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1
Beskari, Mohamed Ali. "Dynamic analysis of diffusion and convection in porous catalysts". Thesis, University of Salford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244857.
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Kwon, Doo Hyun. "Computational Design and Analysis of Molecular Ethylene Oligomerization Catalysts". BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8551.
Testo completoAbstract (sommario):
Linear alpha olefins (LAOs) are key petrochemical precursors for the synthesis of larger polymers, detergents, plasticizers, and lubricants. Most catalytic ethylene oligomerization processes generate a wide distribution of LAO carbon chain lengths. A major ongoing industrial challenge is to develop homogeneous catalysts that result in selective and tunable ethylene oligomerization to 1-hexene and 1-octene alkenes. Quantum mechanical calculations coupled with rapidly advancing technology have enabled the ability to calculate small molecule systems with high accuracy. Employing computational models to advance from empirical to quantitative prediction of product selectivities has become an active area of exploration. In this work, we demonstrate the development and use of a density-functional theory (DFT) transition-state model that provides highly accurate quantitative prediction of phosphinoamidine (P,N) Cr catalysts for controllable selective ethylene trimerization and tetramerization. This model identified a new family of highly selective catalysts that through computational-based ligand design results in a predictable shift from 1-hexene selectivity to 1-octene. Subsequent experimental ligand synthesis and catalyst testing verified the quantitative computational predictions. DFT calculations also provide key insights to factors controlling catalytic activity and present important design criteria for the development of active Cr-based ethylene oligomerization systems. Non-selective ethylene transformations, referred to as full range processes, provide access to a range of LAOs (C4-C20) that are used to produce polyethylene, surfactants, and other commercial products. During full-range oligomerizations, undesired byproducts degrade the purity of LAOs mostly consisting of branched oligomers. Computational mechanistic investigations reveal the origin of linear versus branched selectivity in Fe-catalyzed ethylene oligomerization reactions.
3
Ahuja, Vishal. "Analysis of novel transition metals as catalysts for oxygen delignification". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62909.pdf.
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Fomes, Charles William. "Development of novel oxidation catalysts for carbon isotope ratio analysis". Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343742.
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Lentz, Samuel D. "Development and optimization of NOx reduction catalysts using statistical analysis". Connect to resource, 2009. http://hdl.handle.net/1811/36953.
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Allcock, Gillian C. "The statistical aspects of the analysis and design of enzyme kinetic studies". Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366536.
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Dai, Shuanghua Patrick. "X-ray scattering and thermal analysis study of isotactic polypropylene /". Thesis, Connect to Dissertations & Theses @ Tufts University, 2000.
Cerca il testo completoAbstract (sommario):
Thesis (Ph.D.)--Tufts University, 2000.Submitted to the Dept. of Physics. Adviser: Peggy Cebe. Includes bibliographical references (leaves 246-251). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
8
Mullet, Dianna Rose. "Catalysts of Women's Success in Academic STEM: A Feminist Poststructural Analysis". Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062911/.
Testo completoAbstract (sommario):
This study analyzes senior women faculty's discourses about personal and professional experiences they believe contributed to their advancement in academic careers in science, technology, engineering, and mathematics (STEM). The purpose of the study is to understand factors that activate women's success in STEM disciplines where women's representation has not yet attained critical mass. A poststructuralist emphasis on complexity and changing nature of power relations offers a framework that illuminates the ways in which elite women navigate social inequalities, hierarchies of power, and non-democratic practices. Feminist poststructural discourse analysis (FPDA) methods allow analysis of women's talk about their experiences in order to understand the women's complex, shifting positions. Eight female tenured full professors of STEM at research-focused universities in the United States participated in the study. Data sources were in-depth semi-structured interviews, a demographic survey, and curricula vitae. Findings will help shape programs and policies aimed at increasing female representation and promoting achievement at senior levels in academic STEM fields.
9
Haibo, E. "Quantitative analysis of core-shell nanoparticle catalysts by scanning transmission electron microscopy". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:19c3b989-0ffb-487f-8cb3-f6e9dea83e63.
Testo completoAbstract (sommario):
This thesis concerns the application of aberration corrected scanning transmission electron microscopy (STEM) to the quantitative analysis of industrial Pd-Pt core-shell catalyst nanoparticles. High angle annular dark field imaging (HAADF), an incoherent imaging mode, is used to determine particle size distribution and particle morphology of various particle designs with differing amounts of Pt coverage. The limitations to imaging, discrete tomography and spectral analysis imposed by the sample’s sensitivity to the beam are also explored. Since scattered intensity in HAADF is strongly dependent on both thickness and composition, determining the three dimensional structure of a particle and its bimetallic composition in each atomic column requires further analysis. A quantitative method was developed to interpret single images, obtained from commercially available microscopes, by analysis of the cross sections of HAADF scattering from individual atomic columns. This technique uses thorough detector calibrations and full dynamical simulations in order to allow comparison between experimentally measured cross section to simulated ones and is shown to be robust to many experimental parameters. Potential difficulties in its applications are discussed. The cross section approach is tested on model materials before applying it to the identification of column compositions of core-shell nanoparticles. Energy dispersive X-ray analysis is then used to provide compositional sensitivity. The potential sources of error are discussed and steps towards optimisation of experimental parameters presented. Finally, a combination of HAADF cross section analysis and EDX spectrum imaging is used to investigate the core-shell nanoparticles and the results are correlated to findings regarding structure and catalyst activity from other techniques. The results show that analysis by cross section combined with EDX spectrum mapping shows great promise in elucidating the atom-by-atom composition of individual columns in a core-shell nanoparticle. However, there is a clear need for further investigation to solve the thickness / composition dualism.
10
Nguyen, Tuan Huy Chemical Sciences & Engineering Faculty of Engineering UNSW. "Semiconductor oxide supported Mo and Mo-W carbide catalysts for Fischer-Tropsch synthesis". Awarded by:University of New South Wales. School of Chemical Sciences and Engineering, 2006. http://handle.unsw.edu.au/1959.4/26969.
Testo completoAbstract (sommario):
Fischer-Tropsch synthesis reaction to produce sulphur free hydrocarbons has enjoyed a resurgent in interests due to increases in world oil prices. In this work, the suitability of Mo and Mo-W carbides has been investigated as a possible cost-effective alternative to noble metals in Fischer-Tropsch synthesis. The molybdenum and tungsten monometallic and bimetallic carbides were prepared through precipitation from homogeneous solution to the sulphide followed by carburization with a mixture of propane and hydrogen to produce the resulting metal carbide. A 23 factorial design strategy was employed to investigate the effect of three carburizing variables, namely, time, temperature and gas ratio on the resulting catalyst. In particular, the effect of supports was also examined through four common semiconductor oxide supports, namely: Al2O3, SiO2, TiO2 and ZrO2. Thermogravimetric analysis of the carburization reactions showed that the conversion from metal sulphide to the metal carbides is a multistep process producing different phases of carbides, namely ??-MoC1-x, ??-Mo2C, ?? -WC1-x and ??-W2C, depending on heating rate and temperature. The rate determining step of the carburising reaction is the diffusion of carbon atoms into the metal matrix, hence giving relatively low activation energy values. Statistical analysis of the factorial design revealed that all three carburizing variables affect the final physiochemical makeup of the catalyst. SEM analysis showed that the carbides are well dispersed on the surface of the support and catalyst particles produced are nanoparticles in the range of 25 to 220 nm depending on the support. Fischer-Tropsch activity test showed that monometallic molybdenum carbide is active under Fischer-Tropsch conditions while tungsten carbide is inactive for the conditions studied in this project. However, bimetallic carbide catalyst, consisting of the two mentioned metals gave overall higher reaction rates and decreased methane selectivity. Steady state analysis revealed that there are two active sites on the surface of molybdenum carbide catalyst resulting in two chain growth propagation values when analysed via the Anderson-Schulz-Flory kinetics. Overall, ZrO2 support appeared to be the most suitable support followed by SiO2, TiO2 and Al2O3. Finally, kinetic modelling of data showed that methanation and higher hydrocarbons formation path occurs via combination of the oxygenated intermediate and Eley-Rideal mechanism.
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Tau, Prudence Lerato. "Study of titanium, tantalum and chromium catalysts for use in industrial transformations". Thesis, Rhodes University, 2007. http://hdl.handle.net/10962/d1005028.
Testo completoAbstract (sommario):
PART A The syntheses, spectroscopic and electrochemical characterisation of a series of titanium and tantalum phthalocyanine complexes are reported. The complexes are unsubstituted and substituted at either the peripheral or non-peripheral positions with sulphonates, aryloxy, arylthio or amino groups. The complexes mostly exhibit Qbands in the near-infrared region as well as interesting properties in different solvents. The interaction of differently sulphonated titanium and tantalum phthalocyanine complexes with methyl viologen (MV[superscript 2+]), and hence the stoichiometry and association constants are evaluated. Detailed photophysicochemical properties of the complexes were investigated and are for the first time presented with fluorescence lifetimes easily obtained from fluorescence quenching studies. The transformation of 1-hexene photocatalysed by aryloxy- and arylthio-appended complexes is also presented for the first time. The electrochemical properties of the complexes are unknown and are thus presented. Cyclic (CV) and square wave (SWV) voltammetries, chronocoulometry and spectroelectrochemistry are employed in the study of the complexes. Two oneelectron reductions and a simultaneous 4-electron reduction are observed for the unsubstituted Cl[subscript 3]TaPc. Reduction occurs first at the metal followed by ring-based processes. The tetra- and octa-substituted derivatives however exhibit peculiar electrochemical behaviour where a multi-electron transfer process occurs for complexes bearing certain substituents. For all complexes, the first two reductions are metal-based followed by ring-based processes. A comparative study of the electrocatalytic activities of the complexes towards the oxidation of nitrite is also investigated. The complexes are immobilised onto a glassy carbon electrode either by drop-dry or electropolymerisation methods. All the modified electrodes exhibit improved electrocatalytic oxidation of nitrite than the unmodified electrodes by a twoelectron mechanism producing nitrate ions. Catalytic currents are enhanced and nitrite overpotential reduced to ~ 0.60 V. Kinetic parameters are determined for all complexes and a mechanism is proposed. PART B: The syntheses and electrochemical characterisation of chromium and titanium complexes for the selective trimerisation of ethylene to 1-hexene are presented. The synthesis of the chromium complex requires simple steps while tedious steps are used for the air-sensitive titanium complex. The spectroscopic interaction of the chromium complex with the co-catalyst methylaluminoxane is investigated. The complexes are characterised by electrochemical methods such as cyclic voltammetry and spectroelectrochemistry.
