Wetlands are very valuable ecosystems as they play an integral role in wildlife habitat, water management and greenhouse gas exchange. The exchange of carbon dioxide between prairie wetlands and the atmosphere is poorly understood. The purpose of this study was to identify rates and trends in the growing season carbon dioxide flux from the riparian and open-water zone of a prairie pothole wetland. In addition to providing core open water and riparian zone CO2 flux measurements, relationships between variations in CO2 flux and characteristics of the wetland’s biological, biochemical and hydrometeorological state were assessed. The CO2 effluxes from the pond during the summer of 2006 were approximately four times greater than in 2005, but were much lower in the early fall. Algal chlorophyll-a concentrations were greater in 2005 than 2006 for all three algal assemblages. The mean chlorophyll-a concentrations in 2005 for epiphyton, phytoplankton and metaphyton were 2.75 ± 0.62 g m-2, 87 ± 24 µ L-1, and 318 ± 187 g m-2 respectively. In 2006 mean concentrations for the same assemblages were 0.008 ± 0.001 g m-2, 8 ± 2 µ L-1, and 27 g m-2 respectively. The amount of DOC in the open water in August of 2005 (140 mg DOC L-1) was 70 times greater than in July of 2005 (2 mg DOC L-1). DOC ranged from 30 to 52 mg DOC L-1 in 2006. Although highly productive, the pond proper appeared to be a source of DOC which is concurrent with literature from littoral zone and shallow inland waters. Soil respiration increased upslope from the wetland to the cropped upland in 2005. Net ecosystem exchange was greater in the cattail ring surrounding wetland than the grass and sedge zone beyond the cattails. The riparian vegetation may have been water stressed in late-July (at the climax of the dry period) when net ecosystem exchange decreased. Diurnal net ecosystem exchange in the riparian zone indicates uptake during the day and emissions at night. From this data it appears that the riparian zone may have acted as a CO2 sink in June, July and August and a source in April.

SILVA, Erandir Brasil da. Estudo das propriedades catalíticas da fase ferrita de cálcio (Ca2Fe2O5) nas reações de desidrogenação do etilbenzeno em fase gasosa e degradação do azul de metileno em fase aquosa. 2016. 104 f. Tese (Doutorado em Química)-Universidade Federal do Ceará, Fortaleza, 2016. / Submitted by Aline Mendes (alinemendes.ufc@gmail.com) on 2016-10-11T20:39:22Z No. of bitstreams: 1 2016_tese_ebsilva.pdf: 2452975 bytes, checksum: 2d398ffb4b60622a294ff72b73d40178 (MD5) / Approved for entry into archive by Jairo Viana (jairo@ufc.br) on 2016-10-11T23:27:31Z (GMT) No. of bitstreams: 1 2016_tese_ebsilva.pdf: 2452975 bytes, checksum: 2d398ffb4b60622a294ff72b73d40178 (MD5) / Made available in DSpace on 2016-10-11T23:27:31Z (GMT). No. of bitstreams: 1 2016_tese_ebsilva.pdf: 2452975 bytes, checksum: 2d398ffb4b60622a294ff72b73d40178 (MD5) Previous issue date: 2016 / The calcium ferrite compound was studied in catalytic reactions and their properties were evaluated in the ethylbenzene dehydrogenation reactions in gas phase and photocatalytic degradation of methylene blue in the aqueous phase. Calcium ferrite (Ca2Fe2O5) was synthesized by the polymeric precursor method and evaluated the addition of Li and Co promoters, as the catalytic properties caused by this addition. The samples had crystal phases characterized by X-ray diffraction before and after the reactions in the gas and aqueous phase. important fact was noted crystalline calcium carbonate formation after catalytic reactions in both reaction environments, gaseous and aqueous. Still characterizations were performed as X-ray fluorescence, thermogravimetry, scanning electron microscopy, and nitrogen adsorption isotherms of desorption, and Raman spectroscopy Mössbauer that complement the structural and textural characterization of samples. The application of this material structure and monitoring of this structure allowed to draw parallels with the chemical processes involved in the dehydrogenation reaction of ethylbenzene, besides studying the operation of the CO2 molecule as oxidant in the reaction. In the photocatalytic degradation important phenomena related to the methylene blue dye degradation reaction was observed as a more intense degradation under inert gas flow (N2) than under carbon dioxide flow. It was studied and found to poor stability of the crystalline phase in aqueous media and better stability in a gaseous environment. In the dehydrogenation of ethylbenzene was observed significant deposition of crystalline coke in the absence of carbon dioxide as an oxidizer with relevant properties characterized by thermogravimetry and oxidation programmed temperature analysis that allowed qualify and quantify the type of deposited coke. / O composto ferrita de cálcio foi estudado em reações catalíticas e suas propriedades foram avaliadas nas reações de desidrogenação de etilbenzeno em fase gasosa e degradação fotocatalítica de azul de metileno em fase aquosa. A ferrita de cálcio (Ca2Fe2O5) foi sintetizada pelo método dos precursores poliméricos e avaliou-se a adição de promotores de Li e Co, quanto as propriedades catalíticas causadas por essa adição. As amostras apresentaram fases cristalinas caracterizadas por difração de raio X antes e após as reações em fase gasosa e aquosa. Fato importante observado foi a formação de carbonato de cálcio cristalino após as reações catalíticas em ambos os ambientes de reação, gasoso e aquoso. Ainda foram realizadas caracterizações como fluorescência de raio X, termogravimetria, microscopia eletrônica de varredura, isotermas de adsorção e dessorção de nitrogênio, espectroscopia Raman e Mössbauer que complementaram as caracterizações estruturais e texturais das amostras. A aplicação deste material com estrutura e o acompanhamento dessa estrutura permitiu estabelecer paralelos com os processos químicos envolvidos na reação de desidrogenação de etilbenzeno, além de estudar a atuação da molécula de CO2 como gás oxidante na reação. Na degradação fotocatalítica importantes fenômenos referentes a reação de degradação do corante azul de metileno foram observados, como uma degradação mais intensa sob fluxo de gas inerte (N2) do que sob fluxo de gás carbônico. Foi estudado e verificado a pouca estabilidade da fase cristalina em meio aquoso e uma maior estabilidade em ambiente gasoso. Na desidrogenação de etilbenzeno foi observado expressiva deposição de coque cristalino na ausência de gás carbônico como oxidante, com relevantes propriedades caracterizadas por termogravimetria e oxidação a temperatura programada, análises que permitiram qualificar e quantificar o tipo de coque depositado.

