Download or read book A Model Catalyst Investigation of Mass selected Vanadium and Vanadium Oxide Clusters Deposited on a Titanium Dioxide 110 1x1 Surface written by Scott P. Price and published by . This book was released on 2011 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vanadium oxide particles supported on titania are known to catalyze a number of reactions, including the selective oxidation of methanol to formaldehyde. Although the catalytic activity of this system has been widely studied, several questions related to the exact compositions and structures of the active species remain unanswered. In an effort to gain a deeper fundamental understanding of these catalysts, we utilize a unique apparatus which allows us to deposit mass-selected Vx and VxOy clusters on single-crystal rutile TiO2(110)-(1x1) in ultra high vacuum.
Download or read book Deposition and Investigation of Mass Selected Gold and Silver Clusters on a Titanium Dioxide 110 Surface written by Lauren Beth Benz and published by ProQuest. This book was released on 2007 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: Center of most clusters above 5c-Ti atom sites. Finally, using a combination of STM and temperature-programmed desorption (TPD), the interaction of these clusters with gases important to catalysis is probed.
Download or read book Gaseous Vanadium Vanadium Oxide and Hydroxide Clusters written by Sandra Feyel and published by Logos Verlag Berlin GmbH. This book was released on 2008 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present work explores the reactivities of gaseous vanadium, vanadium-oxide, and oxovanadium-hydroxide clusters toward methanol and small hydrocarbons. Various means of mass-spectrometric techniques, isotopic labeling studies, infrared photodissociation spectroscopy, and complementary DFT-calculations are employed for this purpose. Additionally, the hydrogen-atom abstraction process from methane by polynuclear metal oxides is discussed. This work contributes to a better understanding of the metal-oxide cluster's catalytic activity on a molecular scale.
Download or read book Computational Studies of the Structure of Vanadium Oxide Clusters and Their Reactions with Halocarbons written by Yin Wei and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Surface Chemistry of Vanadium Oxide Catalysts written by Kenneth Baker Lewis and published by . This book was released on 1988 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Characterization of Supported Vanadium Oxide Catalysts written by Bryan Olthof and published by . This book was released on 1998 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Synthesis Methodology Affecting Vanadium Titanium Silicalite 1 Catalyst written by and published by . This book was released on 2006 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vanadium titanium silicalite-1 (V/TS-1) samples (Si/Ti = 50, Si/V = 100) are synthesized by using hydrothermal method. To determine a suitable synthesis method that can control the amounts of titanium and vanadium in the MFI structure of synthesized catalysts, the effects of synthesis methodology (the vanadium salt addition method) and type of vanadium salt (VCl[subscript 3], VO(acac)[subscript 2] and V[subscript2]O[subscript 5] ) are investigated. The synthesized catalysts are characterized using various techniques such as XRF, XRD, BET, SEM, FT-IR, NH -TPD and ESR. The catalytic behavior is evaluated using the gas phase oxidation of 2-propanol (8 vol% oxygen, 5 vol% 2-propanol, balanced with argon). The catalytic reaction is carried out in a microreactor at a temperature range 100-500 degree Celsius, atmosphere pressure. This research shows that the vanadium salt addition method and the type of vanadium salt do not significantly affect the MFI structure as well as the reaction pathway. During the synthesis procedure, the vanadium species existing in the part of cation complex when it dissolved in aqueous solution is easier to be incorporated into the TS-1 structure than the ones exist in the part of anion complex. The surface area of the synthesized catalysts decrease inversely with the amount of vanadium incorporated. The NH[subscript 3] -TPD results indicate that the synthesized catalysts have two different types of acid site; the weaker one desorbed NH[subscript 3] at the temperature range 135-145 degree Celsius and the stronger one desorbed NH [subscript 3] at around 222-242 degree Celsius. For catalytic behavior, it is found that the synthesized V/TS-1 catalysts which have the vanadium active species derived from VCl [subscript 3] bonded on its surface are active in the 2-propanol oxidation and it can inhibit the dehydration and the combustion of 2-propanol. However, the ones which have the vanadium active species derived from VO(acac)[subscript 2] bonded on the catalyst surface do not be active in the 2-propanol oxidation but it can inhibit the 2-propanol combustion. Moreover, it is found that V[subscript 2]O[subscript 5] is not the suitable vanadium source for this synthesis method because V[superscript 5+] tends to stay in the anion complex which is more difficult to be incorporated into the TS-1 structure.
