific sites of the partially dehydroxylated surface act as stable traps for electrons donated by the alkali metal (Na in this case) which forms a Na+ ion distant from the trapped electron. This process results in the formation of thermally stable (H+)(e-) color centers at the surface of the oxide. The procedure could be of interest for the stabilization and activation of supported metal nanoparticles with potential use in catalysis.
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Affiliation(s)
- Francesco Napoli
- Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7-10125, Torino, Italy
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35
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Chizallet C, Costentin G, Che M, Delbecq F, Sautet P. Infrared Characterization of Hydroxyl Groups on MgO: A Periodic and Cluster Density Functional Theory Study. J Am Chem Soc 2007; 129:6442-52. [PMID: 17465545 DOI: 10.1021/ja068720e] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The infrared OH stretching frequencies of the various types of hydroxyl groups on MgO surfaces have been calculated by periodic (VASP) and cluster (Gaussian) DFT simulations. Surface irregularities (mono and diatomic steps, corners, step divacancies, and kinks) have been considered to model the IR spectra of hydroxylated MgO powders. A good correspondence between calculated and experimental frequencies is obtained with the B3LYP functional. Hydrogen-bonding is the parameter which influences most the IR frequency of OH groups, followed by location of OH groups in concave or convex areas of the surface and then oxygen coordination. The evolution of experimental IR spectra upon evacuation at increasing temperature can be rationalized on the basis of calculated thermal stabilities of each kind of OH groups. A new model is finally proposed to help assign the experimental bands, in terms of hydrogen-bonding, local topology of the hydroxylated sites, and coordination of oxygen.
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Affiliation(s)
- Céline Chizallet
- Laboratoire de Réactivité de Surface, Université Pierre et Marie Curie-Paris 6, CNRS 4 place Jussieu, 75252 Paris Cedex 05, France.
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36
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Srnec M, Zahradník R. Small Group IIa–VIa Clusters and Related Systems: A Theoretical Study of Physical Properties, Reactivity, and Electronic Spectra. Eur J Inorg Chem 2007. [DOI: 10.1002/ejic.200600816] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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37
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38
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Cinquini F, Valentin CD, Finazzi E, Giordano L, Pacchioni G. Theory of oxides surfaces, interfaces and supported nano-clusters. Theor Chem Acc 2006. [DOI: 10.1007/s00214-006-0204-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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39
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Chiesa M, Paganini MC, Giamello E, Murphy DM, Di Valentin C, Pacchioni G. Excess electrons stabilized on ionic oxide surfaces. Acc Chem Res 2006; 39:861-7. [PMID: 17115726 DOI: 10.1021/ar068144r] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Surface excess electrons are remarkable chemical entities that provide great opportunities for the design of new materials with precisely tuned electronic and magnetic properties. In this Account, we describe the structure and electronic properties of excess electron centers generated at the surface of insulating oxides. We also outline the elementary mechanisms that are at the basis of the generation of excess electrons at solid surfaces, setting a comparison to the general problem of excess electron localization in condensed media. Emphasis is given to morphological aspects relative to the surface-trapping sites as deduced from combined electron paramagnetic resonance and accurate quantum chemical calculations. The remarkable reactivity featured by the so formed "electron-rich" surfaces is illustrated, describing the reduction of simple diatomic molecules that form adsorbed radical anions via direct surface to adsorbate electron transfer.
