Exploring Scaling Relations for Chemisorption Energies on Transition-metal-exchanged Zeolites ZSM-22 and ZSM-5 PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
Copper exchange on all the different T sites of ZSM-22 and ZSM-5 is considered and the chemisorption energies of dioxygen, OH, and O species are studied. We show that for different T sites the adsorption energies vary significantly. The oxygen adsorption energy on copper-exchanged zeolites is quite similar to those of the most selective catalysts for oxidation reactions, that is, Ag and Au surfaces. The chemisorption energies of oxygen, carbon-, and nitrogen-containing species on different transition metals exchanged in ZSM-22 are also investigated. The study covers three different oxidation states, that is, 1+, 2+, and 3+ for the transition-metal exchanges. Scaling relations are presented for the corresponding species. Lastly, chemisorption of O scales with chemisorption of OH for all three considered exchanges, whereas there are essentially rough correlations for NH2 and N as well as CH3 and C.
Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
Copper exchange on all the different T sites of ZSM-22 and ZSM-5 is considered and the chemisorption energies of dioxygen, OH, and O species are studied. We show that for different T sites the adsorption energies vary significantly. The oxygen adsorption energy on copper-exchanged zeolites is quite similar to those of the most selective catalysts for oxidation reactions, that is, Ag and Au surfaces. The chemisorption energies of oxygen, carbon-, and nitrogen-containing species on different transition metals exchanged in ZSM-22 are also investigated. The study covers three different oxidation states, that is, 1+, 2+, and 3+ for the transition-metal exchanges. Scaling relations are presented for the corresponding species. Lastly, chemisorption of O scales with chemisorption of OH for all three considered exchanges, whereas there are essentially rough correlations for NH2 and N as well as CH3 and C.
Author: Dustin W. Fickel Publisher: ISBN: Category : Crystallization Languages : en Pages : 87
Book Description
ZSM-5 is one of the more important and commonly used zeolites. It is the second most used zeolite in catalysis due to its unique framework and three-dimensional pore structure. The work in this thesis focuses on the formation of ZSM-5 through non-organic synthesis. To understand the formation of this zeolite, solid-solution aqueous-solution (SSAS) theories and thermodynamics are applied to quantify the relationship among the compositions of the resulting crystalline zeolite, the synthesis gel, and the aqueous phase during the synthesis.
Author: Vsevolod F. Kiselev Publisher: Springer ISBN: 9783642738890 Category : Technology & Engineering Languages : en Pages : 0
Book Description
This book deals with adsorption and catalysis on the surface of transition elements and their compounds, many of which are in teresting because of their particular electronic structure. The authors have worked through a vast body of experimental evi dence on the structure and properties of surfaces of transition metals and relevant oxides. Consideration is given mostly to simple (as opposed to mixed) oxides of transition elements, to common metals and to the adsorption of simple gases. A great deal of attention is paid to the nature of active surface sites responsible for chemisorption and catalytic transformations. The description relies mainly on the simplified ligand-field theory, which, however, proves quite satisfactory for predicting the adsorptive and catalytic activity of species. In many cases simple systems were explored with the aid of novel techniques, and it is only for such systems that the mechanism of the ele mentary act of adsorption and catalysis can be given adequate treatment. The present monograph has emerged from our earlier work in Russian, which appeared in the Khimiya Publishing House (Mos cow) in 1981. This English edition has, however, been revised completely to broaden its scope and to include more recent a chievements. For fruitful discussions the authors are grateful to A.A.
Author: Rutger A Van Santen Publisher: World Scientific ISBN: 9814506621 Category : Science Languages : en Pages : 409
Book Description
The molecular basis of surface chemical reactivity forms the central theme of this book. It is an attempt to survey current understanding about the working of heterogeneous catalysts, emphasizing surface chemical bonding in relation to reaction mechanisms.
