Дисертації з теми "Organic synthesis, Catalysis, and methodology development"
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Birrell, James Andrew. "I. Enantioselective Acylation of Silyl Ketene Acetals through Fluoride Anion-Binding Catalysis II. Development of a Practical Method for the Synthesis of Highly Enantioenriched Trans-1,2-Amino Alcohols." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11037.
Повний текст джерелаChemistry and Chemical Biology
Chen, Andrew. "New Radical Reactivity at the Interface of Synthetic Methodology Development and Computational Modeling." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1593586492097279.
Повний текст джерелаPerego, Luca Alessandro. "Transition metal-catalyzed reactions : mechanistic studies and methodology developments." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEE003/document.
Повний текст джерелаIn this thesis, the mechanism of three organic reactions catalyzed by palladium and copper complexes has been elucidated by the use of both experimental and theoretical methods. The first reaction is the synthesis of amides from haloarenes, isocyanides and water as an example of the broad family of palladium-catalyzed imidoylative couplings. Multiple roles of the isocyanide as both a ligand and a substrate in the different steps of the catalytic cycle have been disclosed. The second transformation is the palladium-catalyzed ring opening of benzofurans leading to indoles. Optimal conditions for this transformation have been found and the key aspects of its mechanism clarified. The last reaction, which is the main topic of this thesis, is the addition of amines to allenes catalyzed by copper salts (hydroamination). A characterization of the catalytically active copper(I) species and insight from theoretical calculations suggested how to extend this reaction to other substrates (allenamides, N-allenylazoles, N-allenylsulfonamides) under mild and efficient conditions
Aparece, Mark Docto. "Synthesis of Organoboron Compounds via a Palladium-Induced 1,2-Metallate Shift Mechanism:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108927.
Повний текст джерелаThis dissertation describes the development of various palladium-catalyzed syntheses of organoboron compounds with the 1,2-metallate shift of organoboron “ate” complexes as a common mechanistic feature. Chapter one discusses the history of the 1,2-metallate shift with a focus on reactions promoted by transition metals, followed by my work on the palladium-catalyzed, enantioselective, halide-tolerant conjunctive cross-coupling reaction to enable the use of Grignard reagents and arylbromides. Chapter two discusses the attempt to engage allylic electrophiles in the conjunctive cross-coupling reaction and the discovery and optimization of the vinylidenation reaction to access 1,1-disubstituted boryl alkenes. Unlike other palladium-catalyzed reactions that proceed by a 1,2-metallate shift, the vinylidenation proceeds by a β-hydride elimination rather than a reductive elimination as the final step in the catalytic cycle. Chapter three discusses the development of the enantioselective conjunctive cross-coupling of propargylic electrophiles to access enantioenriched β-boryl allenes. Methanol additive was found to improve both the yield and enantioselectivity of the reaction. 1H NMR studies show that methanol exchanges with the pinacol ligand on the boron “ate” complex
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
Lamb, Alan David. "Asymmetric synthesis of heterocycles via cation-directed cyclizations and rearrangements." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:4c0cf06c-d461-42a4-b4d8-a2a2bd961435.
Повний текст джерелаBrogan, Samantha. "Development of new methodology for the synthesis of fluorine-containing compounds." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7887.
Повний текст джерелаKarim, Rehana. "Development of radical synthetic methodology using solid-phase organic synthesis." Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/34406.
Повний текст джерелаEmmett, Edward J. "Development of catalytic methods to exploit sulfur dioxide in organic synthesis." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:be60729b-5467-4758-8d88-9dff3a2d5810.
Повний текст джерелаXu, Chongsong. "Development of functionalized spiroligomers for metal-binding and asymmetric catalysis." Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/595512.
Повний текст джерелаPh.D.
This thesis describes the synthesis of functionalized spiroligomers and their applications in metal binding, metal-mediated catalysis, and organocatalysis. By synthesizing a family of functionalized bis-amino acids achieved from reductive alkylation, the Schafmeister group has developed access to highly functionalized and shape programmable structures named “spiroligomers.” The rigid backbones of spiroligomers are good at organizing the orientations of functional groups on their side chains. This property enables them as promising candidates for catalysts. Firstly we synthesized a few spiroligomer dimers presenting metal-binding groups such as terpys and bipys. With the right orientation of metal binding groups controlled by adjusting the stereocenter of the spiroligomer, macrocyclic “square” complexes with metals were obtained. The crystal structures of these intriguing complexes were solved. This work rendered the first structurally, spectroscopically and electronically characterized metal-spiroligomer complexes as well as the first crystal structure of spiroligomer. Secondly, the question of whether metal-binding spiroligomers are able to catalyze certain reactions became our major concern. We developed a binuclear copper catalyst that could accelerate a phosphate ester rearrangement, and that demonstrated that when the two copper binding terpyridine groups were best able to approach each other, they accelerated the rearrangement more than 1,000 times faster than the background reaction. Other molecules that did not properly organize the two copper atoms demonstrate considerably slower reaction rates. At last, catalysts based on spiroligomers without metals are also of interests. By displaying two hydrophobic groups in various directions on a monomeric spiroligomer (also can be regarded as a proline derivative), we observed variable activities and enantioselectivities in the catalysis of asymmetric Michael addition (up to 94% ee at -40 °C for one organocatalyst).
