| Ionic liquids (ILs) have received much attention in many areas of organic synthesis, segregation analysis and functional materials due to their potential as a"green solvents". However, they are limited to be widely used in different fields because of high price, large dosage, inconvenient separation and purification of catalyst. One of the effective approaches to solve these problems is to immobilize the ionic liquid on a solid support, in order to transfer the desired catalytic properties of the liquids to a solid catalyst. Currently supported-ionic liquid used in catalytic reaction mainly are concentrated on two areas. Firstly, the acidic ionic liquids are immobilized and used as acid catalytic reaction. Secondly, ionic liquids as supports for transition metal catalyst and further fixed in the medium of organic or inorganic are researched in the study of catalysis.The bimodal mesoporous materials (BMMs) is a new kind of mesoporous materials with a controlled pore structure in the range of 2nm~20nm. There are abundant -OH groups on the surface of BMMs channels. Compared with the single channel of mesoporous sieve, bimodal structure of BMMs is beneficial for large molecular to diffuse inside, and helps to reduce the accumulation of reactant and production in order to improve the reaction efficiency. In this dissertation, preparation and characteristization of BMMs as support and therefore the supported metal catalysis-ionic liquid catalysts were studied by use of XRD, FT-IR, SEM, TEM, and TG-DTA techniques. As a result, it is shown that catalytic behavoiuor of catalysts above for asymmetric dihydroxylation is of high activity and good recycle properties.The main contents of this dissertation are as following:1. Immobilization of IL on functionalized BMMsThe BMMs was synthesized and modified by (3-aminopropyl)triethoxysilane (APTES) solution to improve its loading capability. Then, the [2AlCl3/Et3NHCl] and a series of N, N'- dialkylimidazolium-based ionic liquids were grafted onto the inner surface of BMMs through an aminosilane linker, and the effects of concentration and time of reaction on the structure of BMMs were investigated. The characterizations of XRD,BET and TEM analysis methods indicated that BMMs have bimodal mesoporous with the larger pore of 23.6nm, the smaller pore of 2.9nm, the specific surface area of 959m2/g and pore volume of 2.0cm3/g. The typical channel structure was maintained after modified by APTES and loaded by ionic liquid. However, the order degree of (100) peak for BMMs would be decreased with the increased concentration of ionic liquid. On the basis of FT-IR spectra, a new band at 1560 cm-1 indicated that the functional groups -NH2 was grafted onto inner surface of BMMs. And after loading IL, the bands appearing at 944cm-1 and 1083cm-1 suggested that the IL has been assembled into the modified BMMs via the coordination between -NH2 and [2AlCl3/Et3NHCl]. The results of TG-DTA curves revealed that the weight loss (~10%) during the temperature from 330℃to 650℃can be attributed to the oxidative decomposition of -NH2 and ionic liquid. Meanwhile, when the supported ionic liquid is used in asymmetric dihydroxylation reaction, there was no catalystic activity of osmium catalyst.2. Immobilization of IL by grafting methodThe 1-methyl-3-[3-(trimethoxysiyl)propyl]imidazolium chloride, which contains the cation of the ionic liquid, was prepared and grafted on the surface of the BMMs. The XRD patterns indicated that the mesoporous order degree of ionic liquid hybrid supported by BMMs would be decreased greatly when grafted with above ionic liquid at 105℃for 12h. FT-IR spectrum showed that the peaks located at 1576cm-1 and 1460cm-1 were assigned to the framework vibration feature of imidazole ring. In asymmetric dihydroxylation reaction, the activity of catalysis revealed yield of 57% and e.e of 99% even when the amount of Os catalyst decreased to 0.1%mmol.3. Immobilization of IL by sol-gel methodBy using mixture containing 1-methyl-3-[3-(trimethoxysiyl)propyl]imidazolium chloride and TEOS as silicon source, the mesoporous hybrids were prepared via template mechanism and sol-gel route. According to XRD patterns, the intensity of (100) peak of above the mesoporous hybrids increased with the amount of ionic liquid decreased. TEM images showed the mesoporous structure with the mean pore size of around 2.3nm after calcinations and 1.7nm after extraction. Meanwhile, TG-DTA results suggested that the weight loss (~8%) during the period temperature from 420℃to 440℃was corresponding to the oxidative decomposition of imidazolium ionic liquid. FT-IR spectrum showed that the new bands at 3000cm-1~2700cm-1 and 1600cm-1~1400cm-1 were assigned to the C-H telescopic vibration and the framework vibration feature of imidazole ring, besides the characteristic bands of BMMs appeared in all samples, however, all of characteristic bands for imidazolium ionic liquid disappeared in the samples when calcined at 550oC, which implied that the structure of imidazolium ionic liquid has been destroyed during calcinations. In asymmetric dihydroxylation, the activity of above hybrids revealed higher yield of 87% and e.e of 96%, whereas the catalyst can be reused over four times. |
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