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Morgan, David Rees. "In situ ¹³C NMR monitoring of the dehydration of 2-propanol over H-ZSM-5". Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/52091.
Testo completoAbstract (sommario):
The first in situ ¹³C NMR monitoring of zeolite catalyzed reaction is described. The dehydration of 2-propanol over H-ZSM-5 was observed using solution type techniques. Although this produces broad lines, several mechanistic details were elucidated. This study indicates that: 1) the dehydration does not proceed through a cyclopropyl carbenium ion intermediate, 2) propene oligomerizes on the catalyst and reaches a steady state concentration before propene is desorbed, and 3) the 2-propanol flowing over the catalyst does not react with the oligomerized propene.Master of Science
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Liu, Wei. "Preparation, characterization, and catalytic properties of alkaline earth oxide MO (M=Ca, Mg, Sr, Ba)--modified VOx/SBA-15 catalysts for the oxidative dehydrogenation of n-butane". HKBU Institutional Repository, 2007. http://repository.hkbu.edu.hk/etd_ra/885.
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Nylén, Ulf. "Development of ring-opening catalysts for diesel quality improvement". Licentiate thesis, KTH, Chemical Engineering and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1712.
Testo completoAbstract (sommario):
The global oil refining industry with its present shift inproduct distribution towards fuels such as gasoline and dieselwill most likely hold the fort for many years to come. However,times will change and survival will very much depend onprocessing flexibility and being at the frontiers of refiningtechnology, a technology where catalysts play leading roles.Today oil refiners are faced with the challenge to producefuels that meet increasingly tight environmentalspecifications, in particular with respect to maximum sulphurcontent. At the same time, the quality of crude oil is becomingworse with higher amounts of polyaromatics, heteroatoms(sulphur and nitrogen) and heavy metals. In order to staycompetitive, it is desirable to upgrade dense streams withinthe refinery to value-added products. For example, upgradingthe fluid catalytic cracking (FCC) by-product light cycle oil(LCO) into a high quality diesel blending component is a veryattractive route and might involve a two-step catalyticprocess. In the first step the LCO is hydrotreated andheteroatoms are removed and polyaromatics are saturated, in thesecond step naphthenic rings are selectively opened to improvethe cetane number of the final product.
The present research is devoted to the second catalytic stepof LCO upgrading and was carried out within the framework of aEuropean Union project entitled RESCATS.
From the patent literature it is evident that iridium-basedcatalysts seem to be good candidates for ring-opening purposes.A literature survey covering ring opening of naphthenicmolecules shows the need for extending investigations toheavier model substances, more representative of the dieselfraction than model compounds such as alkylated mono C5 and C6-naphthenic rings frequently employed in academic studies.
Ring-opening catalysts, mainly Pt-Ir based, were synthesisedat KTH by two different methods: the microemulsion and theincipient wetness methods. Characterization of the catalystswas performed using a number of techniques including TPR,TEM-EDX, AFM and XPS etc. Catalytic screening at atmosphericpressure using pure indan as model substance was utilized todetect ring-opening activity and the magnitude of selectivityto desired cetane-boosting products. The development of suchring-opening catalysts is the topic of Paper I.
When designing a catalytic system aimed at refiningpetroleum, it is crucial to monitor the evolution of thesulphur distribution throughout the different stages of theprocess so that catalyst properties and reaction parameters canbe optimised. The final section of this thesis and Paper II arethus devoted to high-resolution sulphur distribution analysisby means of a sulphur chemiluminescence detector (SCD).
Keywords:ring opening, naphthenes, cetane numberimprovement, indan, light cycle oil (LCO), Pt-Ir catalyst,catalyst characterization, aromatic sulphur compounds, GC-SCD,distribution, analysis.
15
Murdoch, Alexander. "Structural and compositional analysis of cobalt palladium model catalyst surfaces". Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3640.
Testo completoAbstract (sommario):
To date there has been much work carried out in the field of surface science to gain a better understanding of the fundamentals of a wide range of catalytic systems and reactions. The central theme of this thesis relates to cobalt based Fischer-Tropsch synthesis (FTS) with particular focus on the structure, composition and surface chemistry of CoPd bimetallic systems and on the interaction of Co with oxide support materials. In the work described in this thesis MEIS and STM are used to examine the growth of Co on Pd{111} and to characterise the structure of CoPd alloys created by thermal treatment of thin Co films. MEIS investigations indicate that Co grows initially as an fcc overlayer, but beyond a few layers, a stacking fault exists resulting in hcp growth. On annealing between 550 and 700 K, a previously unreported ordered surface alloy is observed giving rise to a p(2 x 1) structure which is concluded to be the surface termination of an ordered CoPd bulk alloy. At higher annealing temperatures, long range Moiré structure is observed by STM which MEIS reveals to correspond to a Pd-rich alloy. MEIS is used to investigate adsorbate induced segregation effects at CoPd surfaces on Pd{111}. The adsorption of O2, CO, H2 and CO/H2 mixtures (syngas) were all examined on a range of bimetallic surfaces. Oxygen adsorption on CoPd alloys strongly segregates cobalt to the surface as a result of the facile oxidation reaction. The behaviour of the components of syngas was more complex with the most noticeable effects being observed on surfaces which were more defect rich. The growth, annealing behaviour and adsorption properties of Co particles on oxide and mixed oxide surfaces are examined using MEIS and TPD.
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Nylén, Ulf. "Ring-opening catalysts for cetane improvement of diesel fuels". Doctoral thesis, KTH, Kemiteknik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-537.
Testo completoAbstract (sommario):
The global oil refining industry with its present product distribution essentially shifted towards fuels such as gasoline and diesel will most likely hold the fort for considerable time. However, conditions are changing and refinery survival will very much depend on long-term planning, process and product flexibility and being at the frontiers of refining technology, a technology where catalysts play leading roles. Today oil refiners are faced with the challenge of producing fuels that meet increasingly tight environmental specifications, in particular with respect to maximum sulphur content. At the same time, the average quality of crude oil is becoming poorer with higher amounts of aromatics, heteroatoms (sulphur and nitrogen) and heavy metals. In order to stay competitive, it is of decisive importance for refiners to upgrade dense petroleum fractions of low quality to highly value-added products. A practicable route, for example, is upgrading the catalytic cracking by-product Light Cycle Oil (LCO) into a high-quality diesel-blending component in a two-step catalytic process. In the first step the LCO is hydrotreated over a Pt Pd based acidic catalyst bringing about heteroatom and aromatic reduction and isomerization of C6 to C5 naphthenic structures. In the second step these naphthenic structures are selectively opened over an Ir-based catalyst to improve the cetane value. The present thesis is mainly devoted to the second catalytic step of LCO upgrading and was partly conducted within the framework of the European Union project RESCATS. From the patent literature it is evident that iridium-based catalysts could be good candidates for ring-opening purposes. A literature survey covering ring opening of naphthenic structures made in the beginning of the project (in 2001), showed the need for extending investigations to heavier hydrocarbons, more representative of the diesel fraction than model compounds such as alkylated mono C5 and C6 naphthenic rings frequently employed in previous academic studies. Ring-opening catalysts, mainly Pt-Ir based, were synthesised at KTH by two different techniques: the microemulsion and the incipient wetness techniques. Paper I is a review of the microemulsion technique and its applications in heterogeneous catalysis. Characterization of catalysts was performed employing a multitude of techniques including quantitative TPR, TEM-EDX, XPS, CO FT-IR, NH3-DRIFTS and XRF etc. Catalytic screening at 325 oC and atmospheric pressure with hydrogen and pure indan as model substance was conducted to investigate ring-opening activity in terms of conversion and selectivity to desired cetane-boosting products. This development process is the topic of Papers II-IV. The possible industrial implementation of the best catalyst candidate is demonstrated in Paper V. When designing a catalytic system aimed at refining petroleum, it is crucial to monitor the evolution of the sulphur distribution throughout the different stages of the process so that catalyst properties and reaction parameters may be optimised. The final section of this thesis and Paper VI are devoted to high-resolution sulphur-distribution analysis by means of a sulphur chemiluminescence detector (SCD) following gas chromatographic separation.QC 20101014
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Caglar, Basar. "Nox Storage And Reduction Over Ce-zr Mixed Oxide Supported Catalysts". Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610418/index.pdf.