No description available.

No description available.

Fish naturally experience fluctuating levels of O2 and CO2 in their environment. To cope with the deleterious effects of lowered O2 (hypoxia) or elevated CO2 (hypercapnia), fish exhibit an array of cardiorespiratory adjustments aimed at preserving homeostasis. One of the most significant of these responses is reflex hyperventilation. In zebrafish (Danio rerio), hyperventilation during hypoxia or hypercapnia is thought to be initiated by the activation of chemoreceptor cells, termed neuroepithelial cells (NECs) which detect changes in ambient levels of O2 or CO2. The NECs of larval zebrafish are found throughout the integument and recent studies have shown that these NECs likely mediate the ventilatory responses to hypoxia and the cardiac responses to hypercapnia. However, no study has yet examined the ventilatory response of larval zebrafish to hypercapnia and regardless of developmental stage, the signalling pathways involved in CO2 sensing remain unclear. In the mouse, a background potassium channel (TASK-2) was shown to contribute to the sensitivity of chemoreceptor cells to CO2. Zebrafish have two specific TASK-2 channel paralogs encoded by kcnk5a and kcnk5b. The purpose of this thesis was to determine whether TASK-2 channels are expressed in NECs of larval zebrafish and whether they are involved in CO2 sensing. Immunohistochemical approaches were used to visualize TASK-2 protein (encoded by kcnk5a) within NECs of larvae and adult gill. TASK-2 protein was observed on NECs in both larvae and adult gill. Exposure of larvae to hypercapnia caused an increase in cardiac and breathing frequencies; these responses were blunted in fish experiencing either TASK-2 and/or TASK-2b knockdown. The results of these experiments suggest that TASK-2 has a role in activating NECs thus eliciting cardiorespiratory responses, when larvae are exposed to hypercapnia.

