| Cyclohexene oxide, one of the most important organic intermediates, has attracted great academic interest in the field of organic synthesis. At present, its synthesis methods are divided into the homogeneous and the heterogeneous system, the former possesses many advantages, such as good conversion and high selectivity, however, there are many shortcomings, for example, the catalysts are difficult to be reused, and therefore cost too much. To overcome these limitations, researches focus on the field of heterogeneous reaction system. In the early 1990s, a new theory and method has been carried out to synthesize stabilized catalysts with controllable struture after the MCM-41 mesoporous molecular sieves have been reported.In this dissertation, a series of Ti/BMMs samples were prepared by grafting titanocene dichloride into bimodal mesoporous materials. The catalytic properties of Ti/BMMs were investigated by using epoxidation reaction of cyclohexene as model reaction. Combining with some characterization techniques, the effects of many factors on the epoxidation properties have been studied in details, and the best catalyst and optimum reaction condition were obtained. In addition, the relationship between mechanism of epoxidation reaction and catalyst structure was also discussed.Below are the main results:1. A series of catalysts were prepared by incorporating titanocene dichloride on the surface of BMMs with different ratios and were characterized by XRD, SEM, TEM, TG, UV-vis, ICP and FT-IR, and so on. The results showed that the tetrahedral titanium complexes highly dispersed in the mesoporous surface of BMMs samples with Si/Ti molar ratio of 82.9, 61.5 and 47.9, respectively. However, with the increasing Ti content (Si/Ti molar ratio was lower than 38.1), besides tetrahedral titanium complexes, octahedral Ti species also presented on the basis of UV-vis spectra. Additionally, Ti amount for catalyst with the Si/Ti molar ratio at 61.5 was around 0.47(wt) % by ICP measurement, the resultant catalysts maintain a typical bimodal mesoporous structure, in which, titanium species exist in the form of tetrahedral and dispersed on the mesoporous surface.2. The effects of Si/Ti ratio, heating temperature, reaction temperature, solvents and reaction time on the epoxidation reaction of cyclohexene were investigated. The best reaction conditions were as follow: cyclohexene/TBHP = 1:1.1(molar ratio), chloroform as solvent, Ti/BMMs catalyst with Si/Ti ratio at 61.5, reaction temperature at 60°C and reaction time for 6 hours. Ti/BMMs catalysts showed high catalytic activity with the conversion of cyclohexene up to 61.75 %, selectivity of cyclohexene oxide near 73.54 % and turnover frequency (TOF) achieved 87.88 h-1.3. In addition, the effect of heating temperature on the coordinated environment of Ti ions of catalysts was studied. The results indicated that when calcined at 450°C, Ti/BMMs catalyst could maintain bimodal pore structure and tetrahedral titanium be dispersed on the mesoporous surface. In the case of lower temperature, the mesopores might be blocked since titanocene dichloride was not decomposed fully according to the TG analysis, when above 450°C, the pores structure was damaged on the basis of XRD pattern.4. Meantime, recycling and reuse of Ti/BMMs catalysts were also performed. The results showed that after recycled three times, the catalyst could still maintain a typical bimodal mesoporous structure with high conversion and selectivity, that the cyclohexene conversion reached up to 57.37 % and selectivity of cyclohexene oxide was around 72.61 %.5. Combining with the TG analysis, and the mechanism of cyclohexene epoxidation, some possible reasons for the decreasing of activity of Ti/BMMs were put forward, as follow: (1) The mesopore structure were damaged to some extent after series of recycling, especially at the forth time; (2) Some organic molecules which were by-produced in the cyclohexene epoxidation were absorbed on the mesoporous surface, resulting in that the reactants could not easily diffuse into the active sites; (3) With the increasing of recycling times, the tetrahedral titanium complexes were not only strongly leached, but also turned into other species. In a word, the investigations for decreasing of catalytic activity need to be further done.
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