This thesis focuses on the assembly of non-conventional templated polyoxotungstates, specifically on the 6A group anions such as SO32-, SeO32- and TeO66-, which results in the discovery of 40 new polyoxotungstate compounds from the traditional Dawson-like cluster {SW18} to the nanoscale cluster {Se8W119} cluster. This study demonstrated that the identification and isolation of discrete building blocks to produce versatile and modular species can be assembled in a controlled manner, and it still represents a fundamental objective in the development of inorganic chemistry from the molecule to the nano world. The assembly of Iso-polyoxotungstate fragments can be affected by a few key reaction variables including, but not limited to, pH, temperature, ionic strength, type of cations and solvents. Carefully screening and controlling the reaction conditions can result in the isolation of the different aggregate behaviour of building blocks such as {W11} units. Further, the use of synthetically innocent anions appears to be important in the assembly of Iso-polyoxtungstate with pentagonal units. The Dawson-Like type X ⊂ {W18O54} (X= SIV, SeIV or TeVI) clusters can be reasonably designed and were isolated in a “one-pot” procedure by using a “shrink wrapping” strategy. These clusters are fully characterized by XRD, ESI-MS/CSI-MS and chemical analysis, IR, as well as by preliminary electrochemical studies. The effects of organo-cation, ionic strength and pH are investigated, especially in tungstoselenite and tungstotellurate chemistry. The synthetic methodology is also developed, the combination of building block strategy and solvent & cation exchange methods lead to the isolation of a series of new polyoxotungstate compounds including an “in-situ” reduction product {TeIVW18}, the thermochromic {Se2W18} cluster, and the organic soluble lacunary cluster {Se2W19}. These discoveries lead to a general new polyoxometalate building block approach and start a new field in polyoxotungstate synthesis.

This thesis describes investigations performed into the ion exchange and intercalation properties of aluminium triphosphate, AlH\(_2\)P\(_3\)O\(_{10}\)•2H\(_2\)O (AlTP). Materials synthesised were characterised using a variety of techniques, including powder neutron and X-ray diffraction, Rietveld analysis, thermogravimetic analysis and environmental scanning microscopy. Monovalent ion exchange (with Na, K, Rb, Cs and Ag) gave complete and facile exchange of the host’s hydrogen ions and gave crystalline products. A thermodynamically favoured phase with two waters of crystallisation was observed for all monovalent cation exchanges. The alkali metals also showed metastable phases with differing numbers of waters of crystallisation, four for Na and one for K, Rb and Cs. Unit cells have been assigned to the exchanged phases, with all showing a more than doubling of the \(a\) parameter. Structural characterisation of the rubidium and caesium phases show this to be a result of a change of symmetry to C2/c causing adjacent layers to shift half a unit cell along [010] with respect to one another. Ion exchange with divalent cations (Cu, Mn, Zn, Ca and Sr) has also been shown to be possible, with phases showing altered XRD patterns and decomposition products. Intercalation with a range of increasingly complex amines was found to be possible in AlTP. Multifunctional molecules, including amino acids, were also found to intercalate into AlTP, with evidence in the intercalation of 6-aminohexanoic acid that interactions between intercalated molecules within the inter-lamellar region are possible. Trends were found to be similar to other layered phosphates with respect to the amounts and angles of intercalation of simple monoamines and the effects of pK\(_b\) and sterics upon an amines ability to intercalate into AlTP. In addition, intercalation with silver exchanged AlTP was also found to be possible. This was able to intercalate several similar amines to AlTP, but showed its own unique intercalation properties including the ability to intercalate thiols.

