This thesis is focused on developing metal-organic and organic molecules for photocatalytic water splitting and carbon dioxide reduction. In chapter 1, an overview of hydrogen production, dye-sensitized solar cells and carbon dioxide reduction are provided. The development history and reaction mechanisms of catalytic systems are introduced along with the typical examples in each field. The applications of both metal-organic and organic compounds are covered. In chapter 2, nine molecular organic photosensitizers were designed and synthesized. The nine molecules were employed as the photosensitizing reagent in the fabrication of dye-sensitized solar cells and applied in photocatalytic water reduction via coupling with TiO2 semiconductors and Pt co-catalyst. The highest turnover number (TON) of 10200 was achieved by organic photosensitizer 1g for hydrogen generation. The effect of alkyl chains and triarylamine donor moiety to the photocatalytic performance was investigated. A shorter alkyl chain was found to favor the reaction due to a lower hydrophobicity which in turn may block the interaction between the photocatalyst and water molecules. Besides, the triarylamine donor units facilitated high hydrogen generation rates by reducing the contact between catalytic active sites and the oxidized form of sacrificial reagents. In chapter 3, five earth-abundant metal complexes were synthesized to serve as the catalyst and CdS nanorods (NRs) were prepared to be the photosensitizer for the photocatalytic water reduction. A cobalt dithiolene complex (2a) achieved a TON of 30635 in 20 h under the blue light irradiation at a concentration of 10 µM. A new complex 2c also gave a high TON of 12375 under the same conditions and its TON was further improved to 115213 in 87 h by reducing the concentration of catalyst by ten times. The size effect of CdS NRs was investigated and larger nanoparticles exhibited higher hydrogen production rates. In chapter 4, ten iridium(III) complexes were synthesized and used as dual-functional molecules in photocatalytic carbon dioxide reduction by acting as both the photosensitizing reagent as well as the catalyst. The best performance was achieved by 3j, giving a TON of 230 under the irradiation of blue LED. A push-pull effect brought by trifluoromethyl and methoxy group sucessfully enhanced the carbon dioxide reduction efficiency. The hydrophobicity of n-butyl chain also provided effective protection to the active sites of reaction intermediate. Additional steric hindrance was found to extend the lifespan of photocatalytic systems but led to a drop in the overall conversion efficiency. Chapter 5 summarizes the specific synthetic procedures and characterization parameters of the molecules in chapters 2-4.

Submitted in fulfillment of the requirements for the degree of Doctor of Philosophy: Biotechnology, Durban University of Technology, Durban, South Africa, 2017. / Fossil carbon dioxide emissions can be biologically fixed which could lead to the development of technologies that are both economically and environmentally friendly. Carbon dioxide, which is the basis for the formation of complex sugars by green plants and microalgae through photosynthesis, has been shown to significantly increase the growth rates of certain microalgal species. Microalgae possess a greater capacity to fix CO2 compared to terrestrial plants. Selection of appropriate microalgal strains is based on the CO2 fixation and tolerance capability, both of which are a function of biomass productivity. Microalgal biomass could thus represent a natural sink for carbon. Furthermore, such systems could minimise capital and operating costs, complexity, and energy required to transport CO2 to other places. Prior to the development of an effective CO2 mitigation process, an essential step should be to identify the most CO2-tolerant indigenous strains. The first phase of this study therefore focused on the isolation, identification and screening of carboxyphilic microalgal strains (indigenous to the KwaZulu-Natal province in South Africa). In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO2 concentrations of 0.03 - 15% and NaHCO3 of 0.05 - 2 g/1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (µmax) and the biomass carrying capacity (Bmax). