Dissertations / Theses on the topic 'Modular catalysis'

Au NP have emerged as versatile scaffolds for applications in sensing and catalysis due to their unique features such as high stability, biocompatibility, ease of preparation, size- and shape-dependent optical and electronic properties and high surface area to volume ratio. The surface of Au NP can be readily modified with ligands containing functional groups such as thiols, phosphines and amines, which exhibit strong affinity for gold surfaces. The cooperative and collective effects achieved by the organization of organic components on the particle provide all the characteristics of a multivalent surface. Multivalent interactions on the monolayer surface can, hence, be applied to strengthen an interaction between the surface and small molecules. In particular, the self-assembly of small molecules on the multivalent surface of Au NP permits the realization of dynamic complex chemical systems that can be applied in the fields of catalysis, sensing and for the creation of tunable materials. In the first part of this Thesis, the catalytic abilities of mixed monolayer gold nanoparticles composed of 8-trimethylammonium-octanethiol and different length thiols bearing the 4'-methyl-2,2'-bipyridine•Cu2+ complex has been studied. In particular, the influence of the geometry of the mixed monolayer gold nanoparticles on the efficiency and selectivity of the Diels-Alder reaction between cinnamoyl-1-methyl-1H-imidazole and cyclopentadiene has been studied. At the same time, the effect of the chiral environment obtained through the self-assembly of chiral peptide (Ac-(LLLL)-Leu-Leu-Gly-Trp-Ser(PO3H2)) on the enantioselection was evaluated. The results indicated in one case the formation of additional products. This can be justified considering the steric interactions between the alkyl chains and the catalysts when the catalytic headgroup is level with the monolayer surface. Furthermore, it was demonstrated that the self-assembly of a chiral enviroment on the surface of the Au NP can induce enantioselectivity, although only modestly. In the second part of the thesis, a modular indicator-displacement-assay is presented. Small molecules with biological relevance are selectively recognized under competitive conditions by using Au NP functionalized with thiols terminating with 1,4,7-triazacyclononane (TACN)•Zn2+. The assay relies on the change in affinity of macrocyclic receptors, such as cavitands, cyclodextrins or calixarenes, for monolayer protected gold nanoparticles upon complexation of the respective target analyte. This change affects the equilibrium between the nanoparticles and a fluorescent reporter molecule leading towards a change in intensity of the fluorescent output signal. The recognition modules can be changed in order to tune the selectivity of the assay without affecting the nature of the output signal. The combined use of recognition modules results in an assay able to detect multiple analytes simultaneously and with high selectivity. A study of the orthogonality of the different receptor-analyte couples led to the demonstration of the possible exploitation of these kinds of arrays within the context of molecular computing. In the third part, the possibility to self-assemble the molecular switch 4-(phenylazo)benzoic acid on the surface of Au NP functionalized with thiols terminating with 1,4,7-triazacyclononane (TACN)•Zn2+ was studied in order to reversibly modulate by light, the affinity of small molecules for the surface. The displacement studies of both probes 343Coumarin-GDDD and 6,8-dihydroxy-1,3-pyrenedisulfonic acid by cis/trans 4-(phenylazo)benzoic acid revealed that the two isomers have different affinities for the surface.This key point was then exploited to use light for the reversible up- and downregulation of the catalytic activity of the nanoparticle under investigation.
L’ importanza delle Au NP come supporto versatile per applicazioni nell’ambito della catalisi e dei sensori nasce dalle loro esclusive caratteristiche come, ad esempio, alta stabilità, biocompatibilità, facilità di preparazione, specifiche proprietà ottiche and elettroniche dipendenti dalla forma e dalle dimensioni e dal loro alto rapporto area/volume. Inoltre, la superficie delle Au NP può essere facilmente funzionalizzata mediante leganti contenenti vari gruppi funzionali, come tioli, fosfine e ammine che presentano alta affinità per la superficie d’oro. Gli effetti collettivi e cooperativi ottenuti grazie all’organizzazione di componenti organici sulla particella, fornisce multivalenza alla superficie. Le interazioni multivalenti sul monostrato possono, quindi, essere applicate per rafforzare un’interazione tra la superficie funzionalizzata e piccole molecole. In particolare l’auto assemblaggio di piccole molecole su una superficie multivalente permette la realizzazione di sistemi chimici dinamici che possono essere applicati nel campo della catalisi, dei sensori e per la creazione di sistemi regolabili. Nella prima parte della Tesi, viene studiata la capacità catalitica di nanoparticelle composte da un monostrato misto (in particolare composte da 8-trimetilammonio-octiltiolo e tioli di diversa lunghezza contenenti il complesso metallico 4’-metil-2,2’-bipiridina•Cu2+ . In particolare viene studiata l’influenza della geometria indotta dal monostrato misto sulla efficienza e selettività della reazione di Diels-Alder tra cinnamoil-1-metil-1H- imidazolo e il ciclopentadiene. Allo stesso tempo, viene studiato l’effetto dell’ambiente chirale ottenuto grazie all’autoassemblaggio di un peptide chirale (Ac-(LLLL)-Leu-Leu-Gly-Trp-Ser(PO3H2)) sulla enantioselettività della reazione. I risultati dimostrano che in alcuni casi la geometria può influenzare la formazione di prodotti addizionali. Questo può essere giustificato come il risultato di interazioni steriche tra catene alchiliche e catalizzatore, quando quest’ultimo si trova alla pari della superficie del monostrato. Inoltre, è stato dimostrato che, assemblando un peptide chirale sulla superficie delle Au NP, è possibile indurre enantioselettività, sebbene limitata. Nella seconda parte della Tesi viene presentato un saggio modulare basato sullo spiazzamento di un indicatore. Piccole molecole con rilevanza biologica sono selettivamente riconosciute utilizzando Au NP funzionalizzate con tioli che presentano come gruppo terminale il 1,4,7-triazaciclononano (TACN)•Zn2+. Il saggio si basa sul cambio di affinità di recettori macrociclici come, ad esempio cavitandi, ciclodestrine o calixareni, per le nanoparticelle, dopo avere formato il complesso con la loro rispettiva molecola bersaglio. Questo cambio influenza l’equilibrio tra nanoparticelle e una sonda fluorescente e provoca, di conseguenza, un cambio nel segnale di fluorescenza. I moduli di riconoscimento possono essere cambiati in modo da poter controllare la selettività del saggio senza influenzare la natura del segnale in uscita. L’ utilizzo contemporaneo di tre moduli permette di creare un sistema capace di rivelare più analiti simultaneamente e con alta selettività. Lo studio dell’ortogonalità delle differenti coppie recettore/analita permette di dimostrare la possibilità di utilizzo di questo tipo di sistemi nel campo dei computer molecolari. Nella terza parte viene studiata la possibilità di auto assemblare l’interruttore molecolare acido 4-(fenilazo)benzoico sulla superficie di Au NP funzionalizzate con tioli che presentano come gruppo terminale il 1,4,7-triazaciclononano (TACN)•Zn2+, con lo scopo di modulare con la luce (in modo reversibile) l’affinità di piccole molecole per la superficie. Gli studi di spiazzamento di entrambi i probe cumarina343-GDDD e l’acido 6,8-diidrossi-1,3-pirenedisulfonico promosso dal cis/trans acido 4-(fenilazo)benzoico rivelano che i due isomeri hanno diverse affinità per la superficie delle nanoparticelle. Questo punto chiave viene sfruttato per permettere la regolazione tramite luce dell’attività delle nanoparticelle in esame.

Récemment, l'activation C-H catalysée par des métaux de transition est devenue un outil performant pour construire des liaisons carbone-carbone et carbone hétéroatome à partir de liaisons C-H omniprésentes dans les molécules organiques. Bien que l'activation des liaisons C-H aromatiques ait été largement étudiée ces dernières années, celle des liaisons C-H aliphatiques représente encore un domaine faiblement exploré. Notre équipe s'est depuis plusieurs années intéressée au développement méthodologique de l'activation C(sp3)-H et à son application en synthèse de produits naturels et molécules bioactives. Dans la continuité des récents travaux sur la version asymétrique de cette réaction, cette thèse décrit le développement et la synthèse de nouveaux ligands du type Binepine. Ces ligands chiraux et monodentates nous ont permis de réaliser la synthèse d'indanes chiraux possédant un centre asymétrique quaternaire, de manière hautement énantio- et diastéréosélective. Cette réaction présente comme avantages l'utilisation d'une faible charge catalytique et d'une température de réaction inférieure à 100 °C, sans aucun additif. Le champ d'application de la réaction inclut notamment l'activation des liaisons C-H d'un groupement méthylène, donnant ainsi accès à des systèmes fusionnés, tricycliques. La construction de molécules non-aromatiques via une alcénylation C-H intramoléculaire a été récemment décrite et s'avère très prometteuse pour la synthèse de produits naturels saturés. Dans la continuité de ces travaux innovants, nous avons développé la synthèse de γ-lactames à partir de bromoalcènes acycliques. Cette nouvelle réaction permet de construire de manière simple et efficace des hétérocycles a cinq chainons de façon modulaire, donnant ainsi la possibilité d'envisager des nouvelles déconnections rétrosynthétiques, complémentaires des méthodes déjà établies. Cette nouvelle méthode a pu être appliquée à la synthèse totale de l'alcaloïde marin Plakoridine A, dont la structure centrale cyclique a été synthétisée en quatre étapes avec un rendement global de 37%
Recently, transition-metal-catalyzed C-H activation has emerged as a powerful tool to transform stable C-H bonds into carbon-carbon or carbon-heteroatom bonds. While the activation of aromatic C-H bonds has seen a tremendous development, less effort has been devoted to the more challenging activation of aliphatic C-H bonds. Our group has a long-standing interest in the development of C(sp3)-H activation reactions and their application in the synthesis of natural products and bioactive compounds. In line with previous efforts to develop an asymmetric C(sp3)-H activation, the herein presented work details the synthesis of new Binepine ligands. These monodentate, chiral ligands enabled us to realize a highly dia- and enantioselective C(sp3)-H activation reaction allowing the construction of chiral quaternary carbon centers. Strong points of this robust method are the low catalyst loading, the low reaction temperature and the absence of additives. The substrate scope includes the rare activation of methylene C-H bonds leading to fused tricyclic carbocycles and heterocycles. The construction of non-aromatic molecules through intramolecular C-H alkenylation was recently disclosed and has great potential for the construction of saturated natural products. Based on seminal work, we have developed the synthesis of valuable γ- lactams from acyclic bromoalkenes. This new methodology offers a powerful way to build simple, five-membered N heterocycles in a modular fashion. Notably, it enables a new retrosynthetic disconnection which is complementary to conventional approaches. Finally, we set out to showcase its utility as key step in the total synthesis of the pyrrolidine alkaloid Plakoridine A. The cyclic core structure was accessed in four steps and 37% overall yield

