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The molecular structures of the Si2HX, Si2Li2, SiGeHLi and C2H2 species (where X= H, Li, F and Cl) were studied. All of these species have more than one isomeric form. The critical points on the potential energy surfaces of the Si2HX, Si2Li2and C2H2 species and the minima on the SiGeHLi surface were located. The full six-dimensional potential energy surface (PES) of the Si2Li2 molecule was calculated (for the first time) using the CCSD(T)-F12a/cc-pVTZ-F12 level of theory. The core-valence, zero-point energy and relativistic corrections for the Si2HLi and Si2Li2 species were calculated. Additionally, the electron affinity and Li+ /H+ binding energies for the Si2HLi and Si2Li2 structures were investigated. Furthermore, the anharmonic vibrational-rotational properties for the Si2HLi and Si2Li2 structures were calculated using second-order perturbation theory. The recently developed CCSD(T)-F12a method with the cc-pVTZ-F12 basis set was employed to obtain geometries and relative energies (for the Si2HLi, Si2HF, Si2HCl and Si2Li2 structures) and vibrational frequencies (for the Si2H2 and Si2Li2 structures). The CCSD(T) method with the cc-pVXZ, aug-cc-pVXZ and aug-cc-pV(X+d)Z basis sets, CCSD(T)-F12a/cc-pVXZ (where X=2-4) and the B3LYP/6-311+G(d) levels of theory were also used. Comparison was made of the geometric properties and vibrational frequencies calculated at the different levels of theory. The calculated geometric properties for all the studied species and vibrational frequencies (for the Si2H2 structures) show good agreement with the experimental and theoretical literature. The PES of Si2Li2 was used to perform large scale variational vibrational calculations using the WAVR4 program. The first 2400 totally symmetric energy levels were calculated. The low-lying energy levels were qualitatively correct. Conclusive assignments of the vibrational modes of the Si2Li2 structures were made for the eleven lowest lying energy levels.

This work describes the fabrication of nanospheres from a range of novel polyhydroxyalkanoates supplied by Monsanto, St Louis, Missouri, USA for the delivery of selected actives of both pharmaceutical and agricultural interest. Initial evaluation of established microsphere and nanosphere fabrication techniques resulted in the adoption and optimisation of a double sonication solvent evaporation method involving the synperonic surfactant F68. Nanospheres could be consistently generated with this method. Studies on the incorporation and release of the surrogate protein Bovine Serum Albumin V demonstrated that BSA could be loaded with between 10-40% w/w BSA without nanosphere destabilisation. BSA release from nanospheres into Hanks Balanced Salts Solution, pH 7.4, could be monitored for up to 28 days at 37°C. The incorporation and release of the Monsanto actives - the insecticide Admire® ({ 1-[(6-chloro-3-pyridinyl)methyIJ-N-nitro-2-imidazolidinimine}) and the plant growth hormone potassium salt Gibberellic acid (GA3K) from physico-chemically characterised polymer nanospheres was monitored for up to 37 days and 28 days respectively, at both 4°C and 23°C. Release data was subsequently fitted to established kinetic models to elaborate the possible mechanisms of release of actives from the nanospheres. The exposure of unloaded nanospheres to a range of physiological media and rural rainwater has been used to investigate the role polymer biodegradation by enzymatic and chemical means might play in the in vivo release of actives and agricultural applications. The potential environmental biodegradation of Monsanto polymers has been investigated using a composting study (International Standard ISO/FDIS 14855) in which the ultimate aerobic biodegradation of the polymers has been monitored by the analysis of evolved carbon dioxide. These studies demonstrated the potential of the polymers for use in the environment, for example as a pesticide delivery system.