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The Bmax of I-3 significantly increased from 0.214 to 0.828 g/l when the CO2 concentration was increased from 0.03 to 15% (r = 0.955, p = 0.012). Additionally, the Bmax of I-3 increased with increasing NaHCO3 concentrations (r = 0.885, p = 0.046) and was recorded at 0.153 g/l (at 0.05 g/l) and 0.774 g/l (at 2 g/l). Relative electron transport rate (rETR) and maximum quantum yield (Fv/Fm) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in Fv/Fm with increasing carbon was similar for strains I-3 and the reference strain (I-0). Based on partial 28S ribosomal DNA gene sequencing, strain I-3 was found to be homologous to the ribosomal genes of Chlorella sp. The influence of abiotic parameters (light intensity and light:dark cycles) and varying nutrient concentrations on the growth of the highly CO2 tolerant Chlorella sp. was thereafter investigated. It was found that an increase in light intensity from 40 to 175 umol m2 s-1 resulted in an enhancement of Bmax from 0.594 to 1.762 g/l, respectively (r = 0.9921, p = 0.0079). Furthermore, the highest Bmax of 2.514 g/l was detected at a light:dark cycle of 16:8. Media components were optimised using fractional factorial experiments which eventually culminated in a central composite optimisation experiment. An eight-factor resolution IV fractional factorial had a biomass production of 2.99 g/l. The largest positive responses (favourable effects on biomass production) were observed for individual factors X2 (NaNO3), X3 (NaH2PO4) and X6 (Fe-EDTA). Thereafter, a three-factor (NaNO3, NaH2PO4 and Fe-EDTA) central composite experimental design predicted a maximum biomass production of 3.051 g/l, which was 134.65% higher when compared to cultivation using the original ASW medium (1.290 g/l). A pilot scale flat panel photobioreactor was designed and constructed to demonstrate the process viability of utilising a synthetic flue gas mixture for the growth of microalgae. The novelty of this aspect of the study lies in the fact that a very high CO2 concentration (30%) formed part of the synthetic flue gas mixture. Overall, results demonstrated that the Chlorella sp. was able to grow well in a closed flat panel reactor under conditions of flue gas aeration. Biomass yield, however, was greatly dependent on culture conditions and the mode of flue gas supply. In comparison to the other batch runs, run B yielded the highest biomass value (3.415 g/l) and CO2 uptake rate (0.7971 g/day). During this run, not only was the Chlorella strain grown under optimised nutrient and environmental conditions, but the culture was also intermittently exposed to the flue gas mixture. Results from this study demonstrate that flue gas from industrial sources could be directly introduced to the indigenous Chlorella strain to potentially produce algal biomass while efficiently capturing and utilising CO2 from the flue gas. / D

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering September, 2017 / South Africa emits large amounts of carbon dioxide (CO2) due to its reliance on coal. The emission of CO2 needs to be reduced for clean sustainable energy generation. Research efforts have therefore been devoted to reducing CO2 emissions by developing cost-effective methods for capturing and storing it. Amine-based absorption using monoethanolamine solvent is the most mature technique for CO2 capture despite its huge energy consumption, corrosiveness and difficulty in solvent regeneration. However, CO2 removal by solid adsorbents is a promising alternative because it consumes less energy, and can be operated at moderate temperature and pressure. Metal organic frameworks have received attention as a CO2 adsorbent because they have large