La preparación de nuevos ligandos quirales P-OP (fosfina-fosfinitos y fosfina-fosfitos), fácilmente preparados con una estrategia sintética en dos etapas desde una aproximación covalente, es descrita en la presente Tesis Doctoral. El mejor catalizador de la serie ha demostrado tener propiedades catalíticas excelentes en la hidrogenación asimétrica catalizada por rodio de una amplia variedad de olefinas funcionalizadas. El resultado excelente y el diseño modular de los ligandos sintetizados hacen éstos muy atractivos para futuras aplicaciones.
La presente Tesis Doctoral describe también la preparación de nuevos ligandos quirales que pueden comportarse como catalizadores supramoleculares inspirados en el mecanismo de regulación alostérica de los enzimas.
A library of enantiomerically pure P-OP ligands (phosphine-phoshinites and phosphine-phosphites) straightforwardly available in two synthetic steps from enantiopure Sharpless epoxy ethers is reported in the present PhD. Thesis. The "lead" catalyst of the series has proven to have outstanding catalytic properties in the rhodium-catalysed asymmetric hydrogenation of a wide variety of functionalised alkenes. Their excellent performance and modular design makes them attractive for future applications.
This PhD. Thesis also reports the development of a practical route to chiral diphosphine ligands with supramolecular motifs, with potential for allosteric modulation, which we prepared for future catalytic studies.

This thesis deals with the design and syntheses of chiral,enantiopure pyridinecontaining ligands and their applicationsin asymmetric catalyis.

Chiral pyridyl pyrrolidine ligands and pyridyl oxazolineligands were synthesized and employed in thepalladium-catalysed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate. Theinfluence of the steric properties of the ligands wereinvestigated.

Ditopic ligands, containing crown ether units as structuralelements, were synthesized and some of the ligands were used asligands in the palladiumcatalysed allylic alkylation of1,3-diphenyl-2-propenyl acetate with dimethyl malonate. A smallrate enhancement was observed, compared with analogous ligandslacking the crown ether unit, when these ditopic ligands wereused in dilute systems.

A modular approach was used to synthesize chiralenantiomerically pure pyridyl alcohols and C2-symmetric2,2’-bipyridines, with the chirality originating from thechiral pool. Electronic and steric properties of the compoundswere varied and they were used as ligands in theenantioselective addition of diethylzinc to benzaldehyde. Thesense of asymmetric induction was found to be determined by theabsolute configuration of the carbinol carbon atom. Theelectronic properties of the ligands had a minor influence onthe levels of enantioselectivity induced by the ligands.

Chiral pyridyl phosphinite ligands and pyridyl phosphiteligands were synthesized from the pyridyl alcohols andevaluated as ligands in palladiumcatalysed allylic alkylations.With the phosphinite ligands, the sense of chiral induction wasfound to be determined by the absolute configuration of theformer carbinol carbon atom. A kinetic resolution of theracemic starting material was observed with one of thephosphite ligands. Moderate enantioselectivities wereachieved.

Kewords:asymmetric catalysis, chiral ligand, chiralpool, oxazoline, crownether, ditopic receptor, bipyridine,pyridyl alcohol, modular approach, P,Nligand, diethylzinc,allylic alkylation.

Click chemistry is a molecular synthesis strategy based on reliable, highly selective reactions with thermodynamic driving forces typically in excess of 20 kcal mol-1. The 1,3-dipolar cycloaddition of azides and alkynes developed by Rolf Huisgen saw dramatic rate acceleration using Cu(I) as a catalyst in 2002 reports by Barry Sharpless and Morten Meldal enabling its click chemistry eligibility. Since these seminal reports, the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has become the quintessential click reaction finding diverse utility. The popularity of the CuAAC has naturally led to interest in new catalyst systems with improved efficiency, robustness, and reusability with particular focus on nanomaterial catalysts, a common trend across the field of catalysis. The high surface area of nanomaterials lends to their efficacy as colloidal and heterogeneous nanocatalysts, but the latter boasts the added benefit of easy separation and recyclability. With any heterogeneous catalyst, a common question arises as to whether the active catalyst species is truly heterogeneous or rather homogeneous through metal ion leaching. Differentiating these processes is critical, as the latter would result in reduced efficiency, higher cost, and inevitable environmental and heath side effects. This thesis explores the CuAAC from an interdisciplary approach. First as a synthetic tool, applying CuAAC-formed triazoles as functional, modular building blocks in the synthesis of optical cation sensors by combining azide and alkyne modified components to create a series of sensors selective for different metal cations. Next, single-molecule spectroscopy techniques are employed to observe the CuNP-catalyzed CuAAC in real time. Combining bench-top techniques with single-molecule microscopy to monitor single-catalytically generated products proves to be an effective method to establish catalysis occurs directly at the surface of copper nanoparticles, ruling out catalysis by ions leached into solution. This methodology is extended to mapping the catalytic activity of a commercial heterogeneous catalyst by applying super-localization analysis of single-catalytic events. The approach detailed herein is a general one that can be applied to any catalytic system through the development of appropriate probes. This thesis demonstrates single-molecule microscopy as an accessible, effective, and unparalleled tool for exploring the catalytic activity of nanomaterials by monitoring single-catalytic events as they occur.

In this thesis is reported a simple, fast, economic modular approach for the synthesis of chiral tetraaza-macrocycles containing a pyridine ring (Pc-L*) starting from aminoacids. The characterization of the ligands and of their complexes with copper (I) and silver (I) salts also descrive, including several crystal suitable for X-ray determination. The organometallic reactivity and coordination behavior of these complexes with CO and acetonitrile has been studied. The complexes were succesfully applied as catalysts for cyclopropanation and A3-coupling reaction and for the synthesis of isochromenes starting from propargyl-aldehydes. In any case, excellent results in terms of yields and chemoselectivity were obtained and, concerning the cyclopropanation reaction, very good enantioselectivities on different substrates were achieved. Furthermore, a new class of Pc-L* ligands potentially dianionic is described and the complexation studies of these macrocycles with ruthenium, cobalt, zyrconium and iron are reported.

La catalyse modulable vise à contrôler l’activité catalytique par la modification réversible du site catalytique, sous le contrôle d’un stimulus. Les stimuli connus pour les systèmes artificiels sont chimiques (molécules, ions), physiques (température, lumière) ou électrochimiques (rédox). Ces stimulus contrôlent le passage d’un état à l’autre du catalyseur, donc, par conséquence, l’activité du système catalytique en termes de cinétique et de sélectivités des réactions. Afin d’élargir le champ des applications de la catalyse modulable, une stratégie innovante serait d’introduire un nouveau stimulus pour engendrer des modulations inédites. Ces travaux de doctorat ont ainsi visé à montrer que la catalyse peut être modulée par l’oxygène singulet. Les réactions de cycloaddition [4+2] entre 1O2 et les dérivés du 9,10-diphénylanthracène permettent la formation de 9,10-endopéroxydes de façon quantitative et réversible par le biais d’une cycloréversion thermique. De plus, cette réaction engendre une modification structurelle importante, en transformant un composé polyaromatique plan en un produit endopéroxyde à géométrie concave. Ainsi, un site catalytique pourvu de dérivés anthracènes pourrait avoir deux arrangement spatiaux différents, contrôlé par 1O2 et la chaleur. Une nouvelle famille de catalyseurs modulables a été conçue à partir d’acides phosphoriques chiraux dérivés du (R)-BINOL (1,1’-bi-2-naphtol) substitués par des dérivés anthracènes. La cycloaddition de l’oxygène singulet sur ces dérivés a été optimisée pour obtenir des molécules dont la géométrie et la nature du site catalytique sont modifiés. Les propriétés catalytiques des édifices anthracènes et endopéroxydes ont ensuite été évaluées à l’aide de trois réactions modèles (désymétrisation d’oxétane, aza-Friedel-Crafts et désaromatisation de 2-naphtols). Ces réactions ont ensuite été étudiées par modélisation moléculaire pour une compréhension fine des relations entre la structure et l’activité catalytique. Sur la base des calculs DFT, une optimisation des structures des catalyseurs et de nouvelles réactions modèles ont aussi été proposés. Les résultats obtenus constituent une avancée vers une preuve de concept pour l’utilisation de 1O2 en tant que stimulus en organocatalyse, malgré la complexité chimique induite sur les catalyseurs modèles dérivés des acides phosphoriques chiraux
Switchable catalysis aims to control catalytic activity by modulating the system’s catalytic site, when under the influence of a stimulus. The known stimuli that regulate artificial catalytic systems are chemical (molecules, ions), physical (temperature, light) or electrochemical (redox). These stimuli control the switch between states of the catalyst and of its activity, with effects on its catalytic efficiency, regio- or stereo- selectivity. To broaden the field of applications of switchable catalysis, an innovative strategy would consist in introducing a new stimulus that induces unprecedented modulations. This doctoral work aimed to show that catalysis can be modulated by singlet oxygen. [4+2] cycloaddition reactions between 1O2 and 9,10-diphenylanthracene derivatives allows the formation of the corresponding endoperoxides in a quantitative and reversible (with a cycloreversion via thermolysis) manner. Furthermore, this reaction induces a consequent structural modification, transforming a flat polyaromatic into a endoperoxide product with a concave geometry. Thereby, a catalytic site bearing anthracenes could have two spatial arrangements, controlled by 1O2 and heat. A new family of modular catalysts have been designed from (R)-BINOL (1,1’-bi-2-naphtol) based chiral phosphoric acids, substituted by anthracene moieties. The cycloaddition reaction of singlet oxygen onto these derivatives was optimized to efficiently obtain molecules whose geometry and nature of the catalytic site are modified. The catalytic properties of the anthracene- and endoperoxide-based architectures were then evaluated using three model reactions (oxetane desymmetrization, aza-Friedel-Crafts and 2-naphtol derivatives dearomatization). These reactions were then studied by molecular modelling to refine the comprehension of the structure-activity relation of these catalysts. On the basis of DFT calculations, paths of improvement for the catalysts and the optimisation of the catalysed reactions were proposed. The obtained results are an initial base for the proof of concept for the use of 1O2 as a stimulus in organocatalysis, despite the chemical complexity induced on the model catalysts derived from chiral phosphoric acids

