Gold-containing Mesoporous Molecular Sieves :synthesis, Characterization And Application For Photocatalytic Epoxidation Of Styrene

Gold was usually regarded as chemically inert nature without catalytic performance. There was considerable interest in the reactivity of gold since the discovery that Au nanoclusters supported on reducible metal oxides were highly active for CO and propene oxidation at low temperature. Thereinto, the reason for the high activity of supported Au nanoparticles was a subject of active debate. One view was that the small size of these particles imparted unique chemical properties to the Au not found in bulk gold. Another explanation was a synergetic interaction, that is, the partial electron transfer, between the gold and the metal oxide support. Pratically speaking, the challenge that how highly dispersed supported gold with small particle was made, however, was remaining. With large specific surface area, large pore channel, highly thermal stability and stable structure. Mesoporous materials was employed as good support. Therefore, this dissertation aimed at developing a novel methods to fabricate highly dispersed gold-supported mesoporous materials with high efficiency, followed by application for photocatalytic epoxidation of styrene employing H₂O₂ as oxidant under low temperature. By means of versatile characterization techniques, physical and chemical structures of catalyst were investigated at length. Also, the relationship between catalytic performance and microstructure of catalyst was explored.The major work and achievement in this dissertation were as follows:1. Preparation and application of Au-Ti-SBA-15Au-Ti-SBA-15 mesoporous molecular sieves were successfully prepared by traditional hydrothermal one-pot method, followed by the characterization of XRD, N2-isothermal absorption and desorption curve, FT-IR, TG-DTA, SEM, TEM, 29Si CP-MAS NMR, XPS and so on. The characterization results indicated that Ti4+ was incorporated into framework of SBA-15,also,gold existed on the surface of SBA-15 with clusters. NH3-TPD results demonstrated that Au-Ti-SBA-15 contained two kind of acidic site. Au-Ti-SBA-15 was successfully applied to photocatalytic epoxidation of styrene with H₂O₂ as oxidant. Styrene oxide was major product. Formation of benzaldehyde was completely inhibited. The influence of reaction parameters, such as the molar ratio of H₂O₂/styrene, solvent, reaction time, the amount of NaOH, the amount of catalyst, the ratio of Si/Ti, on the catalytic performance in detail. Catalysts could be reusable, moreover, recovery method was very simple. Above all, all reaction process takes ten minutes to achieve more than 50% conversion of styrene and over 80% selectivty of styrene oxide. In this respect, it was possible to apply it to industrial production. This reaction system embodied the characteristic of green chemistry, energy conservation, clean oxidant, atomic economy.2. Preparation and application of mesoporous Au-TiO₂First of all, mesoporous titania were synthesized by soft-template method. The next thing was the preparation of Au-TiO₂ using impregnation method. Catalysts were characterized by low-angle XRD, high-angle XRD, N2-isothermal adsorption desorption, UV-vis DRS, SEM and elements mapping. The characterization results indicated that mesoporous titania took on uniform size, smooth surface, pure anatase crystalline; also, gold was highly dispersed on the surface of mesoporous titania. The catalyst contributed to photocatalytic epoxidation of styrene.