surface areas, open metal sites, high porosity and they require less energy for regeneration. This research was aimed at optimizing and scaling-up SOD-ZMOF through structural modification for enhanced CO2 adsorption by impregnating it with chitosan. Scaled-up SOD-ZMOF samples were prepared as described elsewhere and impregnated with Chitosan. Physiochemical properties obtained using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Nitrogen physisorption showed that SOD-ZMOF and SOD-ZMOF-chitosan were successfully synthesized. Qualitatively, the surface area of the SOD-ZMOF synthesized using the scaled up protocol is lower than the one prepared using the non-scaled-up protocol XRD pattern of SOD-ZMOF showed that it was crystalline and was in agreement with literature. The XRD peaks of the SOD-ZMOF decreased after chitosan impregnation showing that chitosan was impregnated on SOD-ZMOF. The FTIR spectrum of SOD-ZMOF showed functional groups present in organic linker used to synthesize SOD-ZMOF, and that of the SOD-ZMOF-chitosan revealed the same functional groups but with disappearance of carboxylic acid functional group. N2 physisorption showed a decrease in BET surface area and pore volume after chitosan impregnation on SOD-ZMOF as well. Performance evaluation of the material was carried out with a demonstration adsorption set-up using a 15%/85% CO2/N2 mixture and as a thermal gravimetric analysis (TGA) using 100% CO2. For both the packed-bed column and the TGA experiments, evaluation was conducted on SOD-ZMOF and SOD-ZMOF with chitosan for comparison. About 50 mg of the adsorbent was used at 25 oC, 1 bar and 25 ml/min for the packed-bed column. For the adsorption with the TGA, 11 mg of adsorbent was used at 25 ℃, 1 bar and 60 ml/min. SOD-ZMOF showed improved adsorption capacity after chitosan impregnation. CO2 adsorption capacity of SOD-ZMOF increased by 16% and 39% using packed-bed column and TGA, respectively, after chitosan impregnation. The increase in adsorption capacity was attributed to the impregnated chitosan that has amine groups that display a high affinity for CO2. A traditional approach was used to investigate the effect of adsorption temperature and inlet gas flowrate on the CO2 adsorption capacity of SOD-ZMOF-chitosan. This was done using both the parked bed column and the TGA. Temperature range of 25-80 ℃ and inlet gas flowrate range of 25-90 ml/min were investigated. Adsorption capacity increased with a decrease in temperature and inlet gas flowrate. For the packed-bed column, maximum of 781 mg CO2/ g adsorbent was obtained at 25℃, 1 bar, 25 ml/min and for the TGA a maximum CO2 adsorption capacity of 23 mg/ g adsorbent at 25 ℃, 1 bar, and 60 ml/min was obtained. / MT2018

城市化是影響全球碳循環的最重要的由人類活動主導的影響因素之一。本質上，城市碳儲存和碳釋放，無論以人工的（如能源消耗、建築物、廢物等）或自然組成部份（如城市綠色植被，城市土壤等），都與城市緊密相關。在城市碳循環中，無論人工或自然組成部份都是同等重要，因為在研究中必須同時考慮兩者的貢獻。然而，已有的研究過於片面，且大多數集中于城市能源利用和碳排放方面。該研究試圖將城市系統作為一個整體，定量地探討城市人工及自然組成部份對二氧化碳排放量的貢獻。 / 首先，我們提出一個基於過程的“城市土地的定義，以表述城市土地動態變化的本質，并運用閾值方法成功提取所定義的“城市土地。我們運用多源的遙感數據，包括夜晚燈光影像，LandSat影像及Modis影像，分析城市化過程及相應的土地利用/覆蓋變化。總體而言，在過去25年間，中國城市用地擴張了3.8倍，農田和林地是城市土地擴張的主要來源。 / 其次，以經過校準的夜晚燈光數據作為指示變量，我們開發了一個自上而下的分解模型來估算城市尺度下化石燃料消耗導致的二氧化碳排放。在中國快速城市化的背景下，城市二氧化碳排放量占全國總排放量的比例大幅增加。與農村地區相比，由於較高的收入水平，生活方式的改變及更便利地獲得電力能源，中國城市的人均排放量遠高於全國平均量。這與發達國家的情景截然相反。另外，由於當地經濟規模和結構的影響，東部地區的人均碳排放量低於西部地區。結果還表明，快速增長的經濟和城市化是二氧化碳排放量增加的主要驅動力，且能源效率在2000年之後反而呈現增長趋势，也是促進二氧化碳排放量增加的主要原因。如果國家宣佈并嚴格執行更嚴格的可持續發展目標，則經濟結構及能源結構調整將在減碳方面發揮作用。 / 第三，本研究還根據儲存-變化方法，估算了城市系統的自然組成部份，也就是城市植被和土壤的碳儲存和釋放。結果表明，儲存於城市植被和土壤中碳量與城市化石燃料排放的碳量相當，且城市土壤是主要的碳庫，儲存了約93%的碳。隨著城市不斷擴張，由於大量自然植被被破壞，城市植被變成碳源并向大氣釋放碳；而城市土壤則變成碳庫，吸收了大氣中部份的二氧化碳。鑒於中國未來持續的城市化過程，該研究結果為城市管理者提供了科學依據，以通過提高城市植被和土壤的碳儲量，吸收部份化石燃料燃燒排放的二氧化碳。 / 最後，我們還運用格蘭傑檢驗分析小尺度氣候變量對二氧化碳增加的響應。結果表明，在中國城市化較低地區，氣溫與二氧化碳變化存在雙向格蘭傑因果關係；而在快速城市化地區，如東部沿海城市，僅存在氣溫變化導致二氧化碳排放量增加的單向格蘭傑因果關係。該研究首次在城市尺度解釋了氣候對二氧化碳增量的響應關係。總體而言，本論文綜合地探索了中國快速城市化背景下，城市人工及自然組成部份對二氧化碳排放量的共同貢獻。這些研究結果為當地政府建設低碳城市提供了科學依據和決策支持。 / Urbanization is undoubtedly one of the most significant anthropogenic forces affecting global carbon cycle. Carbon storage and release through anthropogenic (e.g. energy consumption, building, waste) and natural components (e.g. urban vegetation and soil) are intrinsically coupled in urban areas. Both anthropogenic and natural components are equally important for understanding the carbon cycle in urban areas and have to be considered simultaneously. Present studies however mostly one-sided and primarily focus on anthropogenic emissions. Given the substantial scientific gaps, this study aims to build better knowledge on the contributions of urban areas to the increasing atmosphere CO₂ emissions at an urban scale, considering both anthropogenic and natural components simultaneously. / First, a process-based definition of urban areas is proposed to capture the inherent dynamics of urban areas, and a threshold technique is developed to map the defined urban areas in this study. Multi-sensor remotely sensed data are used to analyze the dynamic urbanization and related land use/cover conversions. Overall, urban areas have increased by 3.8 times over the studied period of 1985-2010. Croplands and forests are the major sources of the growing urban areas. / Second, taking calibrated nighttime light imagery as a proxy variable, we develop a top-down model to estimate fossil fuel CO₂ emissions on the urban scale. Driven by the rapid urbanization in China, the contributions of urban areas to the CO₂ emissions have increased substantially. In contrast to the developed counties, per capita CO₂ emissions in urban China are higher than the national average, due to higher income, change in lifestyle and easy access to electricity, whereas per capita CO₂ emissions in eastern China is lower than that in western China, due to the diverse scale and structure of local economy. Our analysis also reveals that the booming economy and urbanization are major drivers of the increasing fossil fuel CO₂ emissions, while the decoupling effect of energy efficiency reverses in the post-2000 period caused by the booming economy. It is foreseeable that economic reconstruction and energy structure would play a significant impact on carbon reduction if stricter environmental targets are released. / Third, carbon storage and change in natural components of urban areas, in particular, urban vegetation and soils, are also estimated in this study. A stock-change method is applied in this study. This study identifies that the amount of carbon storage in urban areas is comparable to that emitted from fossil fuel burning, and urban soils are the major carbon pools in urban areas. Along with urban expansions, urban vegetation becomes sources of carbon due to loss of biomass, whereas urban soils act as sinks of carbon because increasing urban areas enhance the carbon storage in them. Given the foreseeable urbanization in China, our study has implications for urban managers to enhance carbon storage through urban vegetation and soils, hence offsetting CO₂ emissions from fossil fuel burning. / Finally, a local temperature response to the increasing CO₂ in urban areas is analyzed by local Granger causality test. Bidirectional Granger causality presents between surface air temperature and carbon variables in less urbanized regions of China. In the rapid urbanization areas such as eastern coastal regions, only presents the Granger causality from surface air temperature to the fossil fuel CO₂ emissions. This is the first attempt to offer insights of local temperature variables response to the increasing CO₂ across urban China. Our integrated results are novel in exploring the contributions of expanding urban areas to CO₂ emissions across China, including anthropogenic and natural components of urban areas simultaneously. We believe that our findings have clear significance for local governments who strive for constructing low-carbon cities. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Meng Lina. / Thesis (Ph.D.) Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 203-218). / Abstracts also in Chinese.