This study provides a comprehensive understanding of the fine particle grinding process in stirred media mills. Calcium carbonate was chosen as the feed material. The experiments were firstly conducted in a laboratory scale vertically stirred media mill under various grinding conditions. The operating variables including specific energy, rotational speed, solids concentration, grinding media type, chemical additives (dispersant) were investigated. Then, the process was scaled up to a pilot scale mill. The performance of the pilot scale mill was compared to the laboratory scale mill regarding the product size (e.g. d80 ) and instantaneous power draw. Positron Emission Particle Tracking technology (PEPT) was used as a tool to study the motion of the grinding media in the laboratory scale stirred media mill. Some new stirrers were proposed and analysed. The PEPT results obtained under different operating conditions were demonstrated and analysed. The Discrete Element Method (DEM) based on the Hertz-Mindlin contact model was implemented to simulate the motion of the grinding media in both laboratory scale and pilot scale mills. A new type of stirrer is accepted by Imerys and used to produce the calcium carbonate in the industrial scale of grinding process. The energy saving is obtained up to 3 %compared to the standard stirrer currently used.

The periplasmic nitrate reductase (Nap) has been shown to support anaerobic growth of Escherichia coli K-12 under nitrate-limiting conditions. Two of the Nap proteins, NapG and NapH, are predicted to contain four and two [4Fe-4S] clusters, respectively. In this thesis it is reported that, during fermentative growth. Nap plays a role in redox balancing. This role is most pronounced in a strain that lacks menaquinol and tiierefore cannot use the menaquinol-dependent ftunarate reductase to fulfil a redox balancing role during glucose fermentation. Nitrate stimulated the growth of both a AmenBC AnapGH and an isogenic AmenBC nap^ strain to the same extent, even although the Nap activity was extremely low. This showed that the residual 1% electron flow in the strain deleted for NapG and NapH was sufficient to fulfil this redox balancing function. Using artificial quinones, NapG and NapH were shown to be linked to oxidation of quinones with high midpoint redox potentials. NapF^ and NapF' strains were grown anaerobically after either aerobic or anaerobic growth and NapF was shown to be involved in adaptation from aerobic to anaerobic growth. The hybrid cluster protein (HCP) contains two Fe-S clusters, one of which is a hybrid [4Fe-2S-20] cluster. Despite intensive study, its physiological function is unclear. E. coli HCP is detected after anaerobic growth with nitrate or nitrite, so a possible role for it in some stage of the nitrogen cycle has been proposed. To study the regulation of HCP, an hcprlacZ fusion was constructed and transformed into_^r, arcA and norR mutant strains of E. coli. Transcription from the hep promoter was induced during anaerobic growth. Only the jhr mutant was defective in hep expression, suggesting that transcription from the promoter in response to anaerobiosis is dependent on FNR. Nitrate and nitrite fiirther induced transcription from the hep promoter. The parental strain and the narL, narP and narLmrP mutants were grown anaerobically in medium supplemented with nitrite or nitrate. The nitrite and nitrate response of the hep promoter was mediated by both of the response regulator proteins, NarL and NarP. It is argued that NarL plays a dual role at the hep promoter acting as an activator during growth in the presence of a low concentration of nitrite or nitrate and as both repressor and activator in the presence of high nitrite or nitrate concentrations. Gel retardation assays were used to show that FNR and NarL form a complex with the hep promoter, thus confirming that their effect on transcription is direct. A technique involving the rapid amplification of cDNA ends (RACE) was used to demonstrate that transcription of the hcp~hcr operon initiates at a thymine nucleotide located 31 bp upstream of the translation-initiation codon. A A/icp strain was constructed by homologous recombination. When grown in medium supplemented with nitrate, the growth rate and yield of the parental strain and the hhep mutant were the same, suggesting that HCP is not involved in nitrate-dependent growth. Both HCP^ and HCP' strains were equally sensitive to nitric oxide and hydroxylamine. It was concluded therefore that HCP is unable to protect bacteria against nitric oxide or hydroxylamine toxicity in vivo. HCP was overexpressed from a recombinant plasmid and subsequently purified on a nickel column for biochemical studies. A qualitative method using reduced methyl viologen as an electron donor was developed for use in attempts to identify a possible substrate of HCP in vitro. Nitrite, nitrate and hydroxylamine were tested, but no evidence was presented that any of them can be used as an electron acceptor.

No description available.

No description available.

No description available.

