The purpose of this study was to demonstrate the variability of oxygen and carbon dioxide rate of change methods for measuring primary productivity and respiration in an aquatic environment.

Peatlands are multiservice ecosystems: they are the largest terrestrial store of carbon in the UK, unique habitats which provide a home for internationally important species and managed for forestry, farming and game management and shooting. This makes understanding the impact of management practices on their ecology important if they are to be sustainably managed for multi-benefits. Fire has long been used to manage peatlands in the UK to improve grazing and habitat provision for livestock and game. The effect of fire on carbon cycling in blanket bogs is of increasing concern as greenhouse gas emissions from land use is now an important management as well as political issue. Gaps however, still exist in our understanding of the controls on greenhouse emissions from blanket bogs and the impact fire may have on them both directly and indirectly by modifying vegetation composition and environmental conditions. The main objective of this research was to assess the effect of fire on greenhouse gas emissions by measuring methane and ecosystem respiration after burning at blanket bog sites across Scotland for a period of up to 3 years and relating changes in fluxes with changes in vegetation composition and abiotic conditions. In addition, the response of the Sphagnum layer to burning was assessed by looking at the recovery of Sphagnum capillifolium in the field and in a novel laboratory experiment. The indirect effects of fire on methane emissions were further investigated by a laboratory experiment devised to test if high temperatures would be fatal to methanotrophic bacteria in the Sphagnum layer, reducing methanotrophy, and thus a mechanism for fire to increase methane emissions in the short term. The results showed that methane emissions and ecosystem respiration were not significantly different in burnt plots when compared to adjacent unburnt plots at each of the three sites studies. Methane emissions were only weakly correlated to the position of the water table and neither methane fluxes or ecosystem respiration correlated with measures of vegetation composition and above ground biomass. Methanotrophy in Sphagnum was found to be difficult to detect, with a high temperature treatment having no significant effect on rates of methane oxidation. S. capillifolium was found to respond to fire by growing new auxiliary stems if the capitulum was consumed or irreversible damaged physiologically by temperatures experienced at the moss surface, with surface temperatures around 400oC with a temperature residency time of 30 seconds on artificially dried samples the most damaging, but not lethal, treatment. These results suggest that low severity fires which only consume the canopy vegetation, not penetrating the peat and leaving the moss layer mostly intact, do not have significant effects on methane emissions and ecosystem respiration in the short and medium term. In addition, it suggests that S.capillifolium can, under certain circumstances, survive a fire with the characteristics of those studied here. These findings reiterate that best practice burning guidelines must continue to ensure that burning is only carried out on blanket bog when conditions are conducive to fires with the characteristics studied here, which had little effect on important components of the carbon cycle and are survivable by at least one of the most common species of Sphagnum.

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Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Zbigniew M. Drozdowicz. / Ph.D.

