Rozprawy doktorskie na temat „Ethylene epoxidation”
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Ozbek, Murat Olus. "Computational Study Of Ethylene Epoxidation". Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613856/index.pdf.
Pełny tekst źródławhat is the relation between the surface state and the ethylene oxide selectivity?&rdquo
metallic (100), (110) and (111) surfaces of Cu, Ag and Au
and, (001) surfaces of Cu2O, Ag2O and Au2O oxides were studied and compared. For the studied metallic surfaces, it was found that the selective and non-selective reaction channels proceed through the oxametallacycle (OMC) intermediate, and the product selectivity depends on the relative barriers of the these channels, in agreement with the previous reports. However for the studied metallic surfaces and oxygen coverages, a surface state that favors the ethylene oxide (EO) formation was not identified. The studied Au surfaces did not favor the oxygen adsorption and dissociation, and the Cu surfaces favored the non-selective product (acetaldehyde, AA) formation. Nevertheless, the results of Ag surfaces are in agreement with the ~50% EO selectivity of the un-promoted silver catalyst. The catalyst surface in the oxide state was modeled by the (001) surfaces of the well defined Cu2O, Ag2O and Au2O oxide phases. Among these three oxides, the Cu2O is found not to favor EO formation whereas Au2O is known to be unstable, however selective for epoxidation. The major finding of this work is the identification of a direct epoxidation path that is enabled by the reaction of the surface oxygen atoms, which are in two-fold (i.e. bridge) positions and naturally exist on (001) oxide surfaces of the studied metals. Among the three oxides studied, only Ag2O(001) surface does not show a barrier for the formation of adsorbed epoxide along the direct epoxidation path. Moreover, the overall heat of reaction that is around 105 kJ/mol agrees well with the previous reports. The single step, direct epoxidation path is a key step in explaining the high EO selectivities observed. Also for the oxide surfaces, the un-selective reaction that ends up in combustion products is found to proceed through the OMC mechanism where aldehyde formation is favored. Another major finding of this study is that, for the studied oxide surfaces two different types of OMC intermediates are possible. The first possibility is the formation of the OMC intermediate on oxygen vacant sites, where the ethylene can interact with the surface metal atoms directly. The second possibility is the formation of a direct OMC intermediate, through the interaction of the gas phase ethylene with the non-vacant oxide surface. This occurs through the local surface reconstruction induced by the ethylene. The effect of Cl promotion was also studied. Coadsorption of Cl is found to suppress the oxygen vacant sites and also the reconstruction effects that are induced by ethylene adsorption. Thus, by preventing the interaction of the ethylene directly with the surface metal atoms, Cl prevents the OMC formation, therefore the non-selective channel. At the same time Cl increases the electrophilicity of reacting surface oxygen. The direct epoxidation path appears to be stabilized by coadsorbed oxygen atoms. Thus, we carry the discussions on the silver catalyzed ethylene epoxidation one step further. Herein we present that the EO selectivity will be limited in the case of metallic catalyst, whereas, the oxide surfaces enable a direct mechanism where EO is produced selectively. The role of the Cl promoter is found to be mainly steric where it blocks the sites of non-selective channel.
Law, D. "Aspects of ethylene epoxidation catalysis". Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333563.
Pełny tekst źródłaTan, S. A. "The mechanism of ethylene epoxidation". Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383935.
Pełny tekst źródłaGaudet, Jason. "Gas-Phase Epoxidation of Ethylene and Propylene". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/29341.
Pełny tekst źródłaPh. D.
Hague, Mathew. "A microreactor study on the epoxidation of ethylene over silver catalysts". Thesis, University of Manchester, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516163.
Pełny tekst źródłaAnantharaman, Bharthwaj. "Reaction mechanisms for catalytic partial oxidation systems : application to ethylene epoxidation". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32328.
Pełny tekst źródłaIncludes bibliographical references.
