Quantum Chemical Studies Of Deposition And Catalytic Surface Reactions
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Quantum Chemical Studies Of Deposition And Catalytic Surface Reactions
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Author : Emil Kalered
language : en
Publisher: Linköping University Electronic Press
Release Date : 2018-06-19
Quantum Chemical Studies Of Deposition And Catalytic Surface Reactions written by Emil Kalered and has been published by Linköping University Electronic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-06-19 with categories.
Quantum chemical calculations have been used to model chemical reactions in epitaxial growth of silicon carbide by chemical vapor deposition (CVD) processes and to study heterogeneous catalytic reactions for methanol synthesis. CVD is a common method to produce high-quality materials and e.g. thin films in the semiconductor industry, and one of the many usages of methanol is as a promising future renewable and sustainable energy carrier. To optimize the chemical processes it is essential to understand the reaction mechanisms. A comprehensive theoretical model for the process is therefore desired in order to be able to explore various variables that are difficult to investigate in situ. In this thesis reaction paths and reaction energies are computed using quantum chemical calculations. The quantum-chemical results can subsequently be used as input for thermodynamic, kinetic and computational fluid dynamics modelling in order to obtain data directly comparable with the experimental observations. For the CVD process, the effect of halogen addition to the gas mixture is studied by modelling the adsorption and diffusion of SiH2, SiCl2 and SiBr2 on the (0001?) 4H-SiC surface. SiH2 was found to bind strongest to the surface and SiBr2 binds slightly stronger than the SiCl2 molecule. The diffusion barrier is shown to be lower for SiH2 than for SiBr2 and SiCl2 which have similar barriers. SiBr2 and SiCl2 are found to have similar physisorption energies and bind stronger than the SiH2 molecule. Gibbs free-energy calculations also indicate that the SiC surface is not fully hydrogen terminated at CVD conditions since missing-neighboring pair of surface hydrogens is found to be common. Calculations for the (0001) surface show that SiCl, SiCl2, SiHCl, SiH, and SiH2 likely adsorb on a methylene site, but the processes are thermodynamically less favorable than their reverse reactions. However, the adsorbed products may be stabilized by subsequent surface reactions to form a larger structure. The formation of these larger structures is found to be fast enough to compete with the desorption processes. Also the Gibbs free energies for adsorption of Si atoms, SiX, SiX2, and SiHX where X is F or Br are presented. Adsorption of Si atoms is shown to be the most thermodynamically favorable reaction followed by SiX, SiHX, and SiX2, X being a halide. The results in this study suggest that the major Si contributors in the SiC–CVD process are Si atoms, SiX and SiH. Methanol can be synthesized from gaseous carbon dioxide and hydrogen using solid metal-metal oxide mixtures acting as heterogeneous catalysts. Since a large surface area of the catalyst enhances the speed of the heterogeneous reaction, the use of nanoparticles (NP) is expected to be advantageous due to the NPs’ large area to surface ratio. The plasma-induced creation of copper NPs is investigated. One important element during particle growth is the charging process where the variation of the work function (W) with particle size is a key quantity, and the variation becomes increasingly pronounced at smaller NP sizes. The work functions are computed for a set of NP charge numbers, sizes and shapes, using copper as a case study. A derived analytical expression for W is shown to give quite accurate estimates provided that the diameter of the NP is larger than about a nanometer and that the NP has relaxed to close to a spherical shape. For smaller sizes W deviates from the approximative expression, and also depends on the charge number. Some consequences of these results for NP charging process are outlined. Key reaction steps in the methanol synthesis reaction mechanism using a Cu/ZrO2 nanoparticle catalyst is investigated. Two different reaction paths for conversion of CO2 to CO is studied. The two paths result in the same complete reaction 2 CO2 ? 2 CO + O2 where ZrO2 (s) acts as a catalyst. The highest activation energies are significantly lower compared to that of the gas phase reaction. The presence of oxygen vacancies at the surface appear to be decisive for the catalytic process to be effective. Studies of the reaction kinetics show that when oxygen vacancies are present on the ZrO2 surface, carbon monoxide is produced within a microsecond. The IR spectra of CO2 and H2 interacting with ZrO2 and Cu under conditions that correspond to the catalyzed CH3OH production process is also studied experimentally and compared to results from the theoretical computations. Surface structures and gas-phase molecules are identified through the spectral lines by matching them to specific vibrational modes from the literature and from the new computational results. Several surface structures are verified and can be used to pin point surface structures in the reaction path. This gives important information that help decipher how the reaction mechanism of the CO2 conversion and ultimately may aid to improve the methanol synthesis process.
