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>Magister Scientiae - MSc / The use of diesel engines in vehicles and heavy machinery throughout the world has been slowly increasing in the past few decades. This has led to high demand for diesel and gasoline with high octane number. Diesel and gasoline are in high demand due to its qualities as fuels containing low or no sulfur and nitrogen compounds, making them environmentally friendly and the anti- knocking properties respectively. With these reasons and more, researchers have been studying processes like the catalytic oligomerization of olefins to produce synthetic fuels with augmented qualities and properties. The effectiveness of the process will depend on the quality of the catalyst.

In this work the use of the solid acid CsHSO4 as an electrolyte in a hydrogen/oxygen fuel cell or the disassociation of water into hydrogen and oxygen has been investigated. Several issues have been cited in literature regarding the use of CsHSO4 as a solid electrolyte; these include: difficulty interpreting proton conductivity profiles of real membranes, high permeability of the membrane to fuel and product gases, and low mechanical strength. In an attempt to improve our understanding and possibly eliminate these issues, performance characteristics of prepared CsHSO4 membranes have been investigated utilizing various methods of synthesis and membrane fabrication. A consistent method of CsHSO4 membrane construction was developed based on these investigations. In addition, a novel method of sintering to decrease the membrane's permeability to fuel gases was developed and evaluated. The effects of these measures were investigated and tested in a prototype cell for proof of concept of fuel cell and electrolysis applications.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Superparamagnetic iron oxide nanoparticle functionalization is an area of intensely active research, with applications across disciplines such as biomedical science and heterogeneous catalysis. This work demonstrates the functionalization of iron oxide nanoparticles with a quasi-monolayer of 11-sulfoundecanoic acid, 10-phosphono-1-decanesulfonic acid, and 11-aminoundecanoic acid. The carboxylic and phosphonic moieties form bonds to the iron oxide particle core, while the sulfonic acid groups face outward where they are available for catalysis. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectrometry (XPS), and dynamic light scattering (DLS). The sulfonic acid functionalized particles were used to catalyze the hydrolysis of sucrose at 80˚C and starch at 130˚C, showing a higher activity per acid site than the traditional solid acid catalyst Amberlyst-15, and comparing well against results reported in the literature for sulfonic acid functionalized mesoporous silicas. In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. Between the two sulfonic ligands, the phosphonates produced a more tightly packed monolayer, which corresponded to a higher sulfonic acid loading, lower agglomeration, lower recoverability through application of an external magnetic field, and higher activity per acid site for the hydrolysis of starch. Functionalizations with 11-aminoundecanoic acid resulted in some amine groups binding to the surfaces of iron oxide nanoparticles. This amine binding is commonly ignored in iron oxide nanoparticle syntheses and functionalizations for biomedical and catalytic applications, affecting understandings of surface charge and other material properties.

This study describes the development of a novel thin membrane exchange assembly (MEA) from a solid acid material, cesium hydrogen sulfate (CsHSO4), and from a composite anode electrocatalyst for electrolytic splitting of (100 %) H2S feed content gas operating at 135 kPa and 150 °C. A new class of anode electrocatalyst with the general composition, RuO2/CoS2, and an improved proton conductor, CsHSO4, have shown great stability and desired properties at typical operating conditions. This configuration demonstrated stable electrochemical operation for 24 h with a (100 %) H2S fuel stream at 423 K. This same system showed a maximum current density of (19 mA/cm²) at 900 mV. The performance of this new anode electrocatalyst when compared to that of Pt black investigated in a previous study showed an overall superiority in application. We have achieved a 30 % reduction in the overall system performance by fabricating a thin (200 µm) CsHSO4 electrolyte, which reduced the whole MEA thickness from 2.3 mm to 500 µm. The result of permeability measurements proved that this thin solid electrolyte is impermeable to H2S gas and physical integrity was preserved throughout the experimental period. Further resistance losses were compensated by using a high energy planetary milling system to enhance the ionic conductivity of CsHSO4. The difference in stability and electrochemical performance of these cells compared to that of Pt anode based systems is directly attributable to the anode materials developed in this project. Factorial experiments were used to characterize the effect of controllable process variables (electrolyte thickness, time, age of the electrolyte) on the cell current density and interfacial polarization resistances. As expected, cell current density and interfacial polarization resistances were a function of electrolyte thickness and age. Nevertheless, the effect of electrolyte thickness has a more prominent effect on the measured parameters. In addition, these experiments were used to identify regions of optimum system performance. Tafel plots were constructed to investigate the kinetic behavior of various anode based electrocatalysts. Exchange current densities, which are directly a measure of the electrochemical reaction, increased with RuO2/CoS2-based anodes. These experiments also suggested that high levels of feed utilization were possible using these materials. This was an impressive result considering the drastic improvement in electrochemical performance, current density, and sulfur tolerance compared to the other anode configurations.