With the rapid advances in kinetic modeling, building elementary surface mechanisms have become vital to understand the complex chemistry for catalytic partial oxidation systems. Given that there is selected experimental knowledge on surface species and a large number of unknown thermochemical, rate parameters, the challenge is to integrate the knowledge to identify all the important species and accurately estimate the parameters to build a detailed surface mechanism. This thesis presents computational methodology for quickly calculating thermodynamically consistent temperature/coverage-dependent heats of formation, heat capacities and entropies, correction approach for improving accuracy in heats of formation predicted by composite G3- based quantum chemistry methods, and detailed surface mechanism for explaining selectivity in ethylene epoxidation. Basis of the computational methodology is the Unity Bond Index- Quadratic Exponential Potential (UBI-QEP) approach, which applies quadratic exponential potential to model interaction energies between atoms and additive pairwise energies to compute total energy of an adsorbed molecule. By minimizing the total energy subject to bond order constraint, formulas for chemisorption enthalpies have been derived for surface species bound to on-top, hollow and bridge coordination sites with symmetric, asymmetric and chelating coordination structures on transition metal catalysts. The UBI-QEP theory for diatomics has been extended for polyatomic adsorbates with empirical modifications to the theory.
(cont.) Formulas for activation energies have been derived for generic reaction types, including simple adsorption, dissociation-recombination, and disproportionation reactions. Basis of the correction approach is the Bond Additivity Correction (BAC) procedures, which apply atomic, molecular and bond- wise modifications to enthalpies of molecules predicted by G3B3 and G3MP2B3 composite quantum chemistry methods available in Gaussian® suite of programs. The new procedures have improved the accuracy of thermochemical properties for open and closed shell molecules containing various chemical moieties, multireference configurations, isomers and degrees of saturation involving elements from first 3 rows of the periodic table. The detailed mechanism explains the selectivity to ethylene oxide based on the parallel branching reactions of surface oxametallacycle to epoxide and acetaldehyde. Using Decomposition Tree Approach, surface reactions and species have been generated to develop a comprehensive mechanism for epoxidation. As a result of these developments in the thesis, chemisorption enthalpies can now be estimated within 3 kcal/mol of experimental values for transition metal catalysts and enthalpies predicted by G3B3 and G3MP2B3 Gaussian methods can be corrected within 0.5 kcal/mol. Examples of heterogeneous reaction systems involving silver-catalyzed ethylene epoxidation demonstrate the effectiveness of the methodologies developed in this work.
by Bharthwaj Anantharaman.
Ph.D.
Fellah, Mehmet Ferdi. "A Density Functional Theory Study Of Catalytic Epoxidation Of Ethylene And Propylene". Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12611228/index.pdf.
Pełny tekst źródła03 software. Silver and silver oxide were used as catalyst surface cluster models. Surface comparison was made for silver (111), (110) and (100) surfaces. Ethylene oxidation reaction was studied on these silver surfaces. Oxygen effect on ethylene oxide formation reaction was also investigated on silver (111) surface. Ethylene and propylene oxidation reactions were completed on both Ag13(111) and Ag14O9(001) surface clusters. VASP software which utilizes periodic plane wave basis sets was also used to compare trends of reactions for ethylene and propylene oxidations obtained by using Gaussian&rsquo
03 software. According to results, silver (110) surface is more active for ethylene oxide formation than (111) and (100) surfaces. Hill site of (110) surface is much more active than hollow site of (110) surface since oxygen atom weakly adsorbed on hill site. Ethyl aldehyde and vinyl alcohol can not be formed on Ag(111) surface because of those higher activation barriers while ethylene oxide can be formed on cluster. Activation barrier for ethylene oxide formation decreases with increasing oxygen coverage on Ag(111) surface. Ethylene oxametallocycle intermediate molecule was not formed on Ag2O(001) surface while it is formed on surface oxide structure on Ag(111). Ethyl aldehyde and vinyl alcohol are not formed on silver oxide (001) surface. For propylene oxidation, &
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-allyl formation path has the lowest activation barrier explaining why silver is not a good catalyst for the propylene oxide formation while it is a good catalyst for the ethylene oxide formation. This situation is valid for silver oxide. Propylene oxide selectivity increased in the gas phase oxidation. The qualitative relative energy trend obtained by VASP software is the similar with that of calculations obtained by using GAUSSIAN&rsquo
03 software.