Feng, Xiaofei. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 157-168). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

High atmospheric concentrations of CO2 contribute to adverse effects that impact human health and the climate. The need to reduce CO2 is evident, and climate stabilization will require a combination of mitigation, utilization, and even negative emission technologies. Thus, one key approach will be to transform abundant CO2 into a useful feedstock for processes that not only produce value-added products but also match the scale necessary to impact anthropogenic emissions. The tandem CO2 reduction and light alkane transformation reactions over specialized bifunctional catalysts have the potential to produce olefins or synthesis gas by efficiently utilizing the C2-C4 components in shale gas while reducing a greenhouse gas. The reactions of CO2 with light alkanes may occur through two distinct pathways, oxidative dehydrogenation (CO2 + CnH2n+2 → CnH2n + CO + H2O, CO2-ODH) and dry reforming (nCO2 + CnH2n+2 → 2nCO + (n+1)H2, DR). The two reactions can occur simultaneously at temperatures ≥823 K with considerable conversions. Until recently, there has been little understanding regarding the identification of bimetallic catalytic systems that either selectively cleave the C-H bonds to produce olefins or effectively break all the C-C and C-H bonds to produce dry reforming products. In this work, we discuss a combined approach of flow reactor experiments, in situ characterization, and density functional theory (DFT) calculations to help create a design platform for catalysts that are inherently active and selective for the reactions of CO2 and light alkanes. Particularly, it was of interest to use propane as CO2 reduction feedstock due to its increasing abundance and highly marketable respective olefin. Through the combined approach, non-precious Fe3Ni1 and precious Ni3Pt1 supported on CeO2 were identified as promising catalysts for the CO2-ODH and DR of propane, respectively. In situ X-ray absorption spectroscopy measurements revealed the oxidation states of metals under reaction conditions and DFT calculations were utilized to identify the most favorable reaction pathways over the two types of catalysts. While both the CO2-ODH and DR reactions of alkanes produce valuable molecules, the separation of gas phase products is challenging. Therefore, it was highly desirable to develop a tandem reaction scheme in which the reaction of CO2 and alkanes can produce liquid products. Another potential chemistry with increased similarity to the operating conditions of CO2-ODH, is the tandem reactions of CO2-assisted oxidative dehydrogenation and aromatization of light alkanes (CO2-ODA). In this process, alkanes are transformed directly into aromatics without the need for expensive naphtha while increasing the consumption of CO2 per mol of value-added product and facilitating downstream separation because of the production of liquid aromatics. One critical change upon the introduction of CO2 to the dehydrogenation/aromatization pathway is the formation of water. The presence of water under reaction conditions has been shown to be problematic for zeolites as it causes changes in the framework. Phosphorous modification at an optimal loading improved the hydrothermal stability of Ga/ZSM-5, reduced coke formation on the catalyst surface, and allowed for the formation of more liquid aromatics through the CO2-ODAE reaction pathway compared to the direct dehydrogenation and aromatization reaction. With the aid of DFT calculations, the mechanisms for the production of aromatics from ethane were identified, providing insight on the effect of Ga modification on ethylene formation over ZSM-5 as well as the role of CO2 on the aromatization of ethylene. Future efforts should be geared toward enhancing aromatics yield through the design of hydrothermal stable zeolite-based materials with bimetallic active centers that are capable of activating CO2.

With the atmospheric concentration of carbon dioxide steadily increasing and little sign of a reduction in fossil fuel demand worldwide, there is a well-established need for an alternative strategy for dealing with carbon emissions from energy production. One possible solution is the accelerated weathering of ultramafic rocks. Accelerated weathering is an environmentally benign route to a thermodynamically and kinetically stable form of carbon. The chemistry is based on naturally occurring reactions and the raw materials are abundant across the earth's surface. However, the reactions are relatively slow, and achieving reaction rates sufficient to match the carbon dioxide production rate at an energy conversion facility is challenging. This work addresses a number of the challenges facing the integration of accelerated weathering with energy conversion, and presents one view of how the integration could be achieved. This work begins by developing a suite of tools necessary for investigating the dissolution and precipitation of minerals. Chapter 2 starts with a description of the minerals that will be evaluated, and then goes on to develop the techniques that will be used. The first is a differential bed reactor, which is used for measuring the dissolution rates of minerals under tightly controlled conditions. Next a bubble column reactor is developed for the investigating the adsorption of carbon dioxide and the precipitation of mineral carbonates in a single vessel. These techniques, together with a batch reactor for studying direct carbonation reactions, constitute a comprehensive set of tools for the investigation of accelerated mineral weathering. With the necessary techniques developed and proven, Chapter 3 addresses the first challenge faced by accelerated