Carbon capture and storage technologies are required in order to reduce greenhouse gas emissions, while continuing to utilize existing fossil-fueled power generation stations. Of the many developing post-combustion CO2 capture technologies, calcium looping appears promising due to its high thermal efficiency, technical feasibility at commercial-scale, and low sorbent cost. Calcium looping has now been performed at the larger-scale, but there is still a significant quantity of information about sorbent performance, the fate of trace pollutant emissions (specifically SO2 and HCl), dual fluidized bed operating configurations, and impact of realistic operating conditions that still needs to be determined. Based on an economic analysis of the process, three key parameters serve to have the largest potential economic impact: (1) the sorbent deactivation rate, (2) the Ca/C molar ratio, and (3) the rate of sorbent attrition. Therefore, a series of bench-scale, pilot-scale, and continuous pilot-scale testing were conducted to not only explore these parameters from an improvement standpoint, but accurately determine them under conditions expected at the commercial-scale. The presence of HCl did not have a significant impact on sorbent performance provided that steam is present during calcination, although issues with downstream corrosion could be a factor. High CO2 partial pressures during calcination, coupled with high temperatures and the presence of SO2, resulted in dramatically lower cyclic carbonation conversions and a reduced high CO2 capture efficiency regime. Continuous pilot-scale testing generated realistic, and more detrimental, values for sorbent carrying capacity, Ca/C molar ratio, sorbent make-up rates, and rate of sorbent elutriation, that can now be utilized for techno-economic evaluations and scale-up of the technology.

No description available.

90% of global trade is transported by cargo ships, with fossil fuel being the dominant energy source used. As global trade increases, shipping will be in greater demand resulting in increased emissions of carbon dioxide and other pollutants negatively impacting the environment and human health. Carbon dioxide (CO2), our area of interest, is the number one contributing gas to global warming. We, therefore, examine the role of the International Maritime Organization (IMO) in reducing CO2 emissions from shipping, and determine the progress made so far. Our research reveals that progress in this area is on a slow trajectory. The current IMO regulations focus solely on energy efficiency measures that do not appear to be as successful as envisioned in reducing CO2 emissions. In addition, the concept of decarbonization of the sector, which would lead to zero emissions, is delayed. With this in mind, we provide recommendations regarding future IMO actions.

Controlled and selective electrochemical CO2 reduction to hydrocarbons and oxygenates utilizing energy from renewables such as solar energy is a promising alternative approach to store energy in chemical bonds while simultaneously close the anthropogenic carbon cycle, thus to address the twin problems of fossil fuels depletion and environmental challenges. Copper-based electrocatalysts have been demonstrated promising performance for CO2 reduction. However, Cu usually converts CO2 into a mixture, where more than 16 different species have been identified, and the selective yield of any product is limited by the competing reactions. Other major bottlenecks of Cu electrochemical catalyzed CO2 reduction reaction include the competition of hydrogen evolution reaction (HER), high overpotentials needed towards desired product, and lack of high-value products. In this dissertation, we addressed these three issues via surface modification, sulfurization, and coupling cathodic/anodic reactions, respectively. Specifically, (1) we developed a benzimidazole (BIMH)-modified copper foil catalyst, where the formed Cu(BIM)x complexes on Cu surfaces can enhance the Faradaic efficiency (FE) of C2/C3 products. The overall FE for CO2 reduction reaches 92.1% and the undesired hydrogen evolution reaction (HER) is lowered to 7% at -1.07 VRHE. (2) We demonstrated that Cu2S nanoarrays enable the selective CO2 reduction to formate starting at a very low overpotential (~ 120 mV), with high current density (over -20 mA/cm2 at -0.89 VRHE), and good Faradaic efficiency (>75%) over a broad potential window (-0.7 VRHE to -0.9 VRHE). Further- more, Cu2S catalysts show excellent durability without deactivation following more than 15 cycles (1h per cycle) of operation. The notable reactivity toward CO2 reduction to formate achieved by Cu2S nanoarrays may be ascribed to their ability to facilitate CO2 activation by stabilizing the CO2•− intermediate more effectively than pristine Cu foil. (3) We reported that direct electrochemical conversion of CO2 to 2-bromoethanol, a valuable pharmaceutical intermediate, is enabled by coupling the anodic and cathodic reactions with the presence of potassium bromide electrolyte in a membraneless electrochemical cell. The maximum Faradaic Efficiency of converting CO2 to 2-bromoethanol that we achieved is 40 % at -1.01 VRHE with its partial current density of -19 mA cm-2.

