Elementary Processes in Alkane Activation Over Zeolite Catalysts PDF Download
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Author: Carsten Sievers
Publisher:
ISBN:
Category :
Languages : en
Pages : 272
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Book Description
Author: Carsten Sievers
Publisher:
ISBN:
Category :
Languages : en
Pages : 272
Get Book Here
Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Lanthanum exchanged faujasite type zeolites have a great potential as heterogeneous catalysts for isobutane/2-butene alkylation. These porous solids polarize adsorbed alkanes so strongly that a hydride can be abstracted from some octane isomers under near ambient conditions. The resulting formation of carbenium ions and the subsequent cleavage of C-C bonds are catalyzed by Brønsted acidic hydroxyl groups, which are abundant in lanthanum exchanged faujasites. The high concentration of aluminum in the zeolite lattice is also of fundamental importance for efficient incorporation of La3+ cations. The catalytic lifetime of lanthanum exchanged faujasites in isobutane/2-butene alkylation increases with increasing concentration of strongly acidic hydroxyl groups. A time resolved picture of the deactivation of these highly defined materials as catalysts in isobutane/2-buten alkylation was obtained, which will provide drastically improved process and regeneration conditions.
Author: Subhash Bhatia
Publisher: CRC Press
ISBN: 100009863X
Category : Science
Languages : en
Pages : 302
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Book Description
Presented in an easy-to-read form, this book on zeolite catalysis cover all aspects of the subject. It focuses on synthesis, structure, diffusion, deactivation, and industrial applications. This book is an ideal text for courses on catalysis or as a supplementary text for those studying applied or industrial chemistry. It is also a useful resource for anyone who works with zeolites as catalysts in the laboratory, pilot plants, or commercial installations.
Author: E.G. Derouane
Publisher: Springer Science & Business Media
ISBN: 9401709823
Category : Science
Languages : en
Pages : 482
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Book Description
Light alkanes tend to be resistant to many forms of activation. The horizontal approach of the present book covers homogeneous, heterogeneous and biological catalysis, thus allowing readers to gain an awareness of progress and ideas in research areas different from their own. The book contains both general chapters, giving an overview of the subject, and specialised contributions that deal with the details and state of the art. A specialist report is also included which gives a critical insight into current progress and discusses future prospects and major challenges. Audience: Newcomers and senior researchers in the field of alkane activation. The mixed theoretical and practical approach will be of interest to researchers and industrialists alike.
Author: R. W. Joyner
Publisher: Springer Science & Business Media
ISBN: 9780792322849
Category : Science
Languages : en
Pages : 512
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Book Description
The Elementary Reaction Steps in Heterogeneous Catalysis was studies during the first week in November, 1992, by no fewer than 54 participants, drawn from 11 countries, with both industrial and academic backgrounds. The five sessions reported in the book cover: Catalytic reactivity; Surface science studies in catalysis; In situ methods in catalysis; The contribution of theory to catalytic understanding; and Chemical kinetics and chemical engineering. The book ends with Summary lectures, a list of contributors, and an index.
Author: A.E. Shilov
Publisher: Springer Science & Business Media
ISBN: 9781402004209
Category : Science
Languages : en
Pages : 556
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Book Description
hemistry is the science about breaking and forming of bonds between atoms. One of the most important processes for organic chemistry is breaking bonds C–H, as well as C–C in various compounds, and primarily, in hydrocarbons. Among hydrocarbons, saturated hydrocarbons, alkanes (methane, ethane, propane, hexane etc. ), are especially attractive as substrates for chemical transformations. This is because, on the one hand, alkanes are the main constituents of oil and natural gas, and consequently are the principal feedstocks for chemical industry. On the other hand, these substances are known to be the less reactive organic compounds. Saturated hydrocarbons may be called the “noble gases of organic chemistry” and, if so, the first representative of their family – methane – may be compared with extremely inert helium. As in all comparisons, this parallel between noble gases and alkanes is not fully accurate. Indeed the transformations of alkanes, including methane, have been known for a long time. These reactions involve the interaction with molecular oxygen from air (burning – the main source of energy!), as well as some mutual interconversions of saturated and unsaturated hydrocarbons. However, all these transformations occur at elevated temperatures (higher than 300–500 °C) and are usually characterized by a lack of selectivity. The conversion of alkanes into carbon dioxide and water during burning is an extremely valuable process – but not from a chemist viewpoint.