mineral weathering; the dissolution rate of magnesium from a silicate mineral. While the dissolution of this mineral is thermodynamically favorable, the kinetics are prohibitively slow. It is thought that this is because silica from the mineral tends to accumulate on the particle surface creating a passivation layer, which limits the reaction rate of the mineral. In this work, the effects of a combination of chemical chelating agents, catechol and oxalate, are evaluated for their ability to circumvent this passivation layer. The results indicate that catechol and oxalate modify the passivation layer as it forms, both accelerating the dissolution rate of the mineral and maintaining pore volume, leading to greater dissolution rates. This pore modification process is proposed as the primary mechanism by which catechol affects the passivation layer. The combination of catechol and oxalate under acidic conditions is also shown be effective when the ambient solution approaches the saturation point of silica. Finally, the chelating does not impede the precipitation of carbonate products, a critical hurdle for a carbon storage process. The chelating agent work is extended in Chapter 4, with a sensitivity study that evaluates the response of the dissolution rate to changes in both pH and the concentration of the chelating agents. Oxalate and pH are found to exhibit a strong influence on the mineral dissolution rate, while the effect of catechol is more apparent after significant dissolution has taken place. These observations are in agreement with the model of passivation layer modification proposed. In addition, some alternatives to the chelating agent catechol are evaluated. It is found that when used in combination with oxalate, these alternatives appeared equivalent to catechol, but alone they had only a minor effect. Catechol was also noted to have a significant effect on the dissolution rate of iron from the silicate mineral, and a mechanism for this effect was proposed. The direct adsorption of carbon dioxide and precipitation of solid carbonates in a single reaction step presents another challenge for accelerated mineral carbonation. In general, the magnesium carbonates formed at ambient pressure and moderate temperatures tend to be hydrated, and at times contain unused hydroxides, leading to inefficiencies in both transport and storage. It is shown in Chapter 5 that by seeding reaction vessels with the anhydrous form of magnesium carbonate, it is possible to grow this desired phase with minimal formation of the metastable hydrated phases. The formation of this phase is primarily limited by the precipitation rate, but in some situations, carbon dioxide hydration kinetics and magnesium hydroxide precipitation kinetics also play a role. In Chapter 6, these developments in both magnesium silicate dissolution and carbonate precipitation are combined into a proposed technology for the direct capture and storage of carbon dioxide. This application of accelerated mineral weathering is shown to significantly reduce the carbon emissions of an energy conversion technology through life cycle assessment. This novel approach to the mitigation of carbon emissions presents a compelling argument for the continued development of accelerated mineral weathering as a combined carbon capture and storage technology.

Rising concentration of CO2 in the atmosphere is attributed to increasing consumption of fossil fuels. One of the most effective mechanisms to store CO2 captured from power plants is via geological injection of CO2 into formations that contain calcium and magnesium silicate and alumino-silicate minerals and rocks. The mechanism that ensures permanent storage of CO2 within rocks is mineral carbonation. When CO2 is injected into mineral or rock formations rich in calcium or magnesium silicates, they react with CO2 to form calcium or magnesium carbonates, which is also known as carbon mineralization. Calcium and magnesium carbonates are stable and insoluble in water. However, the kinetics of in-situ mineral carbonation involve CO2 hydration, mineral dissolution and formation of carbonates, and the relative rates of these phenomena when coupled, are not very well understood. In this study, the coupled interactions of CO2-reaction fluid-minerals were investigated to determine the optimal conditions for carbon mineralization, and to identify the chemical and morphological changes in the minerals as they react to form carbonates. Carbon mineralization in various minerals and rocks such as olivine ((Mg,Fe)2SiO4)), labradorite ((Ca, Na)(Al, Si)4O8), anorthosite (mixture of anorthite (CaAl2Si2O8), and basalt (rock comprising various minerals) were studied at high temperatures (Tmax = 185 oC) and high partial pressures of CO2 (PCO2, max = 164 atm) which are relevant for in-situ conditions. These minerals and rocks differ considerably in their chemical compositions and reactivity with CO2. A systematic comparison of the effects of reaction time, temperature, partial pressure of CO2, and fluid composition on the conversion of these magnesium and calcium bearing minerals and rocks showed that olivine was the most reactive mineral followed by labradorite, anorthosite, and basalt, respectively. Previous studies at Albany Research Center (Gerdemann et al., 2007; O'Connor et al., 2004) reported that a solution of 1.0 M NaCl + 0.64 M NaHCO3 was effective in achieving high extents of carbonation in olivine, heat-treated serpentine, and wollastonite. However, the independent effects of NaCl and NaHCO3 and their role in mineral carbonation were not sufficiently explained. In this study, the role of varying concentrations of NaCl and NaHCO3 on carbon mineralization of various minerals was elucidated. NaHCO3 buffered the pH and served