Polycyclic Polyprenylated Acylphloroglucinols (PPAPs) are a vast family of natural products, which includes more than 200 members. They contain a stunningly complex molecular architecture which in most cases includes a bicyclo[3.3.1]nonane core. PPAPs have been of interest to the scientific community for their intricate structure, their powerful aid in treating many ailments and large portfolio of biological activities. More particularly, they have been of synthetic interest since 1999 with the first report of an approach to these complicated cores by Nicolaou. Herein, we present the first total synthesis of papuaforin A, papuaforin B, papuaforin C, hyperforin and the formal synthesis of nemorosone following a report by Simpkins and co-workers. We relied on a gold(I)-catalyzed carbocyclization for the construction of the core of this family of natural products. Ginkgolides are isolated from the ginko tree, Ginkgo biloba, a living fossil with records of its existence dating back 280 million years. For centuries, the plant and its extracts have been used extensively for their beneficial properties, especially in China, Japan and India. For example, extract Egb761, one of the most potent fraction, generates over $500 million a year alone. The ginkgolides possess a truly unique compact diterpene framework of six 5-membered rings with a high content oxygen. Eleven oxygens can be found in ginkgolide C for a core containing only 23 carbons. The ginkgolides also include a very unique feature: a tert-butyl group located on the most convoluted ring system: the B ring. Few groups have found success in limning a synthetic route to ginkgolides. Corey’s group was the first to achieve the total synthesis of ginkgolide B in 1987. He was also able to complete ginkgolide A a year later. Crimmins and co-workers also achieved the total synthesis of ginkgolide B a decade later in 1999. Herein, we present our new approach toward ginkgolides through a newly developed methodology for the α-allylation of ketones and the creation of highly hindered contiguous quaternary centers. The synthesis is still at an early stage but a synthetic pathway giving access to the ring B with all the key moieties has been extensively investigated.

The objectives of this project was to ameroliate two waste materials, namely Acid Mine Drainage and Fly Ash and recover the solid residues for conversion into an adsorbent to treat brine. The solid residues were then converted into zeolite P through low temperature hydrothermal treatment. The adsorption capacity of the solid residues, zeolite P derived from the solid residues was compared to the commercial zeolite Y and fresh Arnot fly ash. The quality of the resulting water was assessed using different analytical methods before the reaction with adsorbents and after the reaction and a comparison was done based on the removal efficiency of elements Zeolite P from solid residues was successfully synthesized as confirmed by XRD, BET and FTIR. Brine treatment with fly ash, solid residues, zeolite P and commercial zeolite Y adsorbents was done concentration on the following major elements Na, K, Mg, Ca and Si. Zeolite P had higher or similar removal efficiency that the commercial zeolite Y for the following elements K, Ca and Mg. Fly ash is the only adsorbent that managed to reduce the concentration of Na in brine and also had a good removal efficiency of Mg. Si leached out of all the adsorbents which could be ascribed to Si being the major component of these adsorbents which could indicate some dissolution of these adsorbents under the conditions tested. Overall, zeolite P did not completely remove the major elements, especially for Na, but did result in a cleaner waste stream which would improve brine processing.

El creixent interès per a l’obtenció de compostos enantiomèricament purs, ha conduït a un important desenvolupament de la catàlisi asimètrica. En aquest context, aquesta tesis és centra en la síntesis de vàries famílies de lligands quirals altament modulars a partir de compostos de fàcil disponibilitat. Concretament, s'ha treballat en la síntesis de lligands fosfit-tioèter, fosfit-piridina, fosfit-triazola i lligands hidroaximida i tioamida. Tots ells tenen en comú que són sòlids, estables i per tant de fàcil manipulació. Aquests lligands s'han aplicat en la hidrogenació d’olefines funcionalitzades i no funcionalitzades catalitzada per Rh i Ir, en la reducció de cetones mitjançant transferència d’hidrogen catalitzada per Rh i Ru, en reaccions de substitució alílica catalitzada per Pd i en l'addició d'organoaluminats a aldehids catalitzada per Ni. A més a més, en alguns casos s'han realitzat estudis DFT per tal d'agilitzar el procés d'optimització dels lligands. Així doncs, s'ha aconseguit l'obtenció de diferents compostos químics quirals d'alt interès sintètic (alcohols, alcans funcionalitzats i no funcionalitzats, al·lils substituits) en grans enantioselectivitats i en el millor dels casos s'han aconseguit els productes en la seva forma enantiomèricament pura (>99% ee).
El creciente interés para la obtención de compuestos enantioméricamente puros para la obtención de compuestos enantioméricamente puros, ha conducido a un importante desarrollo de la catálisis asimétrica. En este contexto, esta tesis se centra en la síntesis de varias familias de ligandos quirales altamente modulares a partir de compuestos de fácil disponibilidad. Concretamente, se ha trabajado en la síntesis de ligandos fosfito-tioéter, fosfito-piridina, fosfito-triazoles y ligandos hidroaximida y tioamida. Todos ellos tienen en común que son sólidos, estables y por lo tanto de fácil manipulación. Estos ligandos se han aplicado en la hidrogenación de olefinas funcionalizadas y no funcionalizadas catalizada por Rh e Ir, en la reducción de cetonas mediante transferencia de hidrógeno catalizada por Rh y Ru, en reacciones de sustitución alílica catalizada por Pd y en el adición de organoaluminiatos a aldehídos catalizada por Ni. Además, en algunos casos se han realizado estudios DFT para agilizar el proceso de optimización de los ligandos. Así pues, se ha logrado la obtención de diferentes compuestos químicos quirales de alto interés sintético (ej. alcoholes, alcanos funcionalizados y no funcionalizados, alilos sustituidos) en grandes enantioselectividades y en el mejor de los casos se han conseguido los productos en su forma enantioméricamente pura (> 99% ee).
The growing interest in obtaining enantiomerically pure compounds in obtaining enantiomerically pure compounds has led to a significant development in the field of asymmetric catalysis. In this context, this thesis is focused on the synthesis of several families of highly modular chiral ligands from readily available compounds. Specifically, we worked on the synthesis of thioether-phosphite ligands, phosphite-pyridine, phosphite-triazole and hidroaximide and thioamide ligands. They all have in common that are solid, stable and therefore easy to handle. These ligands have been applied in the Rh- and Ir-catalyzed hydrogenation of functionalized and unfunctionalized olefins, in the Ru- and Rh-catalyzed asymmetric transfer hydrogenation of ketones, in Pd-catalyzed allylic substitution reactions and in the Ni-catalyzed addition of organoalumininum to aldehydes. Moreover, in some cases DFT studies have been performed to speed up the optimization of ligands. Hence, a variety of chiral chemical compounds of high synthetic interest (i. e. alcohols, functionalized and non-functionalized alkanes, substituted allyl) lhigh enantioselectivities were achieved and in some cases the products were obtained in their enantiomerically pure form(> 99% ee).

Catalyst 117 was previously reported in the Jones group and demonstrated to a very good catalyst at 1 mol% catalyst load. With the optimized conditions, a wide range of N-arylimines can be reduced in good yield and enantioselectivity by trichlorosilane. Followed this previous discovery, the project now is extending the application this methodology, investigating the mechanism and designing more efficient catalysts. A chromatography process for the synthesis of catalyst 117 was developed. Asymmetric reduction of both N-aryl and N-alkyl ketimines can be performed using trichlorosilane catalyzed by 117 at 1 mol% catalyst loading. The scalability of this process was demonstrated. This catalyst can also facilitate the reduction of β-enamino esters by trichlorosilane with good yield and high enantioselectivity albeit with the necessity of a high catalyst loading and benzoic acid as an additive. An asymmetric reductive amination of ketones with both aromatic and aliphatic amines was achieved in good yield and high enantioselectivity at 1 mol% catalyst loading. Sterically hindered ketones also undergo reductive amination in good yield and enantioselectivity by a two-step one-pot procedure. The asymmetric synthesis of (+)-NPS R-568 in good yield and high enantioselectivity using the two-step one-pot procedure demonstrated the potential utility of this catalyst to the pharmaceutical industry. Lewis acidic TMSOTf can improve the yield in direct reductive amination, but showed a negative effect on the enantioselectivity. Initial investigations into the mechanism have resulted in unprecedented discoveries. Both the NMR study of catalyst 117 and the discovery of a new highly active catalyst 263 place the Matsumura transition state model into doubt. Although no signals were detectable to support the hypercoordinate silane species by NMR experiments, in-situ ReactIR data showed that there might be some interactions between trichlorosilane and catalysts. A new tentative transition state model was proposed according to the study of structure/activity of catalysts and the preliminary in-situ IR data.