Testo completoAbstract (sommario):
NOx storage and reduction activities of Pt/BaO/CexZr1-xO2 (x= 1, 0.75, 0.5, 0.25, 0) catalysts were investigated by transient reaction analysis and Diffuse Reflectance Infrared Fourier Tramsform Spectroscopy (DRIFTS). Pt/BaO/Al2O3 catalyst was used as reference catalyst. Ce-Zr mixed oxides were synthesized by means of Pechini Method. Pechini method is a sol-gel like method based on mixing the related mixed oxide precursors with an α
-hydroxy carboxylic acid. 10% BaO (w/w) and 1% Pt (w/w) were deposited on synthesized mixed oxide and reference alumina support via incipient wetness impregnation. Prepared catalysts were characterized by BET, XRD and in-situ DRIFTS. Pt/BaO/CexZr1-xO2 catalysts (x= 0.75, 0.5, 0.25) exhibited higher surface than pure ceria and zirconia supported catalysts and highest surface was observed for Pt/BaO/Ce0.5Zr0.5O2. The reducibility of catalysts was tested by Temperature Programmed Reduction (TPR). It was observed that the reducibility of Pt/BaO/CexZr1-xO2 catalysts increases with incorporation of Zr into ceria lattice. Pt/BaO/Ce0.25Zr0.75O2 showed the highest reducibility. The Pt dispersions of catalysts were determined by CO chemisorption. The highest Pt disperison was observed in the presence of Pt/BaO/Ce0.5Zr0.5O2 catalyst. NOx storage and reduction efficiency of the catalysts were determined by transient reaction analysis in a home-built setup at 350oC. The reaction results revealed that all catalysts exhibit similar NOX storage and reduction performance. The NOX storage performances of all catalysts were differentiated via in-situ DRIFTS analysis. Pt/BaO/CexZr1-xO2 (x= 0.75, 0.5, 0.25) catalysts revealed higher performance than the ceria and zirconia supported catalysts. Pt/BaO/Ce0.5Zr0.5O2 catalyst absorbed highest amount of NO on the surface in the form of nitrate. The reduction behaviours of catalysts also were investigated by in-situ DRIFTS. It was observed that nitrates and nitrites were completely removed from the surface after reduction by H2 at 300oC.
18
Kissounko, Natalia. "Study of dynamics in a reaction catalyzed by ht- and ps-ADH cloning, purification and preliminary x-ray screening /". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 80 p, 2008. http://proquest.umi.com/pqdweb?did=1605142871&sid=6&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Halan, Babu [Verfasser]. "Biofilms as living catalysts for fine chemical synthesis: analysis, process design and scale-up / Babu Halan". Aachen : Shaker, 2013. http://d-nb.info/1051574633/34.
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Nandi, Shreya. "Investigation of perovskite-based three-way catalysts using surface analysis techniques and in situ/operando spectroscopy". Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R072.
Testo completoAbstract (sommario):
Le post-traitement catalytique des gaz d’échappement des moteurs à essence nécessite la conversion simultanée de CO,NO et des hydrocarbures. Ce procédé est connu sous le nom de catalyse trois voies (TWC). Les matériaux à base de perovskites comme LaFeO3, décrits comme des supports "intelligents", sont considérés comme des candidats potentiels dans la recherche d’alternatives aux catalyseurs trois voies classiques, dans un contexte de réduction de leur teneur en métaux nobles. Ces catalyseurs massiques présentent en surface une composition souvent différente de leur formule chimique, qui caractérise ces matériaux dans leur volume. Etant donné que, en catalyse hétérogène, la surface est déterminante pour les performances catalytiques, il est impératif de mieux comprendre les caractéristiques de la surface, en particulier dans des conditions aux plus proches de celles de la réaction. Ainsi, des catalyseurs modèles plans à base de LaFeO3,imitant les catalyseurs conventionnels sous forme de poudre, ont été étudiés en combinant des techniques avancées d’analyses de surface comme XPS, LEIS et ToF-SIMS pour étudier les variations de surface à différentes échelles de profondeur. De plus, le comportement des catalyseurs a été étudié sous atmosphère CO par NAP-XPS et GI-XANES. Cette méthodologie a permis de révéler qu’une composition déficitaire en La induit dans la structure permet d’améliorer les performances catalytiques grâce à un effet d’interface entre la perovskite et une phase minoritaire d’oxyde de fer. En outre, les différents modes de fonctionnement catalytiques de poudre de pérovskites substituées au Cu ou Mn ont été déterminés par spectroscopie Raman in situ et operandoThe catalytic after-treatment of exhaust gases from gasoline engines requires simultaneous abatement of CO, NO and hydrocarbons and is commonly called three-way catalysis (TWC). Perovskites based materials like LaFeO3, regarded as intelligent supports, are being considered as potential candidates as alternative TWC in context of reducing noble metal content. Such bulk catalysts often demonstrate variable surface compositions in comparison to the bulk. Since surface determines the catalytic performance in heterogeneous catalysis, deeper understanding of the surface characteristics especially under relevant reaction conditions becomes imperative. To this end, LaFeO3 based model catalysts relevant to conventional catalysts have been investigated by combination of advanced surface analysis techniques like XPS, LEIS and ToF-SIMS to study the existing surface variations. In addition, catalysts behavior was studied under CO atmosphere by NAP-XPS and GI-XANES. This methodology allowed to reveal that inducing a La-deficiency in the structure helps to improve the catalytic performance due to an interfacial effect. In addition, the different catalytic operating modes of Cu or Mn substituted perovskite powders were determined by in situ/operando Raman spectroscopy
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Van, Wyck Neal Edward. "MULTIPHOTON SPECTROSCOPY OF THIN FILMS AND SURFACES (NONLINEAR, WAVEGUIDES, INTERFACES)". Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291294.
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Lakhapatri, Satish L. "Analysis of Deactivation Mechanism on a Multi-Component Sulfur-Tolerant Steam Reforming Catalyst". University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1279327420.
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Woo, Jungwon. "Bulk and Surface Characteristics of Model M1 and M2 Phase Catalysts for Propane Ammoxidation to Acrylonitrile". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1445615206.
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Ault, Trevor Joseph. "A techno-economic analysis of ethanol production from hydrolysis of cellulose with nanoscale magnetic solid acid catalysts". Kansas State University, 2012. http://hdl.handle.net/2097/14746.
Testo completoAbstract (sommario):
Master of ScienceDepartment of Chemical Engineering
Keith Hohn
Acid catalysts have been shown to be very successful in the pretreatment of cellulosic biomass to improve glucose yield and improve overall yield of ethanol. This report presents the results of a techno-economic study that looks into the use of nanoscale magnetic solid acid catalysts for glucose production. Magnetic solid acid catalysts are an improvement over using diluted acid due to eliminating acid-waste generation and corrosion hazards. Their magnetic nature also allows them to be easily separated from reaction products by an external magnetic force. After the technology is analyzed, a series of unit operations is proposed to go from the laboratory scale to the industrial plant scale. The next step was to develop material and energy balances using HYSYS process simulation software. Capital and operating costs are estimated and all the information is combined into a discounted cash flow economic model. The economic portion of the report uses a probabilistic cost assessment. It is used to quantify the range of risks in the project from swings in feedstock costs, differences in yield from catalysts, and any other significant variables. Both capital costs (initial equipment & construction investment) and operating costs (feedstock supply, chemicals, and personnell) are included with ranges of error based on databases and expert opinion. This method of evaluating investment efficiency can be helpful for predicting the cost benefits of proposed future research. The yield and percent catalyst magnetically recovered is assumed based on laboratory research to simplify the model. A 2000 metric tons of biomass per day facility was analyzed. Using the magnetic solid acid catalyst technology, the capital costs are estimated to be $160 million and this technology saves around 10% of capital costs compared to ethanol plants that uses conventional acid hydrolysis. The yield of the magnetic solid acid catalysts should be around 75% to compete with existing ethanol technologies. The metric used for this report is the discount profitability index (DPI) which is the ratio of future cash flows divided by investment. A DPI “hurdle rate” of 1.3 is used, which is similar to industry economic metrics of projects that include new process plants. The calculated DPI for the project is 1.38 DPI which is higher than using conventional cellulose treatment technologies. The recommendation is continue to study this technology’s large scale applicability before attempting any plant pilot studies.
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Wei, Bo. "A novel solar-driven system for two-step conversion of CO2 with ceria-based catalysts". Doctoral thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-152899.
Testo completoAbstract (sommario):
Global warming is an unequivocal fact proved by the persistent rise of the average temperature of the earth. IPCC reported that scientists were more than 90 % certain that most of the global warming was caused by increasing concentrations of greenhouse gases (GHG) produced by human activities. One alternative to combat the GHG is to explore technologies for utilizing CO2 already generated by current energy systems and develop methods to convert CO2 into useful combustible gases. Two-step conversion of CO2 with catalysts is one of the most promising methods. Ceria (CeO2) is chosen as the main catalyst for this conversion in the thesis. It releases O2 when it is reduced in a heating process, and then absorbs O2 from CO2 to produce CO when it is re-oxidized in a cooling process. To make the conversion economic, solar power is employed to drive the conversion system. In this thesis, a flexible system with fluidized bed reactors (FBRs) is introduced. The thermogravimetric analysis (TGA) was carried out to examine the performance of ceria during its reduction and oxidation. Subsequently, the exergy analysis was used to evaluate the system’s capability on exporting work. The theoretical fuel to chemical efficiency varied from 4.85 % to 43.2 % for CO2 conversions. To investigate the operation mechanism of the system, a mathematical model was built up for the dynamic simulation of the system. Variables such as temperatures and efficiencies were calculated and recorded for different cases. The optimum working condition was found out to be at 1300 ⁰C for the commercial type of ceria. Finally, an experimental system was set up. The hydrodynamics and heat transfer in the fluidized bed reactor were studied. A CFD model was built up and validated with the experimental trials around 120 ⁰C. The model was then used as a reliable tool for the optimization of the reactor. The entire work in the thesis follows the procedure of developing an engineering system. It forms a solid basis for further improvements of the system to recycle CO2.QC 20141006
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Wang, Meng. "Steam reforming of model compounds of bio-oil with and without CO₂ sorbent". HKBU Institutional Repository, 2014. https://repository.hkbu.edu.hk/etd_oa/212.