Temple University--Theses
Stevens, Kiri. "Methodology for the synthesis of NP25302 and other bioactive natural products." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:ae18879e-d75e-4280-ba55-1ae08e64034f.
Повний текст джерелаLonca, Geoffroy. "Development of new reactions of organic synthesis catalyzed by gold and copper." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX057/document.
Повний текст джерелаThis manuscript presents the development of gold- and copper-catalyzed methods for the synthesis of heterocyclic compounds and trifluoromethylated products.Firstly, a gold-catalyzed synthesis of trifluoromethyl allenes was developed, relying on a 1,5 hydride shift. This method allows to access, in a very efficient and selective way, a large range of perfluoroalkylated allenes, of which the synthetic potential was also demonstrated.Afterwards, the catalytic power of gold was then used in a synthesis of 2H-1,3-oxazines, relying on a 6-endo type cyclization of azide-yne substrates. This methods allows to access, in very mild condition, an unprecedently large range of polysubstituted oxazines in excellent yields.Finally, a method for the copper-catalyzed radical hydrofunctionalization of alkenols was developed. The strategy involved relies on a 1,5 hydrogen abstraction, in which a benzyloxy moiety plays the role of the hydrogen donor
Borg, Tessie. "Stereoselective Nucleophilic Additions to Aldehydes and Development of New Methodology in Organic Synthesis." Doctoral thesis, KTH, Organisk kemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121172.
Повний текст джерелаQC 20130503
Korkmaz, Cokol Nalan. "Development Of The Methodology For The Synthesis Of Bis-aminoinositols." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613580/index.pdf.
Повний текст джерела-nitroso hydrazide intermediate. Subsequent Curtius rearrangement reaction resulted in the formation of the isocyanate which was converted to the corresponding bis-urethane by treatment with MeOH. Attempt to cleave the oxa-bridge in urethane with sulfamic acid provided the unexpected tricyclic product 148. Furthermore, hydrolysis of isocyanate with aqueous HCl formed the diamine 156. However, O-bridge could not be opened with any reagents used for that of urethane derivative as described above. Then,the cis-diol 157 was synthesized to prevent the neighboring group participitation during the epoxide-opening reaction. Further ring-opening reactions are under investigation.
Snell, Robert Henry. "Development and application of asymmetric C-N bond formation." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:512e617a-2b01-45f3-86ae-c0cf4b874149.
Повний текст джерелаCavitt, Marchello Alfonzo. "Stress relief: Exercising Lewis acid catalysis for donor-acceptor cyclopropane ring-opening annulations, a basis for new reaction methodologies." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54448.
Повний текст джерелаBarber, David M. "The development of nitro-Mannich/hydroamination cascades for the synthesis of substituted N-heterocycles." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:18e7c533-3789-4800-9813-1d5c7bb4e4ea.
Повний текст джерелаCharlton, Andrew. "Towards the development of direct methodology to enantioenriched α-alkylated aldehydes". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:bcfe43bb-1497-4f94-bcc7-6f7c2ae0b3a1.
Повний текст джерелаSow, Boubacar. "Development of the Domino Pericyclic Oxy-Cope/Ene /Claisen /Diels-Alder Reaction and the Synthesis of Complex Bicyclo[3.3.1]alkenones." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/30344.
Повний текст джерелаGoyal, Poorva. "Development of dendritic and polymeric scaffolds for biological and catalysis applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24826.
Повний текст джерелаCommittee Chair: Weck, Marcus; Committee Member: Bunz, Uwe H. F.; Committee Member: Dickson, Robert M; Committee Member: Fahrni, Christoph J; Committee Member: Jones, Christopher W; Committee Member: Murthy, Niren.