as a carbon carrier, resulting in higher carbonate conversions. Except in the case of olivine, NaCl had a negligible effect on enhancing mineral carbonation. Unlike NaHCO3, NaCl does not buffer the pH or serve as a carbon carrier, but Cl- may serve as a weak chelating agent can complex with Mg or Ca in the mineral matrix to enhance dissolution. The competing effects of ionic strength and pH swings as the mineral dissolves and carbonation further complicate the role of NaCl on mineral carbonation. Based on the experimental methodologies developed to study carbon mineralization in minerals and rocks at high temperatures and pressures, alternative applications such as the remediation of hazardous alkaline wastes such as asbestos containing materials were identified. Asbestos is composed of chrysotile, a fibrous hydrated magnesium silicate mineral and a form of serpentine known to cause respiratory illnesses. By treating asbestos containing materials with CO2 in the presence of 0.1 M Na-oxalate, dissolution of chrysotile and precipitation of newer phases such as glushinkite (Mg(C2O4)* 2H2O) and magnesite (MgCO3) occurred, which reduced the chrysotile content in asbestos. Based on the methodologies for studying mineral dissolution and carbonation kinetics, and coupled mineral dissolution and carbonation behavior, a scheme for connecting laboratory scale experiments with simulations to estimate the uncertainties associated with carbon mineralization was developed. The effects of temperature, different dissolution rates, and varying levels of surface area changes due to passivation or reactive cracking on the rates of carbon mineralization were simulated using PhreeqC, a computer program developed for geochemical speciation calculations (Parkhurst & Appelo, 1999). Various studies proposed that microfractures and cracks may occur in geologic formations due to the extensive growth of carbonate crystals (Kelemen & Hirth, 2012; Kelemen & Matter, 2008; Matter & Kelemen, 2009; Rudge et al., 2010). Other studies have suggested that the formation of carbonates may plug the pore spaces and limit further reactivity (Hövelmann et al., 2012; King et al., 2010; Xu et al., 2004). The effects of changes in surface area due to the formation of microfractures or passivation due to carbonate growth on the rates of carbon mineralization were also simulated. Overall the results of these studies demonstrate the effect of various parameters on carbon mineralization and how these parameters can be connected to predict CO2 storage in mineral formations. The frameworks to connect laboratory scale experiments with simulations to determine carbon mineralization rates and to assess the risks associated with CO2 injection in reactive formations, can be used to direct future research efforts to predict the fate of injected CO2 with greater accuracy for sensor placement and optimization of CO2 monitoring technologies.

As the role of cities in addressing climate change has been increasingly recognized over the past two decades, the idea of a low-carbon city becomes a dominant framework to organize urban governance and envision a sustainable urban future. It also becomes a development discourse in the less developed world to guide the ongoing urbanization process. China’s efforts toward building low-carbon cities have been inspiring at first and then obscured by the halt or total failure of famous mega-projects, leading to a conclusion that Chinese low-carbon cities compose merely a strategy of green branding for promoting local economy. This conclusion, however, largely neglects the profound implications of the decarbonization discourse for the dynamics between the central and local governments, which together determine the rules and resources for development practices. The conclusion also hinders the progressive potentials of the decarbonization discourse in terms of introducing new values and norms to urban governance. This dissertation approaches “low-carbon cities” as a part of the decarbonization discourse and employs a discourse-institutional analysis to investigate the relationships between discourse, institutional arrangement, and socio-political resources for development activities. Through an examination of the Shenzhen International Low-Carbon City (SILCC), the dissertation answers three questions: (1) How does the framework of a low-carbon city affect a specific urban development project? (2) What is the role of the state (local/national) in promoting low-carbon development? and (3) What is the influence of the decarbonization discourse on institutions and norms of urban governance? Evidence was gathered during 2014-2017 from three fieldtrips, 39 interviews and the review of government documents and other archives. The dissertation highlights how different levels of government became entangled in developing a local area and how, in doing so, the proponents continuously searched for ways of ‘positioning’ their initiative in discourses that would attract higher level government support, maintain local coalitions, and entice international attention and investment. In this regard, low-carbon cities are a state discursive project. Rather than an established material goal, a low-carbon city is an evolving process in which the decarbonization discourse introduces a new set of values, metrics and governing logics into development practices and redefines the legitimacy and accountability of urban development. Furthermore, the local state leverages the interpretive flexibility within the decarbonization discourse through strategies including carbon labeling, weak carbonization, and carbon exceptionalism. Consequently, the state takes a strategic position to reconfigure the state-society as well as the environment-economy relationships.

