Book Description
Heterogeneous catalysts are an integral part of the chemical value chain that affects our everyday standard of living. The understanding of known catalysts and development of new catalysts are crucial to improving the sustainability of the industry and society at large. This thesis explores such catalysts for three different reactions: aerobic propylene epoxidation, hydrogen peroxide mediated cyclohexene epoxidation, and oxidative dehydrogenation of propane. Epoxides and olefins are important building block chemicals that require better catalysts (or the use of a catalyst at all) to ensure long-term sustainability in their synthesis. This thesis begins by describing the catalyst characterization and reaction kinetics for aerobic propylene epoxidation over Ag/KNO[3]/CaCO[3]. We show that the reaction proceeds in a Langmuir-Hinshelwood fashion, in which propylene and oxygen interact at the catalyst surface to generate the products. We further describe the selectivity enhancement effect of carbon dioxide on the reaction, as well as the effects of water and carbon monoxide on the reaction. Following gas phase epoxidation, we then present new hexagonal tungsten oxide catalysts for the liquid phase epoxidation of cyclohexene using hydrogen peroxide as the oxidant. We demonstrate that the cation composition affects the rate of epoxide formation and pathway selectivity. Furthermore, substitution of silver into the hexagonal tungsten oxide structure shows improved pathway selectivity, albeit at slower reaction rates. Finally, we demonstrate the use of two important characterization techniques for understanding heterogeneous catalysts. We show the development of a shell-isolated nanoparticle-enhanced Raman spectroscopy method for the practical observation of heterogeneous catalysts. In the final chapter, we demonstrate the utility of electron microscopy for the understanding of heterogeneous catalysts.
