Molecular Structure-reactivity Relationships for Propane Oxidation Over Model Mixed Oxide Catalysts PDF Download
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Languages : en
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Mixed Mo-V-Sb-Nb and Mo-V-Te-Nb oxides were recently discovered as highly active and selective catalysts for the propane oxidation to propylene and oxygenates, i.e. acrolein and acrylic acid. Fundamental information is needed for understanding the bulk and surface molecular structure-activity/selectivity relationships and providing rules of rational design of improved mixed metal oxide catalysts for the selective oxidation of propane. The phase composition and catalytic activity of the model Mo-V-Sb-Nb-O system strongly depended on the synthesis route and composition. A number of distinct solid-state phases were observed in this system: Mo6V9O40, MoO3, rutile SbVO4 and the defect "Mo-V-Nb-O" phases. The kinetic studies indicated that the high selectivity to acrylic acid (2̃0 mol.%) was associated with the Mo6V9O40 and the defect "Mo-V-Nb-O" phases. The synthesis of these mixed Mo-V-Sb-Nb-O system was performed using combinatorial chemistry techniques to explore the utility of liquid phase automated synthesis for the reproducible preparation of these catalysts. This study indicated good reproducibility of phase compositions and catalytic properties and provided new insights into the transformation processes that occur in these oxides with time on stream. It was discovered in this research that the model mixed Mo-V-Te-O catalyst represents a simple model system for elucidating the molecular structure-activity/selectivity relationships in propane selective oxidation. This catalyst contains the two major crystalline phases proposed as active and selective for propane oxidation. This research elucidated the effect of the chemical composition, solution pH and thermal treatment on phase composition and catalytic performance. High resolution TEM study established the crystal structures of the hexagonal and orthorhombic phases in terms of their space groups, unit cell parameters, atomic coordinates and elemental compositions. In order to understand the role of the structure, morphology and composition of mixed Mo-V-Te-Nb-O system, novel synthesis approaches employing ordered arrays of colloidal polystyrene spheres (0.4 ưm) were successfully developed. These novel nanocrystalline catalysts with surface areas in the 80-110 m2/g range consisted of 20-50 nm particles of desirable catalytic phases and contained 6-20 nm pores. Kinetic studies demonstrated the acrylic acid yields exceeding 40 mol.% and approaching the commercial targets for the selective oxidation of propane to acrylic acid.
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Languages : en
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Book Description
Mixed Mo-V-Sb-Nb and Mo-V-Te-Nb oxides were recently discovered as highly active and selective catalysts for the propane oxidation to propylene and oxygenates, i.e. acrolein and acrylic acid. Fundamental information is needed for understanding the bulk and surface molecular structure-activity/selectivity relationships and providing rules of rational design of improved mixed metal oxide catalysts for the selective oxidation of propane. The phase composition and catalytic activity of the model Mo-V-Sb-Nb-O system strongly depended on the synthesis route and composition. A number of distinct solid-state phases were observed in this system: Mo6V9O40, MoO3, rutile SbVO4 and the defect "Mo-V-Nb-O" phases. The kinetic studies indicated that the high selectivity to acrylic acid (2̃0 mol.%) was associated with the Mo6V9O40 and the defect "Mo-V-Nb-O" phases. The synthesis of these mixed Mo-V-Sb-Nb-O system was performed using combinatorial chemistry techniques to explore the utility of liquid phase automated synthesis for the reproducible preparation of these catalysts. This study indicated good reproducibility of phase compositions and catalytic properties and provided new insights into the transformation processes that occur in these oxides with time on stream. It was discovered in this research that the model mixed Mo-V-Te-O catalyst represents a simple model system for elucidating the molecular structure-activity/selectivity relationships in propane selective oxidation. This catalyst contains the two major crystalline phases proposed as active and selective for propane oxidation. This research elucidated the effect of the chemical composition, solution pH and thermal treatment on phase composition and catalytic performance. High resolution TEM study established the crystal structures of the hexagonal and orthorhombic phases in terms of their space groups, unit cell parameters, atomic coordinates and elemental compositions. In order to understand the role of the structure, morphology and composition of mixed Mo-V-Te-Nb-O system, novel synthesis approaches employing ordered arrays of colloidal polystyrene spheres (0.4 ưm) were successfully developed. These novel nanocrystalline catalysts with surface areas in the 80-110 m2/g range consisted of 20-50 nm particles of desirable catalytic phases and contained 6-20 nm pores. Kinetic studies demonstrated the acrylic acid yields exceeding 40 mol.% and approaching the commercial targets for the selective oxidation of propane to acrylic acid.