The increasing CO2 level in the atmosphere, mostly attributed to anthropogenic activities, is overwhelmingly accepted to be the main greenhouse gas responsible for climate change. Combustion of fossil fuel is claimed to be the major cause of excess CO2 emission into the atmosphere, but human society will still rely heavily on fossil fuel for energy and feedstock supplements. In order to mitigate the environment-energy crisis and achieve a sustainable developing mode, Carbon Capture, Utilization and Storage (CCUS) is an effective method and attracts considerable interests. Rather than conventional aqueous amine-based liquid absorbent, e.g. the toxic, corrosive and energy intensive monoethanolamine (MEA), solid adsorbents are preferable for CO2 capture. CO2 utilization via CO2 conversion to fuel or other value-added products is favored over CO2 storage. Also it is preferred that no transportation of captured CO2 is required. Capturing and converting CO2 to fuel, such as synthetic natural gas or CH4 is particularly useful if it is produced at the site of CO2 generation. The converted CO2 can then be recycled to the inlet of the power plant or integrated into existed fuel infrastructure eliminating any transportation. This thesis presents a study of the development, performance and characterizations of a newly discovered (second generation) dual functional material (DFM) for CO2 capture and catalytic conversion to methane in two separated steps. This material consists of Ru as the methanation catalyst and “Na2O” obtained from Na2CO3 hydrogenation as the CO2 adsorbent, both of which are deposited on the high surface area γ-Al2O3 support. The Ru, “Na2O” DFM captures CO2 from O2- and steam-containing flue gas at temperature from 250 °C to 350 °C in step 1 and converts it to synthetic natural gas (CH4) at the same temperature with addition of H2 produced from excess renewable energy (solar and/or wind energy) in step 2. The heat generated from methanation drives adsorbed CO2 to Ru by spillover from the adsorption sites and diffuse to Ru for methanation. This approach utilizes the heat in the flue gas for both adsorption and methanation therefore eliminating the need of external energy input. The second generation DFM was developed with a screening process of solid adsorbent candidates. Initial adsorption studies were conducted with powdered samples for CO2 capture capacity, methanation capability, and resistance to an O2-containing simulated flue gas feed. The new composition of DFM was then prepared with tablets for future industrial applications and scaled up to 10 grams suitable for testing in a fixed bed reactor. Parametric and 50-cycle aging studies were conducted in a newly constructed scaled-up fixed bed reactor using 10 grams of DFM tablets in the simulated flue gas atmosphere for CO2 capture. With the presence of O2 in CO2 feed gas for step 1, the Ru catalyst is oxidized but must be rapidly reduced in step 2 to the active metallic state. Parametric studies identified 15% H2 is required for stable operation with no apparent deactivation. The parametric plus 50-cycle aging studies demonstrated excellent stability of the second generation DFM. A kinetic study was also conducted for the methanation step using powdered DFM but prepared via the tablet method to minimize any mass transfer and diffusion influence on the methanation rate. An empirical rate law was developed with kinetic parameters calculated. The methanation rate of captured CO2 is highly dependent on H2 partial pressure (approaching a reaction order of 1) while essentially zero reaction order of CO2 coverage was determined. The kinetic study highlights the importance of H2 partial pressure on the methanation process. Characterizations were conducted on the ground fresh and aged (underwent parametric and aging studies) DFM tablets. BET surface area, H2 chemisorption, X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM) images and scanning transmission electron microscope- energy dispersive spectroscopy (STEM-EDS) mapping were utilized to study the material changes between fresh and aged samples. From fresh to aged, similar BET surface area was measured, improved both Ru and “Na2O” dispersion, and decreased Ru cluster size was observed while no definitive proof of the nature of the sodium species was obtained via XRD. The second generation DFM containing 5% Ru, 6.1% “Na2O” / Al2O3 was shown to possess the capability of capturing CO2 from O2-containing simulated flue gas and subsequent methanation with addition of H2 produced from excess renewable energy (or from chemical processes) with twice the CO2 and CH4 capacity relative to the first generation DFM. Activity, selectivity and stability has been demonstrated for the second generation DFM. We envision swing reactors to be utilized commercially where the flue gas feed for step 1 and H2 for step 2 are throttled alternatively between each reactor for continuous operation.