Testo completoAbstract (sommario):
Hydrogen as a clean energy carrier has drawn great attention. Production of H2 from sustainable bio-oil is considered an alternative for conventional fossil fuel based energy system, since the overall process of bio-oil converting to H2 ideally is carbon-neutral and hence environmental friendly. This study focuses on developing an adequate catalyst for bio-oil steam reforming to produce H2. Ruthenium and/ or nickel based catalysts supported on alumina, ceria-alumina or ceria-silica were synthesized by sol-gel method or incipient wetness impregnation and characterized using BET Surface area analysis, Powder X-Ray diffraction (XRD), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). Steam reforming of selected model compounds, n-propanol, glycerol and acetic acid, was investigated in a fixed bed tubular flow reactor over the prepared catalysts at 450 or 500 °C. The effects of support nature, preparation method, catalyst composition and reaction temperature on the steam reforming activity and stability of catalysts were studied. Catalysts showing better performance in terms of reactant conversion and H2 yield were selected for investigating the steam reforming of an acetic acid/glycerol aqueous mixture, consisting of acetic acid and glycerol with a weight ratio of 3/7 similar to a bio-oil generated from fast pyrolysis of cellulose. The steam-to-carbon ratio (S/C) and the flow rate of feed were constant at 4 and 0.1 ml/min, respectively. The effluent gas was monitored by GC/TCD and the evolution of carbon conversion and product gas distribution as a function of time was studied. Among all catalysts investigated, the one with nominal composition A10C10N1Rnc showed the best performance in steam reforming at 500 °C as indicated by higher and more stable H2 yields achieved regardless the reactant used. In order to investigate the sorption-enhanced steam reforming, three CaO-based CO2 absorbents were synthesized: two derived from calcium acetate with or without MgO support, noted as CAM and CA, respectively, and the other MgO-supported one derived from calcium d-gluconate, denoted as CGM. Results from the 15-carbonation/regeneration-cycle test suggested that the MgO-containing absorbent CAM has the highest CaO molar conversion and stable CO2 absorption capacity. Though significantly higher CO2 absorption capacity was shown from absorbent CA in the first one cycle, CA absorbent soon lost most of the CO2 absorption capacity due to severe sintering. In addition, the CO2 absorption capacity of absorbent CGM might be underestimated due to insufficient carbonation time. The A10C10N1Rnc catalyst and the CAM absorbent were applied in the steam reforming of acetic acid/glycerol mixture at 500°C. However, no significant improvement can be observed in the presence of absorbent CAM
27
Villaseñor, Milán Ángela. "Development and optimization of methods for elemental quantitative analysis of catalysts and polymers through laser ablation-ICP techniques". Doctoral thesis, Universidad de Alicante, 2018. http://hdl.handle.net/10045/97855.
Testo completoAbstract (sommario):
En la presente Tesis Doctoral la técnica de ablación laser acoplada a ICP-OES/MS ha sido empleada para analizar muestras sólidas, como catalizadores usados en el refinado del petróleo y polímeros. Se han llevado a cabo dos tipos de análisis, un análisis global de las muestras que proporciona información general y un análisis localizado que permite obtener información acerca de la distribución espacial de los elementos de interés en las muestras. Las diferentes variables de la técnica ablación láser son estudiadas con el fin de seleccionar aquellas que conducen una señal alta y estable, así como a un menor grado de fraccionamiento. Este estudio se realiza para cada tipo de muestra, ya que los resultados dependen de la matriz estudiada. Además, en esta Tesis doctoral se desarrolla un método de calibración para llevar a cabo un análisis cuantitativo de las muestras sólidas, basado en la deposición de patrones líquidos sobre la muestra sólida. Este método es conocido como “dried droplet calibration approach” (DDCA), y permite cuantificar elementos presentes en muestras sólidas sin necesidad de usar materiales de referencia sólidos. Este nuevo método de calibración compensa el fraccionamiento elemental y los efectos de matriz, proporcionando resultados exactos y preciosos para muestras complejas tales como vidrios, catalizadores y polímeros.
28
Alston, Ben. "Aqueous polyoxometalates : design and analysis of electrochemical catalysts for the indirect reduction of oxygen in PEM fuel cells". Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/16233/.
Testo completoAbstract (sommario):
The applicability of aqueous, mixed addenda polyoxometalates with the general formula [PMo12-xVxO40](3+x)- as catalysts for FlowCath® technology has been demonstrated. These compounds were used as a platinum substitute in the PEM fuel cell cathode for the indirect reduction of oxygen. The effect of increased vanadium substitution within the Keggin structure upon the diffusion coefficient (Do) and the standard rate constant for electron transfer (ko) was investigated via simulation and electrochemical analysis. The apparent decrease in electrode kinetics linked with increased vanadium substitution is explained via simulation modelling, with the VxPOMs systems demonstrating multiple redox processes. The effects of solvent and electrode material upon the voltammetry are also discussed. Self supporting conditions analogous to the in fuel cell were employed to the VxPOM catalysts and their behaviour compared to the [Fe(CN)6]4-/3- redox couple via CV, simulation and RDE analysis. The resulting self-supported [Fe(CN)6]3-/4- system demonstrated significantly increased currents, but less than theoretically expected due to increases in cell resistance. The self-supported VxPOM system electrode processes are hindered due to the formation of a VO20 driven blocking layer reducing the actual potential experienced by the redox active species at the electrode surface. The resulting blocking layer prevented the VxPOM from approaching the electrode surface thus not experiencing the actual potential applied at the electrode surface. Tafel plots based upon the VxPOM systems showed characteristics not resembling ‘classical’ Tafel analysis with curvature preventing extrapolation for exchange current density. An ‘alternative’ analysis method involving the interpolation of the raw rotating disc electrode data to determine the required overpotential to generate a desired current was developed. The regeneration of the V4POM catalysts was investigated which demonstrated a possible change in speciation and a more ordered structure based upon single crystal X-ray analysis. The effects of formulation development of the lead V4POM catalyst upon its electrochemical and fuel cell performance were investigated. Substitution of Na+ counter ions with H+ (HV4POM) showed a decrease in charge transfer resistance (Rc) as well increase in membrane resistance (Rs) and cathodic current. The affects of adding stoichiometric quantities of H3PO4, HBF4 and VOSO4 were investigated with RDE and fuel cell testing indicating improved performance for the HBF4 formulation at fuel cell conditions. The effects of current developments in FlowCath® technology upon the H3PO4 formulation are also discussed.
29
Reineri, Daniele. "Síntese e caracterização dos coprecipitados de cálcio e alumínio com 8-hidroxiquinolina e avaliação catalítica na reação de transesterificação". Universidade Tecnológica Federal do Paraná, 2015. http://repositorio.utfpr.edu.br/jspui/handle/1/1504.
Testo completoAbstract (sommario):
O presente estudo teve como objetivo sintetizar, caracterizar e avaliar a atividade catalítica em reação de transesterificação do material formado após a decomposição térmica dos coprecipitados de cálcio e alumínio com 8-hidroxiquinolina. A síntese do material foi realizada por intermédio da metodologia de coprecipitação, utilizando como agente precipitante a 8-hidroxiquinolina. Para avaliar a presença dos metais cálcio e alumínio sobre as caracteristicas do material, utilizou-se variadas porcentagens destes metais na síntese dos complexos, utilizando-se das mesmas condições reacionais, com pH final igual a 10 e temperatura de 25 ºC. Após a síntese os complexos foram caracterizados por microscopia eletrônica de varredura, espectroscopia de infravermelho, e análise térmica em atmosfera de ar sintético nas razões de aquecimento de 5 ºC, 10 ºC e 20 ºC min-1. Por meio das curvas TG, DTG e DTA verificou-se que a presença do metal alumínio promoveu o processo de sublimação parcial do material. Os materiais obtidos após análise térmica foram caracterizados por microscopia eletrônica de varredura, não sendo observado mudanças significativas na morfologia entre as diferentes razões de aquecimento. Para avaliação catalítica na reação de transesterificação utilizou-se uma razão molar acetato de etila:metanol de 1:6, temperatura de 50 ºC, tempo de reação de 1 hora e 1% de catalisador, sendo os catalisadores obtidos à uma temperatura de calcinação de 700 ºC com uma razão de aquecimento de 10 ºC min-1. A maior conversão (0,98%) foi obtida a partir do material sintetizado com 100% de metal cálcio em sua formulação, entretanto as conversões observadas são baixas devido parcialmente as condições brandas utilizadas.The present study aimed to synthesize and evaluate the activity catalytic in the reaction transesterification of the material formed after decomposition thermal of coprecipitated of calcium and aluminum with 8-hydroxyquinoline. The synthesis of the material was performed by method coprecipitation using as agent precipitating 8-hydroxyquinoline. To evaluate the presence of metal calcium and aluminum on the characteristics of the material, we used different percentages of these metals in the synthesis of complexes using the same conditions reaction, with a pH final of 10 to temperature of 25 ºC. After synthesis the complexes were characterized by scanning electron microscopy, infrared spectroscopy, and thermal analysis in synthetic air atmosphere at heating rates of 5 °C, 10 °C and 20 ºC min-1. Through the curves TG, DTA and DTG was found that the presence of metal aluminum promoted process partial of sublimation the material. The materials obtained after analysis thermal were characterized by scanning electron microscopy, not observed changes significant in morphology between the different reasons heating. For review catalytic on reaction transesterification used a ratio molar of acetate ethyl:methanol 1:6, temperature 50 °C, time reaction 1 hour to 1% catalyst, the catalyst being obtained at temperature a calcination of 700 °C with a rate heating 10 ºC min-1. The highest conversion (0.98%) was obtained from the material synthesized with 100% metal calcium in its formulation, but the conversions are low seen partially due to the conditions mild used.
30
Butts, Robert Andrew. "Kinetic parameters from statistical analysis of TREF profiles and the preparation of MgCl¦2 as supports for polymerization catalysts". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0011/MQ60106.pdf.
Testo completo
31
Brown, Jared C. "UV Visible Spectra Analysis of High Temperature Water Gas Shift Catalysts Made from Iron, Lanthanum, Copper, and Chromium Oxides". BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3222.