Bellavance, Gabriel. "Part A: Development of a Modular Synthetic Approach to Polycyclic Polyprenylated Acylphlorogluginols: Total Synthesis of Papuaforin A, B, C, Hyperforin and Formal Synthesis of Nemorosone. Part B: Studies Toward the Synthesis of Ginkgolides." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34630.
Повний текст джерелаAkanksha, Tyagi. "Development of novel hybrid catalysis for carbon-carbon couplings by titanium oxide photocatalyst and metal cocatalyst." Kyoto University, 2018. http://hdl.handle.net/2433/232379.
Повний текст джерела0048
新制・課程博士
博士(人間・環境学)
甲第21178号
人博第850号
新制||人||203(附属図書館)
29||人博||850(吉田南総合図書館)
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 吉田 寿雄, 教授 内本 喜晴, 教授 田部 勢津久
学位規則第4条第1項該当
Bétournay, Geneviève L. "Development of the 5-exo-dig/Prins Reaction and Efforts towards the Total Synthesis of (±)-Magellanine." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23485.
Повний текст джерелаParra, Montes Claudio. "Development of Organocatalytic Tandem Processes for the Asymmetric Synthesis of Nitrogen-Containing Compounds." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/301627.
Повний текст джерелаMartinez, Ariza Guillermo, and Ariza Guillermo Martinez. "Exploiting Molecular Diversity to Access Biologically Relevant Chemotypes." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621718.
Повний текст джерелаZhao, Senzhi. "NOVEL APPROACHES TO STRYCHNOS AND ASPIDOSPERMA ALKALOIDS." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/367411.
Повний текст джерелаPh.D.
All Strychnos and Aspidosperma alkaloids possess a core pyrrolo[2,3-d]carbazole ABCE tetracycle. In order to develop an efficient and divergent methodology for the synthesis of Strychnos alkaloids, a streamlined synthetic sequence to the ABCE tetracycle has been developed. It features a Mitsunobu activation of an N-hydroxyethyl gramine intermediate and subsequent intramolecular aza-Baylis-Hillman reaction. This method was first applied in the total synthesis of (±)-alstolucine B. Additional key steps in the synthesis included (1) chemoselective intermolecular and intramolecular Michael additions and (2) a Swern indoline oxidation. The second application of this method was in the first total synthesis of (-)-melotenine A, a novel rearranged Aspidosperma alkaloid with potent biological activity. Additional key steps in the synthesis included (1) a Piers annulation of a vinyl iodide and a methyl ketone to prepare the D ring and (2) a site-selective intermolecular vinylogous aldol reaction
Temple University--Theses
Hanchate, Vinayak. "Sulfoximine and Sulfoxonium Ylide Directed C-H Activation and Domino Cyclization: Construction of Heterocyclic and Carbocyclic Rings." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/5074.
Повний текст джерелаCSIR, SERB (EMR/2016/006358)
Furst, Laura. "Radical mediated heterocycle functionalization: methodology development and natural product synthesis." Thesis, 2013. https://hdl.handle.net/2144/13121.
Повний текст джерелаJohnson, Myron Mario. "The development of novel synthetic methodology for the synthesis of oxygenated heterocycles." Thesis, 2014. http://hdl.handle.net/10539/14963.
Повний текст джерелаGao, Xin active 2013. "Formation of C-C bonds via transfer hydrogenation : from methodology development to natural product synthesis." 2013. http://hdl.handle.net/2152/21412.
Повний текст джерелаtext
ANTENUCCI, ACHILLE. "Development of new green strategies based on Brønsted and Lewis acid catalysis in organic synthesis." Doctoral thesis, 2019. http://hdl.handle.net/11573/1382061.
Повний текст джерелаLeung, Priscilla. "The Synthesis and Applications of Sulfoxide Ligands and Methodology Development Towards Beta-Amino Acid Incorporation in Peptides." Thesis, 2011. http://hdl.handle.net/1807/27351.
Повний текст джерелаNgwira, Kennedy John Vijuviju. "Development of novel methodology for the synthesis of the angucycline tetrangulol, benzo[c]phenathridines and benzonaphthopyranones." Thesis, 2017. http://hdl.handle.net/10539/23521.