In this work a modified polyol method was developed to synthesize in-house catalysts. The method was modified for maximum delivery of product and proved to be quick and efficient as well as cost effective. The series of IH catalysts were characterized using techniques such as UV-vis and FT-IR spectroscopy, TEM, XRD, ICP and CV.

N-Containing heterocycles such as substituted pyridines and 2-quinolones are commonly found in drugs and agrochemicals; however, classical methods towards their synthesis often lead to limited substitution patterns. We recently described the first examples of the organocatalytic intramolecular aza-Wittig reaction in the synthesis of azoles and azines from isocyanates. The work described herein is divided into three chapters detailing attempts to expand the scope of the use of isocyanates in heterocycle synthesis. The first chapter describes the development of multicomponent synthesis of substituted pyridines incorporating the intermolecular catalytic aza-Wittig and Diels–Alder reactions; in total 31 exemplar pyridines were prepared in up to 52% yield. The reaction works well for electron-poor and heteroaromatic aldehydes, electron-rich and electron-poor cinnamic acids and push-pull enamines to give a range of substitution patterns. The use of commercially available starting materials and catalytic phosphine oxide means the process offers distinct advantages over classical methods. The development of a tandem catalytic aza Wittig/electrocyclisation process towards benzothienopyridines was also investigated. To this end benzothienoimines and azatrienes were prepared, however, the electrocyclic ring closure of the azatrienes was non-trivial with low yields of the desired pyridines even under harsh conditions. The final chapter outlines the preparation of substituted 2-quinolones from readily available urea starting materials by two methods. The first is a two-pot three-step process incorporating urea-directed oxidative Heck reaction, isocyanate formation and electrocyclisation; in total 9 exemplar 2-quinolones were prepared in up to 61% overall yield. The second is a two-pot threestep process incorporating Heck reaction, isocyanate formation and electrocyclisation; 10 exemplar 2-quinolones were prepared in up to 59% overall yield. The use of the urea directinggroup in the subsequent isocyanate formation negates the necessity for acyl azides and means no further manipulation is required to remove the directing group after 2-quinolone synthesis

De par leur morphologie, les cristaux creux de zéolithe permettent d’étudier les phénomènes de limitations diffusionnelles en catalyse et également d’encapsuler des particules métalliques ; les nano-réacteurs ainsi obtenus ont montré des activités catalytiques originales. Leur synthèse, qui nécessite des caractéristiques structurales particulières, a longtemps été limitée aux zéolithes de structure MFI. Le but de cette thèse était d’étudier différentes voies de synthèse pour préparer des cristaux creux de zéolithe Beta, une des zéolithes les plus utilisées dans l’industrie. Deux voies ont été suivies : l’utilisation d’un zincosilicate de même structure que la zéolithe Beta comme gabarit sacrificiel et une méthode plus classique de désilication sélective. L’encapsulation de nanoparticules de platine dans les cristaux obtenus selon la première voie a été confirmée par l’hydrogénation d’aromatiques substitués. L’’influence de la morphologie sur la diffusion de différentes molécules a été étudiée par ZLC : le temps caractéristique de diffusion a été réduit de 30 à 83 % par rapport à des cristaux conventionnels. Malgré cela, la présence d’une cavité dans les cristaux de zéolithe Beta n’a pas d’effets sur l’activité catalytique dans les réactions d’hydro-isomérisation du nC16 et du craquage du cyclohexane. La thèse discute de la présence/absence de limitations diffusionnelles
Hollow zeolite single crystals have received particular interest in catalysis. The presence of a large cavity in these model zeolites enables the study of diffusional limitation in Catalysis. The cavity also enables the encapsulation of metal nanoparticles. However, their synthesis requires specific structural characteristics and it has been limited for long to zeolites with the MFI structure. The objective of this PhD work was to investigate the synthesis of hollow Beta zeolites (*BEA framework type) and study the impact of the hollow morphology on molecular diffusion and catalysis. Two different strategies have been envisaged: a dissolution/recrystallization approach using CIT-6, a zincosilicate with the same *BEA topology and a selective desilication route. Pt nanoparticles encapsulated in hollow crystals obtained from CIT-6 showed remarkable size-selectivity in the hydrogenation of aromatics. The effect of the hollow morphology in molecular diffusion was studied using the ZLC technique; the characteristic diffusion time of the hollow morphology was reduced by 30-83% compared to the corresponding bulk zeolite. Despite that, the hollow structure had no influence on the catalytic activities for the hydroisomerization of n-C16 and for the cracking of cyclohexane. The presence/absence of diffusional limitation is discussed

Il existe un grand nombre de ligands très efficaces actuellement employés pour la catalyse d’hydrogénation (BINAP, MeO-BIPHEP) et de couplage (S-PHOS, ligands PAP). La plupart d’entre eux possède une symétrie C2. Au cours de la thèse, nous avons étudié l’influence de la symétrie C1 sur les performances catalytiques de mono- et de diphosphines possédant une structure biaryle ou hétéro aromatique/ aromatique. Nous avons également étudié l’influence de leurs propriétés stériques et électroniques. Ces structures ont, pour la plupart, été obtenues par couplage aryne suivi par des réactions d’échange halogène/lithium régiosélectives permettant d’introduire de nombreux types de phosphines sur le noyau biaryle. Le profil électronique i. E. Les propriétés s-donneuses et p-accepteuses de ces nouveaux ligands originaux a été déterminé par les méthodes classiques. Par ailleurs, des tests d’hydrogénation des doubles liaisons C-C et C-O ainsi que des couplages C-C de type Suzuki-Miyaura ont été effectués. Nous avons ainsi montré que pour chaque type de réactions, au moins une de nos phosphines est aussi efficaces que les ligands classiques
Transition metal enantioselective catalysis is certainly among the most challenging and widely investigated area in modern organometallic chemistry. Chiral compounds qualifying as ligands for asymmetric catalysis continue to be designed and synthesized at a frenetic pace and competitors keep on emerging. In the field of atropisomeric biaryl diphosphine ligands, BINAP and MeO-BIPHEP are one of the most efficient one. On the other hand, the literature only shows very few C1-symmetric examples in this ligand class, none of them having a high structural or electronic diversity. In this context, we disclosed the access to the following C1-symmetric mono- and diphosphine ligands and we studied the influence of their steric and electronic properties. Most of them were obtained via aryne coupling, regioselective halogen/lithium exchange, phosphination sequence. Their electronic profile i. E. Their s-donor properties and their p-acidic character were determined according to the classical methods. Finally, we used them in catalytic hydrogenations of C-C and C-O double bonds and C-C Suzuki-Miyaura coupling reactions and we proved that whatever the reaction, at least one of our ligands was as efficient as the classical ones

Tertiary butyl substituted and unsubstituted Schiff base systems containing N,O donor ligands (Salicylaldimines) with aminotriethoxysilane tail were synthesized and complexed to Copper and Cobalt acetate. In this study, the effect of metal, reaction time, nature of oxidant (hydrogen peroxide tertiary butyl hydroperoxide), substituents on thel igand and substrate concentration, were investigated.

Thesis advisor: Jason S. Kingsbury
Chapter 1: The reaction of diazomethane with simple aldehydes to deliver methyl ketones has a long studied history in the art of organic synthesis. Formyl electrophiles have also been homologated with trimethylsilyldiazomethane, diazoacetates, and aryl-diazomethanes that very rarely proceed with catalytic activation. Due to the stigma of handling non-stabilized diazoalkanes this history is limited to examples utilizing αdiazoesters and entirely missing are examples of tertiary αsubstituted ketone synthesis beginning with disubstituted (internal) diazoalkanes. This work describes a general catalytic procedure for convergent ketone production using non-stabilized, mono- and disubstituted diazomethanes. The method involves mild reaction conditions, produces molecular nitrogen as the only byproduct, and includes six examples of chiral ketone synthesis from various aryl, heteroaryl, or aliphatic aldehydes. The latter feature, together with new evidence that the catalytic reaction mechanism invokes a stereospecific, intramolecular C-H migration, sets the stage for an enantioselective synthesis of acyclic ketones by asymmetric carbon insertion. The remarkable tolerance of this transformation to steric crowding in either reaction partner is showcased in a simple, five-step construction of the complete carbon framework in achyrofuran, a complex dibenzofuranoid. Chapter 2: Paraformaldehyde is an inexpensive and readily available source of carbon (~30 USD/kg). Upon heating, the polymer thermally depolymerizes to yield gaseous formaldehyde that can be bubbled through reactions or stored in solution at low temperature. In this work, a new and general strategy for complex ketone synthesis is described based on Sc-catalyzed, double diazoalkyl C-H insertion reactions with formaldehyde as a 1-C source. The method forms di-, tri-, and even tetrasubstituted acetones efficiently, and it has streamlined a synthesis of the Erythroxylon alkaloid (-)-dihydrocuscohygrine in which absolute stereochemistry in a proline-based starting material is preserved. Chapter 3: Use of geminally-substituted diorganometallics often gives new forms of reactivity that are unavailable to their monosubstituted counterparts. With the expanding use of boronic acids in many areas of synthetic organic methodology, an underappreciated research area has been full development of disubstitited gem diboronic ester derivatives for use in tandem reactions, olefination methods, metal catalyzed coupling reactions, and transmetallations to mixed gem diorganometallics. The nature of molecular boron is routinely engaged through its Lewis acidic vacant p-orbital, and, after metalation, this orbital interaction is enlisted to stabilize α-carbanion or α-carbanion like species to allow dependable reactivity in various applications. The platinum-catalyzed geminal diboration of diazoalkanes provides reliable and efficient access to a full range of disubstitited gem diboronic esters enabling the exploration of novel methodologies
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

The objectives of this project were to synthesize and characterise pyridine carboxamide ligands and their palladium complexes and investigate their catalytic activity in the polymerization process of phenylactylene.

