Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
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Book Description
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: Xin Li
Publisher:
ISBN: 9781124883106
Category : Catalysts
Languages : en
Pages :
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Book Description
Acrylic acid and acrylonitrile are important intermediates for producing a number of common chemicals and materials used in paints, adhesives, plastics, fibers, etc. Traditionally, their production has relied on propylene feedstocks, and replacing propylene with the cheaper and more abundant propane as the raw material has attracted a lot of research interest during the past two decades. Several promising catalysts have been discovered, and to date, Mo-V-Nb-Te-O mixed metal oxides are the most efficient for both propane oxidation to acrylic acid and ammoxidation to acrylonitrile. Two orthorhombic phases named M1 and M2 have been identified as the major components, and M1 is generally considered the key factor for propane activation. In particular, the [001] face of the M1 structure has been proposed to provide active centers and the valence distribution on [001] face is believed to play an important role in determining the reaction mechanism. However, the detailed mechanism is not fully understood. This has limited opportunities to further improve catalysts performance or design better catalysts by rational means. This absence can be related to the past failure of generating M1 phase alone in synthesis, and many catalysts studied previously were actually mixtures. Thus, in this work, we carried out investigations of the highly pure M1 catalyst focusing on the synthesis, catalytic behavior, and structural model development. The hydrothermal method has been shown to yield M1 phase with high purity at the expense of a more complicated procedure. The simple slurry method was used by us to synthesize catalyst samples. It is found that, besides M1 and M2, tellurium molybdate TeMo 5 O 16, V-substituted Mo 5 O 14 or (V, Mo) 5 O 14, and Mosubstituted V 2 O 5 or (Mo, V) 2 O 5 are also often formed together. The final phase composition can be significantly affected by nominal metal composition, slurry pH, calcination heating rate, etc. And the relative amount of each phase under different conditions can be directly correlated with respective V/Mo and Te/Mo ratios. Further, an additional purification step where the sample mixture is washed by H 2 O 2 solution was studied, and it is observed that concentrated hydrogen peroxide offers the most effective removal of undesired phases. A complete procedure for obtaining M1 phase in high purity has been developed. Synthesized M1 catalysts were characterized by EDS and XPS, and results suggest that the M1 structure shows high chemical flexibility and can contain vanadium to quite different levels depending on the nominal metal stoichiometry in the slurry. In particular, it is seen that the more vanadium in the slurry, the more vanadium in the final M1 structure. Additionally, no significant difference between the surface and the bulk was observed with respect to metal composition.
Author: Junjun Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 163
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Book Description
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:
Publisher:
ISBN:
Category :
Languages : en
Pages : 189
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Book Description
Approximately 5 million metric tons of acrylonitrile are produced worldwide annually for the manufacture of acrylic fibers, copolymers and reinforced carbon fibers. There is currently intense commercial interest in developing a new catalytic process for acrylonitrile production via propane ammoxidation employing multicomponent mixed metal oxides, which would replace the existing propylene ammoxidation technology. This new technology is expected to lower the production cost by 30% as compared to the existing process because of the lower cost of propane and increased production of valuable co-products, such as acetonitrile. The key to the success of this important technology is the development of novel mixed metal oxide catalysts that can selectively ammoxidize propane to acrylonitrile. Recent developments in macroscale and mesoscale structure-directed self-assembly offer many attractive possibilities for the molecular design of novel catalytic mixed metal oxides. The present work describes the development of novel synthesis approaches for macroporous and mesoporous mixed metal MoVTe(Sb)NbOx catalysts displaying ordered porous structures, high surface areas, flexible compositions and improved thermal stability for propane ammoxidation. This