Повний текст джерелаIn this PhD thesis, we report for the first time, new methodology for the synthesis of angucycline antibiotic natural products. In particular, for the synthesis of 1,8-dihydroxy-3methyltetraphene-7,12-dione, commonly known as tetrangulol. We also report on the synthesis of 1,10,12-trimethoxy-8-methylbenzo[c]phenanthridine in our quest to synthesise phenanthroviridone from an intermediate product in the synthesis of tetrangulol. The Suzuki-Miyaura coupling reaction between 1,4,5-(trimethoxynaphthalen-2-yl)boronic acid and 2-iodo-3-methoxy-5-methylbenzaldehyde afforded intermediate, 3-methoxy-5methyl-2-(1,4,5-trimethoxynaphthalen-2-yl)benzaldehyde. Conversion of this benzaldehyde into the alkyne, 2-(2-ethynyl-6-methoxy-4-methylphenyl)-1,4,5-trimethoxynaphthalene was accomplished utilizing the Corey-Fuchs reaction. Exposure of the derived acetylene to a catalytic platinum(II)-mediated ring closure yielded the required tetracyclic aromatic product, 1,7,8,12-tetramethoxy-3-methyltetraphene which was converted into tetrangulol. Exposure of the related 3-methoxy-5-methyl-2-(1,4,5-trimethoxynaphthalen-2-yl)benzaldehyde O-phenyl oxime to microwave irradiation in an ionic liquid yielded 1,10,12-trimethoxy-8methylbenzo[c]phenanthridine, instead of the desired natural product phenanthroviridone. We also report on the unexpected synthesis of the benzonaphthopyranone core found in other classes of angucycline antibiotics from oxygen analogs of 2-naphthylbenzyl alcohols when exposed to N-bromosuccinimide. Treatment of (2-(1,4-dimethoxynaphthalen-2yl)phenyl)methanol and related analogues with N-bromosuccinimide under an oxygen atmosphere afforded 12-methoxy-6H-dibenzo[c,h]chromen-6-one, 2-Methoxy-6Hbenzo[c]chromen-6-one and of 6H-benzo[c]chromen-6-one. An investigation into possible mechanisms for this transformation was also conducted.
LG2017
(10730742), Henry J. Hamann. "Amine-Boranes: Synthesis and Applications." Thesis, 2021.
Знайти повний текст джерелаWengryniuk, Sarah Elizabeth. "Regioselective Asymmetric a,a-Bisalkylation of Ketones via N-Amino Cyclic Carbamate Chiral Auxiliaries: Methodology Development and Application to the Total Synthesis of both (+)- and (-)-Stigmolone and Apratoxin D." Diss., 2012. http://hdl.handle.net/10161/5574.
Повний текст джерелаThe α-alkylation of ketones is a transformation of central importance to organic synthesis. Our lab recently introduced the N-amino cyclic carbamate (ACC) chiral auxiliaries for asymmetric ketone α-alkylation. ACCs provide significant advantages over existing asymmetric ketone alkylation methods as they are easy to introduce, both deprotonation and alkylation can be run at relatively mild temperatures, stereoselectivity of alkylation is excellent and auxiliary removal is facile. A unique feature of ACCs is their ability to control the regioselectivity of deprotonation through what we have termed Complex Induced Syn-Deprotonation. In what follows, we describe several projects relating to the development and synthetic application of ACCs.
An optimized synthesis of our most successful ACC auxiliary was developed, including an improved method for the formation of the key N-N hydrazide bond.
A detailed mechanistic investigation of four ACC auxiliaries was conducted, examining the regio- and stereoselectivity of the alkylations at the level of the ACC hydrazone. This work culminated in a theoretical study of ACC auxiliaries, conducted through a collaboration with the Houk Group at UCLA.
We also describe the use of ACCs in the development of the first method for the regiocontrolled asymmetric α,α-bisalkylation of ketones. The method proceeds in excellent yield and with >99:1 diastereoselectivity. This method was also extended to the asymmetric α,α,α',α'-tetraalkylation of ketones, enabled by the development of a mild, epimerization-free LDA-mediated isomerization of the α,α-bisalkylated ACC hydrazones.
Additionally, we discuss three synthetic applications of the ACC α,α-bisalkylation methodology. We report an asymmetric formal synthesis of (+)- and (-)-stigmolone, as well as two approaches to the polyketide fragment of the novel cyclic depsipeptide apratoxin D, which have led to the completion of the first asymmetric total synthesis of apratoxin D.
Dissertation
Li, Jian-yuan. "The modification of brucine derivatives as chiral ligands and its application in the asymmetric synthesis." Thesis, 2014. http://hdl.handle.net/1805/6464.