To combat the escalating environmental challenges and alleviate the current energy crisis, CO2 conversion to fuels and chemical feedstocks provides a reliable approach to mitigate the devastating impact of greenhouse emissions on climate change. CO2 conversion/reduction could be carried out by several methods; however, the electrochemical CO2 reduction (CO2R) approach has coupled several advantages. For instance, CO2R occurs in near-ambient reaction conditions and could be driven through the employment of renewable energy resources (wind or solar) to generate electricity. However, this reaction has a large energy barrier which requires a catalyst to facilitate its pathway. In this context, various catalyst designs were developed and investigated during the last decades, such as heterogenous (metal and metal oxide) and homogenous (organic molecules) catalysts. A new class of materials – atomically dispersed metal nitrogen–doped carbon support (M–N–C)– has emerged recently and showed remarkable enhancement for CO2R compared to the state-of-the-art. In particular, Ni–N–C catalysts have demonstrated an improved selectivity toward CO production compared to precious metal catalysts. Researchers have postulated this superior performance to the high atomic utilization (theoretically 100%) of the metal sites under reaction conditions and the enhanced electronic properties. In addition, intermetallic carbides have been included as a promising class of catalysts for CO2R due to their unique physical and chemical characteristics. These catalysts could be synthesized using different precursors; among them, MOFs are currently one of the most promising platforms that generate several catalyst designs. It was demonstrated that MOF’s unique characteristics, such as high surface area and porosity, would be transitioned to the derived catalysts. In this thesis, two MOF architectures (ZIF-8 and MOF-74) were initially selected to be employed as precursors for deriving atomically dispersed Ni–N–C catalysts. Both MOF-derived catalysts were evaluated for CO2R using a customized electrochemical cell (E-cell) with a 3–electrode configuration. The derived Ni–N–C catalysts using ZIF-8 and MOF-74 have achieved enhanced CO selectivity with Faradaic efficiencies (FE) > 90% at less negative applied potentials, –0.68 and –0.76 V vs RHE, respectively. Further, various synthetic conditions were explored in these studies, such as the role of the Ni content and the pyrolysis temperature on the resulted catalyst structure, and the electrocatalytic performance during CO2 electrolysis. Subsequently, one of the MOF topologies – ZIF-8 – was further utilized to develop other designs of electrocatalysts by introducing different synthetic conditions. This has resulted in generating various moieties that are able to produce CO during CO2R. For example, one derived catalyst design consists of homogenously distributed atomically dispersed dual Ni–Zn–NX/C sites. Whereas the other design demonstrated a heterogenous structure of Ni3ZnC-based particles anchored on atomically dispersed dual Ni–Zn–NX/C sites. Both electrocatalyst designs were integrated into a gas diffusion electrode (GDE) and evaluated for CO2R using an MEA-based electrolyzer. Our findings revealed that the co-existence of Ni3ZnC particles and dual Ni–Zn–NX/C active sites in a heterogenous structure has boosted the electrocatalytic activity towards CO production, achieving near unity CO FE at 448 mA/cm2 at an overall cell voltage of 3.1 V. Aside from the electrocatalytic performance, the nature of active sites in the developed catalyst designs has been studied using in-situ and ex-situ X-ray absorption spectroscopy. Other analytical techniques such as transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) have also been used to identify the catalysts’ composition and morphology. / Thesis / Doctor of Philosophy (PhD) / This PhD thesis aims to develop and implement a sustainable technology that tackles increased CO2 emissions in the atmosphere and mitigates the greenhouse effect on climate change. The approach of this thesis focuses on developing efficient catalyst designs for CO2 electroreduction (CO2R) to CO as a beneficial chemical feedstock, and then pursues the practical implementation of these catalysts in an industrially relative reactor design in the form of a membrane electrode assembly (MEA)-type electrolyzer. This study selected atomically dispersed metal-doped nitrogen-carbon (M–N–C) and intermetallic carbide electrocatalysts as promising materials for CO2R. Among different precursors, metal-organic frameworks (MOFs) have been employed to synthesize the desired electrocatalysts due to their unique geometric structure and high surface area. On a fundamental level, our findings demonstrated that all MOF-derived catalysts have exhibited high selectivity towards CO during CO2 R. However, the conversion rates were governed by the nature of the active sites and the implemented electrochemical systems.