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Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

The requirement of external carbon for conventional biological nitrogen removal (BNR) process has stimulated research on more resource-efficient treatment technologies. Bioconversion of methane to methanol using ammonia oxidizing bacteria (AOB), a process relies on the activity of ammonia monooxygenase expressed by AOB, offers an alternative and sustainable carbon source as all the components (ammonia, AOB, and methane) are often available within the water resource recovery facilities. Though the concept of biomethanol production using AOB has been proposed decades ago, previous studies have been primarily focused on the kinetics of methane oxidation in axenic batch cultures. In this study, the overall objectives were to (1) develop a platform for biomethanol production using AOB in a continuous process and (2) investigate the mechanism of methane cometabolism in AOB under chemostat conditions. Pure culture AOB (Nitrosmonas europaea and Nitrosomonas eutropha) and mixed culture nitrifying consortia were cultivated in bioreactors and continuously exposed to methane to study the responses of nitrifying bacteria at reactor level (nitrification performance) and molecular level (genes and proteins expression). The mixed culture experiments successfully demonstrated continuous biomethanol production with two types of bioreactor configurations. Acclimation of the mixed culture nitrifying consortia to co-exposure and co-oxidation of ammonia and methane were shown at multiple levels (reactor performance, biomass concentrations, bacterial activities, and genes expression). Furthermore, the accumulation of nitrite and a more substantive impact on nitrite oxidizing bacteria growth (compared to AOB) indicated the possibility for partial nitrification (ammonia-N to nitrite-N) coupled with biomethanol production, thereby opening the prospect for even more resource-efficient concurrent carbon and nitrogen management and removal. On the other hand, experiments with axenic AOB culture showed that methane exposure negatively and reversibly affected ammonia oxidation and AOB growth. Proteomics and gene expression data from pure culture experiments suggested that AOB modulating their catabolic (energy synthesis) and anabolic (biomass synthesis) pathways in response to methane exposure. Moreover, N. eutropha experiments demonstrated the potential adaptation of AOB to methane supplementation. Comparative transcriptomic analysis of methane cometabolism in N. europaea and N. eutropha showed that AOB upregulated genes involved in ATP production while downregulated genes involved in NADH production, organic molecules synthesis and cell division. In conclusion, this work provides insights for the process optimization for integrated AOB-mediated biomethanol production and (full- or partial-) nitrification processes as well as structured process modeling to facilitate such optimization and process scale-up and adoption. The whole transcriptomic analysis delineates a comprehensive and detailed view regarding methane cometabolism in AOB.

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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.

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.

There has been growing demands towards the efficient production of enantiopure compounds through either asymmetric synthesis or separation from racemic mixtures. Recent studies have examined numerous different methods that may address this challenge. One of these methods involved the interaction of chiral molecules on achiral metal surfaces such as copper to create chiral templates while another method utilizes the interaction of chiral molecules on intrinsically chiral surfaces. Earlier studies using nonhybrid Density Functional Theory (DFT) functional has provided some insights into the geometric structures and relative energies of some of these interactions, but it failed to achieve quantitative agreement with experimental studies. Using dispersion corrected DFT functionals, this thesis present a study of chemisorbed dense adlayers of glycine and alanine on Cu(110) and Cu(3,1,17), physisorbed R-3-methycyclohexanone (R-3MCHO) on Cu(100), Cu(110), Cu(111), Cu(221), and Cu(643)R, and the hydrogenation of formaldehyde and methoxide on Zn or Zr heteroatoms promoted Cu surfaces. In the dense glycine and alanine adlayer study, we have resolved a disagreement between experimental observation made on LEED, STM, and XPD, and we showed that heterochiral and homochiral glycine adlayer coexist on Cu(110). Our model failed to show the minute enantiospecificity for dense alanine adlayer on Cu(3,1,17) which indicated a numeric limitation for computational modeling of surface adsorption. In the physisorbed system, the dispersion corrected methods calculated adsorption energies were in better quantitative agreement with the experimentally observed values than the nonhybrid functionals, but it also created a significant overestimation of total adsorption energies. On the other hand, our model had indicated a previously unexpected adsorbate-induced surface reconstruction on Cu(110). This is promising news in term of computational modeling's capability in examining surface-adsorbate interaction on an atomic scale. As for the hydrogenation of formaldehyde and methoxide on copper surfaces, the model showed that the increased binding strength between the reaction intermediates and the heteroatom promoted copper surfaces to be the primary contributor of the increased reaction rates. Furthermore, our model had also indicated that while clustered heteroatoms are relatively rare, a significant portion of reaction takes place near these clustered structures. It is our hope that the results and techniques presented in this thesis can be used to better understand and predict the interaction of more complex surface-adsorbate interactions.