Quantum Chemistry Approaches To Chemisorption And Heterogeneous Catalysis
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Author : F. Ruette
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-03-14
Quantum Chemistry Approaches To Chemisorption And Heterogeneous Catalysis written by F. Ruette and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-03-14 with Science categories.
The development of "high-tech" materials in contemporary industries is deeply related to a detailed understanding of specific surface properties of catalysts which make particular reactions possible. But this understanding presupposes that there exists a body of theory capable of explaining situations not easily accessible to experimental methods and of relating experimental findings among themselves and with theoretical constructs. For these reasons, theoretical developments in surface physics and surface chemistry of transition metal compounds have been of paramount importance in promoting progress in catalysis, electronic devices, corrosion, etc. Although a great variety of spectroscopic methods for analyzing solids and surfaces at molecular scale have been introduced in recent years, nevertheless, many questions about the adsorption sites and intermediates, the effect of promoters, the poisoning of active sites, the nature of segregation of impurities, the process of surface reconstruction, the mechanisms of reactions, etc. have remained unanswered simply because of the great complexity of surface phenomena. It is in this sense that quantum mechanical method- combined with experimental data - may shed some light on the microscopic properties of new surface materials.
Surface Reactions
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Author : R.J. Madix
language : en
Publisher: Springer
Release Date : 2011-12-21
Surface Reactions written by R.J. Madix and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-12-21 with Technology & Engineering categories.
A treatment of the important aspects of physical chemistry on metal surfaces, including selective oxidation, desulfurization, cyclization, metal-organic chemical vapor deposition, alkane activation and hydrogen dissociation dynamics. Case studies focus on on the chemistry of selected systems, rather than the techniques, to convey the excitement of recent developments.
Quantum Theory Of Chemical Reactions
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Author : R. Daudel
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-03-14
Quantum Theory Of Chemical Reactions written by R. Daudel and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-03-14 with Science categories.
Atom Resolved Surface Reactions
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Author : Philip Rosser Davies
language : en
Publisher: Royal Society of Chemistry
Release Date : 2008
Atom Resolved Surface Reactions written by Philip Rosser Davies and has been published by Royal Society of Chemistry this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Science categories.
This book offers a unique perspective of the impact of scanning probe microscopies on our understanding of the chemistry of the surface at the nanoscale. Research oriented, with the concepts gleaned from Scanning Tunnelling Microscopy being related to the more established and accepted views in surface chemistry and catalysis the authors have addresses the question "How do the models based on classical spectroscopic and kinetic studies stand up to scrutiny at the atom - resolved level?". In taking this approach the reader, new to the field of surface chemistry, should be able to obtain a perspective on how the evidence from STM confirms or questions long standing tenets. An emphasis is given to "how did we get to where we are now" and a large number of figures from the literature are included along with suggestions for further reading. Topics discussed include: - the dynamics of oxygen chemisorption at metal surfaces - control of oxygen states and surface reconstruction - dissociative chemisorption of diatomic and hydrocarbon molecules - nanoparticles and chemical reactivity - STM at high pressures - structural studies of sulfur containing molecules and molecular templating This book will appeal to all those who wish to become familiar with the contribution Scanning Tunnelling Microscopy has made to the understanding of the field of surface chemistry and heterogeneous catalysis and also to those who are new to catalysis, a fascinating and important area of chemistry.
Quantum Theory Of Chemical Reactions
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Author : Raymond Daudel
language : en
Publisher: Springer Science & Business Media
Release Date : 1980
Quantum Theory Of Chemical Reactions written by Raymond Daudel and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 1980 with Quantum chemistry categories.
Heterogeneous Catalysts
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Author : Wey Yang Teoh
language : en
Publisher: John Wiley & Sons
Release Date : 2021-02-23
Heterogeneous Catalysts written by Wey Yang Teoh and has been published by John Wiley & Sons this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-02-23 with Technology & Engineering categories.
Presents state-of-the-art knowledge of heterogeneous catalysts including new applications in energy and environmental fields This book focuses on emerging techniques in heterogeneous catalysis, from new methodology for catalysts design and synthesis, surface studies and operando spectroscopies, ab initio techniques, to critical catalytic systems as relevant to energy and the environment. It provides the vision of addressing the foreseeable knowledge gap unfilled by classical knowledge in the field. Heterogeneous Catalysts: Advanced Design, Characterization and Applications begins with an overview on the evolution in catalysts synthesis and introduces readers to facets engineering on catalysts; electrochemical synthesis of nanostructured catalytic thin films; and bandgap engineering of semiconductor photocatalysts. Next, it examines how we are gaining a more precise understanding of catalytic events and materials under working conditions. It covers bridging pressure gap in surface catalytic studies; tomography in catalysts design; and resolving catalyst performance at nanoscale via fluorescence microscopy. Quantum approaches to predicting molecular reactions on catalytic surfaces follows that, along with chapters on Density Functional Theory in heterogeneous catalysis; first principles simulation of electrified interfaces in electrochemistry; and high-throughput computational design of novel catalytic materials. The book also discusses embracing the energy and environmental challenges of the 21st century through heterogeneous catalysis and much more. Presents recent developments in heterogeneous catalysis with emphasis on new fundamentals and emerging techniques Offers a comprehensive look at the important aspects of heterogeneous catalysis Provides an applications-oriented, bottoms-up approach to a high-interest subject that plays a vital role in industry and is widely applied in areas related to energy and environment Heterogeneous Catalysts: Advanced Design, Characterization and Applications is an important book for catalytic chemists, materials scientists, surface chemists, physical chemists, inorganic chemists, chemical engineers, and other professionals working in the chemical industry.