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Affiliation(s)
- Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Center of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
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40
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Stankic S, Müller M, Diwald O, Sterrer M, Knözinger E, Bernardi J. Size-dependent optical properties of MgO nanocubes. Angew Chem Int Ed Engl 2006; 44:4917-20. [PMID: 15999373 DOI: 10.1002/anie.200500663] [Citation(s) in RCA: 191] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Slavica Stankic
- Institute of Materials Chemistry, Vienna University of Technology, Veterinärplatz 1/GA, 1210 Vienna, Austria
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41
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Carrasco J, Sousa C, Illas F, Sushko PV, Shluger AL. Optical absorption and luminescence energies of F centers in CaO fromab initioembedded cluster calculations. J Chem Phys 2006; 125:074710. [PMID: 16942367 DOI: 10.1063/1.2337292] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We calculated the optical absorption and luminescence energies of electrons trapped at oxygen vacancies in CaO using a consistent embedded cluster method which accounts for the long-range polarization effects and partial covalence of CaO. Optical absorption and luminescence energies of neutral (F center) and positively charged (F+ center) vacancies are calculated by means of time dependent density functional theory using the B3LYP exchange-correlation density functional. Our results demonstrate that using large basis sets to describe a diffuse nature of excited states, and properly accounting for long-range polarization induced by charged and excited defect states, is crucial for accurate predictions of optical excitation and luminescence energies of these defects.
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Affiliation(s)
- Javier Carrasco
- Departament de Quimíca Física, Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain
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42
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Chizallet C, Costentin G, Che M, Delbecq F, Sautet P. Revisiting Acido-basicity of the MgO Surface by Periodic Density Functional Theory Calculations: Role of Surface Topology and Ion Coordination on Water Dissociation. J Phys Chem B 2006; 110:15878-86. [PMID: 16898740 DOI: 10.1021/jp060840l] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Low-coordinated (LC) ions at the MgO surface (noted Mg2+LC and O2-LC with L = 1-5), located on monatomic and diatomic steps, corners, step divacancies, and kinks, have been modeled thanks to periodic density functional theory (DFT) calculations (VASP). Ions of lowest coordination induce the strongest surface geometry relaxation and the highest surface energies. The hydration energies of these sites and thermodynamic stabilities of the resulting surfaces were studied. The factors controlling the interaction strength between water and the surface are the possibility for the hydroxyl group to adopt a bridging geometry between two Mg2+ cations in concave areas of the surface, such as the bottom of the monatomic step, and at second order the surface atomic coordination, and especially the presence of three-coordinated ions. The Lewis basicity and acidity of O2-LC and Mg2+LC, respectively, increase as their coordination number decreases, which implies the same trend for the Brønsted basicity of the Mg2+-O2- pair toward water. However, this trend can be changed if pairs leading to the formation of bridging OH groups are involved, typically on monatomic steps or in step divacancies where O2C-H and O3C-H are obtained, respectively, instead of the expected O1C-H. Thanks to thermodynamic calculations, the state of the surface as a function of temperature can be determined at a given pressure, unraveling the roles of surface topology and ions coordination.
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Affiliation(s)
- Céline Chizallet
- Laboratoire de Réactivité de Surface, UMR 7609 CNRS, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05, France
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43
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Paganini MC, Chiesa M, Dolci F, Martino P, Giamello E. EPR Study of the Surface Basicity of Calcium Oxide. 3. Surface Reactivity and Nonstoichiometry. J Phys Chem B 2006; 110:11918-23. [PMID: 16800495 DOI: 10.1021/jp061131a] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High surface area polycrystalline calcium oxide forms ozonide O3- ions upon O2 adsorption and NO3(2-) anions under low pressures of NO. Both radical anions, detected by electron paramagnetic resonance (EPR), are not observed in the case of the homologous magnesium oxide. This behavior reveals the presence, in CaO, of anomalies with respect to the ideal composition of an ionic oxide which are identified in terms of two main types of defects. The first type consists of positive holes dispersed in the bulk and originated by the unavoidable presence of Na+ ions in the composition of the solid. The decomposition of the surface ozonide shows the formation of a transient surface stabilized O- (the chemical notation of a positive hole associated to an oxide ion) which is for the first time reported at the surface of CaO. The second type of defect consists of surface peroxide groups (present at particular surface sites where they are formed by pairing of two distinct O-) which react with nitric oxide (NO) yielding NO3(2-) radical anions. The presence of peroxide is not related to the presence of impurities but, rather, to a certain propensity of the solid to form such ions at the surface along the dehydration process.