Download or read book Metals Abstracts written by and published by . This book was released on 1988 with total page 1244 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fundamental Studies on the Structure of Surface Oxide Sites on Supported Oxidative Dehydrogenation Catalysts written by Alyssa Marie Love and published by . This book was released on 2018 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: The structure of metal oxide sites on supported metal oxide catalysts has a significant impact on the performance of the catalyst. For example, silica-supported vanadium oxide-a catalyst widely studied for the oxidative dehydrogenation of propane (ODHP) to propene-has a higher selectivity towards propene when the catalyst surface is comprised of primarily dispersed VOx surface species. Conversely, as the loading of vanadium oxide is increased beyond the monolayer coverage threshold, three-dimensional V2O5 particles begin to form which lower the catalyst selectivity towards propene (at higher propane conversions) in favor of COx combustion products. For this catalytic application and for other supported metal oxides, understanding the variables that maximize the dispersion of two-dimensional metal oxide species on a support surface is invaluable information to improve the preparation of these catalysts. This thesis describes the synthesis and detailed characterization of supported oxide catalysts for the oxidative dehydrogenation of catalysts. In this work, vapor-phase grafting techniques were used to investigate the chemical reactions that occur during the synthesis of silica-supported vanadium oxide ODH catalysts. By depositing the neat vanadium precursor, VO(OiPr)3, onto silica dehydrated at 700 degrees C (called V/SiO2(700)), the complexity of variables in the synthesis was significantly decreased (compared to incipient wetness). Key anchoring and restructuring reactions during the formation of vanadium oxide sites on silica were characterized with a combination of infrared (IR), Raman, solid-state nuclear magnetic resonance (NMR), and X-Ray absorption spectroscopic studies, in addition to thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS), inductively coupled plasma (ICP) elemental analysis, etc. Afterwards, key synthesis variables (i.e., isopropanol solvent, H-bonded silanols and Na+ ions on the support surface) were incorporated into this grafting system to develop a more comprehensive model for the dispersion of vanadium oxide under wet impregnation conditions. Efforts to improve Raman sensitivity towards metal oxide surface sites with shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) are also addressed in this work. The methodology and characterization approach presented for the study of supported vanadium oxide catalysts was also applied to the study of promising new ODHP catalysts, including hexagonal boron nitride and silica-supported boron oxide catalysts.
Download or read book Chemisorption and Reactivity on Supported Clusters and Thin Films written by R.M. Lambert and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 534 pages. Available in PDF, EPUB and Kindle. Book excerpt: Heterogeneous catalysis provides the backbone of the world's chemical and oil industries. The innate complexity of practical catalytic systems suggests that useful progress should be achievable by investigating key aspects of catalysis by experimental studies on idealised model systems. Thin films and supported clusters are two promising types of model system that can be used for this purpose, since they mimic important aspects of the properties of practical dispersed catalysts. Similarly, appropriate theoretical studies of chemisorption and surface reaction clusters or extended slab systems can provide valuable information on the factors that underlie bonding and catalytic activity. This volume describes such experimental and theoretical approaches to the surface chemistry and catalytic behaviour of metals, metal oxides and metal/metal oxide systems. An introduction to the principles and main themes of heterogeneous catalysis is followed by detailed accounts of the application of modern experimental and theoretical techniques to fundamental problems. The application of advanced experimental methods is complemented by a full description of theoretical procedures, including Hartree-Fock, density functional and similar techniques. The relative merits of the various approaches are considered and directions for future progress are indicated.
Download or read book Vanadium porous Titania Glass Catalysts written by Yee Hong Chee and published by . This book was released on 1991 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscopy Studies on the Structure and Stability of Model Catalysts written by Fan Yang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An atomic level understanding of the structure and stability of model catalysts is essential for surface science studies in heterogeneous catalysis. Scanning tunneling microscopy (STM) can operate both in UHV and under realistic pressure conditions with a wide temperature span while providing atomic resolution images. Taking advantage of the ability of STM, our research focuses on 1) investigating the structure and stability of supported Au catalysts, especially under CO oxidation conditions, and 2) synthesizing and characterizing a series of alloy model catalysts for future model catalytic studies. In our study, Au clusters supported on TiO2(110) have been used to model supported Au catalysts. Our STM studies in UHV reveal surface structures of TiO2(110) and show undercoordinated Ti cations play a critical role in the nucleation and stabilization of Au clusters on TiO2(110). Exposing the TiO2(110) surface to water vapor causes the formation of surface hydroxyl groups and subsequently alters the growth kinetics of Au clusters on TiO2(110). STM studies on Au/TiO2(110) during CO oxidation demonstrate the real surface of a working catalyst. Au clusters supported on TiO2(110) sinter rapidly during CO oxidation, but are mostly stable in the single component reactant gas, either CO or O2. The sintering kinetics of supported Au clusters has been measured during CO oxidation and gives an activation energy, which supports the mechanism of CO oxidation induced sintering. CO oxidation was also found to accelerate the surface diffusion of Rh(110). Our results show a direct correlation between the reaction rate of CO oxidation and the diffusion rate of surface metal atoms. Synthesis of alloy model catalysts have also been attempted in our study with their structures successfully characterized. Planar Au-Pd alloy films has been prepared on a Rh(100) surface with surface Au and Pd atoms distinguished by STM. The growth of Au-Ag alloy clusters have been studied by in-situ STM on a cluster-to-cluster basis. Moreover, the atomic structure of a solution-prepared Ru3Sn3 cluster has been resolved on an ultra-thin silica film surface. The atomic structure and adsorption sites of the ultrathin silica film have also been well characterized in our study.
