| The primary focus of this dissertation is the thermal and photocatalytic oxidation of 2-propanol on TiO2 (110) and (100) rutile planes. The object of this study is to establishing what factors govern catalytic oxidation on TiO2. Specifically, the role of surface structure, site geometry, and reactive intermediates must be understood in order to optimize TiO2 as a catalytic material. The catalytic activity of the (110) and (100) surfaces was probed using the oxidation of 2-propanol to determine how the aforementioned factors effected reactivity on TiO2. The average reaction probability per residence time for thermal catalytic oxidation of 2-propanol in the presence of O2 on the (110) and (100) planes is 0.01 and 0.09, respectively. The photocatalytic oxidation channel on these two planes exhibits a similar disparity. The average reaction probability per residence time for a 2-propanol molecule in the presence of O2 on the (110) and (100) planes was 0.08 and 0.03, respectively. The inversion in the branching ratio between the thermal and photocatalytic oxidation on these two surfaces can be attributed to the distance between the titanium binding site and bridging oxygen atoms being shorter on the (100) than on the (110) surface. This closer proximity on the (100) surface allows for a hydrogen bonding interaction to occur, which results in dissociation of bound 2-propanol and permits the thermal oxidation channel to proceed. Due to the difference in site geometry, this hydrogen bonding interaction and the consequent dissociation of 2-propanol is not achieved on the (110) plane, making only the photocatalytic pathway active. In addition, the effect of surface structure was investigated by creating oxygen vacancy sites on the (110) surface. These sites yield an enhancement in the photocatalytic oxidation of 2-propanol from 0.08 to 0.15. In conclusion, this work has demonstrated that surface structure, site geometry and reactive intermediates all play important roles in catalytic oxidation on TiO2, and that a complete understanding of how these factors influence oxidation chemistry is necessary for the future optimization of TiO2 as an oxidation catalyst. |