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Affiliation(s)
- Maria Cristina Paganini
- Dipartimento di Chimica IFM, Università di Torino and N.I.S., Nanostructured Interfaces and Surfaces, Center of Excellence, via P. Giuria 7, I-10125 Torino, Italy
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44
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Sterrer M, Fischbach E, Heyde M, Nilius N, Rust HP, Risse T, Freund HJ. Electron Paramagnetic Resonance and Scanning Tunneling Microscopy Investigations on the Formation of F+ and F0 Color Centers on the Surface of Thin MgO(001) Films. J Phys Chem B 2006; 110:8665-9. [PMID: 16640421 DOI: 10.1021/jp060546t] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The formation of surface color centers (F(S) centers) by electron bombardment of thin MgO(001) films is investigated using electron paramagnetic resonance and low-temperature scanning tunneling microscopy. At low electron doses both techniques indicate the formation of singly occupied color centers (F(S)(+)), whereas at high electron doses the doubly occupied type (F(S)(0)) is dominant. It is suggested that with increasing electron dose F(S)(+) centers are transformed into F(S)(0). Tunneling spectra of individual F(S)(0) centers reveal a large distribution of energetic positions of occupied and unoccupied states, which is caused by local variations of the coordination number of the defects and explains the broad signals usually detected with integrating spectroscopic techniques.
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Affiliation(s)
- Martin Sterrer
- Department of Chemical Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany. sterrer@ fhi-berlin.mpg.de
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45
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New frontier in transmission IR spectroscopy of molecules adsorbed on high surface area solids: Experiments below liquid nitrogen temperature. Catal Today 2006. [DOI: 10.1016/j.cattod.2005.11.011] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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46
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Chiesa M, Giamello E, Di Valentin C, Pacchioni G, Sojka Z, Van Doorslaer S. Nature of the chemical bond between metal atoms and oxide surfaces: new evidences from spin density studies of K atoms on alkaline earth oxides. J Am Chem Soc 2006; 127:16935-44. [PMID: 16316239 DOI: 10.1021/ja0542901] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have studied the interaction of K atoms with the surface of polycrystalline alkaline-earth metal oxides (MgO, CaO, SrO) by means of CW- and Pulsed-EPR, UV-Vis-NIR spectroscopies and DFT cluster model calculations. The K adsorption site is proposed to be an anionic reverse corner formed at the intersection of two steps, where K binds by more than 1 eV, resulting in thermally stable species up to about 400 K. The bonding has small covalent and large polarization contributions, and the K atom remains neutral, with one unpaired electron in the valence shell. The interaction results in strong modifications of the K electronic wave function which are directly reflected by the hyperfine coupling constant, (K)a(iso). This is found to be a very efficient "probe" to measure the degree of metal-oxide interaction which directly depends on the substrate basicity. These results provide an original and general model of the early stages of the metal-support interaction in the case of ionic oxides.
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Affiliation(s)
- Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino, Italy.
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47
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Chiesa M, Paganini MC, Giamello E, Di Valentin C, Pacchioni G. Electron Traps on Oxide Surfaces: (H+)(e−) Pairs Stabilized on the Surface of 17O Enriched CaO. Chemphyschem 2006; 7:728-34. [PMID: 16477669 DOI: 10.1002/cphc.200500564] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
(H+)(e-) pairs generated at the surface of polycrystalline CaO are analyzed for the first time in terms of the interaction of the unpaired electron spin with the nuclear spin of the 17O anions of the surface. CaO crystals enriched in the 17O isotope are prepared and the corresponding hyperfine coupling constants are measured in electron paramagentic resonance (EPR) spectra. The results are analyzed on the basis of cluster model density functional theory calculations. The computed hyperfine coupling constants for (H+)(e-) pairs formed on the edge, corner, and reverse corner sites of the CaO surface allow a tentative assignment of two observed spectral features to specific morphological surface sites.