This thesis described the development of new catalytic system for the conversion of natural gas (methane) to liquid products such as methanol and formaldehyde. This technology can allow the exploitation of small and medium size gas fields without the need to build an expensive gas to liquid plants or long pipelines. The technology is based on a concept of non-separating membrane reactor where an inorganic membrane paper serves as a catalyst support through which a reaction mixture is flowing under mild conditions and short residence times.

Les travaux réalisés dans le cadre de cette thèse sont consacrés à l’étude de réactions de cyclisations de 2-pyridylallènes à l’aide de différentes espèces électrophiles. Des 2-pyridylallènes tétrasubstitués ont ainsi été synthétisés et cyclisés en conditions acides, avec différents halogènes électrophiles, des chalcogènes ainsi que de l’or (I) pour donner de nouveaux motifs indoliziniums. Des indolizines 1,3-substitués iodées en position 2 ont également été obtenues permettant une post-fonctionnalisation par couplage croisé. L’utilisation d’or (I) comme électrophile mène à de nouveaux complexes dont les ligands rassemblent les critères structuraux pour être considérés comme des NHCs. Les propriétés électroniques (σ-donation et π-acidité) de ce type de ligand ont été évaluées théoriquement et expérimentalement : si ces composantes électroniques se sont toutes deux révélées très élevées, la σ-donation semble surpasser celle des NHCs décrits dans la littérature. Certains complexes chiraux ont pu être efficacement utilisés en catalyse énantiosélective. Il apparaît clairement que la présence du groupement oxyde de phosphine est nécessaire pour obtenir une énantiosélectivité élevée dans le cas de l’hydroxyalkoxylation intramoléculaire d’un y-allénol. Ainsi, un très bon rapport énantiomérique de 91:9 et un rendement quantitatif ont été obtenus
This PhD work focused on the electrophile-induced cyclisation of 2-pyridylallenes. Various tetrasubstituted 2-pyridylallenes were synthesized and cyclized in acidic conditions, using electrophilic halogens, chalcogens and gold (I) species to afford new indoliziniums scaffolds. The synthesis of 1,3-indolizines bearing an iodine atom in position 2 was also performed, allowing a further late 2-functionnalization step by cross coupling reactions. Using gold (I) as an electrophile gave access to new gold complex bearing NHC type ligands. The electronic properties (σ-donation et π acidity) of this type of ligand were theoretically and experimentally investigated: if both of them were found especially strong, the σ-donation seems to overcome that of the NHCs described since then. Some chiral complexes have been used efficiently in enantioselective catalysis. It appeared clearly that the presence of the phosphine oxyde moiety is necessary to obtain a high enantioselectivity during the intramolecular hydroxyalkoxylation of γ-allenol. An excellent enantiomeric ratio of 91:9 and a quantitative yield were obtained

La tesi nasce dalla volontà di agire sull’area della Darsena di Ravenna, strategica in quanto via d’acqua navigabile che congiunge il mare con il centro città ma dal potenziale ancora poco sfruttato. Il progetto è studiato per essere inserito come catalizzatore urbano, creando spazi di interazione attraverso elementi modulari galleggianti e riconfigurabili per adattarsi a programmi d’uso flessibili; tali elementi si aggregano formando un sistema che ristruttura lo spazio dell’attuale banchina, cambiandone la percezione da barriera a waterfront urbano. La necessità di ottenere una struttura con capacità di crescita e flessibilità programmatica sfocia in un approccio modulare seguendo il principio massima variazione/minimo numero di elementi i cui principi aggregativi si basano sulla tassellazione “Cairo”. Vengono studiate le possibilità di incorporare variazione ed eterogeneità all’interno del sistema senza comprometterne la modularità fino ad integrare percorsi multilivello. La definizione delle morfologie delle parti che compongono i moduli si basano sullo studio dei principi di galleggiamento, stabilità e yacht design: a partire dalla forma dello scafo adatta ai principi di tiling definiti in precedenza, tutte le parti che compongono le varie tipologie di modulo sono progettate cercando continuità e integrazione tettonica (geometrica, strutturale, funzionale e percettiva). Vengono proposte soluzioni integrate sia per le problematiche tipiche delle strutture galleggianti sia per l’inserimento di attività all’interno della soluzione architettonica. Vengono prototipati di una serie di moduli, scelti in modo da dimostrare i principi di ricombinazione, continuità, modularità e tiling.

Actualment la creixent demanda de compostos enantiomèricament purs (fàrmacs, productes agroquímics, additius…) ha impulsat el desenvolupament de la catàlisi asimètrica, sobretot emprant compostos organometàl•lics quirals com a catalitzadors. La síntesi de nous lligands quirals és essencial per descobrir bons sistemes catalítics en catàlisi asimètrica. Els sucres són una font important de lligands per l’elevada disponibilitat i baix preu. Els objectius d’aquesta tesi son el desenvolupament de dues noves llibreries de lligands derivats de sucre. Concretament tioèter-fosfit i furanòsid monofosfit, per la seva aplicació en diverses reaccions asimètriques catalitzades per metall de transició, tals com la hidrogenació d’olefines funcionalitzades catalitzades per rodi, la hidrogenació d’olefines mínimament funcionalitzades catalitzada per iridi, les reacció de substitució al•lílica catalitzades per pal•ladi, i les adicions 1,2 a aldehids catalitzades per níquel.
The growing demand for enantiomerically pure compounds has led to important advances in asymmetric catalysis, especially using chiral organometallic compounds. In this context the search of new catalysts is very important, mainly focusing on the properties of the chiral ligands. This has led to the development of new chiral ligands. An important source of chiral ligands is derivatives carbohydrate derivatives because of their high availability, their low cost and their high functionality. The objectives of this thesis are to develop two new chiral ligands carbohydrate derivatives. Specifically thioether-phosphite and furanoside monophosphite, for application in several important asymmetric catalytic reactions as Rh- and Ir-catalyzed hydrogenation of functionalized and unfunctionalized olefins, respectively; Pd-catalyzed allylic substitution; and Ni-catalyzed 1,2-addition of trialkylaluminum reagents to aldehydes.

Over the recent past, organometallic chemistry has grown and the impact of catalytic applications in various chemical technologies has rapidly evolved from the realm of academic laboratories into full-scale industrial processes. Pyrrole-imine ligands were prepared by condensation of pyrrole-2-carboxylaldehyde with propyl amine, 2,6-diisopropylanaline, poly(propylene) imine dendrimer and 3-aminopropyl-triethoxysilane to give the desired ligands in good yields. These ligands were charaterized via combination of techniques to establish the molecular structure. Microanalysis was performed to confirm the purity of the product.

Ce manuscrit présente le développement de nouvelles réactions énantiosélectives d’insertion-carbocyclisation en cascade, catalysées par le rhodium(I) et initiées par les acides boroniques, pour la formation d’hétéro- et de carbocycles chiraux fonctionnalisés. Pour ces transformations asymétriques, les diènes chiraux, notamment les ligands Ar-MSBod, sont les plus adaptés et permettent d’atteindre des énantiosélectivités élevées, ce qui a conduit à la conception d’une voie alternative de synthèse de ces diènes monosubstitués. Les premiers travaux ont porté sur la préparation de cycles à cinq chainons chiraux, à partir d’énynes-1,6, via une réaction en cascade énantioconvergente. La deuxième partie est consacrée à une réactivité particulière des espèces vinylrhodium(I) dans certaines conditions : le transfert-1,4 de rhodium. En tirant parti de ce concept, trois familles de molécules chirales ont été synthétisées avec des énantiosélectivités élevées : des benzoxépanes, des tétralones et des tétralols. La troisième partie a été dédiée à l’élaboration de réactions en double cascade, permettant la création de trois liaisons carbone-carbone en une seule étape, pour la formation de polycycles complexes hautement fonctionnalisés
This manuscript presents the development of new enantioselective insertion-carbocyclization cascade reactions, catalyzed by rhodium(I) complexes and initiated by boronic acids, for the formation of chiral hetero- and carbocycles. In such transformations, chiral dienes, especially Ar-MSBod ligands, are the most suited and allow to reach high enantioselectivities, which lead to the development of an alternative way for their synthesis. Early works focused on the preparation of chiral 5 membered rings, from 1,6-enynes, through an enantioconvergent cascade reaction. The second part is focused on a special reactivity of vinylrhodium(I) species in certain conditions: the rhodium 1,4-shift. Taking advantage of this concept, three families of chiral molecules were synthesized with high enantioselectivities: benzoxepanes, tetralones and tetralols. The third part was dedicated to the conception of double cascade reactions, allowing the creation of three carbon-carbon bonds in one step, in order to synthesize highly functionalized complex polycycles

