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Fischer-Tropsch synthesis (FTS), involves the hydrogenation of CO under high pressure and is an alternative process to refining to produce fuels and fine chemicals. Industrially it is carried out using oxide-supported cobalt nanoparticles (CoNPs). The interaction between the CoNPs and the support can have a big influence on catalyst performance, affecting the availability of active surfaces, the stability of the nanoparticles and/or their electronic state. Here I use spatially resolved spectroscopy/microscopy to better understand the metal support interactions in Co/Rutile model systems possessing a range of Co nanoparticle sizes (6~24 nm). In chapter 3 I observe that CoNPs spread on the surface of rutile adopting a fried-egg-like shape after reduction in H2, which increases not only the amount of surface cobalt, but also the interaction between metal and support leading to the formation of non reducible cobalt titanate (inactive for FTS). In chapter 4 I find that the initial Co3O4 nanoparticles can be directly reduced to CoO/Co0 as a result of plasma treatment generating oxygen vacancies (Ovac) on the rutile surface. In chapter 5 I observe that dissociation of CO occurs on nanoparticles (≥ 15 nm) and that the Ovac surrounding these particles is consumed. Nanoparticles smaller than this are unaffected, except in the presence of both CO and H2 when small NPs (≤ 12 nm) (re)oxidise. In chapter 6, reduced TiO2-x is observed to appear at the periphery of CoNPs after H2 reduction. Surfactant coverings can inhibit TiO2 reduction and stop CoNPs aggregation, with FTS reactivity enhanced in this catalyst. In summary, this nano-spectroscopic study of these samples allowed us to better understand the influence of the cobalt-rutile interface on the evolving properties of the cobalt nanoparticles under various gas atmospheres. It is hoped that this can enable a better understanding of their influence on FTS performance.

The evolution of commodity markets calls for advanced models to capture and analyze complex properties of the markets. This dissertation focuses on a large sector: the US natural gas market, and consists of three papers where three stochastic models are proposed to investigate the distinct characteristics of the market. Model parameters are estimated by maximizing the likelihood functions with the aid of the Kalman filter and the Kim filter. The first paper explores the multi-factor structure and risk premiums implied from the natural gas spot and futures. The model features a two-short-term/one-long-term structure, time-varying risk premiums and a seasonal risk premium. We find that three factors and the seasonal risk premium are needed to accurately describe the term structure of the natural gas futures. The coefficients for the time-varying risk premiums are significant. We also reveal a negative correlation between the seasonal risk premium and the uncertainty of the natural gas total consumption. The second paper deals with the changing slope of the natural gas futures long-end curve. We develop a Markov regime-switching model with a regime-dependent drift term under the equivalent martingale measure. The model has two factors and three regimes to capture three basic cases of the changing slope. The estimation results show that the model is able to produce a downward/flat/upward slope in each regime and classifies the regime status generally consistent with the observation. Through detailed model comparisons, we find that models without the regimes or the two factors lead to poor results. The third paper considers the variance dynamics of the natural gas futures returns. We directly model and estimate the variance dynamics. The model incorporates two variance factors, the Samuelson effect and seasonality. The estimation is implemented using a dataset of synthesized variance swap rates on the futures across the term-structure dimension. The rates are computed by integrating prices of relevant futures options across the strike dimension. The results indicate the existence of the Samuelson effect, seasonal variance and a negative variance risk premium. In addition, the two-factor setup exhibits its advantage along the term-structure dimension.

Chemical treatments using solvents and surfactants can be used to increase the productivity of gas-condensate wells with condensate banks. CMG’s compositional simulator GEM was used to simulate such treatments to gain a better understanding of design questions such as how much treatment solution to inject and to predict the benefits of such treatments. GEM was used to simulate treatments in vertical wells with and without hydraulic fractures and also horizontal wells. However, like other commercial compositional simulators, the flash calculations used to predict the phase behavior is limited to two phases whereas a three-phase flash is needed to accurately model the complex phase behavior that occurs during and after the injection of treatment solutions. UTCOMP is a compositional simulator with three-phase flash routine and attempts were made to use it to simulate such well treatments. However, this is a very difficult problem to simulate and all previous attempts failed because of numerical problems caused by inconsistent phase labeling (so called phase flipping) and the discontinuities this causes in the relative permeability values. In this research, a new relative permeability model based on molar Gibbs free energy was developed, implemented in a compositional simulator and applied to several difficult three-phase flash problems. A new way of modeling the residual saturations was needed to ensure a continuous variation of the residual saturations from the three-phase region to the two-phase region or back and was included in the new model. The new relative permeability model was implemented in the compositional reservoir simulator UTCOMP. This new relative permeability model makes it is unnecessary to identify and track the phases. This method automatically avoids the previous phase flipping problems and thus is physically accurate as well as computationally faster due to the improved numerical performance. The new code was tested by running several difficult simulation problems including a CO2 flood with three-hydrocarbon phases and a water phase. A new framework for doing flash calculations was also developed and implemented in UTCOMP to account for the multiple roots of the cubic equation-of-state to ensure a global minimum in the Gibbs free energy by doing an exhaustive search for the minimum value for one, two and three phases. The purpose was to determine if the standard method using a Gibbs stability test followed by a flash calculation was in fact resulting in the true minimum in the Gibbs free energy. Test problems were run and the results of the standard algorithm and the exhaustive search algorithm compared. The updated UTCOMP simulator was used to understand the flow back of solvents injected in gas condensate wells as part of chemical treatments. The flow back of the solvents, a short-term process, affects how well the treatment works and has been an important design and performance question for years that could not be simulated correctly until now due to the limitations of both commercial simulators and UTCOMP. Different solvents and chase gases were simulated to gain insight into how to improve the design of the chemical treatments under different conditions.

Traditionally, dry friction non-linear elements have been treated as vibration dampers, in parallel with elastic elements. However, in some practical systems (including automotive drivelines) the dry friction element (with high saturation torque) exists by itself and it functions as a key power transmission path for both mean and dynamic loads. First, to address such path issues, we examine multi-degree of freedom torsional systems with time-invariant normal load. A procedure to predict pure stick to stick-slip boundaries, based on a linear system theory, is developed when the torsional system is excited by harmonic excitation. For non-linear studies, both discontinuous and smoothened friction formulations are examined. The effects of a secondary inertia are analytically and numerically investigated. Results show that the secondary mass significantly affects the quasi-discontinuous nature of the system response. Next, in order to fully understand the non-linear frequency characteristics generated by stick-slip vibration, a new analytical method is developed based on assumed torque and velocity profiles. Super-harmonics are efficiently calculated and effect of the mean torque is qualitatively identified. Further, a refined multi-term harmonic balance proposed and associated computational issues are addressed. Studies show that the mean load significantly affects the response as it could induce asymmetric stick-slip motions. Second, the effect of time varying actuation pressure (or the normal load) on the dry friction element on transient and steady state responses has been studied. Analytical solution for pure slip motion is obtained based on an approximate linear system model. Effects of time-varying parameters, such as phase, frequency and amplitude of the actuation pressure are observed over several frequency regimes. The negative friction slope is found to be the major cause of judder-induced phenomena such as bifurcations and quasi-periodic or chaotic responses. Some instabilities such as abrupt jumps in the amplitude-frequency maps of relative velocity are also seen around the super-harmonic peak frequencies.