Recently, the increasing level of atmospheric CO₂ has been widely noticed due to its association with global warming, provoking a growth in environmental concerns toward the continued use of fossil fuels. To mitigate the concentration of atmospheric CO₂, various strategies have been implemented. Among options to turn waste CO₂ into useful fuels and chemicals, carbon capture and utilisation along with renewable hydrogen production as the source materials for methanol production is more preferable. In the 1960s, the highly active and economic Cu/ZnO/Al₂O₃ catalyst was developed for CO₂ hydrogenation reaction to methanol, since then, metal nanoparticles and nanocomposites have been extensively investigated and applied. Especially, bimetallic catalysts have emerged as an important class of catalysts due to their unique properties and superior catalytic performances compared to their monometallic counterparts. This thesis presents the evolution of the catalyst development for CO₂ hydrogenation to methanol: Firstly, we introduced the CuZn-based catalysts with Zn content increased in the bimetallic CuZn system via a heterojunction synthesis approach. Secondly, we increased the active CuZn sites via introducing ultra-thin layered double hydroxide as the catalyst precursor for methanol production from CO₂ and H₂. Thirdly, a new class of Rh-In bimetallic catalysts were studied, which shows high methanol yield and selectivity under thermodynamically unfavourable methanol synthesis conditions owing to the strong synergies of Rh-In bimetallic system. Fourthly, for the renewable methanol production from H₂ and CO₂, the hydrogen source must come from the green production routes. Therefore, an in-depth study of a nanocomposite system, CdS-carbon nanotubes-MoS₂, for photocatalytic hydrogen production from water has been demonstrated. Finally, the conclusion of this thesis is given and an outlook is presented for the future development in this research area.

Stable dinuclear complexes bis(heptane-2,4,6-trionato)dicopper(II) [Cu2(daa)2], bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II) [Cu2(dba)2], bis(1,5-diphenyl-1,3,5-pentanetrionato)dicobalt(II) [Co2(dba)2], and [6,11-dimethyl-7,10-diazahexadeca-5,11-diene-2,4,13,15-tetranato(4-)-N7N10O4O13;O2O4O13O15] copper(II)cobalt(II) [(CuCo(daaen)] were supported on Cab-O-Sil by the batch impregnation technique. The supported samples were characterized by UV-Vis, elemental analysis, X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermal gravimetric analysis (TGA). Elemental analysis and TGA data confirm that the Cu2(daa)2 complex loses one of its coordinated ligands upon adsorption onto silica in THF at greater than 4.43 wt% Cu loading. By contrast, at all Cu loadings the Cu2(dba)2 complex was adsorbed on the silica surface in CH2Cl2 without loss of ligand. XRD and DRIFTS results confirmed the formation of Cu2(dba)2 multilayer films on the Cab-O-Sil surface for samples containing greater than 2.64 wt% copper. The dinuclear cobalt complex and copper-cobalt complex also do not lose their coordination ligands upon adsorption on the surface. These two metal complexes are amorphous and did not produce XRD patterns. However, DRIFTS results confirm that the binuclear cobalt complex and the copper-cobalt complex begin forming multilayer films between 1.21and 2.53 wt% Cu. The Cu2(dba)2/silica precatalysts were subsequently converted to the catalysts by decomposing the organic ligands at 450 degrees Celsius followed by activation with 2% H2 at 250 degrees Celsius and were evaluated for methanol synthesis and methanol decomposition reactions. Kinetic studies demonstrated that the 3.70% Cu/silica[Cu2(dba)2] catalyst is more active for methanol decomposition than it is for methanol synthesis. The supported dinuclear cobalt and copper-cobalt precatalysts were converted to the catalyst by heating at 450 degrees Celsius followed by activation of the catalysts with 50% H2. Four different catalysts, 3.5% Co/silica[Co2(dba)2], 6.7% Co/silica[Co2(dba)2], 2.3% Co/silica[CuCo(daaen)], and 5.5% Co/silica[Co2(daa)2] were evaluated for the Fischer-Tropsch reaction at 350 degrees Celsius in a batch reactor. The supported binuclear cobalt catalyst produced C1-C7 alkanes and a significant amount of CO2. By contrast, the catalyst formed from heterobinuclear CuCo(daaen) showed the ability to convert syngas to aromatics with a narrow product distribution. In addition, the 6.7% Co/silica[Co2(dba)2] multilayer catalysts have above 98% conversion rates and 60% liquid hydrocarbon selectivity in a flow reactor.