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Affiliation(s)
- Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Center of Excellence, Via P. Giuria 7, 10125 Torino, Italy.
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48
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Giordano L, Pacchioni G. Charge transfers at metal/oxide interfaces: a DFT study of formation of Kδ+and Auδ−species on MgO/Ag(100) ultra-thin films from deposition of neutral atoms. Phys Chem Chem Phys 2006; 8:3335-41. [PMID: 16835682 DOI: 10.1039/b604288k] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Ultra-thin oxide films grown on a metal substrate and of thickness smaller than 1 nm may exhibit unusual properties with respect to thicker films or single crystal oxide surfaces. In a previous study [G. Pacchioni, L. Giordano and M. Baistrocchi, Phys. Rev. Lett., 2005, 94, 226104] we have suggested that a Au atom adsorbed on a MgO/Mo(100) thin film becomes negatively charged by direct electron tunneling from the Mo metal and that this is related to the low MgO/Mo(100) work function. Here we show, based on periodic DFT supercell calculations, that charge transfer can occur also in the opposite direction by adsorption of electropositive K atoms on MgO/Ag(100) films. We predict the occurrence of a charge transfer also for Au on MgO/Ag(100) films despite the fact that here the work function is 1 eV larger than in MgO/Mo(100). The formation of a layer of adsorbed negative (Au delta-/MgO/Ag) or positive (K delta+/MgO/Ag) adsorbates results in an increase or decrease, respectively, of the MgO/Ag(100) work function as predicted by the classical Gurney model for ionic adsorbates on metal surfaces.
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Affiliation(s)
- Livia Giordano
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi, 53-20125, Milano, Italy
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49
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Sterrer M, Heyde M, Novicki M, Nilius N, Risse T, Rust HP, Pacchioni G, Freund HJ. Identification of Color Centers on MgO(001) Thin Films with Scanning Tunneling Microscopy. J Phys Chem B 2005; 110:46-9. [PMID: 16471496 DOI: 10.1021/jp056306f] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Localized electronic defects on the surface of a 4 monolayer (ML) thin MgO(001) film deposited on Ag(001) have been investigated by low-temperature scanning tunneling microscopy and spectroscopy. Depending on the location of the defect, we observe for the first time different defect energy levels in the band gap of MgO. The charge state of defects can be manipulated by interactions with the scanning tunneling microscope tip. Comparison with ground state energy levels of color centers on the MgO surface obtained from embedded cluster calculations corroborates the assignment of the defects to singly and doubly charged color centers.
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Affiliation(s)
- Martin Sterrer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Chemical Physics, Faradayweg 4-6, D-14195 Berlin, Germany.
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50
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Stankic S, Sterrer M, Hofmann P, Bernardi J, Diwald O, Knözinger E. Novel optical surface properties of Ca2+ -doped MgO nanocrystals. NANO LETTERS 2005; 5:1889-93. [PMID: 16218704 DOI: 10.1021/nl0511418] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Surface doping of oxide nanoparticles is important in fields ranging from heterogeneous catalysis to optoelectronics. Here, we report the solvent-free synthesis of mixed calcium-magnesium oxide nanocrystals in the size range between 5 and 40 nm. Although CaMgO mixtures are thermodynamically forbidden on a macroscopic scale, Calcium ions can be distributed homogeneously in MgO using chemical vapor deposition (CVD) as a nonequilibrium technique. Subsequent thermal activation leads to calcium ion segregation into the nanocrystal surface which, in addition to the synthesis parameters, provides efficient means for manipulating the optical surface properties of insulating oxide nanocrystals. A novel material with unexpected photonic behavior, such as enhanced photoluminescence emission which is also red-shifted with respect to those of CaO and MgO, was found.
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Affiliation(s)
- Slavica Stankic
- Institute of Materials Chemistry, Vienna University of Technology, Veterinärplatz 1/GA, A-1210 Vienna, Austria
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