Повний текст джерелаThe modification of brucine derivatives as chiral ligands and the use of a multifaceted chiral ligand, brucine diol, under different reaction conditions to produce various optical isomers is described. In Chapter 1, the generation of a number of brucine derivatives is described. Taking the advantage of brucine-diol’s excellent molecular recognition capability for multiple organic functional groups, we focused on the synthetic modifications of brucine-diol and the synthesis of brucine N-oxide. We also produced various brucine derivatives with different functional moieties in good yields and selectivities. In Chapter 2, we described the investigation of brucine N-oxide catalyzed Morita-Baylis-Hillman (MBH) reaction of alkyl/aryl ketones. Brucine N-oxide was used as a nucleophilic organic catalyst in the MBH reaction of alkyl vinyl ketone. In addition, asymmetric MBH reactions of alkyl vinyl ketones with aldehydes were investigated using a dual catalysis of brucine N-oxide and proline. In this dual catalyst system, proline was found to form iminium intermediates with electron-deficient aryl aldehydes, while the N-oxide activated vinyl ketones provided enolates through the conjugate addition. Our dual catalysis approach also allowed the development of MBH reaction of aryl vinyl ketones. In Chapter 3, brucine diol-copper complex catalyzed asymmetric conjugate addition of glycine (ket)imines to nitroalkenes is discussed. Stereodivergent catalytic asymmetric conjugate reactions for glycine (ket)imines with nitroalkenes were achieved using various chiral catalysts derived from a single chiral source, brucine diol. Both syn- and anti-conjugate addition products were obtained with high diastereoselectivity and enantioselectivity. In Chapter 4, enantiodivergent production of endo-pyrrolidines from glycine (ket)imines using brucine diol-copper complex is described. The [3+2] cycloaddition reaction of glycine imines and activated alkenes was performed to produce endo-pyrrolidines. The reversal of enantioselectivity was observed for endo-pyrrolidines between concerted and stepwise reaction pathways. The three new brucine derivatives produced in this study would potentially work as organocatalysts and chiral ligands with metal ion in asymmetric synthesis. The brucine diol-metal complex catalyzed reactions laid a good foundation for catalytic asymmetric reactions, where a single chiral source was used to control the absolute and the relative stereochemical outcomes of reactions. Understanding the molecular-level interactions between catalyst and substrates will provide insightful mechanistic details for the stereodivergent approaches in asymmetric catalysis.
WEI, Hua. "Development of Innovative Electrodes for the Electrocatalytic Conversion of Small Molecules." Doctoral thesis, 2021. http://hdl.handle.net/11570/3191397.
Повний текст джерелаNitrogen plays an indispensable role for all life on earth and for the development of human beings. Industrially, nitrogen gas is converted to ammonia (NH3) and nitrogen-rich fertilisers to supplement the amount of nitrogen fixed spontaneously by nature. At present, the only industrial-scale ammonia synthesis technology is the process developed by Haber and Bosch in the early 20th century using gas phase N2 and H2 as the feeding gases. However, the Haber-Bosch process requires harsh conditions, complex equipment and high energy consumption, and operates with low conversion rates, which are inconsistent with economic and social growing development requirements. Compared to the Haber-Bosch method, electrocatalysis is one of the promising routes that can integrate electricity produced from renewable energy technologies for the production of ammonia at room temperature and ambient pressure. A specific challenge is related to the development of novel electrocatalysts/electrodes with the aim to achieve a low-cost, large-scale and delocalized production of ammonia. In view of the above key scientific issues, this PhD work focuses on three main aspects of the electrocatalytic nitrogen reduction reaction (NRR): i) engineering and design of the electrocatalyst, ii) electrode and cell design of the electrochemical device and iii) improvement and optimization of the reaction conditions, to enhance the performances of ammonia synthesis. Most of the research activities of this PhD work about synthesis and characterization of the electrocatalytic materials and assembling/testing of the electrodes in unconventional electrochemical devices were carried out at the laboratory CASPE (Laboratory of Catalysis for Sustainable Production and Energy) of the University of Messina. Moreover, during the three years, a period of 12 months was spent in cotutelle with the École supérieure de chimie, physique, électronique de Lyon (CPE Lyon), where advanced synthesis routes were explored for the preparation of organometallic-based electrocatalysts to be used as more active electrodes in NRR. The PhD thesis is organized in five main chapters. Chapter 1 focuses on N2 fixation issues and on describing the industrial Haber-Bosch process, with an overview of the general implications related to its high energy requirements. The alternative methods based on the electrochemical nitrogen fixation are then presented, with a wide description of pros and cons related to the milder conditions (i.e., room temperature and atmospheric pressure) and by discussing the elements to be developed