Author: Yu-Hao Yeh Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
A significant challenge in the design of future hypersonic aircraft is engine cooling and one solution that has been proposed is to use the fuel as a coolant. The amount of energy that can be taken up by the thermal heat capacity of the fuel is limited but additional heat can be removed if the fuel is reformed via endothermic reactions prior to entering the combustion chamber. Two possible reactions that have been investigated in this thesis are the acid-catalyzed cracking reactions that occur in acidic zeolites and the aromatization reactions that occur over Ga- and Zn-exchanged zeolites. The first part of this dissertation was aimed at understanding the adsorption properties of alkanes on acidic zeolites in order to understand the reactions on these materials. Calorimetric measurements with CH4 on three zeolites with widely differently pore dimensions demonstrated heats decreased strongly with increasing pore size. Calorimetric measurements for a series of alkanes on H-ZSM-5 demonstrated that hydrogen bonding increased in a regular manner with the size of the alkane. In the second part of this dissertation, supercritical, high-pressure reactions of n-hexane over H-ZSM-5, with and without the addition of Pt, Ga, or Zn, were studied and reaction endothermicities were determined from the product distributions and from actual heat-flow measurements. The nature of the catalytic sites in these materials was also investigated using simultaneous Temperature-Programmed-Desorption (TPD) and Thermogravimetric analysis (TGA) of propyl amines. Adsorption studies showed that, at low ion-exchange levels, less than 0.5 Zn/Al, each added Zn cation in H(Zn)ZSM-5 displaced one Brønsted-acid site. FTIR of adsorbed acetonitrile-d3 and calorimetric measurements of adsorbed CO at 195 K indicated that the exchanged Zn cations form Lewis-acid centers. The heat flows measured directly for reaction at 60 bar and both 673 and 773 K indicated the acid-catalyzed cracking of n-hexane over H-ZSM-5 zeolite catalysts was ineffective for endothermic reforming applications. Aromatization reactions over H(Zn)-ZSM-5 exhibit much better endothermicities under these conditions. Measurements of the product distributions showed that the reaction endothermicity for H(Zn)-ZSM-5 at lower conversions was likely due to formation of significant amounts of benzene, toluene, and xylene but that these were converted to higher molecular weight products at high conversions. In the development of new catalysts, careful attention must be paid to the product selectivities. The present thesis, with systematic studies of metal-exchanged zeolites, should greatly increase our understanding of how metal cation at ion-exchange sites affect the reactions. The advances will help in predicting reactions and broadening the application, not only to use zeolites for endothermic reforming but in other important reforming reactions in the future.
Author: Henk van Koningsveld Publisher: Elsevier ISBN: 0080524613 Category : Science Languages : en Pages : 419
Book Description
This compendium describes all known zeolite framework types. The first part gives a pictorial description of how the framework can be built using periodic building units (PerBUs). The PerBUs are built from smaller units composed of a limited number of T-atoms (such as Si, Al, P, Ga, B, Be etc.) by applying simple operation(s) to the smaller unit, e.g. translation, rotation. The zeolite framework types are analysed in terms of these component PerBUs. The second part covers the larger cages, cavities and/or channels in the zeolite framework together with the framework type codes (FTCs) in which they appear. In addition, two appendices are included for easy-referencing. Two appendices are added. The first giving a survey of cages as type characteristics with their FTCs. The second summarizing those channels and cavities that appear in more than one framework type. The Compendium of Zeolite Framework Types contains complementary information to the data in the "Atlas of Zeolite Framework Types" (Baerlocher et al (2001) Elsevier, London). The latter contains the topological symmetry, unit cell data and pore dimensions. * How zeolites can be built using simple building units* Description of the channels and cages in all zeolites known to date* Survey of those channels and cages that appear in more than one zeolite
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Author: Luis M. Aparicio
Author: Tara Lyn Schaeffer
Author: Dustin W. Fickel
Author: Vsevolod F. Kiselev
Author: Rutger A Van Santen
Author: Peter A. Jacobs
Author: Yu-Hao Yeh
Author: Timothy Irwin Morrison
Author: Henk van Koningsveld