Author: M. Guisnet
Publisher: World Scientific
ISBN: 1848166370
Category : Science
Languages : en
Pages : 359
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Book Description
In chemical processes, the progressive deactivation of solid catalysts is a major economic concern and mastering their stability has become as essential as controlling their activity and selectivity. For these reasons, there is a strong motivation to understand the mechanisms leading to any loss in activity and/or selectivity and to find out the efficient preventive measures and regenerative solutions that open the way towards cheaper and cleaner processes. This book covers in a comprehensive way both the fundamental and applied aspects of solid catalyst deactivation and encompasses the state-of-the-art in the field of reactions catalyzed by zeolites. This particular choice is justified by the widespread use of molecular sieves in refining, petrochemicals and organic chemicals synthesis processes, by the large variety in the nature of their active sites (acid, base, acid-base, redox, bifunctional) and especially by their peculiar features, in terms of crystallinity, structural order and textural properties, which make them ideal models for heterogeneous catalysis. The aim of this book is to be a critical review in the field of zeolite deactivation and regeneration, by collecting a series of contributions by experts in the field which describe the factors, explain the techniques to study the causes and suggest methods to prevent (or limit) catalyst deactivation. At the same time, an anthology of commercial processes and exemplar cases provides the reader with theoretical insights and practical hints on the deactivation mechanisms and draws attention to the key role played by the loss of activity on process design and industrial practice.
Author: Rajamani Pachayappan Gounder
Publisher:
ISBN:
Category :
Languages : en
Pages : 194
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Book Description
The catalytic consequences of confinement within zeolite voids were examined for several elimination (alkane cracking and dehydrogenation, alkene cracking, alkanol dehydration) and addition (alkene hydrogenation, alkylation and oligomerization) reactions catalyzed by Brønsted solid acids. These reactions are mediated by cationic transition states that are confined within voids of molecular dimensions (0.4-1.3 nm) and proceed at rates that reflect the Gibbs free energies of late ion-pairs at transition states relative to those for the relevant reactants. Ion-pair stabilities depend on electrostatic interactions between organic cations and catalyst conjugate anions and on dispersion interactions between these cations and framework oxygen atoms. The former interactions are essentially unaffected by confinement, which influences weakly Brønsted acid strength, while the latter depend strongly on the sizes and shapes of voids and the species confined within them. The catalytic effects of confinement in stabilizing ion-pairs are prevalent when transition states are measured relative to gaseous reactants, but are attenuated and in some cases become irrelevant when measured with respect to confined reactants that are similar in composition and size. Zeolite voids solvate confined species by van der Waals forces and mediate compromises in their enthalpic and entropic stabilities. Confinement is generally preferred within locations that benefit enthalpic stability over entropic freedom at low temperatures, in which free energies depend more strongly on enthalpic than entropic factors. For example, the carbonylation of dimethyl ether (400-500 K) occurs with high specificity within eight-membered (8-MR) zeolite voids, but at undetectable rates within larger voids. This specificity reflects the more effective van der Waals stabilization of carbonylation transition states within the former voids. In contrast, entropic consequences of confinement become preeminent in high temperature reactions. Alkane activation turnovers (700-800 K) are much faster on 8-MR than 12-MR protons of mordenite zeolites because the relevant ion-pairs are confined only partially within shallow 8-MR side pockets and to lesser extents than within 12-MR channels. The site requirements and confinement effects found initially for elimination reactions were also pertinent for addition reactions mediated by ion-pair transition states of similar size and structure. Ratios of rate constants for elimination and addition steps involved in the same mechanistic sequence (e.g., alkane dehydrogenation and alkene hydrogenation) reflected solely the thermodynamic equilibrium constant for the stoichiometric gas-phase reaction. These relations are consistent with the De Donder non-equilibrium thermodynamic treatments of chemical reaction rates, in spite of the different reactant pressures used to measure rates in forward and reverse directions. The De Donder relations remained relevant at these different reaction conditions because the same elementary step limited rates and surfaces remained predominantly unoccupied in both directions. Rate constants for elementary steps catalyzed by zeolitic Brønsted acids reflect the combined effects of acid