research began with systematic exploration of synthesis of mesoporous Nb2O5 oxides as a departure point in the subsequent synthesis of mixed M-Nb-O (M=Mo, V, Te, Sb) oxides employing Nb2O5 as the major component or the catalytic support. Nb2O5 was chosen for this study as the most stable metal oxide possessing the highest Tammann temperature among all constituent metal oxides (MoOx, VOx, TeOx and SbOx). Thermally stable (up to 500 °C) and well-defined two-dimensional hexagonal mesostructured niobium oxides were obtained possessing the surface areas of up to 210 m2/g. The pore size of mesoporous niobium oxides was for the first time tuned in a wide range from 4.6 to 21 nm by varying synthesis conditions. As compared with previous studies, mesoporous niobium oxides with tunable pore sizes obtained in this work possessed more attractive pores structures which make them promising as catalytic supports or a major component in the synthesis of improved MoVTeNbOx catalysts for selective (amm)oxidation of propane. Thermally stable mesoporous binary (Nb-M-O, M=Mo, V, or Sb), multicomponent (MNbOx, M=Mo+V+Te) and supported (M/Nb, M=Mo+V+Te+Nb) mixed metal oxide catalysts were for the first time synthesized by evaporation-induced self-assembly and incipient-wetness impregnation techniques. These mixed metal oxide phases displayed good thermal stability of amorphous inorganic wall (up to 400°C), large pore sizes (5-23 nm), high surface areas (up to 232 m2/g) and flexible inorganic wall compositions. Improved dispersion of active components in the Nb2O5 matrix and over the Nb2O5 support was observed. However, the desirable M1 phase was not observed in the products of thermal transformation of these mesoporous mixed metal oxides probably due to insufficient thickness of inorganic walls in these phases. In order to investigate nucleation of the catalytic M1 phase and further improve the thermal stability of the ordered porous structure, MoVTeNbOx phases displaying both macroporous and mesoporous structures were prepared by a dual templating approach employing colloidal arrays of polystyrene spheres and non-ionic surfactants. The MoVTeNbOx phases possessing such dual porosity were obtained after polystyrene spheres and non-ionic surfactants were removed in a low temperature calcination step. These hierarchical MoVTeNbOx phases displaying bimodal pore structure transformed into macroporous rutile phase possessing nanocrystalline inorganic walls at high temperature. These MoVTeNbOx rutile phases possessed high surface areas (70 m2/g), desirable pore architectures, robust nanocrystalline inorganic walls and enhanced thermal stability (up to 600 °C). Although these macroporous MoVTeNbOx rutile catalysts displayed lower activity in propane ammoxidation and lower acrylonitrile selectivity in propane ammoxidation as compared to the active and selective M1 phase, the novel synthesis method reported in these studies represents a promising general approach to design novel complex mixed metal oxides for a wide range of applications in selective oxidation catalysis.
Author: Noritaka Mizuno
Publisher: John Wiley & Sons
ISBN: 3527627553
Category : Science
Languages : en
Pages : 356
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Book Description
Filling a gap in the current literature, this comprehensive reference presents all important catalyst classes, including metal oxides, polyoxometalates, and zeolites. Readers will find here everything they need to know -- from structure design to characterization, and from immobilization to industrial processes. A true must-have for anyone working in this key technology.
Author: Alexandre C. Dimian
Publisher: John Wiley & Sons
ISBN: 3527621598
Category : Technology & Engineering
Languages : en
Pages : 527
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Book Description
This practical how-to-do book deals with the design of sustainable chemical processes by means of systematic methods aided by computer simulation. Ample case studies illustrate generic creative issues, as well as the efficient use of simulation techniques, with each one standing for an important issue taken from practice. The didactic approach guides readers from basic knowledge to mastering complex flow-sheets, starting with chemistry and thermodynamics, via process synthesis, efficient use of energy and waste minimization, right up to plant-wide control and process dynamics. The simulation results are compared with flow-sheets and performance indices of actual industrial licensed processes, while the complete input data for all the case studies is also provided, allowing readers to reproduce the results with their own simulators. For everyone interested in the design of innovative chemical processes.