Thesis (M.S.M.E.)--University of Delaware, 2008. / Principal faculty advisor: Suresh G. Advani, Dept. of Mechanical Engineering. Includes bibliographical references.

The production of high premium fuel is an issue of priority to every refinery. The trans-hydrogenation process was devised to convert two low value refinery cracked products to premium products; the conversion processes involve the combination of dehydrogenation and hydrogenation reactions as a single step process. The low value refinery products (i.e. alkanes and alkynes or alkadienes) have been converted to alkenes (olefins) by trans-hydrogenation using catalysts system based on VOx, CrOx and Pt all supported on alumina. Although trans-hydrogenation has been disclosed in many patents over decades, only little academic literature is available. The success of the process over various catalysts has been claimed in many of these patents. However, further studies are still required to ascertain the actual reaction mechanism, mitigating carbon deposition and catalyst deactivation, and the role of different catalysts to optimize the reaction desired products. The current research work evaluates the potential of CrOx/Al2O3, K-CrOx/Al2O3, Pt/Al2O3 and K-Pt/Al2O3 to investigate the trans-hydrogenation of the pentane (P)/1-hexyne (1HY) system, the pentane (P)/1,5-hexadiene (1,5-HD) system and the pentane (P)/2,4-Hexadiene (2,4-HD) system over a range temperatures (523-773 K). The fresh catalysts were first characterised by N2 adsorption using the BET method, X-ray diffraction, Raman spectroscopy, Thermogravimetric analysis, Temperature programme oxidation (TPO), Temperature programmed reduction (TPR), Electron paramagnetic resonance (EPR), Atomic absorption spectroscopy (AAS) and colorimetric analysis. The Free energy (ΔG) for the reaction of pentane with 1-hexyne, 1,5-hexadiene and 2,4-hexadiene shows that trans-hydrogenation is thermodynamically favoured at most temperatures for the reaction of pentane with 1-hexyne, however this is not always the case when hexadienes are the hydrogen acceptors. When 2,4-HD is the acceptor, ΔG is +ve at all the reaction temperatures tested. When pentane or hexyne/hexadiene or a 5:1 mixture was passed over the catalyst, in the temperature range of 523K -773 K, it was found that trans-hydrogenation process had taken place but many of the products are alkylated olefinic and alkylated hydrocarbons. Regarding all systems previously mentioned above, the ratio of olefin to alkylated olefin products was ~50:50 at 773K, however, this ratio was found to vary at other temperatures. The lowest ratio of ~10:90 was obtained at 523K. Dissociation of the hydrocarbon reactant was also observed leading to production of cracked products such as CH4, C2H4 and subsequent formation of a carbonaceous overlayer on the catalyst surface. This was not the case with the 2,4-hexadiene reactant, the trans-hydrogenation is poor, as expected from the free energies. The trans-hydrogenation process was shown to improve the conversion of pentane when co-fed with the hexyne to ~26% and to ~90% when co-fed with 1,5HD using the chromia catalyst at 773K, both values are much higher than the equilibrium conversion of the pentane dehydrogenation. Higher conversions of the pentane were subsequently obtained with other catalysts, but the chromia/alumina and K-CrOx/Al2O3 catalyst exhibits greater trans-hydrogenation activity. With the 2,4HD acceptor, very low conversions of pentane were obtained with all the catalysts: in general conversions lower than when the pentane was run alone were obtained. The products observed were unique for each catalyst. However, it was observed that for each catalyst, only the distribution of the products changed with temperature. This also accounted for changes in both the cracking products and the carbon laydown on the catalyst. The deactivation regeneration cycles shows very similar conversion of both reactants. There is a small deactivation observed for the longer time run; however these were not very significant. It was observed that some of the major products were consumed with time, but are used for the formation of other major products. However, this is more prominent with pentane/hexyne run using the CrOx/Al2O3 catalyst.