Surface Science Of Catalysis
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Author : Daniel J. Dwyer
language : en
Publisher:
Release Date : 1992
Surface Science Of Catalysis written by Daniel J. Dwyer and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with Language Arts & Disciplines categories.
Presents an excellent overview of the impact of surface science on the field of catalysis. Explores the exciting new advances in surface science and catalysis, which for the first time allow for direct spectroscopic and kinetic observation of surface reactions. Twenty-two chapters cover fundamental aspects of catalytic reactions at surfaces, applications of surface probes to the study of catalytic reactions and kinetics, and novel aspects of catalytic reactions at surfaces. Highlights the success of surface science techniques in the study of industrially important catalytic processes, including hydrogenation of CO to produce hydrocarbons and methanol, the oxidation of methane to methanol, and conversions of CO to carbon dioxide.
Surface And Nanomolecular Catalysis
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Author : Ryan Richards
language : en
Publisher: CRC Press
Release Date : 2006-05-25
Surface And Nanomolecular Catalysis written by Ryan Richards and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006-05-25 with Science categories.
Using new instrumentation and experimental techniques that allow scientists to observe chemical reactions and molecular properties at the nanoscale, the authors of Surface and Nanomolecular Catalysis reveal new insights into the surface chemistry of catalysts and the reaction mechanisms that actually occur at a molecular level during catalys
Reactions Of Organic Molecules On Metal Surfaces Studied By Stm
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Author : Markus Wahl
language : en
Publisher: Cuvillier Verlag
Release Date : 2007-02-08
Reactions Of Organic Molecules On Metal Surfaces Studied By Stm written by Markus Wahl and has been published by Cuvillier Verlag this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007-02-08 with Science categories.
Two distinct systems of surface reactions involving complex organic molecules were studied on single crystal metal surfaces by Scanning Tunneling Microscopy (STM), Low Energy Electron Diffraction (LEED) and X-ray Photoelectron Spectroscopy (XPS) under ultra high vacuum conditions. The first system focused on the Pt-cinchona alkaloid system, which is a powerful catalytic system in the field of enantioselective heterogeneous catalysis. Herein, an achiral reactant molecule is hydrogenated over a cinchona alkaloid modified platinum surface. The aim of the STM study was to gain direct insight in the molecular processes which occur during adsorption of modifiers and reactants involved. Therefore, the adsorption of cinchonidine (CD), cinchonine (CN) and 2,2,2-trifluoroacetophenone (TFAP) was investigated on both Pt(111) and Pd(111) single crystal surfaces. Different adsorption modes could be identified and a change in adsorption geometry upon addition of hydrogen could be followed. Our work showed, that the discrimination of different surface species by their mobility and the time-resolved observation of their surface chemical processes by STM provides a powerful tool for the investigation of complex catalyst systems. Such studies complement other surface analytical methods and quantum chemical calculations and help to gain insight into the mechanistic aspects. The second system is an example of how surface reactions can be used to efficiently self-assemble large complex structures. For this purpose a perylene derivative, 4,9-diaminoperylene-quinone-3,10-diimine (DPDI), was deposited on a Cu(111) single crystal surface and investigated by STM. These highly mobile precursor molecules are then transformed via a thermally induced surface-assisted dehydrogenation reaction by annealing in-situ at 300 °C. The resulting molecules form autocomplementary species of hydrogen-bond donor and acceptors and thereby can interact with each other via H-bonding. Due to strong so-called resonance-assisted hydrogen-bondings (RAHB) and an exact register with the Cu surface a highly robust and porous hexagonal network structure is formed. This structure is well-suited for the incorporation or trapping of guest molecules. By trapping and manipulation of C60 and octaethylporphyrin (OEP) molecules inside this network it was possible to built exemplary nanosized supramolecular “ball-bearings” and “rotor-stator” systems.