Pour répondre aux enjeux économiques et sociaux modernes, le développement de catalyseurs organométalliques à base de métaux abondants et bon marché, comme alternatives aux catalyseurs historiques basés sur les métaux précieux, connaît un essor constant depuis deux décennies. L’objectif du présent travail doctoral a été de développer des catalyseurs à base de manganèse, troisième métal de transition le plus abondant après le fer et le titane, et précédemment principalement utilisé en oxydation, pour les réactions de (dé)-hydrogénation. / To meet modern economic and social challenges, the development of inexpensive and abundant metal-based organometallic catalysts, as alternatives to historical catalysts based on precious metals, has been growing steadily for two decades. The aim of this doctoral work was to develop catalysts based on manganese, which is the third most abundant transition metal after iron and titanium, and previously mainly used in oxidation, for (de)-hydrogenation reactions.

Des complexes NHC du gallium(III) et de l’indium(III) ont été préparés. Ces composés, simples à synthétiser, se sont révélés être beaucoup plus stables que les sels commerciaux de type MX₃ (M = Ga, In ; X = Cl, Br, I). Ces complexes, une fois activés par AgSbF₆, présentent un fort caractère acide de Lewis. [IPr-GaCl₂][SbF₆] s’est ainsi montré très actif en tant qu’acide de Lewis π et a été utilisé comme catalyseur dans différentes réactions impliquant l’activation de fonctions carbonées insaturées. Il a ainsi permis d’effectuer des hydroarylations inter- et intramoléculaires d’alcynes, d’alcènes et d’allènes. La généralité de cette transformation a pu être démontrée dans une réaction tandem de cycloisomérisation/Friedel-Crafts entre un arényne et un nucléophile aromatique. La capacité des complexes cationiques de gallium et d’indium à activer des alcènes a également pu être mise à profit pour la réduction de dérivés styréniques en présence de cyclohexa-1,4-diène comme source d’hydrogène. Et parce que ces complexes permettent la génération de dérivés du styrène par hydroarylation d’alcynes, une cyclisation réductrice d’arénynes sans précédent a pu être développée. Enfin le complexe [IPr-GaCl₂][SbF₆] a été utilisé dans des réaction impliquant l’eau en tant que réactif. Quelques alcynes ont ainsi pu être hydratés et des esters γ,δ-insaturés ont été transformés en lactones. En résumé, nos complexes cationiques de gallium et d’indium peuvent être utilisés dans des réactions généralement considérées comme relevant du domaine des métaux de transition nobles (Au, Pt, Ru…). / NHC complexes of gallium(III) and indium(III) have been prepared. These compounds, easy to synthesize, proved to be much more stable than the commercially-available salts MX₃ (M = Ga, In ; X = Cl, Br, I). These complexes, once activated by AgSbF₆, show a strong Lewis acid character. For instance, [IPr-GaCl₂][SbF₆] showed a high activity as π-Lewis acid and was used as catalyst in several reactions triggered by the activation of unsaturated C-C bonds such as inter- and intramolecular hydroarylations of alkynes, alkenes and allenes. The versatility of this transformation was demonstrated in a cycloisomerization/Friedel-Crafts tandem reaction between an arenyne and an aromatic nucleophile. The ability of cationic complexes of gallium and indium to activate alkenes was also used for the reduction of styrene derivatives with 1,4-cyclohexadiene as hydrogen source. Also, because these complexes are able to generate styrene derivatives by hydroarylation of alkynes, an unprecedented reductive cyclization of arenynes could be developped. Moreover, [IPr-GaCl₂][SbF₆] was used in reactions involving water as reagent. Several alkynes were hydrated and γ,δ-unsaturated esters were transformed into lactones. In summary, our cationic complexes of gallium and indium can be used in reactions generally catalyzed by noble metals (Au, Pt, Ru…).

L'utilisation de dioxyde de carbone comme source de carbone C1 pour produire des plateformes chimiques ou comme source de carburant est une alternative à la pétrochimie et pourrait permettre son recyclage. Actuellement, les principaux procédés décrits pour la valorisation du CO2 font appel à des réducteurs en quantités stoechiométriques (ce qui génère des déchets), des métaux nobles (disponibilité limitée, toxicité et coût élevé). Dans cette course environnementale et économique, une des réponses, mais aussi un des challenges de la chimie moderne, est la préparation de nouveaux complexes organométalliques de fer et leur utilisation en catalyse. Basé sur notre expertise dans le domaine de la synthèse, de la catalyse et du développement de complexes organométalliques, ce projet propose de développer de nouvelles méthodologies rapides, efficaces, sélectives et éco-compatibles pour la réduction du dioxyde de carbone et des carbonates par hydrogénation avec des complexes bifonctionnels de fer. / The use of carbon dioxide as a source of carbon C1 to produce chemical platforms or as a fuel source constitute an alternative to petrochemicals and could allow its recycling. Currently, the main described processes for the recycling and the valorization of CO2 are using reducing agents in stoichiometric amounts (which generates waste) or noble metals (limited availability, toxicity and high costs). In this environmental and economical race, one of the challenges of modern chemistry is the preparation of new organometallic iron complexes and their use in catalysis. Based on our expertise in the field of synthesis, catalysis and development of organometallic complexes, this work proposes to develop new fast, efficient, selective and eco-compatible methodologies for the reduction of carbon dioxide and carbonates by hydrogenation with bifunctional iron complexes.