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Category :
Languages : en
Pages : 6
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This final report describes major accomplishments in this research project which has demonstrated that the M1 phase is the only crystalline phase required for propane ammoxidation to acrylonitrile and that a surface monolayer terminating the ab planes of the M1 phase is responsible for their activity and selectivity in this reaction. Fundamental studies of the topmost surface chemistry and mechanism of propane ammoxidation over the Mo-V-(Te,Sb)-(Nb,Ta)-O M1 and M2 phases resulted in the development of quantitative understanding of the surface molecular structure – reactivity relationships for this unique catalytic system. These oxides possess unique catalytic properties among mixed metal oxides, because they selectively catalyze three alkane transformation reactions, namely propane ammoxidation to acrylonitrile, propane oxidation to acrylic acid and ethane oxidative dehydrogenation, all of considerable economic significance. Therefore, the larger goal of this research was to expand this catalysis to other alkanes of commercial interest, and more broadly, demonstrate successful approaches to rational design of improved catalysts that can be applied to other selective (amm)oxidation processes.
Author: Sameer Ali Al-Ghamdi
Publisher:
ISBN:
Category :
Languages : en
Pages : 500
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Propane conversion to propylene has been the subject of intensive researches. This is due to the increasing demand for propylene. Current propylene production processes suffer from several limitations. Oxidative dehydrogenation (ODH) is a promising alternative technology for propylene production overcoming the drawbacks of current processes. However, selectivity control in ODH is still a challenge preventing it from an industrial application. This is due to the formation of undesired carbon oxides. Thus, the development of a selective catalyst is crucial for the commercialization of ODH. Vanadium oxide catalysts have been proposed as the most active and selective catalyst for propane ODH. Moreover, new reactor concepts such as fluidized-bed might also help to make the ODH a feasible alternative for olefins productionas, offering some outstanding advantages in comparison to conventional reactors. This dissertation provides fundamental understanding of structure-reactivity relationship of vanadium oxide catalyst for propane ODH in a fluidized-bed reactor using the lattice oxygen of vanadium oxide catalysts in the absence of gas-phase oxygen. Supported vanadium oxide catalysts with different vanadium loadings (5-10 wt %) supported on?-Al2O3 is used. The prepared catalysts are characterized using several techniques such as BET surface area, H2-TPR, NH3-TPD, O2 Chemisorption, Laser Raman Spectroscopy, Pyridine FTIR and XRD. Characterization of the catalysts reveals that monomeric VOx species are predominant at low vanadium loadings while polymeric VOx species increase with higher loadings until monolayer surface coverage is reached. Moreover, the catalysts display moderated acidity compared to that of the bare alumina due to the relative increase in the number of Brønsted acid sites. Successive-injections propane ODH experiments in the CREC Riser Simulator over partially reduced catalyst show good propane conversions (12%-15%) and promising propylene selectivity (68-86%) at 475-550 0C. Product selectivities are found to augment with the catalyst's degree of reduction suggesting that a certain degree of catalyst reduction is required for better propylene selectivity. Compared to average propylene yields of 5% and 15% obtained in FCC and steam cracking technologies, respectively, promising value of 7% was obtained in the present propane ODH study over vanadium oxide catalyst and under oxygen free conditions. Such result would encourage further investigation of propane ODH in the absence of molecular gas oxygen as promising alternative/supplementary technology for the production of propylene. A kinetic model relating reaction rate to the catalyst's degree of oxidation is proposed. Non- linear regression leads to model parameters with low confidence intervals, suggesting the adequacy of the proposed model in predicting the ODH reaction under the selected reaction conditions.