for a future implementation of this technology, including a description of the possible reaction mechanism, which is still unclear in literature. Chapter 2, instead, refers to the electrocatalytic materials developed in this PhD work for the preparation of the electrodes: 1) the Metal-organic Frameworks (MOFs), a class of porous materials very promising for their peculiar characteristics of high surface area, tunable properties, organic functionality and porosity, as well as for the possibility of creating specific catalytic active sites thanks to both the functional groups and the metal ion centres; 2) the MXenes, a class of metal carbide or nitride materials with a two-dimensional (2D) structure, which have recently attracted a large interest for a broad range of applications, including catalysis and N2 fixation, for their unique properties of metallic conductivity and hydrophilic nature of the hydroxyl or oxygen terminated surfaces. In Chapters 3-5, the experimental results are presented and discussed. Chapter 3 concerns the preparation of a series of Fe-MOF-based (Fe@Zn/SIM-1) electrodes and their testing in NRR by using an advanced engineered three-phase reactor, working in gas-phase. This novel device operates at room temperature and atmospheric pressure, with counter and reference electrodes immersed into an anode half-cell (where the oxidation of H2O to O2 occurs) containing a liquid electrolyte (the anolyte), while the cathode half-cell for NRR operates in gas phase without a liquid electrolyte (electrolyte-less conditions). This type of electrocatalytic reactor is thus quite different from the conventional electrocatalytic reactors operating in liquid phase, with the main advantages of avoiding issues related to the low N2 solubility and transport in the electrolyte, and allowing an easier recovery of ammonia. The results obtained from these electrocatalytic tests in gas-phase were very useful to improve the design of the MOFs-based electrodes, evidencing the limits of these kinds of materials in terms of N content, stability and possibility to prepare more advanced electrocatalysts by carbonization. A wide part of this chapter was dedicated to the development of new experimental strategies for avoiding false positive in the detection of ammonia, which is one of the topics most studied from scientists working in NRR in the last two years. As accurate protocols were recently suggested in literature, also using advanced analytical techniques (i.e. using 15N labelled nitrogen), an easier methodology based on UV-visible spectrophotometric analysis (coupled with blank tests with inert gases) was suggested in this work to avoid ammonia contaminations and false positives, although more sophisticated analytical techniques may definitely confirm the real source of ammonia. In Chapter 4, a series of improved Fe-MOF-based materials (Fe-based and Fe-alkali metal-based MOF UiO-66-(COOH)2), synthesized by cation exchange reaction technique to replace the proton of carboxylic acid with an iron cation, are presented. With respect to Fe@Zn/SIM-1, this new class of MOFs are more stable in water and do not contain nitrogen atoms in their structure. Results evidenced that 80% cation exchange Fe@UiO-66-(COOH)2 (with an effective Fe content of around 8 wt.%) was the best electrocatalyst among the tested Fe-based MOF synthesized materials. The performances in NRR highly depended on cell and electrode design. More in detail, an ammonia yield of 1.19 μg•h-1•mgcat-2 was obtained with an assembling configuration of layers ordered as i) Nafion (the membrane), ii) Fe-based MOF (the electrocatalyst), iii) GDL (the carbon gas diffusion layer) and iv) a further layer of Fe-MOF. The effect of applied voltage was also explored, indicating an optimal voltage of -0.5 V vs. RHE to maximize activity in NRR and limiting the side hydrogen evolution reaction. Moreover, as currently used in the industrial catalysts for Haber-Bosh process, the introduction of potassium in the electrocatalysts was also investigated, in order to facilitate charge transfer from K- ions to the iron-based catalyst surface, balancing the dissociative chemisorption between H2 and N2, and suppressing side reactions, thus improving both activity and stability. These results were very promising, although a further experimentation is needed to improve their performances in NRR, to overcome limitations related to MOF materials themselves, majorly due to their low conductivity and stability. Finally, Chapter 5 refers to the exploration of advanced MXene materials (Ti3C2 MXene) and to the attempt of synthesizing a 3D nanoarchitecture starting from 2D-dimensional MXene-based catalysts. To understand the role of the nanostructure of MXene materials in NRR, Ti3C2 nanosheets were treated with KOH to obtain a final shape of three-dimensional (3D) porous frameworks nanoribbons. Specifically, the objective of this research was to investigate how the conversion of Ti3C2 nanosheets to 3D-like nanoribbons influence the NRR reactivity in the gas-phase electrochemical device. A full characterization of MXenes nanoribbons (SEM, TEM, HRTEM, XRD, XPS and EDX) was also presented. Results showed that the 3D-type nanostructure (nanoribbons) leads to a significant enhancement of the N2 fixation activity due to the formation of exposed Ti-OH sites. A linear relationship was observed between ammonia formation rate and amount of oxygen on the surface of Ti3C2 MXene.