Author: Christian Hess
Publisher: Royal Society of Chemistry
ISBN: 1847559875
Category : Science
Languages : en
Pages : 453
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Book Description
The book gives a comprehensive up-to-date summary of the existing information on the structural/electronic properties, chemistry and catalytic properties of vanadium and molybdenum containing catalysts. It discusses the importance of nanoscience for the controlled synthesis of catalysts with functional properties and introduces the necessary background regarding surface properties and preparation techniques, leading from a textbook level to the current state of knowledge. Then follows an extensive survey and analysis of the existing open and patent literature - an essential knowledge source for the development of the new generation of partial oxidation catalysts. Important examples from current research on partial oxidation reactions are reviewed from experts in the field. The next chapter discusses the importance of 2- and 3-dimensional model systems for a fundamental understanding of the structure of transition metal oxide catalysts and its correlation to reactivity. Finally, an outlook on research opportunities within the area of partial oxidation reactions is presented.
Author: Jacques C. Vedrine
Publisher: Elsevier
ISBN: 0128116323
Category : Technology & Engineering
Languages : en
Pages : 620
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Book Description
Metal Oxides in Heterogeneous Catalysis is an overview of the past, present and future of heterogeneous catalysis using metal oxides catalysts. The book presents the historical, theoretical, and practical aspects of metal oxide-based heterogeneous catalysis. Metal Oxides in Heterogeneous Catalysis deals with fundamental information on heterogeneous catalysis, including reaction mechanisms and kinetics approaches.There is also a focus on the classification of metal oxides used as catalysts, preparation methods and touches on zeolites, mesoporous materials and Metal-organic frameworks (MOFs) in catalysis. It will touch on acid or base-type reactions, selective (partial) and total oxidation reactions, and enzymatic type reactions The book also touches heavily on the biomass applications of metal oxide catalysts and environmentally related/depollution reactions such as COVs elimination, DeNOx, and DeSOx. Finally, the book also deals with future trends and prospects in metal oxide-based heterogeneous catalysis. - Presents case studies in each chapter that provide a focus on the industrial applications - Includes fundamentals, key theories and practical applications of metal oxide-based heterogeneous catalysis in one comprehensive resource - Edited, and contributed, by leading experts who provide perspectives on synthesis, characterization and applications
Author: Donald T. Sawyer
Publisher: Springer Science & Business Media
ISBN: 1489923209
Category : Science
Languages : en
Pages : 310
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Book Description
This monograph consists of manuscripts submitted by invited speakers who participated in the symposium "Industrial Environmental Chemistry: Waste Minimization in Industrial Processes and Remediation of Hazardous Waste," held March 24-26, 1992, at Texas A&M University. This meeting was the tenth annual international symposium sponsored by the Texas A&M Industry-University Cooperative Chemistry Program (IUCCP). The program was developed by an academic-industrial steering committee consisting of the co-chairmen, Professors Donald T. Sawyer and Arthur E. Martell of the Texas A&M University Chemistry Department, and members appointed by the sponsoring companies: Bernie A. Allen, Jr., Dow Chemical USA; Kirk W. Brown, Texas A&M University; Abraham Clearfield, Texas A&M University; Greg Leyes, Monsanto Company; Jay Warner, Hoechst-Celanese Corporation; Paul M. Zakriski, BF Goodrich Company; and Emile A. Schweikert, Texas A&M University (IUCCP Coordinator). The subject of this conference reflects the interest that has developed in academic institutions and industry for technological solutions to environmental contamination by industrial wastes. Progress is most likely with strategies that minimize waste production from industrial processes. Clearly the key to the protection and preservation of the environment will be through R&D that optimizes chemical processes to minimize or eliminate waste streams. Eleven of the papers are directed to waste minimization. An additional ten papers discuss chemical and biological remediation strategies for hazardous wastes that contaminate soils, sludges, and water.
Author: Isabella Nova
Publisher: Springer Science & Business Media
ISBN: 1489980717
Category : Science
Languages : en
Pages : 715
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Book Description
Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts presents a complete overview of the selective catalytic reduction of NOx by ammonia/urea. The book starts with an illustration of the technology in the framework of the current context (legislation, market, system configurations), covers the fundamental aspects of the SCR process (catalysts, chemistry, mechanism, kinetics) and analyzes its application to useful topics such as modeling of full scale monolith catalysts, control aspects, ammonia injections systems and integration with other devices for combined removal of pollutants.