Author: Daniel Duprez
Publisher: World Scientific
ISBN: 1783263342
Category : Science
Languages : en
Pages : 1035
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This book offers a comprehensive overview of the most recent developments in both total oxidation and combustion and also in selective oxidation. For each topic, fundamental aspects are paralleled with industrial applications. The book covers oxidation catalysis, one of the major areas of industrial chemistry, outlining recent achievements, current challenges and future opportunities. One distinguishing feature of the book is the selection of arguments which are emblematic of current trends in the chemical industry, such as miniaturization, use of alternative, greener oxidants, and innovative systems for pollutant abatement. Topics outlined are described in terms of both catalyst and reaction chemistry, and also reactor and process technology.
Author: Junjun Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 163
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The selective ammoxidation of propane into acrylonitrile catalyzed by the bulk Mo-V-Te-Nb-O system received considerable attention because it is more environmentally benign than the current process of propylene ammoxidation and relies on a more abundant feedstock. This process consists of a series of elementary steps including propane oxidative dehydrogenation (ODH), ammonia and O2 activation, and N-insertion into C3 surface intermediates. However, the limited fundamental understanding of the reaction mechanism and the roles of the different cations have hindered the progress in further improving the activity and selectivity of these catalysts required for the commercial application. In this thesis, we present and discuss the results of the density functional theory (DFT) calculations performed to investigate the overall propane ammoxidation pathway employing the cluster models of the proposed selective and active sites present in the surface ab plane of the so-called M1 phase, which is the main catalytic phase present in the bulk mixed Mo-V-Te-Nb oxides. The activation energies for the oxidative dehydrogenation (ODH) of propane and sequentially formed intermediates (isopropyl, propene, and allyl) were calculated for different surface cation sites. Propane activation on V5=O was found to be the rate-limiting step (Ea = 1.2 eV), consistent with the current proposed reaction mechanism for propane activation on the bulk mixed Mo-V-Te-Nb oxides and the current understanding of V5+ as the active site for alkane activation present in V-based mixed oxides. Furthermore, a linear relationship was established between the H adsorption energy and the activation energy for H abstraction from various C3 intermediates, which is highly useful for predicting the energy barriers of H abstraction from C3 species based solely on H adsorption energy. The energy barriers of ammonia activation on different surface sites and NH insertion into the allyl species were investigated and discussed in terms of the hypothetical reaction pathway reported in the literature. These elementary reaction steps were indicated to be energetically barrier-less. The formation of acrylonitrile over Te=O as the H abstraction site from the surface absorbed precursor was found to be a barrier-less step. The overall reaction pathway was then explored using micro-kinetic models to study the selectivity of propane ammoxidation to acrylonitrile on the Mo-V-Te-Nb-O M1 phase. The calculated coverages of surface intermediates on Mo and V active sites from the micro-kinetic model indicated that NH is the dominant species on the surface as compared to surface O species which may explain why the M1 phase is so selective in transforming the gas-phase p-allyl intermediate into acrylonitrile as opposed to combustion products. This thesis reports the very first theoretical study of a complete mechanism of propane ammoxidation over surface ab planes of bulk mixed Mo-V-Te-Nb-O M1 phase. Improved understanding of the surface structure - reactivity relationships for propane ammoxidation to acrylonitrile over this model mixed metal oxide system gained in this research offers a possibility of not only molecular engineering of such mixed metal oxide catalysts for propane (amm)oxidation, but also fundamentally advancing the field of selective alkane (amm)oxidation over bulk mixed metal oxides.
Author: Susannah L. Scott
Publisher: Springer Science & Business Media
ISBN: 0387306412
Category : Science
Languages : en
Pages : 341
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Book Description
With the recent advent of nanotechnology, research and development in the area of nanostructured materials has gained unprecedented prominence. Novel materials with potentially exciting new applications are being discovered at a much higher rate than ever before. Innovative tools to fabricate, manipulate, characterize and evaluate such materials are being developed and expanded. To keep pace with this extremely rapid growth, it is necessary to take a breath from time to time, to critically assess the current knowledge and provide thoughts for future developments. This book represents one of these moments, as a number of prominent scientists in nanostructured materials join forces to provide insightful reviews of their areas of expertise, thus offering an overall picture of the state-- the art of the field. Nanostructured materials designate an increasing number of materials with designed shapes, surfaces, structures, pore systems, etc. Nanostructured materials with modified surfaces include those whose surfaces have been altered via such techniques as grafting and tethering of organic or organometallic species, or through various deposition procedures including electro, electroless and vapor deposition, or simple adsorption. These materials find important applications in catalysis, separation and environmental remediation. Materials with patterned surfaces, which are essential for the optoelectronics industry, constitute another important class of surface-modified nanostructured materials. Other materials are considered nanostructured because of their composition and internal organization.