L'azote joue un rôle indispensable pour toute vie sur terre et pour le développement des êtres humains. Industriellement, l'azote gazeux est converti en ammoniac (NH3) et en engrais riches en azote pour compléter la quantité d'azote fixée spontanément par la nature. À l'heure actuelle, la seule technologie de synthèse de l'ammoniac à l'échelle industrielle est le procédé mis au point par Haber et Bosch au début du XXe siècle, qui utilise les phases gazeuses N2 et H2. Cependant, le procédé Haber-Bosch nécessite des conditions difficiles, des équipements complexes et une consommation d'énergie élevée, et fonctionne avec de faibles taux de conversion, ce qui est incompatible avec les exigences d’un développement durable. Par rapport à la méthode Haber-Bosch, l'électrocatalyse est l'une des voies prometteuses qui permet d'intégrer l'électricité produite à partir de technologies d'énergies renouvelables pour la production d'ammoniac à température ambiante et à pression ambiante. Un défi spécifique est lié au développement de nouveaux électrocatalyseurs/électrodes dans le but de parvenir à une production d'ammoniac à faible coût, à grande échelle et délocalisée. Compte tenu ces défis scientifiques, ce travail de doctorat se concentre sur trois aspects principaux de la réaction électrocatalytique de réduction de l'azote (NRR) : i) ingénierie et conception de l'électrocatalyseur, ii) conception de l'électrode et de la cellule du dispositif électrochimique et iii) amélioration et optimisation des conditions de réaction, afin d'améliorer les performances de la synthèse de l'ammoniac. La plupart des activités de recherche de ce travail de doctorat sur la synthèse et la caractérisation des matériaux électrocatalytiques et l'assemblage/le test des électrodes dans des dispositifs électrochimiques non conventionnels ont été menées au laboratoire CASPE (Laboratory of Catalysis for Sustainable Production and Energy) de l'université de Messine. En outre, une période de 12 mois a été passée en cotutelle avec l'École supérieure de chimie, physique, électronique de Lyon (CPE Lyon), où des voies de synthèse avancées ont été explorées pour la préparation d'électrocatalyseurs à base de composés organométalliques qui ont été utilisés comme électrodes plus actives dans la RRN. Cette thèse de doctorat est organisée en cinq grands chapitres. Le chapitre 1 se concentre sur les questions de fixation de l'azote et sur la description du processus industriel de Haber-Bosch, avec un aperçu des implications générales liées à ses besoins élevés en énergie. Les méthodes alternatives basées sur la fixation électrochimique de l'azote sont ensuite présentées, avec une large description des avantages et des inconvénients liés aux conditions plus douces (c'est-à-dire la température ambiante et la pression atmosphérique) et en discutant des éléments à développer pour une future mise en œuvre de cette technologie, y compris une description du mécanisme de réaction possible, encore débattu dans la littérature. Le chapitre 2 fait référence aux matériaux électrocatalytiques développés pour la préparation des électrodes : 1) les matériaux hybrides organiques-inorganiques de type MOF, une classe de matériaux poreux très prometteurs pour leurs caractéristiques particulières de surface spécifique élevée et leurs propriétés ajustables ainsi que pour la possibilité de créer des sites catalytiques actifs spécifiques grâce aux groupes fonctionnels et aux centres d'ions métalliques ; 2) les MXènes, une classe de matériaux en carbure ou nitrure de métal à structure bidimensionnelle (2D), qui ont récemment suscité un grand intérêt pour un large éventail d'applications, notamment la catalyse et la fixation de N2, pour leurs propriétés uniques de conductivité métallique et de nature hydrophile des surfaces terminées par un hydroxyle ou un oxygène. Les chapitres 3 à 5 présentent et analysent les résultats expérimentaux. Le chapitre 3 concerne la préparation d'une série d'électrodes à base de Fe-MOF (Fe@Zn/SIM-1) et leur test dans la réaction NRR en utilisant un réacteur triphasé de pointe, fonctionnant en phase gazeuse. Ce nouveau dispositif fonctionne à température ambiante et à la pression atmosphérique, avec des électrodes de comptage et de référence immergées dans une demi-cellule anodique (où se produit l'oxydation de H2O en O2) contenant un électrolyte liquide (l'anolyte), tandis que la demi-cellule cathodique pour le NRR fonctionne en phase gazeuse sans électrolyte liquide. Ce type de réacteur électrocatalytique