Acrolein is an indispensable chemical intermediate with a rising demand in recent years. The concern of the increase of propylene prices due to the shrinking supply of nonrenewable crude oil makes the acid-catalyzed gas-phase glycerol dehydration to acrolein a prime candidate for research. Our analysis showed that the sustainable acrolein production from glycerol was both technically and economically viable. Alumina2700® (Al) and Silica1252® (Si) loaded with silicotungstic acid (HSiW) possessed distinct features while provided equally good acrolein yield (73.86mol% and 74.05mol%, respectively) optimally. Due to the unique non-equilibrium characteristics, non-thermal plasma (NTP) could promote a variety of chemical reactions; however, its application in a dehydration process remained blank. This study used the reaction of glycerol dehydration to acrolein to probe whether NTP could 1) improve acrolein yield during dehydration, 2) suppress the coke formation and regenerate the catalyst, and 3) modify the properties of the catalyst. The dielectric barrier discharge configuration was used to generate NTP; various NTP field strengths and also their interaction with temperature and the catalyst were investigated. The results showed that NTP improved the glycerol conversion and that NTP with a proper field strength increased acrolein selectivity. The optimal acrolein yields of 83.6 mol% and 83.1 mol% were achieved with 3.78 kV/cm NTP and 4.58 kV/cm NTP at 275°C for HSiW-Al and HSiW-Si, respectively. The application of NTP-O2 (5% oxygen in argon, 4.58 kV/cm) during glycerol dehydration significantly suppressed coke formation on HSiW-Si. NTP-O2 could regenerate the deactivated HSiW-Si at low temperatures by removing both soft and hard coke at various rates. NTP-O2 with higher field strength, at medium operation temperature (150ºC) and in argon atmosphere was more effective for coke removal/catalyst regeneration. Applying NTP to the catalyst fabrication showed some capabilities in modifying catalyst properties, including enlarging surface area, preserving mesopores, increasing acid strength and Brønsted acidity. NTP with argon as the discharge gas performed better in these modifications than NTP with air as the discharge gas.

Complex reaction kinetics of the solid acid alkylation of isobutane with butenes over a proton-exchanged Y-zeolite has been modeled at the elementary step level. Starting with a computer algorithm that generated the reaction network based on the fundamentals of the carbenium ion chemistry, the formation of over 100+ product species has been modeled in order to gain understanding of the underlying phenomena leading to rapid catalyst deactivation and product selectivity shifts observed in experimental runs. An experimental investigation of the solid acid alkylation process was carried out in a fixed bed catalytic reactor operating with an excess of isobutane under isothermal conditions at moderate temperatures (353-393 K) in liquid phase. Experimental data varying with run-time for a set of butene space-times and reaction temperatures were collected for parameter estimation purposes. A kinetic model was formulated in terms of rate expressions at the elementary step level including a rigorous modeling of deactivation through site coverage. The single event concept was applied to each rate coefficient at the elementary step level to achieve a significant reduction in the number of model parameters. Based on the identification of structural changes leading to the creation or destruction of symmetry axes and chiral centers in an elementary step, formulae have been developed for the calculation of the number of single events. The Evans-Polanyi relationship and the concept of stabilization energy were introduced to account for energy levels in surface-bonded carbenium ions. A novel functional dependency of the stabilization energy with the nature of the carbenium ion and the carbon number was proposed to account for energy effects from the acid sites on the catalyst. Further reductions in the number of parameters and simplification of the equations for the transient pseudohomogeneous one-dimensional plug-flow model of the reactor were achieved by means of thermodynamic constraints. Altogether, the single event concept, the Evans-Polanyi relationship, the stabilization energy approach and the thermodynamic constraints led to a set of 14 parameters necessary for a complete description of solid acid alkylation at the elementary step level.