Please read the abstract in the dissertation. Copyright / Dissertation (MEng)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

As a part of the production of nitride nuclear fuel for use in fast nuclear reactors, zirconium is hydrided followed by nitriding and mixing with uranium nitride. This work concludes a study of unwanted metallic particles present in a powder that is supposed to be a zirconium hydride. Sponge zirconium was hydrided at different temperatures and different time intervals, and the resulting hydride was milled into a powder. The powders were analyzed using SEM and XRD after which the powders were pressed into pellets for light optical microscopic study. The primary goals were determination of the structure of the particles and thereafter elimination of them. It was seen that hydriding at 500 C results in less metal particles but more experiments need to be conducted to confirm this.

I rapporten framgår det en termodynamisk analys för reverse water gas shift med att sammanmata etanol för att undvika det långsammaste steget i reaktionen för att producera högre alkoholer. Ifrån ett termodynamiskt perspektiv, verkar det möjligt att utgå ifrån reverse water gas shift för att producera högre alkoholer vid 100 bar med en temperatur på 300C . Reaktionen är exotermisk, vilket gynnas av det låga temperaturer och det rekommenderas höga tryck p.g.a. en mol kontraktion. Jämviktshalterna var låga, det föreslås att ta bort vatten ifrån jämvikten.  I den matematiska modellen utgick det ifrån en kedja-reaktion för att producera högre alkoholer med reverse water gas shift i processförhållanden på 10–200 bar. I modellen utfördes en senstivty-analysis för jämvikten på tryck och vattenborttagning. Genom att ta bort vatten ifrån jämvikten låg CO2 utbytet kring 95% vid 200 bar även vid låga tryck som 10 bar. Inom CO2 hydrering till högre alkoholer är det begränsat med data och reaktionsmekanismen bakom reaktionen är inte riktigt förstådd. Experimentella försök krävs för att få en mer ökad förståelse. I modellen beskrevs CO2 hydrering och resterande reaktioner som en funktion av en sigmoid. Inom litteraturstudien kom det fram till att det fanns ingen kommersiell tillgänglig membran förtillfället för att ta bort vatten inom krävande process förhållanden. Tekniken ser dock lovande ut. / In this work, a thermodynamic analysis for CO2 hydrogenation by co-feeding ethanol to higher alcohols was performed with the HSC software package. The results suggested a high pressure and a low temperature for the reaction. However, it yielded low equilibrium compositions for the higher alcohols even at a high pressure of 100 bar at 300C . Increasing the equilibrium compositions for the higher alcohols can be done by removing water.  A mathematical model was used to analyse the rate-limiting step in a process for the production of higher alcohols from CO2.  In this process, reverse water gas shift (RWGS) reaction was used to convert CO2 to CO, subsequently, the obtained CO reacts with ethanol and hydrogen to produce higher alcohols directly. The mathematical model was developed in MATLAB to simulate how the reaction could behave by feeding CO2, H2 and ethanol at different pressures ranging from 10-200 bars. The water removal effect on the equilibrium is measured in terms of CO2   conversion by achieving 95% for removing water.  The results indicated that the process can be used to convert CO2 to higher alcohols and at a lower pressure. The limiting factor for CO2 hydrogenation is the reaction mechanism, it’s an urgent problem for the development of the catalysts. In this model it was assumed to be a logistic function. The conversion of CO2 into higher alcohols is an important problem that is required to be addressed by more experimental verifications to understand the mechanism. The literature review shows that there is no available membrane for removal of water for the process currently, due to the harsh process conditions, mainly because of the membrane stability. However, membrane technology is a promising method for separation of water/organic mixtures that can be studied further in the future.