Hydrogen could replace fossil fuels for power generation and transportation and contribute to a low carbon economy. However, current methods of producing hydrogen e.g. steam methane reformation of natural gas are not sustainable and also contribute to COi emissions. Dark fermentation of carbohydrate-rich waste organics and energy crops to hydrogen using mixed microflora could contribute to the mix of technologies for producing hydrogen sustainably. Naturally available mixed microflora can be enriched e.g. by heat treatment to select for hydrogen producers, typically clostridia. Fermentation endproducts from the hydrogen-producing stage could be fed to a second anaerobic digestion stage to recover more energy as methane and to stabilise the effluent. Although anaerobic digestion is well established, fermentative hydrogen production is not. This work evaluated the feasibility of hydrogen production from two energy crops, grass and fodder maize in batch culture without pretreatment; investigated the effect of increase in substrate (sucrose) concentration, attractive from an energy point of view, on the yield and stability of hydrogen production in continuous culture; examined the performance of a mesophilic high rate anaerobic digester treating effluent from a continuous hydrogen-producing bioreactor; demonstrated the possibility of changeover of substrate - sucrose, starch and xylose - during continuous hydrogen production and evaluated the effect of sparging with CO2 , a process gas, on hydrogen production. It was demonstrated for the first time that hydrogen production from grass and fodder maize by direct fermentation in batch culture (2.3 L reactor, 35°C, pH 5.2-5.3) is possible, with hydrogen yields of 75.6 ml/g dry matter wilted perennial rye grass and62.4 ml/g dry matter of fodder maize. In continuous culture (pH 5.2-5.3, 35°C, 12 hour hydraulic retention time (HRT)), stable hydrogen production was achieved up to 40 g/L sucrose concentration - with decreasing hydrogen yields, from 1.7±0.2 mol/mol hexose added at 10 g/L to 1.2±0.3 mol/mol hexose at 40 g/L - beyond which the system became unstable. The decrease in hydrogen yield and lack of stability at higher substrate concentrations was attributed to feedback inhibition by volatile fatty acids (VFAs). Effluent from the hydrogen reactor was readily degraded in an upflow anaerobic filter up to an organic loading rate of 10 gCOD/L/d (2 d HRT) and/or a sodium concentration of 1.87 g/L. Reduction of sodium levels in the methane reactor by using calcium hydroxide as alkali in the hydrogen reactor was found to extend the efficiency of degradation of VFAs; overall COD reduction for the two stage system fed with 20 g/L sucrose increased from 83% (with NaOH as alkali) to 91% with Ca(OH)2 . It was easier to switch from starch to sucrose and vice versa during continuous hydrogen production; however switching from sucrose or starch to xylose was slower, requiring operation for about 1 day in batch culture before continuous operation could commence. Sparging with CO2 improved hydrogen yield from sucrose by at least 71% and appeared to inhibit homoacetogenesis from starch. This work verifies the potential technical feasibility of generating hydrogen, a clean energy carrier, sustainably from carbohydrate-rich waste organics and energy crops.

L’utilisation des combustibles fossiles (énergies non renouvelables) est responsable de l’augmentation de la concentration en gaz à effet de serre dans l’atmosphère. Lors de l'examen des solutions de rechange, l’hydrogène comme vecteur énergétique est le plus séduisant. Le stockage de l’hydrogène en phase solide sous forme d’hydrures, est l’une des solutions non polluantes futures pour le stockage et le transport de l’énergie. Parmi les matériaux candidats, le borohydrure de sodium (NaBH4) et l’hydrure de magnésium (MgH2) ont été sélectionnés au vu de leur capacité gravimétrique élevée en hydrogène. La réaction d'hydrolyse de NaBH4 a été étudiée dans un calorimètre en phase liquide couplée à un compteur à gaz, afin de suivre en même temps, la cinétique de production d’hydrogène et l’évolution de la chaleur de réaction. Nous avons préparé des catalyseurs à base de cobalt supporté sur différents supports (hydrotalcites, KF/Al2O3, hétéropolyanions) ayant des propriétés acido-basiques différentes. Les supports et les catalyseurs à base de cobalt ont été caractérisés par DRX, MEB+EDX, ICP et BET. Co/hétéropolyanions a montré une cinétique très élevée pour la production d'hydrogène accompagnée d'une conversion totale dans la réaction d'hydrolyse. L’absorption et la désorption de l’hydrogène ont été étudiées sur l’hydrure de magnésium. Afin d’améliorer la cinétique de sorption de MgH2, nous avons préparé des mélanges MgH2-MT (MT = métal de transition Co, Ni, Fe, Cr, Mn), MgH2-MTmélangé (MT = métal de transition Co, Ni, Fe,), MgH2-MTnano (MT = métal de transition Conano, Ninano, Fenano, Cunano, Znnano) et MgH2-nLiBH4-MTnano (MT = métal de transition Conano, Ninano, Fenano) par broyage à billes de haute énergie. Leurs propriétés physico-chimiques ont été étudiées par DRX et MEB+EDX. La température de