Download or read book Molecular Chemistry of Vanadium and Palladium Model Catalysts on Oxide Surfaces written by Oliver Dachwald and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fundamental Understanding of Transition Metal Oxide Catalysts for Selective Oxidations written by Yan Li and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: High surface area VOx/CeO2 model catalysts were developed to understand the effects of support on VOx catalysts in selective oxidation reactions. The VOx/CeO2 model catalysts were prepared by depositing highly dispersed VOx species on CeO2 nanoparticles including nanorods, nanocubes and nanopolyhedra with dominating low index (100), (110) and (111) facets. To understand and eliminate the possible interference of sodium residuals from CeO2 synthesis, we first investigated effects of Na on the surface structure and catalytic properties of VOx/CeO2 catalysts using oxidative dehydrogenation (ODH) of methanol as a probe reaction. Experimental results indicate that the effects of sodium on VOx/CeO2 are highly dependent on the Na/V ratio. At low Na/V ratios (Na/V0.25), sodium addition has minimal effect on its activity and selectivity to formaldehyde formation. At high Na/V ratios (Na/V0.25), sodium alters the nature of the active sites via V-O-Ce bond cleavage and V-O-Na bond formation, leading to significantly reduced activity of VOx/CeO2 catalysts. The selectivity to formaldehyde also decreases with increasing Na/V ratio. With safe exclusion of sodium interference, VOx catalysts supported on CeO2 nanorods, nanocubes and nanopolyhedra were employed to investigate the effects of support facets on VOx catalysts in ODH of methanol. In the presence of mixed facets, surface vanadia species preferentially deposit on CeO2 (100) facets, presumably because of its higher surface energy. At the same surface vanadium densities, VOx species on (100) facets show better dispersion, followed by (110) and (111) facets. The VOx species on CeO2 nanorods with (110) and (100) facets display higher activity and lower apparent activation energies compared to that on CeO2 nanopolyhedra with dominating (111) facets and CeO2 nanocubes with dominating (100) facets. The higher activity of VOx/CeO2(110) might be related to the more abundant oxygen defects present on the (110) facets. Further Study on VOx/CeO 2 (100) model catalysts was conducted. Experimental results show that the higher oxygen defect densities of smaller CeO2 nanocubes supported VOx catalysts effectively promote the redox property and lower the activation energy for methoxyl decomposition. These results further confirm the important role of oxygen vacancies in promoting the activity of VO x species in methanol oxidation.
Download or read book Model Catalyst Studies of Active Sites and Metal support Interactions on Vanadia and Vanadia supported Catalysts written by and published by . This book was released on 1990 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report is divided into the following: HREELS studies of adsorption on Rh/TiO2 model catalysts; photoemission studies of the Rh/TiO2 interaction; V-O-Ti interactions in supported vanadia catalysts; and surface physics and chemistry of vanadium oxides.
Download or read book A Surface Science Approach to Understanding Supported Vandia Catalysts written by Gordon Sek-Yin Wong and published by . This book was released on 2003 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Oxygen Interchange on Vanadium Oxide Catalysts written by Richard F. Mann and published by . This book was released on 1970 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is often difficult to compare results for heterogeneous reactions as the data reported in the literature are presented in various ways. A common example of this difficulty is the reporting of oxygen adsorption rate constants in various units. In the paper a number of studies involving oxygen interchange with vanadium pentoxide or vanadium pentoxide - potassium sulfate promoted catalysts are re-examined. Where possible, a first-order oxygen adsorption rate constant is evaluated from published data on rates of oxidation and rates of isotopic exchange, and expressed in units of 1/h-sq m of catalyst surface. The rate constants so evaluated and compared as to catalyst composition, temperature, and activation energy show reasonable agreement, even though a variety of catalysts, processes, and techniques are involved. (Author).