Hydration of neutral and ionic species at interfaces plays an important role in a wide range of natural and artificial, fundamental processes, including in energy systems as well as biological and environmental systems. Owing to the hydration water at the interface, the rate and extent of various types of chemical reactions may be significantly enhanced. The hydration of ions does not only affect the physical structure and dynamics of water molecules, but also chemical energy transfers through the formation of highly structured water complexes that form in the bulk water. Indeed, dehydration could promote the energy levels of aqueous compounds. These shifts in energy states may receive wide applications such as in energy storage with anhydrous salts, enhancement of the free energy of binding ligands to biological systems, and gas separation using a water-modified basicity of ionic sorbents. Of particular interest in this study is a novel technology for direct air capture of carbon dioxide, driven by the free energy difference between the hydrated and dehydrated states of an anionic exchange resin and its effect on the affinity of CO2 to the resin. In this dissertation, we first demonstrate an unconventional reverse chemical reaction in nano-confinement, where changes in the amount of hydration water drive the direction of an absorption/desorption reaction, and apply this novel mechanism of controlling the behavior of a sorbent to air capture of CO2. The reduction of the number of water molecules present in the pore space promotes the hydrolysis of CO32- to HCO3- and OH-. This phenomenon has led to a nano-structured CO2 sorbent that binds CO2 spontaneously in ambient air when the surrounding is dry, while releasing it when exposed to moisture. We name this phenomenon of loading and unloading a sorbent with water a hydration swing. Wide application of hydration swings to absorb CO2 requires a detailed understanding of the molecular mechanisms of the hydration induced energy change at the ion hydration/solid interface. Using atomistic simulations, the mechanism of CO2 absorption with respect to water quantity was elucidated via the explorations of the reaction free energy of carbonate ion hydrolysis in a confined nano-environment. Next, based on the understanding of the underlying driving mechanism, a systematic study of the efficiency of effective hydration-driven CO2 capture with respect to different pore sizes, hydrophobic/hydrophilic confined layers, temperatures, and distances of cations may further benefit the optimization of the CO2 capture system, in terms of the energetically favorable states of hydration ions in dry and wet conditions. This part of the research may sheds some insights on future research of designing high efficiency CO2 capture sorbent according to adjust the above described parameters. This unconventional reverse chemical reaction is not restricted to carbonate ions in nano-confined space. This is an universal phenomenon where hydrated ions carrying several water molecules in nanoscopic pores and in the natural atmosphere under low relative humidity. Such formations of hydrated ions on interfaces with the high ratio of ions to water molecules (up to 1:1) are essential in determining the energetics of many physical and chemical systems. In this dissertation, we present a quantitative analysis of the energetics of ion hydration in nanopores based on computational molecular modeling of a series of basic salts with the different quantities of water molecules. The results show that the degree of hydrolysis of basic salts with several water molecules is significantly different from the conventional degree of hydrolysis of basic salts in bulk water. The reduction of water molecules induces divalent and trivalent basic ions (S2-, CO32-, SO32-, HPO42-, SO42-, PO43-) to hydrolyze water into a larger amount of OH- ions, conversely, it inhibits monovalent basic ions (CN-, HS-) from hydrolyzing water. This finding opens a vast scope of new chemistry in nanoconfined water. Ion hydrations containing interfaces play an important role in a wide range of natural and fundamental processes, but are much less noticeable currently. This thesis sheds some lights on a vast number of chemical processes of hydrated ion pairs containing interfaces, and design possibility for more efficient energy-saving sorbents.

This Dissertation investigates the kinetics of CO2 methanation over nickel and cobalt catalysts. Methanation was studied for both Ni/γ-Al2O3 and Co/ZrO2 catalysts, which were synthesised using an incipient wetness impregnation technique and subsequently characterised using analyses based on gas adsorption, XRD, TPR and thermogravimetry. Separately a CO hydrogenation reaction, the Fischer-Tropsch process, was modelled numerically to examine the influence of mass transfer in practical, commercial pellets of catalyst. The kinetics of methanation was investigated for Ni/γ-Al2O3 over a wide range of reactant partial pressures using a gradientless, spinning-basket reactor operated in batch mode and in a laboratory-scale, continuous fixed-bed reactor. Langmuir-Hinshelwood kinetic models were developed to represent the observed kinetics in each reactor: these models were then compared. For the batch reactor, a rate expression based the dissociation of a chemisorbed CO intermediate being the rate-limiting step was found to be consistent with the experimental results. However, results from the fixed-bed suggested that the hydrogenation of an adsorbed C atom determined the rate of reaction. These differences in the kinetics on Ni/γ-Al2O3 between the fixed-bed and batch reactors suggest that a Langmuir approach using a single, rate-determining step may not be representative across all conversions. The rate over the Co/ZrO2 catalyst was characterised in the fixed-bed reactor over a range of reactant partial pressures at temperatures between 433 K and 503 K. The rate was observed to be dependent on hydrogen partial pressure and temperature, with the rate increasing with both. Previous research has reported a wide range of values of the apparent activation energy, with a study suggesting it was sensitive to pressure. Accordingly, the apparent activation energy was investigated for pressure sensitivity over a range of pressures between 5 and 15 barg: it was found to be constant. The values determined (~88-91±8 kJ/mol) were notably consistent with those reported for CO hydrogenation on cobalt. Kinetic schemes based on Langmuir-Hinshelwood and power law equations were evaluated, with the results best described by a reaction scheme based on the carbide pathway, with a rate-determining step of CH hydrogenation. A reaction-diffusion model of the Fischer-Tropsch process in a 2-D hollow cylinder was developed and analysed across a range of Thiele moduli and the extents of error in both effectiveness factor and selectivity were quantified relative to one-dimensional sphere and slab analogues. The errors between 2-D and 1-D analogues were found to be most significant between Thiele moduli of ~0.25 and ~3. Hollow cylinder effectiveness factors were bounded by those of sphere and slab above and below Thiele moduli of ~0.75 and ~1.15 respectively for the conditions examined, with the effectiveness factors exceeding those of both sphere and slab models between these moduli. A comparison of the hollow cylindrical pellets against spheres of equivalent volume demonstrated that hollow cylinders provided improved fixed-bed performance, with improved effectiveness factors and selectivities due to the lowered diffusion lengths of the hollow cylindrical geometry.