Author: Robert Davis
Publisher: World Scientific
ISBN: 1848166893
Category : Science
Languages : en
Pages : 329
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Book Description
Catalyst technologies account for over $1 trillion of revenue in the U.S. economy alone. The applications range from medicines and alternative energy fuel cell technologies to the development of new and innovative clothing fibers. In this book, a World Technology Evaluation Center (WTEC) panel of eight experts in the field assesses the current state of research and development in catalysis by nanostructured materials, its sources of funding, and discusses the state of the field with respect to productivity and leadership in various nations around the world. In addition to showing the numerous and highly advantageous practical applications of the field, the panel concludes that Western Europe is currently the most productive region, followed closely by the United States. Still, the research and development output of the People's Republic of China has recently surpassed that of Japan and is now poised to surpass that of the U.S. as well. As such, this assessment is a timely review of the field's progress, taking into account the increasing contributions from Asia, and will be essential reading for professionals, whether they are seeking an in-depth summary of the state of the art or a broad view of trends affecting the discipline.
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Publisher: Royal Society of Chemistry
ISBN: 1782622691
Category : Science
Languages : en
Pages : 256
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Book Description
Industrial and academic scientists face increasing challenges to find cost-effective and environmentally sound methods for converting natural resources into fuels, chemicals and energy. With over 7000 papers published in this field of catalysis each year, keeping up with the literature can be difficult. Catalysis Volume 27 presents critical and comprehensive reviews of the hottest literature published over the last twelve months. Covering major areas such as chemical transformations using two-dimensional hybrid nanocatalysts, conversion of biomass-derived syngas to fuels and catalytic oxidation of organic pollutants in aqueous solution using sulfate radicals, this book is a useful reference for anyone working in catalysis and an essential resource for any library.
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Publisher: Newnes
ISBN: 0080965296
Category : Science
Languages : en
Pages : 7694
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Book Description
Comprehensive Inorganic Chemistry II, Nine Volume Set reviews and examines topics of relevance to today’s inorganic chemists. Covering more interdisciplinary and high impact areas, Comprehensive Inorganic Chemistry II includes biological inorganic chemistry, solid state chemistry, materials chemistry, and nanoscience. The work is designed to follow on, with a different viewpoint and format, from our 1973 work, Comprehensive Inorganic Chemistry, edited by Bailar, Emeléus, Nyholm, and Trotman-Dickenson, which has received over 2,000 citations. The new work will also complement other recent Elsevier works in this area, Comprehensive Coordination Chemistry and Comprehensive Organometallic Chemistry, to form a trio of works covering the whole of modern inorganic chemistry. Chapters are designed to provide a valuable, long-standing scientific resource for both advanced students new to an area and researchers who need further background or answers to a particular problem on the elements, their compounds, or applications. Chapters are written by teams of leading experts, under the guidance of the Volume Editors and the Editors-in-Chief. The articles are written at a level that allows undergraduate students to understand the material, while providing active researchers with a ready reference resource for information in the field. The chapters will not provide basic data on the elements, which is available from many sources (and the original work), but instead concentrate on applications of the elements and their compounds. Provides a comprehensive review which serves to put many advances in perspective and allows the reader to make connections to related fields, such as: biological inorganic chemistry, materials chemistry, solid state chemistry and nanoscience Inorganic chemistry is rapidly developing, which brings about the need for a reference resource such as this that summarise recent developments and simultaneously provide background information Forms the new definitive source for researchers interested in elements and their applications; completely replacing the highly cited first edition, which published in 1973
Author: Debaprasad Shee
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages :
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