Modern society increasingly depends on reliable and secure energy supplies for economic growth and social prosperity. Thus, it is crucial to implement a low-carbon energy carrier based on renewable energy sources to ensure energy security and tackle climate change. Hydrogen (H2) is undoubtedly one of the most promising energy carriers to achieve a low-carbon energy future scenario. However, before the hydrogen economy can become completely viable, the safe and compact storage of H2 is an issue that must be overcome. This thesis concentrates on the development of potential “modular” solid state H2 storage solutions for portable power applications. A wide range of potential H2 storage materials was investigated with the aim of providing an improved performance in the form of a low desorption onset temperature, fast desorption kinetics and a high H2 gravimetric capacity. This research work focused on the study of light metal hydride – hydroxide systems, in particular the nanostructured MgH2-Mg(OH)2 system, and ammonia borane (AB) composites, specifically AB within a porous carbon-based matrix composites. The nanostructured MgH2-Mg(OH)2 “modular” H2 release system was investigated as a candidate exothermic filler material combined with an industrial MgH2 matrix to produce a novel solid state H2 storage hybrid tank. It was postulated that the heat of the reaction of the exothermic filler material could initiate and propagate a reaction in the matrix hydride and additionally contribute to the H2 yield. Detailed information about the thermodynamic and kinetic behaviour of the MgH2-Mg(OH)2 system, under operational conditions, was obtained. The thermal decomposition of this system was found to be a two-step process, associated with two H2 releases, resulting from: 1) almost simultaneous decomposition of Mg(OH)2 and hydrolysis of MgH2 at 616 K (exothermic event) and 2) decomposition of unreacted MgH2 at 743 K (endothermic event). The formation of a MgO layer on the unreacted MgH2 resulting from the previous hydrolysis was found to retard the H2 release. The formation of MgH2-MgO core-shell structures was investigated and confirmed by kinetic measurements, ex-situ Scanning Electron Microscopy / Energy Dispersive X-ray Spectroscopy (SEM/EDX) analysis and ex-situ Powder X-ray Diffraction (PXD) experiments. Kinetics measurements performed under operational conditions proved the H2 release of the system to be very slow (≈ 20 hours at 573 K). The mechanism for H2 evolution of this system was elucidated by in-situ Powder Neutron Diffraction (PND) performed at the Institut Laue-Langevin (ILL) in Grenoble, confirming the observations by thermal analysis methods and ex-situ PXD experiments. The use of additives (graphite and silicon carbide) was investigated to enhance the kinetic and thermodynamic properties in the system. The incorporation of SiC proved to be successful in improving the H2 release of the first step. However, no further kinetic improvements were observed by incorporating additives. Besides, the H2 capacity was slightly reduced by the introduction of 10 wt. % of C/SiC and traces of water were released alongside H2. AB-based nanocomposites and nanoconfined samples were also investigated with the aim of synthesising novel solid-state H2 storage materials with enhanced desorption properties. Highly ordered mesoporous carbons (FDU-25, CGY-1), activated carbons (AX21, Sigma AC, MAST Carbon TE7), and graphene (Angstron, Alfa), were employed to prepare nanocomposites (via ball milling or solution impregnation) in different ratios. A double-solution impregnated composite with a 2:3 weight ratio of AB to activated carbon (AC) showed the best performance with a dehydrogenation onset of 353 K and the suppression of borazine and boron-based by-products. The use of an external NiCl2 filter absorbed any released gaseous ammonia and no by-products were detected with a mass spectrometer sensitivity of 100 ppb. The nanoconfinement of AB in AC hosts was investigated by simultaneous Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) at the Elettra synchrotron in Trieste. The results confirm that the nanoconfinement of ammonia borane was successfully induced and central to the performance improvements of the H2 storage material. To underpin the validity of the results and allow a quantitative comparison of the performance of these new developed materials with previously assessed systems, the reproducibility and repeatability of the measurements was ensured by means of intra and inter-laboratory comparisons. This was accomplished by using the facilities at the European Commission Joint Research Centre (JRC), Energy Storage Unit in Petten (The Netherlands) and the laboratories of the School of Chemistry in University of Glasgow (UK).