strength and solvation. Their individual catalytic consequences can be extricated using Born-Haber thermochemical cycles, which dissect activation energies and entropies into terms that depend on specific catalyst and reactant properties. This approach was used to show that thermal, chemical and cation-exchange treatments, which essentially change the sizes of faujasite supercage voids by addition or removal of extraframework aluminum species, influence solvation properties strongly but acid strength only weakly. These findings have clarified controversial interpretations that have persisted for decades regarding the origins of chemical reactivity and acid strength on faujasite zeolites. Born-Haber thermochemical relations, together with Marcus theory treatments of charge transfer reaction coordinates, provide a general framework to examine the effects of reactant and catalyst structure on ion-pair transition state enthalpy and entropy. The resulting structure-function relations lead to predictive insights that advance our understanding of confinement effects in zeolite acid catalysis beyond the largely phenomenological descriptions of shape selectivity and size exclusion. These findings also open new opportunities for the design and selection of microporous materials with active sites placed within desired void structures for reasons of catalytic rate or selectivity. The ability of zeolite voids to mimic biological catalysts in their selective stabilization of certain transition states by dispersion forces imparts catalytic diversity, all the more remarkable in light of the similar acid strengths among known aluminosilicates. This offers significant promise to expand the ranges of materials used and of reactions they catalyze.
Author: Pedro J. Pérez
Publisher: Springer Science & Business Media
ISBN: 9048136989
Category : Science
Languages : en
Pages : 277
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Book Description
Over the past decade, much research effort has been devoted to the design and synthesis of new reagents and catalysts that can influence carbon-hydrogen bond activation, mainly because of the prospect that C−H activation could enable the conversion of cheap and abundant alkanes into valuable functionalized organic compounds. Alkane C-H Activation by Single-Site Metal Catalysis presents the current state-of-the-art development in the catalytic systems for the catalytic trans-formations of alkanes under homogeneous conditions. Chapter 1 offers a comprehensive summary of the main discoveries realized so far. Chapter 2 reviews the so-called electrophilic activation, initiated by Shulpín in the late 60s, and the base for the Catalytica system. Chapter 3 examines the catalytic borylation of alkanes, discovered by Hartwig, whereas chapter 4 provides an updated vision of the alkane dehydrogenation reaction. Chapter 5 covers the oxygenation of C-H bonds, a field of enormous interest with bioinorganic im-plications, and finally chapter 6 presents the functionalization of alkane C-H bonds by carbene or nitrene insertion. The history of C-H bond activation, and the current research described in this book, highlight the current research and present the reader with an outlook of this field which continues to be explored by an increasingly visionary and enthusiastic group of organic, organometallic, biological and physical chemists.
Author: Michel Guisnet
Publisher: World Scientific Publishing Company
ISBN: 1911299530
Category : Science
Languages : en
Pages : 359
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Book Description
In chemical processes, the progressive deactivation of solid catalysts is a major economic concern and mastering their stability has become as essential as controlling their activity and selectivity. For these reasons, there is a strong motivation to understand the mechanisms leading to any loss in activity and/or selectivity and to find out the efficient preventive measures and regenerative solutions that open the way towards cheaper and cleaner processes. This book covers the fundamental and applied aspects of solid catalyst deactivation in a comprehensive way and encompasses the state of the art in the field of reactions catalyzed by zeolites. This particular choice is justified by the widespread use of molecular sieves in refining, petrochemicals and organic chemicals synthesis processes, by the large variety in the nature of their active sites (acid, base, acid-base, redox, bifunctional) and especially by their peculiar features, in terms of crystallinity, structural order and textural properties, which make them ideal models for heterogeneous catalysis. The aim of this book is to be a critical review in the field of zeolite deactivation and regeneration by collecting contributions from experts in the field which describe the factors, explain the techniques to study the causes and suggest methods to prevent (or limit) catalyst deactivation. At the same time, a selection of commercial processes and exemplar cases provides the reader with theoretical insights and practical hints on the deactivation mechanisms and draws attention to the key role played by the loss of activity on process design and industrial practice./a
