Development of Novel Nanocatalysts for Green Chemical Processes

Abstract

The key aim of this thesis was to develop titanium-containing mesoporous catalysts (Ti-MCM-41) and supported Pt catalysts on mesoporous materials (Pt/Al-MCM-41) with specific functionality to direct the target reactions by a green method. Both catalysts have high surface area and size-confined nano-pore to enhance the activity for oxidation reactions. A one-pot room-temperature direct synthesis method was developed for a series of amorphous Ti-MCM-41 with and without Brønsted acid sites (BAS). The investigation was focused on the relationship between the acidity and the formation of surface active sites for cyclohexene oxidation using hydrogen peroxide. The formation of intermediates peroxo-titanium and superoxo-titanium was confirmed by diffuse reflectance UV-visible spectroscopy and electron paramagnetic resonance (EPR) spectroscopic studies. The relationships between Ti precursors and the local coordination structure of Ti-MCM-41 were investigated and evaluated in cyclohexene oxidation. DRUV-visible and EPR spectroscopies investigation have provided evidence that the nature of the oxo intermediates formed on contact with H2O2 depends on the intrinsic local structure and environment of the Ti ions. Well dispersed and size-confined Pt nanoparticles into Al-MCM-41 were successfully prepared and evaluated in benzyl alcohol oxidation. With a small amount of acidic OH groups covered by Pt particles over Pt/Al-MCM-41 exhibited excellent conversion and selectivity due to the electron transfer between Pt and the supports. The influence of the alkali-treatment of Pt/Al-MCM-41 on the mesoporous structure for benzyl alcohol oxidation was investigated. Alkali-treatment apparently influenced the pore properties and the surface area of the catalysts. The catalysts prepared with acidic supports had higher conversion than those with alkali-treated catalysts.