Les carbènes N-hétérocycliques représentent une alternative intéressante aux ligands phosphinés en catalyse homogène. Le développement d'une version chirale de ces ligands carbènes constitue le but principal de ce travail de thèse. Tout d'abord, une large gamme de sels d'oxazolinyl/imidazolium, précurseurs des ligands bidentates cibles, a été synthétisée à l'aide d'une approche modulaire. Nous avons ensuite réalisé la complexation du représentant achiral de cette famille de ligands sur divers centres métalliques tels que du palladium(II) ou du rhodium(I). Le complexe de palladium(II) permet le couplage des chlorures d'aryles activés pour les réactions catalytiques de Heck et Suzuki. Les études réalisées sur les complexes neutres pentacoordinés de rhodium(I) ont mis en lumière deux processus fluxionnels que sont la pseudo-rotation de Berry et un échange intermoléculaire de ligand bromure. Nous avons également étudié la réaction d'hydrosilylation asymétrique des cétones à l'aide des complexes chiraux de rhodium(I). Le système catalytique a été optimisé grâce notamment à la modularité des ligands. Il présente une activité catalytique remarquable et montre un excellent caractère énantiosélectif pour les cétones prochirales à substituants aryle-alkyle et surtout dialkyle avec des excès énantiomériques atteignant 95%. Enfin, la dernière partie décrit la synthèse d'un ligand carbène/bisoxazoline tridentate chiral qui pourrait posséder un fort pouvoir d'induction asymétrique. Un complexe de rhodium(III) a été préparé. Sa structure moléculaire obtenue par diffraction des rayons X confirme la coordination tridentate et méridionale du ligand
This work, part of the field of homogeneous catalysis, describes the development of chiral N heterocyclic carbenes based on a modular assembly between oxazoline and imidazolylidene units. First a large library of imidazolium salts, precursors for the bidentate ligands oxazolinyl-imidazolylidene, was obtained by a single coupling step. The second part is devoted to the coordination chemistry of the achiral representative of this family of ligands. Several transition metal complexes were synthesized and analyzed by X-ray diffraction studies. The palladium(II) complex was found to catalyze the coupling of activated aryl chlorides in catalytic Heck and Suzuki reactions. Cationic, chiral rhodium(I) complexes were then applied as catalysts in the asymmetric catalytic hydrosilylation reaction of prochiral ketones. The optimized catalytic system is remarkably active and induces high enantioselectivity for aryl-alkyl ketones and, in particular, for dialkyl ketones (enantiomeric excess up to 95%). In the last part the synthesis and complexation on a rhodium(III) centre of a chiral, tridentate bisoxazoline-carbene ligand are reported. This carbene is effectively tridentate with a quasi planar skeleton and could be highly efficient as a stereoinducting ligand for asymmetric catalysis

This study focused on the development of binuclear and multinuclear catalyst for use in vinylic monomer oligomerization and polymerization. The main objective was to develop new homogeneous catalysts systems with hopefully improved activity, selectivity and stability.

The direct methanol fuel cell or DMFC is emerging as a promising alternative energy source for many applications. Developed and developing countries, through research, are fast seeking a cheap and stable supply of energy for an ever-increasing number of energy-consuming portable devices. The research focus is to have DMFCs meeet this need at an affordable cost is problematic. There are means and ways of making this a reality as the DMFC is found to be complementary to secondary batteries when used as a trickle charger, full charger, or in some other hybrid fuel cell combination. The core functioning component is a catalyst containing MEA, where when pure platinum is used, carbon monoxide is the thermodynamic sink and poisons by preventing further reactions at catalytic sites decreasing the life span of the catalyst if the CO is not removed. Research has shown that the bi-functional mechanism of a platinum-ruthenium catalyst is best because methanol dehydrogenates best on platinumand water dehydrogenation is best facilitated on ruthenium. It is also evident that the addition of other metals to that of PtRu/C can make the catalyst more effective and effective and increase the life span even further. In addition to this, my research has attempted to reduce catalyst cost for DMFCs by developing a low-cost manufacturing technique for catalysts, identify potential non-noblel, less expensive metallic systems to form binary, ternary and quarternary catalysts.

Le but de cette thèse était d'explorer la chimie de surface des systèmes bimétalliques platine-zinc et leur activité catalytique dans la réaction d'oxydation du CO. La recherche sur ce système bimétallique a été menée sur deux fronts: une étude de surface du système modèle , une couche unique de ZnO discontinue épitaxiée sur du Pt (111), utilisant la microscopie à effet tunnel et le rayonnement synchrotron à proximité de la photoémission par rayons X à pression ambiante, et une étude davantage axée sur la «nanomatériau» du même système bimétallique, en utilisant la chimie complexe de la synthèse colloïdale , microscopie électronique à transmission et à balayage, et enfin XPS de laboratoire.Tout d'abord, une surface modèle constituée d'un film monocouche de ZnO supporté sur du Pt (111) a été fabriquée dans des conditions de vide très poussé. Sa chimie de surface a été explorée par STM puis par rayonnement synchrotron NAP-XPS dans des conditions opératoires. Nous avons pu prouver que ce système était bien un cas typique de catalyse inverse. Les effets synergiques dus à la présence des deux matériaux ont été bien observés, mais uniquement à basse température (jusqu'à 410 K). Au-delà de cette température, les effets de transport de masse empêchent la comparaison de la réactivité des surfaces de ZnO / Pt (111) et de Pt (111). Nous avons montré que des intermédiaires de réaction doivent être formés dans la zone frontière entre le ZnO et le platine, lorsque le film de ZnO est discontinu. Nous avons mis en évidence le rôle clé joué par les hydroxyles présents dans les plaques de ZnO, qui sont dus à la dissociation de H2 ou de H2O de l’atmosphère résiduelle des plaques de platine. En particulier, nous avons détecté par NAP-XPS la présence d'une espèce carboxyle (due à l'association de OH avec CO), qui précède la désorption du CO2. Au-dessus de 410 K, un formiate apparaît et cette dernière espèce est probablement spectatrice du processus d'oxydation du CO. Le transfert des connaissances accumulées dans les précédentes études de la science des surfaces et des catalyseurs modèles au cas plus réaliste des nanocristaux de l’alliage PtZn, tout en aidant à identifier certains phénomènes courants, il montre également ses limites. En fait, les nanocristaux revêtus de leurs ligands oléylamine ont des caractéristiques que les surfaces des modèles UHV ne possèdent pas, en raison du processus de fabrication de la CN lui-même: nous avons trouvé des indices spectroscopiques de la présence d’eau (éventuellement un sous-produit de la réaction, résultant d’une entre la cétone et l'amine); de plus, un recouvrement de la surface du platine par des atomes d'hydrogène est actuellement une explication de nombreux phénomènes observés. Trouver les conditions expérimentales pour produire des nano-alliages bimétalliques à partir de deux précurseurs métal-acac2 était une tâche ardue, bien plus que celle de déposer physiquement un film mince sur un monocristal d’UHV. Nos efforts ont été récompensés car nous avons pu produire des CN en alliage PtZn. C'est l'un des principaux points de la présente étude. La présence de Pt(acac)2 empêche le zinc (dont l'oxydation complète en ZnO, comme c'est le cas lorsque le Zn(acac)2 seul est présent dans l'oléylamine. L'XPS monochromatisé montre que le zinc fabrique un alliage avec le platine, où il reste métallique alors qu’une autre fraction est sous la forme de ZnO, il n’est pas clair si deux canaux de réaction sont en concurrence (alliage PtZn versus oxydation de Zn par l’eau), ou Zn est oxydé par la suite, c’est-à-dire après exposition à l’air. Les CN alliés ont été étudiés en détail par des méthodes avancées de microscopie électronique (y compris dans des conditions opératoires), de diffraction et d’EDS [...]
The purpose of this thesis was to explore the surface chemistry of platinum-zinc bimetallic systems, and their catalytic activity in the oxidation reaction of CO. The research on this bimetallic system was carried out on two fronts: a surface science study of the model system, a discontinuous ZnO single layer epitaxied on Pt(111), using scanning tunneling microscopy and synchrotron radiation near ambien pressure x-ray photoemission, and a more “nanomaterial science” oriented study of the same bi-metallic system, using complex colloidal synthesis chemistry, transmission and scanning electron microscopy, and finally laboratory XPS. First, a model surface consisting of a ZnO monolayer film supported on Pt(111) was fabricated under ultra-high vacuum conditions. Its surface chemistry was explored by STM and then by synchrotron radiation NAP-XPS under operando conditions. We were able to prove that this system was indeed a typical case of inverse catalysis. Synergetic effects due to the presence of both materials were well seen, but only at low temperatures (up to 410 K). Beyond that temperature, mass transport effects prevent the reactivity of the ZnO/Pt(111) and Pt(111) surfaces from being compared. We have shown that reaction intermediates must be formed in the border area between ZnO and platinum, when the ZnO film is discontinuous. We have highlighted the key role played by the hydroxyls present only ion the ZnO patches, which are due to the dissociation of H2 or H2O from the residual atmosphere on the platinum patches. In particular, we have detected by NAP-XPS the presence of a carboxyl species (due to the association of OH with CO), which precedes the desorption of CO2. Above 410 K, a formate appears, and the latter species is likely a spectator in the CO oxidation process. The transfer of the knowledge accumulated in the preceding surface science and model catalysts studies, to the more realistic case of nanocrystals of the PtZn alloy, while it helped identify some common phenomena, it also shows its limitations. In fact the NC coated with their oleylamine ligands have characteristics that UHV model surfaces do not possess, due to the NC fabrication process itself: we have found spectroscopic hints of the presence of water (possibly a byproduct of the reaction, arising from a condensation reaction between the ketone and the amine); in addition, a capping of the platinum surface by H atoms, is, at present, explanatory of many observed phenomena. Finding the experimental conditions to produce bimetallic nano-alloys from two metal-acac2 precursors was a daunting task, much more than that of physically depositing a thin film on a UHV monocrystal. Our efforts were rewarded as we were able to produce PtZn alloy NCs. This one of the main points of the present study. The presence of Pt(acac)2 prevents zinc (whose from being fully oxidized to ZnO, which is the case when Zn(acac)2 alone is present in oleylamine. Monochromatized XPS shows that zinc makes an alloy with platinum, where it remains metallic, while another fraction is under the form of ZnO. It is not completely clear whether two reaction channels are in competion (PtZn alloying versus Zn oxidation by water), or Zn is oxidized afterwards, i.e. after exposure to air. The alloyed NCs have been studied in detail by advanced methods of electron microscopy (including under operando conditions), diffraction and EDS. Unlike the case of the surface model where the STM images were particularly telling, we do not have at this stage of the study an exact model of the interface between the metal alloy and the zinc oxide that surrounds it. On the other hand, we know that the core of the NCs is occupied by the PtZn alloy, and that the outer planes are identical to those of pure platinum. [...]