désorption de l’hydrogène et la quantité d’hydrogène dégagée ont été étudiées par TPD. La cinétique d’absorption de l’hydrogène et la réversibilité du stockage de l’hydrogène ont été étudiées par isotherme PCT pour le système MgH2-MTnano. MgH2-10-Ninano présente la meilleure propriété de stockage réversible de l’hydrogène, MgH2-10-Conano et MgH2- 10-Fenano sont aussi de bons candidats potentiels / The use of fossil fuels (non-renewable) is the main raison of increasing the green house in the atmosphere. Among the considered alternatives, hydrogen is seen as the most attractive energy carrier. The storage of the hydrogen in the solid phase in the form of hydrides is one of the clean future solutions for storage and transport of energy. Among potential materials, sodium borohydride (NaBH4) and magnesium hydride (MgH2) were selected regarding their high hydrogen gravimetric capacity. The hydrolysis reaction of NaBH4 was studied in a liquid phase calorimetry coupled to a gas-meter, in order to monitor simultaneously the kinetics of the hydrogen production and the evolution of the reaction heat. We prepared cobalt supported catalysts using various supports (hydrotalcites, KF/Al2O3, heteropolyanions) with different acid-base properties. The supports and the catalysts were characterized by XRD, SEM+EDX, ICP and BET. Co/heteropolyanions showed a very high kinetics for the production of hydrogen accompanied by a total conversion in the hydrolysis reaction. The absorption and desorption of hydrogen were studied using magnesium hydride. In order to improve the sorption kinetics of MgH2, we have prepared the MgH2-MT (MT= transition metal Co, Ni, Fe, Cr, Mn), MgH2-MTmixture (MT= transition metal Co, Ni, Fe), MgH2-MTnano (MT = transition metal Conano, Ninano, Fenano, Cunano, Znnano) and MgH2-nLiBH4-MTnano (MT = transition metal Conano, Ninano, Fenano) mixtures by high energy ball milling. Their physicochemical properties were studied by XRD and SEM+EDX. The temperature of hydrogen desorption and the amount of hydrogen generated were investigated by TPD. The kinetics of hydrogen absorption and the reversibility of hydrogen storage were investigated with PCT isotherm for the system of MgH2-MTnano. The sample MgH2-10-Ninano presents the best property for reversible hydrogen storage; MgH2- 10-Conano and MgH2-10-Fenano are also good potential candidates

Hydrogen storage in lightweight hydrides continues to attract significant interest as the lack of a safe and efficient storage of hydrogen remains the major technological barrier to the widespread use of hydrogen as a fuel. The metal borohydrides Ca(BH₄)₂ and LiBH₄ form the subject of this thesis; three aspects of considerable academic interest were investigated by density functional theory (DFT) and molecular dynamics (MD) modelling. (i) High-pressure crystal structures of Ca(BH₄)₂ were predicted from a structural analogy between metal borohydrides and isoelectronic metal oxides. The structural stability of hydrogen storage materials under high pressure is an important aspect, as high-pressure polymorphs may provide structures with better hydrogen desorption properties. The isoelectronic analogue of Ca(BH₄)₂ is TiO₂, and structural equivalents of Ca(BH₄)₂ in the baddeleyite, columbite and cotunnite structures of TiO₂ were found to be stable at elevated pressure. Thermodynamic stability was evaluated by computing the Gibbs energy with respect to pressure and temperature. The pressure-dependence of the Helmholtz energy was determined to described a third-order Birch-Murnaghan equation of state, and the harmonic approximation was used to compute the vibrational energy levels and the Helmholtz energy as a function of temperature. The proposed structures are consistent with reports of two hitherto unidentified high-pressure phases observed experimentally. (ii) The disordered structure of the high-temperature phase of LiBH4 was studied by ab initio molecular dynamics (MD) at temperatures ranging from 200-535 K. It was found that the model emerging from analysis of the MD simulations properly accounts for dynamical disorder and fundamentally differs from the published experimental and theoretical structures. The validity of the MD model was corroborated by comparison of calculated pair distribution functions, vibrational spectra and a crystallographic model with neutron diffraction data; good agreement was found. A reassignment of the space group from P63mc to P63/mmc is proposed based on evidence for additional symmetry from MD simulations. (iii) Finally, a new MD-based method was developed to simulate fast ionic diffusion in LiBH₄. The colour diffusion algorithm - a nonequilibrium molecular dynamics method originally developed for the study of model fluids - was adapted and applied to self-diffusion of atoms in a solid for the first time. Calculated diffusion coefficients agreed very well with published measurements, and diffusion pathways that include collective particle effects were determined directly from the simulation results, thereby opening up a promising and efficient new method for the study of phenomena such as superionic conduction.