Testo completoAbstract (sommario):
Hydrogen is a vital component in several different chemical reactions as well as a potential fuel source for the future. The water gas shift (WGS) reaction converts CO and water to hydrogen and CO2. The objective of this work is to first, characterize the potential benefits of the addition of lanthanum oxide (lanthana) to the iron-chromium-copper (Fe-Cr-Cu) oxide catalysts industrially used in high temperature water gas shift processes, and second, analyze these catalysts using in-situ UV-Visible spectroscopy. The benefits of each component in the catalyst are discussed as well as potential benefits from the addition of lanthana. Lanthana is a rare earth oxide that dramatically increases the surface area of the iron based WGS catalysts, and small concentrations of other rare earth oxides (i.e. cerium) have been shown to increase the rate of desorption of CO2 from iron surfaces (Hu Yanping 2002). Lanthana has similar chemical properties to other rare earth oxides tested and has not been previously tested as an additive to the WGS catalyst. Therefore catalysts with 0, 1, 2, 5, 10, and 20 wt% lanthana were made via a co-precipitation method in order to measure changes in activity, physical stability, and thermal stability. Catalyst characterization techniques utilized include electron dispersive X-ray spectroscopy (EDX), temperature programmed reduction (TPR) with hydrogen, and nitrogen physisorption (BET). The kinetic analysis was performed utilizing both mass spectroscopy (MS) and gas chromatography (GC). The addition of 1 wt% lanthana to the Fe-Cr-Cu catalysts increases WGS reaction rates of the catalyst at 425°C and 350°C, however the 0% La catalyst has the highest rates at 375°C and 400°C. The 0% La catalyst shows significant drop off in rate at 425°C, suggesting that the lanthana provides a small thermal stabilizing, i.e. the addition of lanthana prevents catalyst sintering at higher temperatures. Traditionally, chromia acts as the sole thermal stabilizer in these catalysts. The addition of large amounts of lanthana inhibits the chromia stabilizing effect, however small additions of lanthana appear to have an additional catalyst promotional effect without interfering with the chromia thermal stabilization. The increased WGS reaction rates at higher temperatures could allow for greater throughput of reactants in industrial settings. Higher concentrations of lanthana decrease the activity due to what is believed to be disruption of the chromia stabilizing effect as well as reduced amount of the active phase of catalyst. In-situ UV-Visible analysis shows that the oxidation state of the iron in the catalyst has a direct correlation to the UV-Visible light absorbance of the surface of the iron catalyst. Extent of reduction is traditionally measured with a synchrotron which is significantly more expensive than UV-Vis spectroscopy. This study uses the more economical UV-Vis spectrometer to determine similar information. The lanthana doped catalysts show an over-reduction of iron during WGS conditions (i.e. rapid reduction of Fe2O3 to Fe3O4 and FeO).
32
Rankin, Andrew Gordon McLaughlin. "Applications of multinuclear solid-state NMR spectroscopy to the characterisation of industrial catalysts". Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/12793.
Testo completoAbstract (sommario):
This thesis describes applications of advanced multinuclear solid-state nuclear magnetic resonance (NMR) experiments to the characterisation of industrially-relevant catalyst materials. Experiments on γ-Al₂O₃ introduce the use of solid-state NMR spectroscopy for the investigation of disordered solids. The existence of Al(V) sites on the surface of this material is demonstrated, showing that removal of adsorbed H₂O may facilitate a rearrangement effect in γ-Al₂O₃ that promotes the formation of these Al environments. A range of aluminium oxide-based supported metal catalysts has been investigated. Studies of these systems by ¹H and ²⁷Al solid-state NMR spectroscopy indicate that a metal-support interaction (MSI) exists between surface cobalt oxide crystallites and the γ-Al₂O₃ support, and is strongest for materials containing small, well dispersed Co oxide crystallites. It is shown that the hygroscopic nature of γ-Al₂O₃ allows the extent of the MSI to be visualised by ¹H MAS NMR, by observing the extent of the proton-metal oxide interaction resulting from the presence of adventitious adsorbed H₂O. The surface/bulk chemistry of Co spinel aluminate materials is also investigated. ¹H, ²⁹Si, ²⁷Al and ¹⁷O solid-state NMR techniques are used to gain insight into the structural nature of silicated alumina catalysts. The combination of isotopic enrichment and dynamic nuclear polarisation (DNP) surface-enhanced NMR spectroscopy can provide a definitive and fully quantitative description of the surface structure of Si-γ-Al₂O₃ (1.5 wt% Si), and the role of adventitious surface water is highlighted. Analysis of silicated aluminas prepared by “sequential grafting” and “single shot” approaches shows that silica growth on γ-Al₂O₃ follows two distinct morphologies. ¹⁷O gas exchange enrichment is also shown to be successful in facilitating ¹⁷O solid-state NMR studies of these materials. It is demonstrated that double (²⁹Si and ¹⁷O) enrichment of Si-γ-Al₂O₃ (1.5 wt% Si) can facilitate access to ²⁹Si-¹⁷O 2D correlation experiments, even at low silica loading. An exploratory investigation of Ti-alumina model catalysts has also been carried out using ¹H, ²⁷Al and ¹⁷O solid-state NMR spectroscopy. These studies indicate that Ti-γ-Al₂O₃ and Ti-Al M50 may be structurally distinct materials.
33
Karamullaoglu, Gulsun. "Dynamic And Steady-state Analysis Of Oxidative Dehydrogenation Of Ethane". Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606269/index.pdf.
Testo completoAbstract (sommario):
In this research, oxidative dehydrogenation of ethane to ethylene was studied over Cr-O and Cr-V-O mixed oxide catalysts through steady-state and dynamic experiments. The catalysts were prepared by the complexation method. By XRD, presence of Cr2O3 phase in Cr-Oand the small Cr2O3 and V2O4 phases of Cr-V-O were revealed. In H2-TPR, both catalysts showed reduction behaviour. From XPS the likely presence of Cr+6 on fresh Cr-O was found. On Cr-V-O, the possible reduction of V+5 and Cr+6 forms of the fresh sample to V+4, V+3 and Cr+3 states by TPR was discovered through XPS. With an O2/C2H6 feed ratio of 0.17, Cr-O exhibited the highest total conversion value of about 0.20 at 447°
C with an ethylene selectivity of 0.82. Maximum ethylene selectivity with Cr-O was obtained as 0.91 at 250°
C. An ethylene selectivity of 0.93 was reached with the Cr-V-O at 400°
C. In the experiments performed by using CO2 as the mild oxidant, a yield value of 0.15 was achieved at 449°
C on Cr-O catalyst. In dynamic experiments performed over Cr-O, with C2H6 pulses injected into O2-He flow, the possible occurrence of two reaction sites for the formation of CO2 and H2O was detected. By Gaussian fits to H2O curves, the presence of at least three production ways was thought to be probable. Different from Cr-O, no CO2 formation was observed on Cr-V-O during pulsing C2H6 to O2-He flow. In the runs performed by O2 pulses into C2H6-He flow over Cr-V-O, formation of CO rather than C2H4 was favored.
34
Sen, Fatih. "The Preparation And Analysis Of New Carbon Supported Pt And Pt+second Metal Nanoparticles Catalysts For Direct Methanol Fuel Cells". Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614728/index.pdf.
Testo completoAbstract (sommario):
In this thesis, firstly, carbon-supported platinum nanoparticle catalysts have been prepared by using PtCl4 and H2PtCl6 as starting materials and 1-hexanethiol, and tert-octanethiol, as surfactants for the first time. Secondly, these prepared catalysts were heated to 200 °C, 300 °
C, and 400 °
C for 4 h under argon gas. Lastly, PtRu/C catalysts, which have different atomic percent ratios of Pt and Ru (Pt/Ru: 0.8, 2.1 and 3.5), were prepared using PtCl4 and RuCl3 as starting materials and tert-octanethiol as a surfactant. Each was characterized by X-ray diffraction, transmission electron microscopy, energy dispersive analysis, X-ray photoelectron spectroscopy, cyclic voltammetry, and elemental analysis, and their activities were determined toward the methanol oxidation reaction. It has been found that all prepared catalysts are more active toward methanol oxidation reaction compared to the commercial catalysts. It was also found that increasing the temperature during the heat treatment process results in an enlargement of platinum particle size and a decrease in catalytic activity in the methanol oxidation reaction. Transmission electron microscopy shows that platinum nanoparticles are homogeneously dispersed on the carbon support and exhibited a narrow size distribution with an average particle size of about 2-3 nm in diameter. X-ray photoelectron spectra of all catalysts indicated that most of the platinum nanoparticles (>
70 %) have an oxidation state of zero and rest (<
30 %) have a +4 oxidation state with (Pt 4f7/2) binding energies of 71.2-72.2 and 74.3-75.5 eV, respectively.
35
Song, Hua. "Investigation of Reaction Networks and Active Sites in Bio-ethanol Steam Reforming over Cobalt based Catalysts". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243999804.
Testo completo
36
Shirvani, Tara. "The role of catalysts and algae in forming a sustainable solution for a global food and fuel crisis". Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:30af0957-1ed6-4ea7-949b-f120606ab22e.
Testo completoAbstract (sommario):
This thesis undertakes three separate lifecycle analyses to determine the emissions and fossil energy demand required to process algae biomass into renewable fuel and animal feed. A complete well-to-wheel fuel-cycle analysis is conducted for the production of biodiesel and jet biofuel from algae biomass. The environmental impacts of algae-based fuels for the road transportation and aviation industry are benchmarked against analogue conventional fossil fuels. This thesis demonstrates that algae biofuel production can only realize its inherent environmental advantage of reduced GHG emissions, once every step of the production chain is fully optimized and decarbonized. This includes smart co-product utilization, offsetting fertilizers through wastewater recycling, reusing exhaust gases as additional CO2 source and using decarbonized electricity, heat and indirect energy. The definition of a Catalyst Sensitivity Index (CSI) demonstrates how catalytic efficiency increases can impact the fossil energy consumption and the greenhouse gas emissions balance of catalyst-dependent processes. The CSI will allow the industry to highlight 'best practice catalysts' and draw conclusions for what efficiency gains one could anticipate with higher performance catalysts. For countries where a decarbonized electricity and heat grid is not available to guarantee low-carbon algae fuel production and the looming resource scarcity around marine feed production has become more pressing, the alternative use of algae for aquafeed production is recommended. This thesis analyses major routes towards the future cost-competitive production of microbial biomass as sustainable fish meal and oil source to meet a global demand for depleting fish feed supplies. A comprehensive economic cost analysis and lifecycle assessment demonstrates the feasibility of replacing global fish meal and fish oil supplies with low-carbon and affordable algae feed by the year 2030. This research reveals how algae feed production has the potential to transform a pressing resource tipping point into a turning point.
