Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 68-77). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 68-77). Also available on the Internet.

Heterogeneous reactions have the potential to significantly impact urban ozone formation and total reactivity of the atmosphere. This dissertation used comparisons between photochemical modeling predictions and field measurements to examine heterogeneous N₂O₅ chemistry in Southeast Texas. Heterogeneous reactions of N₂O₅ can lead to two different products: nitric acid (HNO₃) and nitryl chloride (ClNO₂). The formation of HNO₃ results in a loss of reactive nitrogen from the atmosphere. In contrast ClNO₂ photolysis forms Cl radicals and NO₂, both of which promote ozone formation in the troposphere. Preliminary modeling identified key uncertainties and the need to perform more refined modeling which included updated PM emissions estimates, an updated gas-phase N₂O₅ hydrolysis reaction rate constant, updated reactive uptake coefficients, and the inclusion of ClNO₂ as a product of heterogeneous N₂O₅ uptake. Refined modeling which incorporated all of these improvements was carried out and was the first comprehensive modeling of this chemistry performed for an urban air pollution episode. Comparisons of aerosol surface area concentrations, N₂O₅ concentrations, HNO₃ concentrations, and ClNO₂ concentrations with ambient data showed that model predictions were reasonable. The exceptions to this were 1) over-predictions of aerosol surface area concentration peaks at altitudes above 1500 meters and 2) over-prediction of N₂O₅ concentrations in the Houston Ship Channel. Further analysis is needed to identify the reasons for these over-predictions. Other key findings from this modeling include the model prediction of inland chlorine concentrations high enough to form ClNO₂ and the prediction that a large portion of atmospheric chlorine is cycled through ClNO₂, therefore making the inclusion of ClNO₂ into photochemical models essential for properly simulating chlorine chemistry. In addition, modeling suggested that the chemistry leads to significant increases of NO[subscript x] at night, but decreases in daytime NO[subscript x] concentrations and that the overall effect was to decrease ozone concentrations. Further investigation into the effect of ClNO₂ as a chlorine source showed that likely ozone increases in the Houston area caused by the presence of this compound are on the order of several ppb. Further analyses showed that vertical dispersion and local atmospheric composition moderated the effect of nitryl chloride on ozone mixing ratios. / text

The syntheses and catalytic properties of four new 1,2-acenaphthenyl N-heterocyclic carbene-supported palladium(II) catalysts are presented. The acenaphthenyl carbene can be prepared using either mesityl or 2,6-diisopropyl N-aryl substituents. In addition, two new heterogeneous analogs were synthesized with 2,6-diisopropyl N-aryl substituents that were anchored through the backbone to an insoluble silica-support. Comprehensive catalytic studies of the Suzuki coupling of aryl halides with aryl boronic acids were carried out. In general, the homogeneous diisopropyl-functionalized catalyst was found to exhibit superior selectivity and reactivity. A comparison of the performances of the aforementioned catalysts in toluene, dichloromethane and aqueous solutions are also presented. In organic solvents, the catalysts were found to be proficient for the homogeneous Suzuki coupling of aryl iodides, bromides and chlorides with boronic acids at low temperatures (35‒40 °C). Similar reactions that were carried out in aqueous media resulted in the formation of insoluble colloidal catalytic species. Nevertheless, these species still retained high activities in terms of in the Suzuki reaction with aryl chlorides. Moreover, the heterogeneous Pd precipitates can be easily recovered for subsequent use by means of filtration. The activation energies that were determined for the aryl bromide-based Suzuki reactions were found to fall in the range, 159.2‒171.2 kJ mol⁻¹ in organic solvents and 111.3‒115.9 kJ mol⁻¹ in water. The corresponding activation energy for the aryl chloride was found to be 321.8 kJ mol⁻¹ in aqueous media using the homogeneous diisopropyl-functionalized carbene catalyst. Conversely, the heterogeneous catalyst exhibited reactivity toward aryl iodides and bromides exclusively, and required significantly higher temperatures and catalyst loadings in both toluene and water. Additional experimental trials that were performed in tetrahydrofuran solution at lower temperatures resulted in substantially larger catalytic conversions. The heterogeneous catalyst allowed for easy separation and recovery. However, the catalyst exhibited a significant decrease in reactivity toward the aryl halides after two consecutive trials. / text

No description available.

Light intensity distribution studies in the heterogeneous photocatalytic reactors were carried out successfully with potassium ferrioxalate chemical actinometry, reproducible light intensity estimates of the irradiation source were obtained. The increased light intensity in the reactor system increased the absorption as determined by actinometry. It was found that reflectivity was a dependent variable but mesh opening area was an independent variable. The photocatalytic mineralization of dichoroacetic acid DCAA, in the presence of TiO2 immobilized on a plate in an externally irradiated bubble column photoreactor had been investigated. The mass transfer and activity evaluation were measured. It was found that increasing the catalyst thickness, increased the photoactivity until it reaches the optimum loading, further loading increase caused the reaction rate to remain constant. This phenomenon was observed with increased lamp power (intensity) and initial solute concentration. However, the catalyst activity was not influenced by the increasing concentration of dissolved oxygen. The reaction rate for DCAA photomineralization was expressed using the Langmuir-Hinsheldwood model.

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