Thesis advisor: Matthias M. Waegele / Depositing metal-organic frameworks (MOFs) on the surfaces of metal nanoparticles (NPs) to enhance catalytic selectivity has recently attracted great attention; however, a solid understanding of how the NP-MOF interface promotes catalytic selectivity is lacking. In this thesis, we have conducted three fundamental studies and further applied the knowledge to other types of catalysts using enzymes. The first part of this thesis focuses on understanding the NP-MOF interfacial structures and their impact on catalytic performance. We have systematically probed the NP-MOF interface generated by three commonly used approaches by IR and Raman spectroscopy. We have revealed significant differences in interfacial chemical interactions between them, and have found that these differences in interfacial structure dramatically impact selectivity. For example, the interface generated by the coating approach contains trapped capping agents. This trapped capping agent reduces crotyl alcohol selectivity for the hydrogenation of crotonaldehyde. The second part of this thesis focuses on addressing the trapped capping agents at the NP-MOF interface. We developed an approach to creating a direct NP-MOF interface by utilizing weakly adsorbed capping agents during the MOF coating process. Their dynamic nature allows for their gradual dissociation from the NP surface with the assistance of the organic MOF linkers. Thus, direct chemical interactions can be built between NP and MOF, generating a clean and well-defined interface. Direct evidence on capping agent dissociation and formation of chemical interactions was obtained by Raman and IR spectroscopy. Combined with transmission electron microscopy and X-ray diffraction, we have revealed the relative orientation and facet alignment at the NP-MOF interface. The third part of this thesis investigates how various MOF components affect the selectivity of hydrogenation reactions catalyzed at the MOF-NP interface. We found that the replacement of Zr-oxo nodes with Ce-oxo nodes yields the highest selectivity for cinnamyl alcohol (~87%), whereas the functionalization of the terephthalic acid linker with -OH, CH3, -NO2 and NH2 groups only moderately modulates the selectivity relative to the Zr-UiO-66 (~58%). Reaction kinetics studies demonstrate that coating Pt NPs with Ce-UiO-66 increases the rate of C=O hydrogenation, which infrared spectroscopic observations suggest is due to the interaction of the C=O group with the Ce-oxo node. This work highlights the critical role of metal-oxo nodes in regulating the catalytic selectivity of metal NPs in specific reactions. The fourth part of this thesis extends the interface control to other catalysts involving enzymes. We compared the interfacial interactions of catalase in solid and hollow MOF microcrystals. The solid sample with confined catalase was prepared through a reported method. The hollow sample was generated by hollowing the MOFs crystal, sealing freestanding enzymes in the central cavities of the hollow MOF. By monitoring this hollowing process, we observed that the enzymes gradually changed from a confined form to a freestanding form. The freestanding enzymes in the hollow MOFs show higher activity in the decomposition of hydrogen peroxide, attributed to their lesser chemical interactions and confinement. This study highlights the importance of the freestanding state for the biological function of encapsulated enzymes. Taken together, the four sections in this thesis establish design rules for refining MOF-based catalyst design. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

In 2015, more than 80% of energy consumption was based on fossil resources. Growing population especially in developing countries fuel the trend in global energy consumption. This constant increase however leads to climate change caused by anthropogenic greenhouse gas (GHG) emissions. GHG, especially CO2 mitigation is one of the top priority challenges in the EU. Amongst the solutions to mitigate future emissions, carbon capture and utilization (CCU) is gaining interest. CO2 is a valuable, abundant and renewable carbon source that can be converted into fuels and chemicals. Methanol (MeOH) is one of the chemicals that can be produced from CO2. It is considered a basic compound in chemical industry as it can be utilised in a versatility of processes. These arguments make methanol and its production from CO2 a current, intriguing topic in climate change mitigation. In this master’s thesis first the applications, production, global demand and market price of methanol were investigated. In the second part of the thesis, a methanol plant producing chemical grade methanol was simulated in Aspen Plus. The studied plants have three different annual capacities: 10 kt/a, 50 kt/a and 250 kt/a. They were compared with the option of buying the CO2 or capturing it directly from flue gases through a carbon capture (CC) unit attached to the methanol plant. The kinetic model considering both CO and CO2 as sources of carbon for methanol formation was described thoroughly, and the main considerations and parameters were introduced for the simulation. The simulation successfully achieved chemical grade methanol production, with a high overall CO2 conversion rate and close to stoichiometric raw material utilization. Heat exchanger network was optimized in Aspen Energy Analyzer which achieved a total of 75% heat duty saving. The estimated levelised cost of methanol (LCOMeOH) ranges between 1130 and 630 €/t which is significantly higher than the current listed market price for fossil methanol at 419 €/t. This high LCOMeOH is mostly due to the high production cost of hydrogen, which corresponds to 72% of LCOMeOH. It was revealed that selling the oxygen by-product from water electrolysis had the most significant effect, reducing the LCOMeOH to 475 €/t. Cost of electricity also has a significant influence on the LCOMeOH, and for a 10 €/MWh change the LCOMeOH changed by 110 €/t. Finally, the estimated LCOMeOH was least sensitive for the change in cost of CO2. When comparing owning a CC plant with purchasing CO2, it was revealed that purchasing option is only beneficial for smaller plants.