L'hydrure d'aluminium AlH3 ou alane est à la fois un matériau très important et une espèce chimique fascinante qui reçoit actuellement un regain d'intérêt lié à son utilisation potentielle pour différentes applications : (i) comme additif énergétique pour les ergols solides, (ii) comme agent réducteur dans les piles alcalines et (iii) comme source possible d'hydrogène pour des piles à combustibles basses températures. L'alane a une capacité de stockage volumique d'hydrogène de 0,148 g mL-1 soit deux fois plus que l'hydrogène liquide (0,07 g mL-1). Sa capacité de stockage d'hydrogène est supérieure à 10 % en masse. Malheureusement, le coût de production d'alane est élevé ce qui limite son utilisation notamment dans le domaine de la propulsion. L'objectif de cette thèse était d'optimiser la synthèse de l'alane α pur, variété cristalline considérée comme la plus stable et ainsi d'en réduire les coûts de production. Différentes méthodes de synthèse sous atmosphère contrôlée ont été mises en oeuvre. Il a été montré que le traitement thermique sous vide d'un complexe éthéré de AlH3 permettait de s'affranchir de l'utilisation de toluène et ainsi de réduire la quantité de solvants et de réactifs de 25 % tout en obtenant une phase α pure mise en évidence par DRX. Des essais de stabilisation contrôlés par ATD-ATG ont montré que la température de décomposition à pression atmosphérique de l'alane α était de 174 °C contre 160 °C pour la phase α non stabilisée. Une autre voie de synthèse, sans solvant et à l'aide d'une presse fabriquée au laboratoire a été explorée. Un plan d'expériences a été réalisé afin d'identifier les paramètres influant le plus sur le rendement en alane α et la pureté de la phase obtenue. L'alane synthétisé par ces différentes méthodes a été caractérisé par DRX, MEB, MET, ATD-ATG et ICP-OES. Un transfert technologique de la synthèse en solution a été opéré vers les partenaires industriels de ce travail. / Aluminium hydride or alane (AlH3) is a very important and fascinating material that draws increasing attention due to its potential uses: (i) as an energetic component in rocket propellants, (ii) as a reducing agent in alkali batteries and (iii) as a possible hydrogen source for low temperature fuel cells. It exhibits a density of 1,48 g cm-3, a volumetric hydrogen capacity of 0,148 g mL-1, that is more than twice as much as that of liquid hydrogen (0,07 g mL-1). Its hydrogen mass capacity slightly exceeds 10 wt.-%. Unfortunately, production of alane suffers from a high cost that hinders its opportunity to be an excellent candidate for propulsion. Moreover, only the α phase of alane is known to be stable enough to be stored and used. This work aims at developing cheaper methods for alane production while keeping a maximum selectivity towards the formation of α phase. Preparation using a classical organometallic synthesis in ether was implemented. An etherate complex was formed, the ether was removed under vacuum and finally an adequate thermal treatment led to pure α phase of alane as identified by powder X-ray diffraction. A toluene free synthesis method was implemented and resulted in a cost reduction of 25 %. The stability of the material was characterized through thermal analysis (DTA-TGA). The morphology and purity of the alane were characterized using TEM, SEM and ICP-OES. Alane was synthesized using doping compounds and resulted in a significant increase in the decomposition temperature from ca. 160 °C to ca. 174 °C. Syntheses without solvent were studied using a homemade reactor and following a design of experiment to identify the key parameter towards the highest yield in α-AlH3. The synthesis method in ether was transferred to our industrial partners.