In this study, the main objective was to investigate the tolerance of platinum based binary anode catalysts for CO poisoning from 10ppm up to1000ppm and to identify the
best anode catalysts for PEMFCs that tolerates the CO fed with reformed hydrogen.

In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.

The production of biodiesel (methyl esters) from vegetable oils represents analternative means of producing liquid fuels from biomass, and one which is growing rapidly in commercial importance and relevance due to increase in petroleum prices and the environmental advantages the process offers. Commercially, biodiesel is produced from vegetable oils, as well as from waste cooking oils and animal fats. These oils are typically composed of C14-C20 fatty acid triglycerides. In order to produce a fuel that is suitable for use in diesel engines, these triglycerides are usually converted into the respective mono alkyl esters by base-catalyzed transesterification with short chain alcohol, usually methanol. In the first part of this study, the transesterification reactions of three different vegetable oils
sunflower (SFO), soybean (SBO) and waste cooking oil (WCO) with methanol was studied using potassium hydroxide as catalyst in a conventional batch process. The production of biodiesel from waste cooking oil was also studied via continuous operation systems (employing the use of low frequency ultrasonic technology and the jet loop reactor). The characterisation of the feedstock used and the methyl ester products were determined by different analytical techniques such as gas chromatography (GC), high performance liquid chromatography (HPLC) and thin layer chromatography (TLC). The effects of different reaction parameters (catalyst amount, methanol to oil ratio, reaction temperature, reaction time) on methyl ester/FAME yield were studied and the optimum reaction conditions of the different process systems were determined. The optimum reaction conditions for production of methyl esters via the batch process with the fresh oil samples (SFO and SBO) were established as follows: a reaction time of 60 min at 60 º
C with a methanol: oil ratio of 6:1 and 1.0 KOH % wt/wt of oil
while the optimum reaction conditions for the used oil (WCO) was observed at a reaction time of 90 min at 60 º
C, methanol: oil ratio of 6:1 and 1.5% KOH wt/wt of oil. The optimum reaction conditions for the transesterification of the WCO via ultrasound technology applied in a continuous system in this study were: a reaction time of 30 min, 30 º
C, 6:1 methanol/oil ratio and a 0.75 wt% (KOH) catalyst concentration. The ultrasound assisted transesterification reactions performed at optimum conditions on the different oil samples led to higher yields of methyl esters (96.8, 98.32 and 97.65 % for WCO, SFO and SBO respectively) compared to methyl esters yields (90, 95 and 96 % for WCO, SFO and SBO respectively) obtained when using conventional batch procedures. A considerable increase in yields of the methyl esters in the ultrasound assisted reaction process were obtained at room temperature, in a remarkably short time span (completed in 30 min) and with a lower amount of catalyst (0.75 wt % KOH) while the results from the continuous jet loop process system showed even better results, at an optimum reaction condition of 25 min of reaction, a methanol: oil ratio of 4:1 and a catalyst amount of 0.5 wt%. This new jet loop process allowed an added advantage of intense agitation for an efficient separation and adequate purification of the methyl esters phase at a reduced time of 30 min. The use of homogeneous catalysts in conventional processes poses many disadvantages
heterogeneous catalysts on the other hand are attractive on the basis that their use could enable the biodiesel production to be more readily performed as a continuous process resulting in low production costs. Consequently, a solid base catalyst (KNO3/FA) prepared from fly ash (obtained from Arnot coal power station, South Africa) and a new zeolite, FA/Na-X synthesized from the same fly ash were used as solid base catalysts in the transesterification reactions in the conversion of a variety of oil feedstock with methanol to methyl esters. Since fly ash is a waste product generated from the combustion of coal for power generation, its utilization in this manner would allow for its beneficiation (as a catalytic support material and raw material for zeolite synthesis) in an environmentally friendly way aimed at making the transesterification process reasonably viable. Arnot fly ash (AFA) was loaded with potassium (using potassium nitrate as precursor) via a wet impregnation method while the synthesized zeolite FA/Na-X was ion exchanged with potassium (using potassium acetate as precursor) to obtain the KNO3/FA and FA/K-X catalysts respectively. Several analytical techniques were applied for characterization purposes. The results of the XRD and XRF showed that the AFA predominantly contained some mineral phases such as quartz, mullite, calcite and lime. The high concentration of CaO in AFA was apparent to be beneficial for the use of fresh fly ash as a support material in the heterogeneous catalysed transesterification reactions. XRD characterisation of KNO3/FA results indicated that the structure of KNO3/FA gradually changed with the increase in KNO3 loading. The catalyst function was retained until the loading of KNO3 was over 10 %. IR spectra showed that the KNO3 was decomposed to K2O on the fly ash support during preparation at a calcination temperature of 500 º
C. The CO2-TPD of the KNO3/FA catalysts showed that two basic catalytic sites were generated which were responsible for high catalytic abilities observed in the transesterification reactions of sunflower oil to methyl esters. On the other hand, XRD results for the as- received zeolite synthesized from AFA showed typical diffraction peaks of zeolite NaX. SEM images of the FA /NaX showed nano platelets unique morphology different from well known pyramidal octahedral shaped crystal formation of faujasite zeolites and the morphology of the FA /KX zeolite did not show any significant difference after ion exchange. The fly ash derived zeolite NaX (FA /NaX) exhibited a high surface area of 320 m2/g. The application of the KNO3/FA catalysts in the conversion reactions to produce methyl esters (biodiesel) via transesterification reactions revealed methyl ester yield of 87.5 % with 10 wt% KNO3 at optimum reaction conditions of methanol: oil ratio of 15:1, 5 h reaction time, catalyst amount of 15 g and reaction temperature 160 °
C, while with the use of the zeolite FA/K-X catalyst, a FAME yield of 83.53 % was obtained for 8 h using the ion exchanged Arnot fly ash zeolite NaX catalyst (FA/KX) at reaction conditions of methanol: oil ratio of 6:1, catalyst amount of 3 % wt/wt of oil and reaction temperature of 65 º
C. Several studies have been carried out on the production of biodiesel using different heterogeneous catalysts but this study has been able to uniquely demonstrate the utilization of South African Class F AFA both as a catalyst support and as a raw material for zeolite synthesis
these catalyst materials subsequently applied sucessfully as solid base catalysts in the production of biodiesel.

The main objective of this work it to produce membrane electrode assemblies (MEAs) that have improved performance over MEAs produced by the conventional manner, by producing highly efficient, electroactive, uniform catalyst layers with lower quantities of platinum electrocatalyst. The catalyst coated membrane (CCM) method was used to prepare the MEAs for the PEM fuel cell as it has been reported that this method of MEA fabrication can improve the performance of PEM fuel cells. The MEAs performances were evaluated using polarisation studies on a single cell. A comparison of polarisation curves between CCM MEAs and MEAs produced in the conventional manner illustrated that CCM MEAs have improved performance at high current densities (>
800 mA/cm2).

G1 and G2 dendrimeric salicylaldimine ligands containing both substituted and unsubstituted aryl rings were synthesized via a Schiff base condensation of the appropriate salicylaldehyde and the peripheral amino groups of the corresponding G1 and G2 polypropyleneimine dendrimers. The new ligands were characterized using FTIR, 1H NMR and 13C NMR spectroscopy, elemental analysis and ESI mass spectrometry. The dendrimeric ligands were converted to multinuclear nickel complexes by reaction with nickelacetate. The metal complexes were characterized by FTIR spectroscopy, elemental analysis and ESI mass spectrometry.

Some of the dendritic complexes were evaluated as catalyst precursors in the oligomerization of &alpha
-olefins such as ethylene and 1-pentene, using aluminium alkyls such as EtAlCl2 and modified methylaluminoxane (MMAO) as activators. All the dendrimeric catalysts evaluated are active in the oligomerization reactions. From the oligomerization results it was observed that there is a clear dendritic effect, in that both catalyst activity as well as selectivity are impacted by the dendrimer generation. In most cases it was observed that the second generation complexes show higher activity than the corresponding first generation complexes.

The dendrimeric complexes were also evaluated as catalyst precursors in the vinyl polymerization of norbornene. In this case methylaluminoxane (MAO) were employed as an activator. Once again it was noted that a dendritic effect is operative, with second generation metallodendrimers having a higher activity than the first generation complexes.

In summary, it has been shown during this study that bimetallic Fe and Mn containing catalysts can be prepared by wet impregnation and not by ion exchange because of the competition between two different metals at different oxidation number. Only a single metallic phase catalyst could be prepared successfully by using ion exchange.

The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly.