Spontaneous pulsations have been observed in the output of a CO2 laser. The temporal waveforms, transverse mode patterns, and laser lines are simultaneously measured under various operation conditions. The experimental data show that these pulsations have a direct connection with the transverse modes. We interpret the oscillations as being caused by mode beating, and the frequency shift of the oscillation as resulting from mode pulling. The theoretical explanations for these effects are in good agreement with the experimental results.

This thesis mainly concerns the application of electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA) to the study of CO(subscript)2 corrosion of mild steel and its inhibition. The primary focus is on the use of EIS and ENA to monitor inhibitor film performance and to evaluate inhibitor film persistency.EIS was shown to be a suitable technique to study CO(subscript)2 corrosion product scale, and inhibitor films. The formation and deterioration of protective scales and inhibitor films is found to be accompanied by characteristic spectral changes and a rapid change in electrode impedance. EIS data were used to calculate corrosion related parameters such as the resistances and capacitances of inhibitor layers, and the charge transfer resistance and double layer capacitance. These parameters were used to analyse inhibitor mechanisms, determine corrosion rates and the persistence of inhibitor films.ENA is also a suitable technique to monitor the formation and deterioration of inhibitor films. It has the advantage of being able to monitor rapid processes which occur within one second. Several technical and theoretical developments were made in this thesis including the development of a new method of instantaneous corrosion rate measurement to study fast corrosion processes (the continuous noise resistance calculation method). Experimentally, the noise resistance was confirmed to be similar to linear polarisation resistance in the systems studies. The theoretical background and the advantages and disadvantages of the ENA technique are also discussed.Corrosion product scales formed under different conditions were investigated using EIS and surface analysis techniques. Temperature, pressure and exposure time were confirmed to be the important factors influencing the degree of protection given by the scale. The morphology of corrosion scales ++ / showed an obvious correlation to their protective ability. Electron microscopy revealed two types of crystal structures on corroded steel coupons. The smaller crystals associated with one of these structures was found to contribute most to corrosion protection.Several typical CO(subscript)2 corrosion inhibitors, including an imidazoline and a quaternised amine, were studied by EIS. A multi-layer model was employed to explain the EIS characteristics and self-repairing ability of imidazoline films. A quaternised amine film is most probably a physically or electrostatically adsorbed molecular layer which forms rapidly and desorbs easily.The deterioration of films, formed by commercial batch treatment inhibitors, was found to occur in three stages which were indicated or characterised by Bode phase-angle plots. A method to determine inhibitor film persistency was developed. This method is based on determining the three stages of inhibitor film deterioration, and the continuous measurement of corrosion rate, which is accessible at the second and third stages of film deterioration.

The current atmospheric CO2 partial pressure of 36 Pa is expected to nearly double by the end of the 21st Century.Increases of this magnitude are likely to profoundly change the biochemistry, growth and morphology of plants, particularly C3 species.The research in this thesis focuses on the micronutrient Zinc (Zn), because this element is associated with a number of macromolecules which play key roles in plant growth and development, particularly on the shoot apex.The main objective of the work was to study the influence of elevated CO2 Zn nutrition of rice in the vegetative phase.A second objective was to investigate whether high CO2 reduced Zn concentrations in grain of cv. Jarrah and a Japanese cultivar, Akitakomachi, grown in either controlled environments, or in the field in a FACE (Free Air CO2 Enrichment) experiment. The greater Zn use efficiency of cvv. IR8 and Jarrah at elevated CO2, and the fact that high CO2 completely overcame chronic Zn deficiency at low Zn supplies, indicates that it may be possible , under future CO2 scenarios, to produce rice in areas where low soil Zn availability currently limits yield. / Master of Science (Hons)