In this research we investigated the generation of methanol and the utilization of CO2 using heterogeneous catalysts. Heterogeneous catalysts are frequently used in industry due to their multiple benefits, which include long-term thermal and mechanical stability, as well as reusability. Our research has demonstrated a variety of heterogeneous catalysts for sustainable methanol production and CO2 utilization, including the novel dendritic mesoporous metal oxides support. We have also designed and screened multiple active metals on the dendritic mesoporous metal oxide catalysts, modified active metal dispersion, and further reduced metal oxides to utilize silica-based catalysts, among other things. Comprehensive characterization of the final products was performed using N2 adsorption and desorption, XRD, HR-TEM, SEM, ICP-OES, XPS, H2-TPD, CO2-TPD, Raman spectroscopy, pulse-chemosorption and DRIFT, in order to determine the chemical and physical properties of the catalysts. The catalysts were found to have the following characteristics. We obtained a CO2 conversion of 25.5 % and a MeOH yield of 6.4 % after at least three cycles of usage in an avantium fixed bed reactor system with a PdCu/CZ-3 catalyst. Additionally, continuous methanol production with a higher yield (6.9 %) has been achieved using our PdZn/CZ-3 catalysts, and the best ultra-dispersed Pd nanoparticles over CZZ catalyst produces more than 12 % methanol yield with constant selectivity to methanol even after a lengthy catalytic test (more than 100 h), demonstrating their industrial viability. Additionally, our PdZn/CeTi-DMSN exhibits a high methanol production of up to 10% and better long-term stability with lower metal oxides content. The adsorption and activation of CO2 to react with the spilled over hydrogen to generate methanol has been researched for the CO2 hydrogenation and utilization reaction. Catalysts' redox, acidic, and basic characteristics all play a crucial part in this reaction and in the formation of the various products. With 2.0 percent Pd, the supported dendritic CeZrZn catalyst exhibits the highest catalytic performance (29.1% conversion and 40.6% MeOH selectivity). Comprehensive analysis revealed in this research not only identified effective catalysts with high activity for a variety of applications, but also established a link between catalytic performance and the material's nature. These discoveries may also aid the researcher in the near future in resolving global environmental problems.

Carbon nanomaterials, such as carbon nanotubes and graphene, have attracted significant interest over the past several years due to their outstanding and unusual combination of physical properties. These properties can be modified in a controllable way by chemical functionalization in order to enable specific technological applications. One example is hydrogenation, achieved by the exposure of these materials to a source of atomic hydrogen. This process has been considered for hydrogen storage purposes and for the control of the band gap of these materials for applications in carbon-based electronics. Hydrogen atoms are chemisorbed onto the surface of these materials, introducing sp3-hybridized C–C bonds in a structure originally formed by delocalized sp2 C–C bonding. This bonding transition causes severe structural and morphological changes to the graphene layers/walls. Also, it has been demonstrated that the exposure of multi-walled carbon nanotubes (MWCNTs) to a H2 plasma leads to the formation of diamond nanocrystals embedded within the nanotube walls. This thesis presents a computational analysis of the effects of hydrogen chemisorption on the structure and morphology of graphene and single-walled carbon nanotubes (SWCNTs), as well as of the different nanostructures that can be generated upon formation of inter-shell and inter-layer sp3 C–C bonds in MWCNTs and few-layer graphene (FLG), respectively. The analysis is based on a synergistic combination of atomic-scale modeling tools, including first-principles density functional theory (DFT) calculations and classical molecular-dynamics (MD) and Monte Carlo (MC) simulations. The results demonstrate that SWCNTs and graphene swell upon hydrogenation and provide interpretations to experiments reported in the literature; this swelling depends strongly on the hydrogen surface coverage. A MC/MD-based compositional relaxation procedure generates configurations whose arrangements of H atoms are in excellent agreement with experimental observations. Detailed structural analysis of the hydrogenated surfaces is carried out, providing information which cannot be extracted easily from conventional experimental techniques. The findings of the analysis are used to explain the limitations on the maximum H storage capacity of SWCNT bundles upon their exposure to an atomic H flux. Furthermore, it is demonstrated that the structures resulting from formation of inter-shell or inter-layer C-C bonds are stable and provide seeds for the nucleation of crystalline carbon phases embedded into the shells and layers of the MWCNT and FLG structures, respectively. The key parameter that determines the type and size of the generated nanocrystals is the chiral-angle difference between adjacent layers/walls in the original structure. A novel type of carbon structure, consisting of fullerene-like caged configurations embedded within adjacent graphene layers, has been discovered for the case where the graphene layers are rotated with respect to each other; interestingly, one class of these structures retains the unique and desired electronic properties of single-layer graphene.