37
Naidoo, Preloshni. "A comparative analysis of the chemical composition of linear low density polyethylene polymers synthesised with 1- hexene comonomer under different catalytic conditions". Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80272.
Testo completoAbstract (sommario):
Thesis (MSc)--Stellenbosch University, 2013.ENGLISH ABSTRACT: A comparative study of the chemical composition of linear low density polyethylene polymers, synthesised with 1 - hexene as comonomer was conducted. Catalyst trials were conducted on the linear low density 1 - hexene polymer grade material to evaluate alternative catalysts. A comparative analysis was performed in order to investigate if the samples synthesised under catalyst trial conditions showed any significant differences in terms of crystallinity and mechanical properties with the reference sample that was synthesised using the reference catalyst. The results showed that the macro product properties, namely melt flow Index, density, and level of hexene extractables are different for the trial samples in comparison with the reference sample. The differences observed implied that the trial samples were synthesised with differences on a molecular level. The differences in the chemical composition between the reference sample and the comparative samples were fully explored using a wide range of analytical techniques, namely crystallisation analysis by fractionation (CRYSTAF), temperature rising elution fractionation (TREF), differential scanning calorimetry (DSC), Carbon 13 nuclear magnetic resonance (13C NMR), Size exclusion chromatography (SEC), Positron analysis lifetime spectroscopy (PALS) and micro hardness analysis. The results of the characterisation studies indicated the following: - Crystallinity and hardness analysis of the reference sample, catalyst trial sample 1 and catalyst trial sample 2 indicate that the catalyst trial sample 2 having a low cocatalyst concentration is the most crystalline of all the samples. - The reference sample, catalyst trial sample 1 and catalyst trial sample 2 were further fractionated using TREF at fractionation temperature intervals of 10°C. TREF analysis indicates that the bulk of the material is observed to elute between 70°C - 10°C. - 13C NMR analyses of the TREF fractions identified four populations of fractions that could be selectively removed, allowing the bulk of the material to be recombined. As these highly crystalline fractions were removed, there was an observed decrease in the total crystallinity of the bulk recombined material. This trend was further verified by the free volume analysis. - Free volume analysis indicated of the bulk recombined material indicated a general increase in the T3 lifetime and T4 lifetime intervals. Free volume analysis further confirmed a decrease in crystallinity of the bulk recombined material as highly crystalline material was removed. - Micro hardness analysis of the polymers further verified the crystallinity trends observed. As the molecular composition of the polymer changed due to removal of highly crystalline fractions, the total mechanical strength of the material indicated by the hardness value decreased. The study showed that by changing the chemical composition of the polymer by removing highly crystalline fractions, there was an observed change in the mechanical properties of the polymer. It can be concluded that the samples synthesised under catalyst trial conditions show significant differences in terms of crystallinity and mechanical properties in comparison with the sample that was synthesised using the standard reference catalyst.
AFRIKAANSE OPSOMMING: ‘n Vergelykende analise studie is onderneem van die chemiese samestellings van lineêre lae digtheid poliëtileen polimere, gesintetiseer met 1-hekseen as ko-monomeer. Alternatiewe kataliste is ge-evavuleer ten opsigte van lineêre lae digtheid 1-hekseen Sasol polimeer graad materiaal. Die vergelykende analise is uitgevoer om die monsters onder katalis proef kondisies te evalueer en te merk of enige beduidende verskille in terme van kristalliniteit en meganiese eienskappe met die verwysings monster voorkom. Die resultate toon dat die makro-produk eienskappe, naamlik smelt vloei indeks, digtheid en vlak van hekseen onttrekking, verskillend is vir die proef monsters in vergelyking met die verwysings monster. Die waargenome verskille impliseer dat die proef monsters op molekulêre vlak verskil. Die verskille in chemiese samestelling tussen die verwysings monster en die vergelykende monsters is ten volle ondersoek deur gebruik te maak van 'n wye verskeidenheid van analitiese tegnieke, naamlik kristallisasie analise fraksionering (CRYSTAF), temperatuur stygende eluering fraksionering (TREF), differensiële skandeer kalorimetrie (DSC), koolstof 13 kernmagnetiese resonansie (13C KMR), gelpermeasie chromatografie (SEC), positron analise leeftyd spektroskopie (PALS) en mikro-hardheid analise. Die resultate van die karakterisering studies het die volgende aangedui:- Kristalliniteit en hardheid analises van die verwysings monster en katalis proef monsters 1 en 2 het getoon dat katalis proef monster 2, wat ‘n lae ko-katalis konsentrasie bevat, die mees kristallyn is. - Die verwysings monster en katalis proef monster 1 en 2 is gefraksioneer met behulp van ‘n TREF met temperatuur tussenposes van 10°C. TREF analise toon dat oormaat materiaal ge-elueer word tussen 70°C en 100°C. - 13C KMR analise van die TREF fraksies het 4 verskillende fraksies geidentifiseer wat selektief verwyder kan word. Dit laat ook toe dat die grootste deel van die materiaal weer geherkombineer kan word. Soos die hoogs kristallyne fraksies verwyder is, is ‘n afname in die totale kristalliniteit van die geherkombineerde materiaal waargeneem. Hierdie tendens is bevestig deur vrye volume analises. - Vrye volume analises van die geherkombineerde materiaal toon ‘n algemene toename in die T3en T4 leeftyd aan. Vrye volume analises toon verder dat ‘n afname in die kristalliniteit van die geherkombineerde materiaal plaasvind soos meer kristallyne fraksies verwyder word. - Verdere mikro-hardheid analises van die polimere bevestig die waargenome kristalliniteit tendense. Soos die molekulêre samestelling van die polimere verander as gevolg van die verwydering van die hoogs kristallyne fraksies, so neem die totale meganiese sterkte van die materiaal af; soos aangedui deur die afname in hardheid waarde. Die studie toon dat die verandering van die chemiese samestelling van die polimeer, deur die verwydering van hoogs kristallyne fraksies, 'n waargenome verandering in die meganiese eienskappe van die polimeer laat plaasvind. Daar kan afgelei word dat die monsters, vervaardig onder die katalis proef voorwaardes, beduidende verskille toon in terme van kristalliniteit en meganiese eienskappe in vergelyking met die monster vervaardig deur die huidige verwysings katalis.
38
MacArthur, Katherine E. "Quantitative structural and compositional characterisation of bimetallic fuel-cell catalyst nanoparticles using STEM". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:6ce29b0c-1e7e-4604-ba5b-22f2ebd03d4e.
Testo completoAbstract (sommario):
Platinum-based catalysts for hydrogen fuel-cell applications have progressed greatly with the addition of a second element in either a mixed-alloy or core-shell structure. Not only do they contain a reduced amount of the more expensive platinum metal but they have been shown to demonstrate a significant improvement in catalytic activity. Further improvement of these systems can only be made by careful investigation of such catalyst panoparticles on an atomic scale. These nanoparticles provide a significant characterisation challenge due to their minute size and beam sensitivity. A new method of quantifying the annular dark-field (ADF) scanning transmission electron microscope (STEM) signal on an absolute scale has been developed to address this problem. Experimental images are scaled to a fraction of the incident beam intensity from a detector map. The integrated intensity of each individual atomic column is multiplied by the pixel area to yield a more robust imaging parameter: a scattering cross section, σ. Using this cross section approach and simulated reference data, I show it is possible to count the number of atoms in individual columns. With some prior knowledge of the sample, this makes it possible to reconstruct the 3-dimensional structures of pure platinum nanoparticles. Such an approach has subsequently been extended to bimetallic particles here the elements are close in atomic number, using the platinum-iridium system as an example. In the same way that the cross section can be calculated from ADF image intensity, it is possible to calculate an energy dispersive x-ray (EDX) partial scattering cross section, beneficial especially because of the simplicity of its implementation. In sufficiently thin samples such that the number of x-ray counts is linearly proportional to sample thickness, we can determine element-specific atom counts. Finally, it is possible to combine EDX and ADF cross sections to provide us with quantitative structural and compositional information.
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Wang, Xingli [Verfasser], Peter [Akademischer Betreuer] Strasser, Frédéric [Gutachter] Jaouen e Peter [Gutachter] Strasser. "Copper-based nanostructured catalysts for efficient and selective CO2 electroreduction – synthesis, catalytic performance, and mechanistic analysis / Xingli Wang ; Gutachter: Frédéric Jaouen, Peter Strasser ; Betreuer: Peter Strasser". Berlin : Technische Universität Berlin, 2020. http://d-nb.info/1209601494/34.
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Stokoe, Robert B. "Conformational and mechanistic studies on asymmetric cyanohydrin synthesis : an analysis of the dipeptide catalysts cyclo-[(S)-His-(S)-Phe], cyclo-[(S)-His-(S)-Leu] and related compounds". Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320398.
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ROCHA, SORAYA M. R. da. "Síntese e caracterização de precursores para catalisadores termicamente estáveis à base de lantanideos pelo método sol-gel". reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11271.
Testo completoAbstract (sommario):
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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SILVA, SIRLANE G. da. "Estudo do efeito do suporte em catalisadores de Cobalto e Níquel para obtenção de Hidrogênio a partir da reforma a vapor do etanol". reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10177.
Testo completoAbstract (sommario):
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Kováč, Martin. "Katalyzátory pro kladnou elektrodu kyslíko-vodíkového palivového článku". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218699.
Testo completoAbstract (sommario):
Master's thesis deals with new methods of preparing catalytic materials for positive electrode of an oxygen-hydrogen fuel cell and the influence of potassium permanganate or doping agent molar mass change on theirs attributes. Further it studies the use of proper measuring methods designed to qualify theirs attributes and the presentation of achieved results. In particular methods of linear sweep and cyclic voltammetry and the processing of data using Koutecky-Levich and Tafel plot and wave log analysis. Values of half-wave and onset potential and kinetic coefficient have been measured and calculated.