Hydrogen (H2) represents an energy carrier endowed with the potential to contribute to the design of a robust and reliable global energy system by complementing electricity as well as liquid fuels use in an environmentally responsible manner provided that the pertinent H2 production technologies (conventional and new ones) can reach techno-economically attractive performance levels in the presence of irreducible (macroeconomic, fuel market, regulatory) uncertainty. Indeed, the role of H2 in the global energy economy is widely recognized as significant in light also of fast-growing demand in the petrochemical and chemical processing sector as well as future regulatory action on greenhouse gas emissions. Pd and Pd/Alloy-based catalytic membrane reactor (CMR) modules potentially integrated into H2 production (HP-CMR) process systems offer a promising technical pathway towards H2 production with enhanced environmental performance in a carbon-constrained world. However, the lack of accumulated operating experience for HP-CMR plants on the commercial scale poses significant challenges. Therefore, any preliminary attempt to assess their economic viability is certainly justified. A comprehensive techno-economic performance assessment framework has been developed for HP-CMRs with CO2 capture capabilities. A functional Net Present Value (NPV) model has been developed first to evaluate the economic viability of HP-CMRs. The plant/project value of HP-CMR is compared to other competing technology options such as traditional coal-gasification and methane steam reforming-based hydrogen production plants with and without CO2 capture. Sources of irreducible uncertainty (market and regulatory) as well as technology risks are explicitly recognized and the effect of these uncertainty drivers on the plant’s/project’s value is taken into account using Monte-Carlo techniques. Therefore, more realistic distribution profiles of the plant’s economic performance outcomes are generated rather than single-point value estimates. It is shown that future regulatory action on CO2 emissions could induce appealing NPV-distribution profiles for HP-CMRs in the presence of uncertainty and technology risks. Finally, the valuation assessment is complemented with a sensitivity analysis for different representative values of the discount rate that span a reasonable range associated with business and financing risks. It apparently indicates that creatively structured financing mechanisms leading to a reduction of the cost of capital/discount rate could induce more appealing economic performance outcomes and valuation profiles. Furthermore, the proposed research work aims at the development of a methodological framework to assess the economic value of flexible alternatives in the design and operation of HP-CMR plants with carbon capture capabilities under the aforementioned sources of uncertainty. The main objective is to demonstrate the potential value enhancement associated with the long-term economic performance of flexible HP-CMR project investments by managing the uncertainty associated with future environmental regulations. Within the proposed context, promising design flexibility concepts for HP-CMR plants are introduced and operational as well as constructional flexibility options are identified and assessed. In particular, operational flexibility will be realized through periodic and temporary shutdowns of the carbon capture unit in response to regulatory uncertainties. Constructional flexibility will be realized by considering the installation of a carbon capture unit at three strategic periods: 1) installation in the initial design phase, 2) retrofitting at a later stage and 3) retrofitting with preinvestment. Monte Carlo simulations and financial analysis will be conducted in order to demonstrate that, in the presence of irreducible uncertainty, design flexibility options could lead to economic performance enhancement of HP-CMR plants by actively responding to the above sources of uncertainty as they get resolved over the plant’s lifetime.

This thesis describes strategies for and examples ofcellulose fiber modification.The ability of an engineered biocatalyst, acellulose-binding module fused to theCandida antarcticalipase B, to catalyze ring-openingpolymerization of e-caprolactone in close proximity tocellulose fiber surfaces was explored. The water content in thesystem was found to regulate the polymer molecular weight,whereas the temperature primarily influenced the reaction rate.The hydrophobicity of the cellulose sample increased as aresult of the presence of surface-deposited polyester.

A two-step enzymatic method was also investigated. Here,Candida antarctica lipase B catalyzed the acylation ofxyloglucan oligosaccharides.The modified carbohydrates werethen incorporated into longer xyloglucan molecules through theaction of a xyloglucan endotransglycosylase. The modifiedxyloglucan chains were finally deposited on a cellulosesubstrate.

The action ofCandida antarcticalipase B was further investigated inthe copolymerization of e-caprolactone and D,L-lactide.Copolymerizations with different e-caprolactone-to-D,L-lactideratios were carried out. Initially, the polymerization wasslowed by the presence of D,L-lactide. During this stage,D,L-lactide was consumed more rapidly than ε-caprolactoneand the incorporation occurred dimer-wise with regard to thelactic acid units.

Morphological studies on wood fibers were conducted using asol-gel mineralization method. The replicas produced werestudied, without additional sample preparation, by electronmicroscopy and nitrogen adsorption. Information concerning thestructure and accessibility of the porous fiber wall wasobtained. Studies of never-dried kraft pulp casts revealedmicro-cavities and cellulose fibrils with mean widths of 4.7(±2) and 3.6 (±1) nm, respectively.

Finally, cationic catalysis by simple carboxylic acids wasstudied. L-Lactic acid was shown to catalyze the ring-openingpolymerization of ε-caprolactone in bulk at 120 °C.The reaction was initiated with methylß-D-glucopyranoside, sucrose or raffinose, which resultedin carbohydrate-functionalized polyesters. The regioselectivityof the acylation was well in agreement with the correspondinglipase-catalyzed reaction. The polymerization was alsoinitiated with a hexahydroxy-functional compound, whichresulted in a dendrimer-like star polymer. The L-lactic acidwas readily recycled, which made consecutive reactions usingthe same catalyst possible.

Keywords:Candida antarcticalipase B, cationic catalysis,cellulose-binding module, dendrimer, enzymatic polymerization,fiber modification, silica-cast replica, sol-gelmineralization, organocatalysis, xyloglucanendotransglycosylase

Cette thèse concerne l’étude de la réaction photoélectrochimique de réduction du CO2 (PEC CO2RR) sur le semi-conducteur de type p CuCo2O4 en abordant le rôle cocatalytique des RTIL à base d'imidazolium par microscopie photoélectrochimique à balayage (SPECM). Le CuCo2O4 a été étudié dans différents électrolytes supports, notamment une solution aqueuse, une solution de mélange binaire (25 vol.% [C2mim][BF4]/H2O et 25 vol.% [C4mim][BF4]/H2O) et des liquides ioniques pur pour explorer par SPECM le rôle des RTIL dans les performances des PEC. Un courant de photoréduction significativement amélioré sous l'éclairage UV-vis et visible est obtenu dans une solution à 25 vol.% [C2mim][BF4]/H2O. Seul le CO généré par la PEC CO2RR a été détecté sur une fibre optique à double sonde - ultra-microélectrode (OF-UME) développée au laboratoire et sur une électrolyse en volume sous illumination. La formation de CO à des potentiels plus positifs que la valeur thermodynamique est rapportée ici et il est clairement indiqué que la réduction directe du CO2 à la surface de l'électrode n'est pas le mécanisme. Un schéma de réaction possible pour la PEC CO2RR par l'intermédiaire de [C2mim]+ est proposé. Ainsi, nos résultats ont démontré pour la première fois le rôle cocatalytique de [C2mim]+ pour le PEC CO2RR. En outre, la CO2RR électrochimique a également été étudiée sur divers catalyseurs de métaux de transition, d'azote et de carbone (M–N–Cs). 25%Fe25%Co–N–C a montré la meilleure performance parmi les M–N–Cs étudiés. La présence de sites Co a fourni un effet synergique pour la génération de microcubes distribués riches en Fe, qui agissent comme des sites actifs dans la CO2RR électrochimique
This thesis studies photoelectrochemical CO2 reduction reaction (PEC CO2RR) on p-type semiconductor CuCo2O4 addressing the cocatalytic role of imidazolium based RTILs by scanning photoelectrochemical microscopy (SPECM). CuCo2O4 was studied in different solvent supporting electrolyte systems including: aqueous solution (0.1 M KHCO3 and 0.1 M Na2SO4), binary mixture solution (25 vol.% [C2mim][BF4]/H2O and 25 vol.% [C4mim][BF4]/H2O) and pure RTILs ([C2mim][BF4], [C4mim][BF4]) to explore by SPECM the role of RTILs in CuCo2O4 semiconductor PEC performance. Significantly enhanced photoreduction current under both UV-vis and visible light illumination is reported in 25 vol.% [C2mim][BF4]/H2O solution. Only CO generated from PEC CO2RR was detected using an in-situ detection method based on a home-made dual tip optical fiber-ultramicroelectrode (OF-UME) and from bulk electrolysis under illumination. The formation of CO at potentials more positive than the thermodynamic value clearly points out that direct CO2 reduction on the electrode surface is not the mechanism. A possible reaction scheme for the PEC CO2RR mediated by [C2mim]+ is proposed. Thus, our results have demonstrated for the first time the cocatalytic role of [C2mim]+ for the PEC CO2RR. In addition, electrochemical CO2RR has also been studied on various synthesized transition metal–nitrogen–carbon catalysts (M–N–Cs) by rotating disk electrode. 25%Fe25%Co–N–C exhibited the best performance among the studied M–N–Cs in this thesis. The presence of Co sites in that catalyst provided synergic effect for the generation of distributed Fe-rich microcubes, which act as active sites in electrochemical CO2RR

Architecture is never complete. The theoretical discourse of the thesis explored the need of a building to change. This change is unpredictable, though expected. The project proposal within the informal context of Phumolong, Mamelodi, aimed to address this unavoidable nature of architecture. The focus of the project was to provide improved services within an informal settlement, whilst generating social upliftment. The thesis investigated the current and future requirements of the informal dweller. It explored the possibility of generating public space through the establishment of a catalyst. The connection of services and public amenities has been exploited to generate an environment where the building acts as generator and it supports social interaction. Inevitably the servant core provides implicit reasoning as renewed stimulus to public gathering. The project proposal addressed the integration of the informal user with a building system through the architectural process. This is achieved through phased development, investigating assembly and use of civic programmes. A quantitative approach towards the research was initially undertaken. However, the fluid nature of the informal settlement enthused a more qualitative approach. The need and right of the informal dweller to be served, and have access to public services and amenities justified the design proposal. The changing fabric, user, programme and needs of the community contribute to the rate of change of a building. The changing context of Phumolong required a flexible and adaptable design intervention allowing for future interpretation. These variables influenced architecture as a cognitive process. The design as a product within the realm of architecture represents the process of learning from the past, reacting to the present and preparing for the future. Ultimately the design intervention exists as an ongoing process of progressive change. Copyright
Dissertation (MArch(Prof))--University of Pretoria, 2010.
Architecture
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In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.