est donc très différent des réacteurs électrocatalytiques classiques fonctionnant en phase liquide, avec les principaux avantages d'éviter les problèmes liés à la faible solubilité et au transport de N2 dans l'électrolyte, et de permettre une récupération plus facile de l'ammoniac. Les résultats obtenus lors de ces essais électrocatalytiques en phase gazeuse ont été très utiles pour améliorer la conception des électrodes à base de MOFs, mettant en évidence les limites de ce type de matériaux en termes de teneur en N, de stabilité et de possibilité de préparer des électrocatalyseurs plus avancés par carbonisation. Une grande partie du chapitre 3 a été consacrée au développement de nouvelles stratégies expérimentales pour éviter les faux positifs dans la détection de l'ammoniac, qui est l'un des sujets les plus étudiés par les scientifiques travaillant dans la NRR ces deux dernières années. Comme des protocoles précis ont été récemment suggérés dans la littérature, utilisant également des techniques analytiques avancées (c'est-à-dire utilisant de l'azote marqué à 15N), une méthodologie plus facile basée sur l'analyse spectrophotométrique UV-visible (couplée à des essais à blanc avec des gaz inertes) a été suggérée dans ce travail pour éviter les contaminations par l'ammoniac et les faux positifs, bien que des techniques analytiques plus sophistiquées puissent définitivement confirmer la source réelle d'ammoniac. Dans le chapitre 4, une série de matériaux améliorés à base de Fe-MOF (incluant un dopage additionel par un métal alcalin du MOF UiO-66-(COOH)2), synthétisés par une technique de réaction d'échange de cations pour remplacer le proton de l'acide carboxylique par un cation de fer, sont présentés. En ce qui concerne le Fe@Zn/SIM-1, cette nouvelle classe de MOF est plus stable dans l'eau et ne contient pas d'atomes d'azote dans sa structure. Les résultats ont montré que l'échange cationique à 80 % Fe@UiO-66-(COOH)2 (avec une teneur effective en Fe d'environ 8 % en poids) était le meilleur électrocatalyseur parmi les matériaux synthétisés de MOF à base de Fe testés. Les performances du NRR dépendaient fortement de la conception de la cellule et de l'électrode. Plus en détail, un rendement en ammoniac de 1.19 μg•h-1•mgcat-2 a été obtenu avec une configuration d'assemblage de couches ordonnées comme i) Nafion (la membrane), ii) MOF à base de Fe (l'électrocatalyseur), iii) GDL (la couche de diffusion de gaz carbonique) et iv) une autre couche de Fe-MOF. L'effet de la tension appliquée a également été exploré, indiquant une tension optimale de -0,5 V par rapport à la RHE pour maximiser l'activité dans le NRR et limiter la réaction latérale d'évolution de l'hydrogène. En outre, comme c'est le cas actuellement dans les catalyseurs industriels pour le procédé Haber-Bosh, l'introduction de potassium dans les électrocatalyseurs a également été étudiée, afin de faciliter le transfert de charge des ions K- à la surface du catalyseur à base de fer, en équilibrant la chimisorption dissociative entre H2 et N2, et en supprimant les réactions secondaires, ce qui améliore à la fois l'activité et la stabilité. Ces résultats étaient très prometteurs, bien qu'une nouvelle expérimentation soit nécessaire pour améliorer leurs performances dans les NRR, afin de surmonter les limitations liées aux matériaux MOF eux-mêmes, principalement en raison de leur faible conductivité et de leur stabilité. Enfin, le chapitre 5 fait référence à l'exploration des matériaux avancés à base de MXène (Ti3C2 MXène) et à la tentative de synthèse d'une nanoarchitecture 3D à partir de catalyseurs à base de MXène en 2D. Pour comprendre le rôle de la nanostructure des matériaux à base de MXène dans la NRR, des nanofeuilles de Ti3C2 ont été traitées au KOH pour obtenir une forme finale de nanorubans à armature poreuse tridimensionnelle (3D). Plus précisément, l'objectif de cette recherche était d'étudier comment la conversion des nanofeuilles de Ti3C2 en nanorubans tridimensionnels influençait la réactivité du NRR dans le dispositif électrochimique en phase gazeuse. Une caractérisation complète des nanorubans MXenes (SEM, TEM, HRTEM, XRD, XPS et EDX) a également été présentée. Les résultats ont montré que la nanostructure de type 3D (nanorubans) conduit à une amélioration significative de l'activité de fixation du N2 en raison de la formation de sites Ti-OH exposés. Une relation linéaire a été observée entre le taux de formation d'ammoniac et la quantité d'oxygène à la surface du Ti3C2 MXene.