Sullivan, Mark. "Alkali nitroxy-anions in the ultra-selective catalytic process for ethylene epoxidation". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303276.
Pełny tekst źródłaDellamorte, Joseph C. "Investigation of silver based catalysts for ethylene epoxidation high throughput studies and characterization /". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 288 p, 2009. http://proquest.umi.com/pqdweb?did=1821286341&sid=9&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Pełny tekst źródłaGava, Paola. "Modeling the catalyst selectivity in the ethylene epoxidation reaction : a first principles study". Doctoral thesis, SISSA, 2007. http://hdl.handle.net/20.500.11767/3933.
Pełny tekst źródłaKursawe, Ansgar. "Partial Oxidation of Ethene to Ethylene Oxide in Microchannel Reactors". Doctoral thesis, Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-60728.
Pełny tekst źródłaPeat, Karen Louise. "The mechanisms of ethylene epoxidation on the K+Cl+NO promoted Ag/#alpha#-Alâ†2Oâ†3 catalyst". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318421.
Pełny tekst źródłaKristiansen, Paw. "In situ X-Ray Spectroscopy of Ethylene Epoxidation over Ag and studies of Li-ion batteries and Cu sulfidation". Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-209204.
Pełny tekst źródłaNguyen, Ngoc Linh. "Toward Realistic DFT Description of Complex Systems: Ethylene Epoxidation on Ag-Cu Alloys and RPA Correlation in van der Waals Molecules". Doctoral thesis, SISSA, 2012. http://hdl.handle.net/20.500.11767/4699.
Pełny tekst źródłaGilbert, Benjamin. "Synthèse de films nanocomposites Ag/YSZ, Ag/CGO & Ag(Cu)/CGO par pulvérisation cathodique magnétron réactive pour l’électrocatalyse de l’éthylène en oxyde d’éthylène". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0257.
Pełny tekst źródłaEthylene oxide (EO) is an essential building block for the chemical industry. It is produced by the ethylene epoxidation reaction over a silver-based catalyst. Nevertheless, to achieve high selectivity, industrial processes use chloride additives in the gas phase and alkaline moderators on the catalyst. The aim of this study is to increase EO selectivity without chloride additives thanks to Ag/fluorite oxides electrocatalysts synthesized by reactive magnetron sputtering and incorporated in a 3-electrodes configuration cell designed for electrochemical promotion of catalysis, EPOC. Three porous systems (Ag/YSZ, Ag/GDC, Ag(Cu)/GDC) have been synthesized by reactive magnetron sputtering. Ag/YSZ 4 Pa 25 mA nanocomposite thin film exhibits a botryoidal microstructure characteristic of silver segregation inside the YSZ matrix. Ag/GDC 4 Pa 70 mA nanocomposite thin film exhibits a brain like-morphology with open nanoporosities. Ag(Cu)/GDC 4 Pa 70 mA nanocomposite thin film consists of multi-phase hydrophobic entropic nanowires. During catalytic tests under ethylene epoxidation conditions in reducing medium, Ag/GDC 4 Pa 70 mA showed the maximum EO selectivity of 16.55 % at 220 °C and, under polarization, selectivity boost of 2.78 % occur without the appearance of NEMCA effect
Kursawe, Ansgar. "Partial Oxidation of Ethene to Ethylene Oxide in Microchannel Reactors: Partial Oxidation of Ethene to Ethylene Oxidein Microchannel Reactors". Doctoral thesis, 2009. https://monarch.qucosa.de/id/qucosa%3A19374.
Pełny tekst źródłaGriebel, Arndt. "Zur Rolle der Silberoxide bei der heterogen katalysierten Epoxidation von Ethylen". Phd thesis, 2010. https://tuprints.ulb.tu-darmstadt.de/2052/1/Dissertation_Griebel.pdf.
Pełny tekst źródłaGriebel, Arndt [Verfasser]. "Zur Rolle der Silberoxide bei der heterogen katalysierten Epoxidation von Ethylen / eingereicht von Arndt Griebel". 2010. http://d-nb.info/1000486230/34.
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