Dispersed niobia catalysts were prepared via a non-aqueous synthesis route. The effects of the type of oxide support, the support thermal pre-treatment, the calcination temperature and the niobia loading on the activity and selectivity for mesityl oxide (MO) synthesis at 160C were investigated in an autoclave reactor. The morphological and chemical properties of the catalysts were characterized via EDXRF, XRD, BET and Raman spectroscopy. The strength and nature of the acid sites were elucidated via in situ DRIFT spectra of the adsorption of pyridine as well as the temperature programmed desorption of NH3 interacting with the surface oxide phase. All four catalyst parameters had significant effects on the catalytic properties. Significantly, the nature of the acidity was clearly linked to the catalyst activity and particularly the catalyst stability. Catalysts exhibiting predominantly Lewis acidity invariably deactivated despite good initial activity, with the final acetone conversion dependent on the catalyst formulation. In contrast, catalysts exhibiting Bronsted acidity showed no evidence of catalyst deactivation after 8 hours of reaction. A plausible mechanism which explains these observations is proposed. Catalysts exhibiting Lewis acidity were more active when the supports were first activated at elevated temperature, likely due to a stronger support-surface oxide interaction as a consequence of increased surface coordinative unsaturation of the support. SiO¬2 supported catalysts exhibiting Bronsted acidity were more active if the supports were initially activated at 100C. Evidently, the hydroxyl groups on the oxide support contribute to the generation of Bronsted acidity. Different oxide supports gave rise to distinct acidic and catalytic properties in the niobia overlayer. The most striking example of this was the direct comparison of niobia dispersed onto two kinds of silica supports following the same preparative method. Unique and very strong acid sites were observed in niobia dispersed onto a commercial SiO¬2 catalyst carrier that were not observed in niobia dispersed onto fumed SiO¬2. For SiO2 catalysts, the activity increased linearly with niobia loading regardless of calcination temperature. In contrast, Al2O3 catalysts exhibited an initial increase in activity for MO synthesis with niobia loading followed by a decrease in activity after reaching a maximum activity below 1/3 monolayer coverage. The effect was more pronounced for catalysts exhibiting Bronsted acidity. It is proposed that adlineation sites are primarily responsible for catalytic activity in Nb2O5/-Al2O3 catalysts exhibiting Bronsted acidity. Niobia catalysts were developed using commercially available catalyst carriers as supports. The macrokinetics of MO and MIBK syntheses were investigated in a benchtop fixed bed flow reactor. The catalysts showed excellent activity for MO and MIBK syntheses at 160°C, typically 0.9 to 1.3 [g/hr*gcat]. However, the MIBK selectivity was constrained from 82 to 85% due to the coproduction of 2-propanol and diisobutyl ketone. The productivity for MO synthesis was found to be strongly dependent on the space velocity suggesting product inhibition. The intrinsic kinetics of the one-step synthesis of MIBK over a 15.2 wt% Pd/Nb2O5/SiO2 catalyst was investigated in an autoclave reactor. A kinetic model was developed and is reported. The one step synthesis of MIBK was investigated at the pilot plant scale via catalytic distillation (CD). An important finding was that while operating at 100% reflux, the accumulation of water in the reactive section resulted in the suppression of the DAA dehydration reaction. The in situ removal of water from the reactive section via an overhead distillate stream operating at 83 to 97% reflux directly resulted in an increase in MIBK productivity and hydrogen uptake efficiency by factors of about 20 yielding a moisture free reboiler product stream with as high as 53 wt% MIBK. The process was found to be controlled by the external mass transfer of hydrogen. Interestingly, the results suggest that the catalyst wetting efficiency affects the transport of hydrogen to the active sites as evidenced by the dependence of MO conversion on the reflux flow rate. The condition of minimum reflux flow rate and maximum hydrogen flow rate resulted in 97% MO conversion and 90 wt% MIBK selectivity.