Atmospheric CO2 concentrations are at their highest level on record. Scientific evidence has demonstrated a direct correlation between the rise of CO2 levels and an increase of the global median temperature (~1°C higher than compared to the pre-industrial revolution times) due to the greenhouse gas effect. The change in climate due to this rapid increase of CO2 levels is already negatively affecting our ecosystem and lives, with unpredictable consequences in the future. The main source of anthropogenic CO2 emissions is attributed to the combustion of fossil fuels for energy production and transportation. Global indicators signal that carbon-intensive fuels will continue to be utilized as a main energy source despite the rising implementation of renewable energy sources. In order to curb CO2 emissions, several carbon dioxide capture, utilization and sequestration (CCUS) technologies have been suggested. The current state-of-the-art CO2 capture technology utilizes toxic and corrosive aqueous amine solutions that capture CO2 at room temperature but require heating above the water boiling point temperatures to separate CO2 from the amine solution; the latter of which is to be recycled. Once the CO2 is purified, it is necessary to transport it to its sequestration site or an upgrading processing plant. These are complicated schemes that involve many energy-intensive and costly processes. To address the shortcomings of these technologies, we propose a Dual Function Material (DFM) that both captures CO2 and catalytically converts it to methane in-situ. The DFM consists of a catalytic metal intimately in contact with an alkaline metal oxide supported on a high surface area carrier. The process operates within the flue gas at 320°C for both CO2 capture and methane generation upon the addition of renewable H2. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2 and steam-containing flue gas. Ruthenium, rhodium, and nickel are known CO2 methanation catalysts, provided they are in the reduced state. All three were compared for performance under DFM flue gas conditions. Ni is a preferred methanation catalyst based on price and activity; however, its inability to be reduced to its active state after experiencing O2-containing flue gas during the capture step was an outcome determined in this thesis. The performance of a variety of alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) and carriers (Al2O3, CeO2, CeO2/ZrO2 (CZO), Na-Zeolite-X (Na-X-Z), H-Mordenite Zeolite (H-M-Z), SiC, SiO2 and ZrO2-Y) were also studied. Selection of the best materials was based on CO2 capture capacity, net methane production and hydrogenation rates that were evaluated with thermogravimetric analysis and in fixed bed reactor tests. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. Ru remained active towards methanation even after exposure to O2 and steam-containing simulated flue gas. Alkaline adsorbents, in combination with reduced Ru, were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate with slightly lower methanation kinetics. To date, we have demonstrated that -Al2O3 is the most suitable carrier for DFM application relative to other materials studied. The Ni-containing DFM, pre-reduced at 650°C, was highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320oC. This thesis reports that small amounts of precious metal (≤ 1% Pt, Pd or Ru) enhance the reduction (at 320°C) and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. While ruthenium is most effective, Pt and Pd all enhance reduction of oxidized Ni. Another objective of this thesis was to investigate whether a portion of the Ru, at its current loading of 5%, could be replaced with less expensive Ni while maintaining its performance. The findings show that the main advantage of the presence of Ni is a small increase in CO2 adsorption and increase in methane produced, at the expense of a lower methanation rate. Extended cyclic aging studies corroborate the stable performance of 1% Ru, 10% Ni, 6.1% “Na2O”/Al2O3. Characterization methods were used to monitor physical and chemical changes that may have occurred during aging studies. Measurements of the BET surface area, H2 chemisorption, XRD pattern, TEM images and STEM-EDS mapping were utilized to study and compare the structural and chemical changes between fresh and aged Ru doped Ni DFM samples. While similar BET surface areas were observed for the fresh and aged samples, some redispersion of the Ru and Ni sites was confirmed via H2 uptake and the observed decreases in Ru and Ni cluster size in the aged sample in comparison to the fresh. XRD patterns confirm an almost complete disappearance of the NiOx and RuOx species and the appearance of catalytically active Ru0 and Ni0 peaks on the aged sample compared to the fresh one. Further details of these methods, findings and conclusions are described in this thesis.