A Surface Science Approach to Understanding Supported Vandia Catalysts PDF Download
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Author: Gordon Sek-Yin Wong
Publisher:
ISBN:
Category :
Languages : en
Pages : 291
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Author: Gordon Sek-Yin Wong
Publisher:
ISBN:
Category :
Languages : en
Pages : 291
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Author: Johannes W. Niemantsverdriet
Publisher:
ISBN:
Category :
Languages : en
Pages : 149
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Author: M. Bowker
Publisher:
ISBN: 9780854048984
Category : Catalysis
Languages : en
Pages : 412
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Author: Xiaolin Zheng
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 165
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Book Description
One of the key issues in the field of catalysis is to relate the catalyst structure/composition to its activity/selectivity. One way to understand this relationship is to understand the individual role each catalyst component plays in the chemical reaction. Industrial catalysts can be extremely complex in structure and to understand their reaction kinetics, researchers often study simpler surfaces such as single crystals using surface science techniques. This introduces a well-known problem in the field of catalysis commonly referred to as the "pressure and materials gap." Typically, industrial catalyst research is performed under process conditions, which means operating pressures of one atmosphere or higher. Under these conditions, it is difficult to extract intrinsic kinetic properties of the catalyst which are properties that are directly related to the catalyst structure and composition. To find these intrinsic kinetic properties, scientists turn to surface science techniques using different types of spectroscopic tools to study reaction properties on single crystal surfaces under ultra-high vacuum (UHV) conditions. Experiments using single crystals and surface science techniques have helped establish that some crystal planes are more active and/or selective than others. Although surface science approaches are successful in obtaining fundamental information on a variety of catalytic reactions on the atomic level, current catalytic reactions are still carried out under atmospheric pressures or greater and on much more complex materials than single crystal surfaces. This dissertation introduces a new approach to characterize catalysts that vary in compositional/structural complexity in order to understand their performance in a conventional reactor/reaction environment under both atmospheric pressure and ultra-high vacuum conditions. Experiments performed under both pressure regimes were carried out using the same apparatus, the Temporal Analysis of Products (TAP) reactor. The catalysts under investigation are bulk transition metals (Pt), transition metals deposited on metal oxide supports (Pt/SiO2), and mixed metal oxides (VPO). The catalysts are applied to two types of reaction systems, CO oxidation and selective oxidation of hydrocarbons. The goal of the experiments is to understand and distinguish the role of each component of the catalyst during chemical reaction. Using the TAP reactor, the number of active sites, reaction mechanisms, adsorption/desorption rate constants, and rates of reaction can be determined.
Author: Carrie Ann Farberow
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The design of improved heterogeneous catalysts requires a detailed understanding of the governing surface chemistry. Significant advances over the past two decades in electronic structure calculation algorithms and high performance computing have made theoretical tools indispensable in the quest to understand catalysis at the atomic scale. In this dissertation, first principles electronic structure calculations based on density functional theory (DFT) and microkinetic modeling are combined with experimental studies, including surface science, electrocatalysis and reaction kinetics, to elucidate reaction mechanisms and design improved catalysts for a variety of reactions important to energy and environmental applications. Chapters 3 and 4 of this dissertation focus on the fundamental end of the catalysis research spectrum. In this work, experimental surface science studies, using high-resolution, high-speed scanning tunneling microscopy are combined with periodic, self-consistent DFT calculations to improve our understanding of two important processes, hydrogen diffusion and water adsorption, on a metal oxide thin film. In Chapter 5, first principles calculations are utilized to study the vapor phase reaction between hydrogen and oxygen on a homogeneous bimetallic PdAg alloy surface. A successful example of catalyst design for an electrocatalytic application is demonstrated in Chapter 6 using a combined theoretical and experimental approach. A core-shell alloy, composed of an Ir-Re core and Pt and Pd shell layers, is shown to be an effective low cost electocatalyst for the oxygen reduction reaction. Finally, in Chapters 7 and 8 of this dissertation, DFT calculations are combined with experimental reaction kinetic studies using a microkinetic model to bridge the pressure and materials gap, in a study of nitric oxide reduction by hydrogen on a platinum catalyst. In this work, we show the impact of nitric oxide surface coverage on the reaction energetics and elucidate the reaction pathways governing the activity and selectivity of the reaction on Pt under realistic reaction conditions.
Author: Ronnie T. Vang
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The catalytic reactions studied include hydrocarbon conversion over platinum, the transition metal-catalyzed hydrogenation of carbon monoxide, and the photocatalyzed dissociation of water over oxide surfaces. The method of combined surface science and catalytic studies is similar to those used in synthetic organic chemistry. The single-crystal models for the working catalyst are compared with real catalysts by comparing the rates of cyclopropane ring opening on platinum and the hydrogenation of carbon monoxide on rhodium single crystal surface with those on practical commercial catalyst systems. Excellent agreement was obtained for these reactions. This document reviews what was learned about heterogeneous catalysis from these surface science approaches over the past 15 years and present models of the active catalyst surface.
Author: Ryan Anthony Ciufo
Publisher:
ISBN:
Category :
Languages : en
Pages : 216
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The fundamental understanding of both the reactions at catalytic surfaces and the ways in which these surfaces change throughout a catalytic cycle and lifetime are important for both academic and industrial disciplines. To develop these understandings on complex catalytic systems, ultra-high vacuum techniques such as molecular beam studies, temperature programmed desorption, reflection-absorption infrared spectroscopy and Auger electron spectroscopy can be used to study the simplest interactions between gas molecules and surfaces. These interactions can be studied from a bottom-up approach to learn about the system in question, upon which additional complexities can be added. To parallel these experimental techniques, a number of computational methods can be used to support findings and guide new experiments. Ab-initio electronic structure calculations allow for a better understanding of adsorbate-surface interactions, while long timescale dynamic simulations provide insight into the time evolution and kinetics of catalysts and catalytic surfaces. Empirical and machine-learning guided potentials can be developed to lessen computational cost while retaining accuracies comparable to ab-initio calculations. Fitting such potentials ultimately allows for larger calculations to be performed and longer timescales to be simulated. The above methods will be applied to a number of industrially and academically relevant catalytic systems, including studying the interaction of H2 and CO with Cobalt based Fischer-Tropsch catalysts and the interaction between hydrogen and palladium surfaces. Additionally, the development of a machine learning package to fit and use interatomic potentials will be discussed
Author: Claude R. Henry
Publisher:
ISBN:
Category :
Languages : en
Pages : 94
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Author: Hui-Feng Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 118
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