Dispersed niobia catalysts were prepared via a non-aqueous synthesis route. The effects of the type of oxide support, the support thermal pre-treatment, the calcination temperature and the niobia loading on the activity and selectivity for mesityl oxide (MO) synthesis at 160C were investigated in an autoclave reactor. The morphological and chemical properties of the catalysts were characterized via EDXRF, XRD, BET and Raman spectroscopy. The strength and nature of the acid sites were elucidated via in situ DRIFT spectra of the adsorption of pyridine as well as the temperature programmed desorption of NH3 interacting with the surface oxide phase. All four catalyst parameters had significant effects on the catalytic properties. Significantly, the nature of the acidity was clearly linked to the catalyst activity and particularly the catalyst stability. Catalysts exhibiting predominantly Lewis acidity invariably deactivated despite good initial activity, with the final acetone conversion dependent on the catalyst formulation. In contrast, catalysts exhibiting Bronsted acidity showed no evidence of catalyst deactivation after 8 hours of reaction. A plausible mechanism which explains these observations is proposed. Catalysts exhibiting Lewis acidity were more active when the supports were first activated at elevated temperature, likely due to a stronger support-surface oxide interaction as a consequence of increased surface coordinative unsaturation of the support. SiO¬2 supported catalysts exhibiting Bronsted acidity were more active if the supports were initially activated at 100C. Evidently, the hydroxyl groups on the oxide support contribute to the generation of Bronsted acidity. Different oxide supports gave rise to distinct acidic and catalytic properties in the niobia overlayer. The most striking example of this was the direct comparison of niobia dispersed onto two kinds of silica supports following the same preparative method. Unique and very strong acid sites were observed in niobia dispersed onto a commercial SiO¬2 catalyst carrier that were not observed in niobia dispersed onto fumed SiO¬2. For SiO2 catalysts, the activity increased linearly with niobia loading regardless of calcination temperature. In contrast, Al2O3 catalysts exhibited an initial increase in activity for MO synthesis with niobia loading followed by a decrease in activity after reaching a maximum activity below 1/3 monolayer coverage. The effect was more pronounced for catalysts exhibiting Bronsted acidity. It is proposed that adlineation sites are primarily responsible for catalytic activity in Nb2O5/-Al2O3 catalysts exhibiting Bronsted acidity. Niobia catalysts were developed using commercially available catalyst carriers as supports. The macrokinetics of MO and MIBK syntheses were investigated in a benchtop fixed bed flow reactor. The catalysts showed excellent activity for MO and MIBK syntheses at 160°C, typically 0.9 to 1.3 [g/hr*gcat]. However, the MIBK selectivity was constrained from 82 to 85% due to the coproduction of 2-propanol and diisobutyl ketone. The productivity for MO synthesis was found to be strongly dependent on the space velocity suggesting product inhibition. The intrinsic kinetics of the one-step synthesis of MIBK over a 15.2 wt% Pd/Nb2O5/SiO2 catalyst was investigated in an autoclave reactor. A kinetic model was developed and is reported. The one step synthesis of MIBK was investigated at the pilot plant scale via catalytic distillation (CD). An important finding was that while operating at 100% reflux, the accumulation of water in the reactive section resulted in the suppression of the DAA dehydration reaction. The in situ removal of water from the reactive section via an overhead distillate stream operating at 83 to 97% reflux directly resulted in an increase in MIBK productivity and hydrogen uptake efficiency by factors of about 20 yielding a moisture free reboiler product stream with as high as 53 wt% MIBK. The process was found to be controlled by the external mass transfer of hydrogen. Interestingly, the results suggest that the catalyst wetting efficiency affects the transport of hydrogen to the active sites as evidenced by the dependence of MO conversion on the reflux flow rate. The condition of minimum reflux flow rate and maximum hydrogen flow rate resulted in 97% MO conversion and 90 wt% MIBK selectivity.