Abstract
This thesis aims at elucidating one of the oldest and biggest obstacle that the 19th and 20th century chemists have been working on in the field of chemical kinetics. Both heterogeneous and homogeneous catalysis investigates this phenomenon using similar and different criteria depending on the type of reaction and catalytic system used. There has been a lot of scientific reports that have demonstrated that the concentration, temperature, viscosity, diffusion and pH; all contribute to the rate constant of reactions occurring in liquid, gas and solid phases. However, the mechanism of reactions in nano-scopic level still remains a subject of controversy. The introduction of well-ordered mesoporous transition metal oxide materials, e.g. Co3O4, Fe2O3, MnO2, CuO, NiO, Cr2O3, CeO2 and SiO2, as a control, have contributed significantly to the understanding of kinetics in heterogeneous catalysis. The addition of minute quantities of noble transition metals in the mesoporous metal oxide framework creates a synergy for elevated rate constants.
The oxidation and degradation reaction of environmentally toxic chemicals, such as rhodamin B, methylene blue, morin and 4-nitrophenol were investigated in aqueous media in the presence of an oxidant and the prepared mesoporous catalysts. In this investigation, intrinsic structure activity relationships were obtained and compared to the literature reports. The dependence of the concentration of morin and H2O2 on the rate constant was evident when mesoporous Co3O4 calcined to 150 ΒΊC was used. This was a result of fine-tuned properties such as the total surface area, crystallite size and pore size of the Co3O4-150. The mechanism of this oxidation reaction was modelled and fitted to Langmuir-Hinshelwood mechanism and the surface activity parameters, such as the surface rate constants, equilibrium rate constants and Freundlich exponents were all determined and compared to the literature. Mesoporous CuO as a catalyst was shown to degrade rhodamine B with very high percentage decrease in the maximum wavelength ππππ₯. The dependence of large crystallite sizes of CuO was observed in the rhodamine B oxidation and compared to other mesoporous transition metal oxides. The Langmuir-Hinshelwood mechanism was modeled, and thermodynamic parameters were determined in this study. The recyclability and diffusion limitation studies revealed that the Co3O4-150 and CuO were stable even after the 4th cycle, with no leaching...
Ph.D. (Chemistry)