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Haire, Andrew Richard. "Probing the influence of bimetallic composition on the Pd/Au catalysed synthesis of vinyl acetate monomer". Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1018.
Testo completoAbstract (sommario):
Scanning Tunnelling Microscopy (STM) was utilised together with the high resolution depth-profiling capabilities of Medium Energy Ion Scattering (MEIS), a technique traditionally associated with single crystal substrates, to probe the mean size and depth dependent composition profile of bimetallic PdAu nanoparticles on planar oxide surfaces as functions of the starting composition and annealing temperature. In order to fit composition profiles to experimental MEIS data, a new analysis tool has been designed that models the particles as flat-topped structures with a hexagonal base which can be divided into a number of shells, each shell corresponding to a particular ion pathlength inside the material. The reliability of this method will be discussed in detail. Fitting results show that the surface layers are always significantly enriched in Au compared to the bulk alloy composition. By comparing MEIS data for clean surfaces data for modified surfaces it was found that Pd generally segregates towards the particle surface on adsorption of acetic acid. The interaction of potassium acetate with Au/Pd{111} alloy surfaces of varying composition has been investigated using Temperature Programmed Desorption (TPD) and Reflection Absorption Infra Red Spectroscopy (RAIRS). At lower coverage, potassium acetate reacts reversibly with the surface to form CO and carbonate. Formation of surface acetate is observed on Pd-rich surfaces only. At higher coverage, acetate is the major surface species formed on all samples examined.
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Lundgren, Stina. "Efficient Synthesis and Analysis of Chiral Cyanohydrins". Doctoral thesis, Stockholm : Kungliga Tekniska högskolan (KTH), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4315.
Testo completo
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Kebe, Seydina Ibrahima. "Synthèse de matériaux monolithiques pour la séparation et la catalyse en phase liquide : problématiques environnementales et du développement durable". Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1127/document.
Testo completoAbstract (sommario):
Les matériaux polymères ont connu un engouement considérable avec l’avènement de l’ère du pétrole et connaissent aujourd’hui encore un succès considérable notamment au travers de la valorisation de ressources naturelles mais également d’applications spécifiques à haute valeur ajoutée, liées à des domaines aussi divers que la chimie analytique, l’exploration spatiale, la médecine où l’enjeu premier est souvent la conception d’objet miniaturisés. Dans ce travail de thèse nous avons développé des matériaux polymères à taille micrométrique, immobilisés soit dans des microcanaux (diamètre interne = 75 µm) ou à la surface de substrats de verre (épaisseur de quelques centaines de µm). Une morphologie de type monolithique a été choisie afin de conférer auxdits matériaux des propriétés de perméabilité, résistance mécanique et thermique compatibles avec des applications dans le domaine de la chimie en flux. Afin de contrôler les propriétés d’interaction aux interfaces des matériaux, un monolithe générique, présentant des unités ester de N-hydroxysuccinimide en surface, a été préparé et fonctionnalisé à façon. Ainsi ont été immobilisés des segments moléculaires jouant le rôle de sélecteurs – pour des applications en électrochromatographie – ou de ligands de nanoparticules métalliques – pour applications en catalyse supportée – via des méthodes classiques (substituion nucléophile) ou originales (photo-addition radicalaire thiol-ène) de greffage.Les matériaux ont été caractérisés par une combinaison de méthodes spectroscopiques, microscopiques, de diffraction, de thermogravimétrie permettant de corréler les propriétés électrochromatographiques ou catalytiques avec la structure interfaciale des matériaux monolithiques. A titre d’exemples d’application, nous pouvons citer la séparation électrochromatographiques de molécules toxiques tels les polluants organiques (aniline, phénols, hydrocarbures aromatiques polycycliques, polychlorobiphényles) et les conservateurs pour les crèmes cosmétiques (parabènes), de biomarqueurs (hydrocarbures aromatiques polycycliques, bases pyrimidiques). Ces analyses ont été réalisées avec des solutions modèles de laboratoire mais aussi des matrices réelles (crèmes cosmétiques, analogues d’échantillons extraterrestres). Aussi les réactions catalytiques de réduction de nitroarènes, d’oxydation d’alcool aromatique, de couplage carbone-carbone et la détection par spectroscopie Raman exaltée de surface de pesticides (trifuraline) et d’intermédiaires de synthèse (para-nitrophénol) ont été réaliséesPolymeric materials have gained immense popularity with the golden age of petroleum and they still today meet with great success through Green polymer chemistry approaches and numerous high added value dedicated application in scientific domains such as analytical chemistry, medicine, space investigations, where one of the key for success is the design of miniaturized objects. In this contribution, micro-sized monolithic materials have been designed though either in microchannel immobilization (I.D. = 75 µm) or surface attachment on glass substrates (hundredths of microns in thickness). Polymers exhibiting monolithic morphology were considered to benefit of high permeability, mechanical and thermal resistances which are mandatory to flow chemistry applications. With the aim to control the interfacial interaction ability, a generic monolith having N-hydroxysuccinimide ester groups was used and on purpose functionalized. Molecular segments acting as selector – for electrochromatographic applications – of metal nanoparticles ligands – for supported catalysis applications – have been immobilized on the monolith surface via classical (nucleophilic substitution) or original (photo-induced thiol-ene click) grafting reactions.The so-designed materials were characterized through spectroscopic, microscopic, diffraction, thermogravimetric methods providing insight into correlation between the observed separation and catalytic abilities and the interfacial structure of the monolith. As representative examples of application, one may cite the electrochromatographic separation of toxic molecules such as organic pollutants (phenols, anilines, polycyclic aromatic hydrocarbons, polychlorobiphenyls), preservatives in cosmetics (parabens) and biomarkers (polycyclic aromatic hydrocarbons, pyrimidic bases). The analyses were conducted on model solutions and complex matrices (cosmetics, extraterrestrial analog samples). Flow catalytic reaction meant for the reduction of nitroarenes, the oxidation of aromatic alcohol, the carbon-carbon coupling and the sensitive detection of pesticides and synthesis intermediates (para-nitrophenol) have been achieved
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Reece, Christian. "Kinetic analysis and modelling in heterogeneous catalysis". Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/103737/.
Testo completoAbstract (sommario):
A combination of Temporal Analysis of Products, Temperature Programmed Reduction, and Density Functional theory techniques have been used to perform kinetic analysis on data from heterogeneous catalysis experiments. A new method of data filtering has been developed for Temporal Analysis of Products, and has been applied to a system of 4 Pt−Mo2C, and the current methodology has been expanded upon to calculate rate coefficients for the oxidation of CO to CO2 via the Boudard reaction. From the kinetic constants it appears that a phase change occurs in the material at approximately 200�C. The current theory for analysing Temperature Programmed Reduction has been applied in a new methodology which is able to perform the deconvolution of thermograms with high accuracy, while also calculating the kinetic parameters related to the reduction processes. This new methodology has been applied to a system of CeO2 calcined at 400, 500 and 600�C and the strengths and limitations of the methodology are explored. From the deconvolution procedure it was found that there are three distinct reduction processes occurring on the CeO2 and that a phase change occurs between 400 and 500�C. Finally Density Functional Theory combined with classical dynamics has been used to explore the mechanism of the hydrogenation of Levulinic Acid to gamma-Valerolactone over a CuZrO2 catalyst. It was found that the Levulinic Acid is more likely to hydrogenate then cyclise, and from using molecular dynamics simulations it was shown that the solvent H2O plays a very important role in the cyclisation of the hydrogenated intermediate.
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Autin, Laura. "Étude des cinétiques de réticulation et de la dynamique moléculaire de réseaux silicones : compréhension des mécanismes catalytiques par analyse viscoélastique et RMN". Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10258.
Testo completoAbstract (sommario):
La catalyse de polycondensation des silicones, et notamment des élastomères vulcanisables à froid bicomposants, constitue un enjeu scientifique, environnemental et économique. Le dilaurate de dibutyl étain (DLDBE), classé CMR2, très largement utilisé dans l'industrie du silicone sera prochainement interdit par la nouvelle réglementation REACH. L'objectif de cette étude est donc d'étudier de nouveaux systèmes catalytiques des réactions de polycondensation. L'effet des différents constituants de la formulation (masse molaire du PDMS réactif, concentration en réticulant, concentration en catalyseur) sur la cinétique de réticulation et sur les propriétés finales a été étudié par combinaison des techniques de rhéologie, RMN et taux de gonflement. Principalement, ce travail consiste en l'étude approfondie de deux catalyseurs : une guanidine et un complexe de zinc et les résultats montrent que la construction des réseaux est plus ou moins différente selon la catalyse. En effet, un dérivé de l'étain conduit à une construction en deux étapes d'hydrolyse et de condensation, dont l'hydrolyse est d'abord favorisée. En comparaison, les complexes de zinc tendent à se comporter d'une façon très similaire, bien que l'hydrolyse des alcoxysilanes soit plus importante. Au contraire, une catalyse basique favorise très largement la condensation par rapport à l'hydrolyse. La guanidine réagit très rapidement avec les fonctions silanols. Ensuite, l'hydrolyse des alcoxysilanes se produisant dans une moindre proportion, le réseau tridimensionnel se construit. Ces travaux ont donc montré que le complexe de zinc étudié est un bon remplaçant du DLDBESilicones condensation catalysis, and more especially room temperature vulcanizable compounds, is a very important scientific, environmental and economic issue. The catalysis species, derivated from tin dilaurate, which are now classified as a CMR2 compound (toxic for reproduction), have been widely used in the silicone industry. The new REACH regulation is going to forbid its use very soon. This study aims to work on new catalytic systems. The influence of the components of the formulation on the kinetics and mechanical properties has been study by different methods: rheology, NMR and swelling measurements. More precisely, this work focuses on two catalysts: one guanidine and zinc complexes. Results have shown that the network construction depends on the catalysis. In fact, while using a tin compound, the construction occurs in two steps, in which hydrolysis is the most important. As a comparison, zinc complexes present the same behaviour as tin compounds even though the hydrolysis step is much more important. On the contrary, it’s known that basic catalysis enhances the condensation step. Then, the guanidine quickly reacts with the silanol functions. Then, in a second step, the alkoxysilanes hydrolysis occurs in a smaller proportion. The tridimensional network is getting built. This work mainly showed that zinc complexes can easily replace tin compounds
49
Penkala, Bartosz. "Low Temperature Oxygen Mobility Applied to Catalysis". Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS022.
Testo completoAbstract (sommario):
Accomplir les spécifications des nouvelles réglementations concernant les gaz d'échappement de post-traitement des technologies automobiles, par exemple, TWC, implique la disponibilité et l'utilisation de matériaux catalytiquement actifs et notamment des composés tampons d'oxygène, ce qui peut réversible stocker et libérer de grandes quantités de l'oxygène. Oxyde de cérium dopé présente encore aujourd'hui le seul composé de référence pour un support approprié, en raison de sa grande capacité de stockage de l'oxygène et possibilité de créer facilement des lacunes en ions d'oxygène. Cependant, pour des raisons économiques et de l'abondance naturelle très limitée à quelques pays, la substitution de l'oxyde de cérium semble être obligatoire; Dans ce contexte, nous notons que l'oxyde de cérium est partie de la liste des 13 matières premières économiquement importants qui ont été identifiés par la Commission européenne comme soumis à un risque élevé d'interruption de l'alimentation. Dans ce contexte, les oxydes de type brownmillérite sont d'un intérêt potentiel, car ils révèlent oxygène mobilité ionique jusqu'à la température ambiante. En outre, ils permettent de régler la présence de défauts étendus par exemple frontières anti-phase au cours de conditions de synthèse, et qui se sont avérés diminuer de manière significative l'énergie d'activation pour la diffusion d'oxygène. Nous avons ainsi pu montrer que vice-riche nano-Ca2Fe2O5, traditionnellement connue comme une ligne phase stoechiométrique, peut être oxydé dans des conditions douces à CaFeO3, tandis que l'oxydation de Ca2Fe2O5 ordinaire nécessite généralement des conditions de réaction extrême, soit 1100 ° C et plusieurs GPa pression partielle d'oxygène. Ainsi, l'introduction d'une forte concentration de défauts semble être un concept prometteur pour transformer ligne phases stoechiométriques même traditionnellement connus pour devenir une sorte d'éponge de l'oxygène et de se comporter en tant que composé de stockage / tampon d'oxygène à des températures très modérées. Ce comportement est donc comparable à la capacité de stockage d'oxygène d'oxyde de cérium dopé, et dispose d'un potentiel réel pour l'application dans la catalyse. Par conséquent, le brownmillérite Ca2Fe2O5 semble être un candidat prometteur pour étudier en raison de ses oxygène connue propriétés de conductivité ionique.Objectif principal de ce travail est d'établir la relation fondamentale entre structure / microstructure, propriétés de mobilité de l'oxygène et de l'activité catalytique, simultanément entrepris pour deux systèmes: Ca2Fe2O5 avec la structure brownmillérite-type et CeO2 avec une structure de type fluorite. Nous essentiellement exploré les critères sous-jacents qui régissent leur composition chimique / activité catalytique, utilisant de l'oxygène comportement d'échange des isotopes par TG expériences couples de MS. D'autres études utilisant la spectroscopie Raman essentiellement permis de conclure à partir d'une dynamique de réseau modifiées pour différents isotopes de l'oxygène à la différence entre masse et la participation à l'oxygène de la surface au mécanisme d'oxydation du CO en CO2. Pour une meilleure compréhension mécaniste de l'oxydation de CO, nous avons développé un nouveau test catalytique, par rapport à une variation dynamique de la pression partielle d'oxygène dans le récipient de réaction, ce qui permet de conclure à la fois sur l'activité catalytique du catalyseur et sa libération de l'oxygène / comportement absorption , non accessible par le test d'activité catalytique classique interprétée sous un flux de gaz constant. De cette façon, nous avons eu un nouvel aperçu de différencier la participation de la surface et de l'activité vrac d'oxygène pour les catalyseurs à base d'oxyde de cérium et Ca2Fe2O5 différenteAccomplishing specifications of new regulations regarding automotive exhaust after-treatment technologies, e.g. TWC, imply the availability and usage of catalytically active materials and especially oxygen buffer compounds, which can reversibly store and release high quantities of the oxygen. Doped cerium oxide presents still today the only reference compound for a suitable support, due to its high oxygen storage capacity and ability to easily create oxygen ion vacancies. However, for economic reasons and very limited natural abundance to a few countries, the substitution of ceria appears to be mandatory; in this context we note that ceria is part of the list of 13 economically important raw materials which were identified by the European Commission as subject to a high risk of supply interruption.In this context, Brownmillerite-type oxides are of potential interest, since they reveal oxygen ion mobility down to ambient temperature. Furthermore, they allow to adjust the presence of extended defects e.g. anti-phase boundaries, during synthesis conditions, and which have been shown to significantly decrease the activation energy for oxygen diffusion. We were thus able to show that defect-rich nano-Ca2Fe2O5, traditionally known as a stoichiometric line-phase, can be oxidized under mild conditions to CaFeO3, while the oxidation of ordinary Ca2Fe2O5 usually requires extreme reaction conditions, i.e. 1100°C and several GPa oxygen partial pressure. Thus, introducing a high concentration of defects seems to be a promising concept to transform even traditionally known stoichiometric line-phases to become a kind of oxygen sponge and behave as oxygen storage/buffer compound at very moderate temperatures. This behavior is thus comparable to the oxygen storage capacity of doped cerium oxide, and offers a true potential for application in the catalysis. Consequently, the Brownmillerite Ca2Fe2O5 appears to be a promising candidate to study due to its known oxygen ion conductivity properties.Primary aim of this work is to establish fundamental relation between structure/microstructure, oxygen mobility properties and catalytic activity, simultaneously undertaken for two systems: Ca2Fe2O5 with Brownmillerite-type structure and CeO2 with Fluorite-type structure. We essentially explored the underlying criteria governing their chemical/catalytic activity, using oxygen isotope exchange behavior by TG couples MS experiments. Further studies using essentially Raman spectroscopy allowed concluding from a modified lattice dynamics for different oxygen isotopes to differentiate between bulk and surface oxygen participation to the oxidation mechanism of CO to CO2. For a deeper mechanistic understanding of the CO oxidation, we developed a new catalytic test, based on a dynamic variation of the oxygen partial pressure in the reaction vessel, allowing to conclude simultaneously on the catalytic activity of the catalyst and its oxygen release/uptake behavior, not accessible by the classical catalytic activity test performed under constant gas flow. In this way we got a new insight to differentiate the participation of surface and bulk oxygen activity for different Ca2Fe2O5 and ceria based catalysts
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Margeriat, Alexandre. "Conversion catalytique des vapeurs de pyrolyse et molécules modèles". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1340/document.
Testo completoAbstract (sommario):
La pyrolyse rapide de biomasse lignocellulosique produit des bio-huiles avec des rendements élevés mais ces liquides contiennent de nombreux composés oxygénés, une acidité élevée et de ce fait sont instables. Un hydrotraitement poussé de ces huiles est nécessaire avant qu'elles puissent être utilisées comme combustibles liquides. Afin de réduire le coût et d'améliorer les performances de l'hydrotraitement ultérieur, plusieurs stratégies ont été proposées pour réduire les teneurs en oxygène et en acides, comme l'ajout d'un lit catalytique après la pyrolyse. La conversion catalytique des vapeurs de pyrolyse permet une désoxygénation partielle avant la condensation des vapeurs. Dans ce contexte, nous avons étudié la conversion de molécules modèles, l'acide acétique et le gaïacol, sur différents catalyseurs acides afin d'identifier des phases actives performantes et de comprendre les mécanismes réactionnels. Dans un deuxième temps, un test de pyrolyse semi-continu combiné avec un réacteur catalytique a été conçu et mis en place et les meilleurs catalyseurs acides sélectionnés pour les molécules modèles ont été testés pour la conversion de bois de hêtre. Après conversion, un protocole de séparation des fractions a été appliqué et les fractions gaz, liquide et solide ont été caractérisées par différentes méthodes (?-GC, GC×GC, GPC, RMN…). Une attention particulière a été portée à la quantification des monomères dans la fraction liquide par GC×GC. Les bilans massiques atteignent plus de 90% et des bilans carbones ont été également réalisés dans les différentes fractions. L'ensemble des caractérisations et la comparaison entre pyrolyse avec et sans étape catalytique permet d'améliorer la compréhension du rôle du catalyseur dans la conversion des vapeurs de pyrolyseFast pyrolysis of biomass yields bio-oils with high levels of oxygen-containing components, high acidity and low stability. Further upgrading of these oils is necessary before they can be used as liquid fuels. Several low-cost strategies have been proposed for reducing the oxygen and acid contents including the catalytic conversion of pyrolytic vapors before vapor condensation. In this context, a first step in this work was the study of model molecules conversion, acetic acid and guaiacol, on different acid catalyst to understand reaction mechanisms and determine the best catalyst. In a second time, a semi-continuous pyrolysis test combined with a catalytic reactor was built and use to test the best acid catalysts found on model molecules, for the conversion of beech wood chips. A product recovery protocol was implanted to recover all the gas, liquid and solid fractions. Those fractions were characterized in depth by various techniques (?-GC, GC×GC, GPC, RMN…). A special focus was made on the quantification of monomers in the bio-oils by GC×GC. Mass balance reached 90% and carbon balance were established for some experiments. The performed characterizations as well as the comparison between catalytic and thermal experiments allowed to get more insights in the role of the catalyst on pyrolytic vapors conversion