| The successful synthesis of titanium rnolecuiar sieve TS-1 which is an environment benign catalyst has been considered to be a milestone in zeolite catalysis in 80th. Since TS-1 zeolite contains a very small percentage of Ti substituting Si and there is no charge on the framework, it is usually recognized that there should be no strong acidity in TS-1 zeolite. While TS-1 was initially described as a redox catalyst, it is now being increasingly recognized "simply as a Lewis acid solid", in which the tetracoordinated titanium atoms bind to the hydroperoxide and enhance the electrophilieity of the oxidant. Thus, it should be of very important to study the acidity in TS-1 zeolite, in this thesis, the acidity of TS-1 and its effect on the product distribution of styrene oxidation reaction were investigated by using Solid-State M AS N MR t echniques. Combining with t he r esults d erived from E SR technique and theory calculation, the mechanism of selective oxidation of styrene reaction was proposed. The main results in this dissertation are summarized as follows:1. The results taken from 1H MAS NMR of TS-1 zeolite and 31P MAS NMR of trimethylphosphinne adsorbed on the catalyst support strongly the existence of both Bnjinsted and Lewis acid sites in TS-1 zeolite. The codrdinate-unsaturated Ti sites in zeolite framework and the tetrahedral Ti sites are recongized as the Lewis acid sites of TS-1, whereas the defects within the zeolite lattice such as Ti-OH groups and partof SiOH are associated with the Bronsted acid sites. The characters of propyiene oxide into methoxypropanol as a test reaction confirmed the results obtained from MASNMR.2. By conducting in-situ oxidation reaction of TMP adsorbed on TS-1 and HZSM-5 zeolites using air as oxidant via 31P solid-state MAS NMR spectra, we have for the first time clearly evidenced that among the various framework titanium species (such as the Ti(OSi)3OH group, the distorted tetrahedral Ti species and the coordinately unsaturated Ti sites like tri-coordinated Ti), only those which correspond to the Lewis acid sites are the active oxidation centers of TS-1. When using urea-hydroperoxide as oxygent, just the trimethylphosphine adsorbed oa the Lewis acid sites in TS-1 zeolite was oxidized. It further confirmed that the hydroperoxo-titanium species formed by the interaction between the titanium in Lewis acid sites and urea-hydroperoxide are the active oxidation centers, and the titanium in the framework as Lewis acid sites enhances the oxidation ability of hydroperoxide.3. Phenylacetaldehyde and benzaldehyde are found to be the major products in the c atalytic o xidation o f styrene o ver T S-1 zeolite, and styrene epoxide is not as speculated detected. By means of UV-Vis, 27A1 MAS NMR, JH MAS NMR and 31P MAS NMR with TMP as a probe molecule, it can be concluded that the formation of these products are closely related to the different titanium species or acid sites in the zeolite system. TheBronsted acid sites originating from Si-OH-Aland framework titanium species catalyze the formation of phenylacetaldehyde, while non-framework titanium species such as TiOx nano-particles promote the carbon-carbon bond cleavage, thus resulting in the formation of benzaldehyde. With adding of the sodium hydroxide in this system, the selectivity of benzaldehyde was enhanced.4. With urea-hydroperoxide as oxidant, the oxidation of styrene catalyzed by different TS-1 zeolites with or without Bronsted acid sites was investigated through in-situ MAS NMR method. It was found that the formation of phenylacetaldehyde was due mainly to the conversion of moiety acetals under acidic system, while not to the ring opening of styrene epoxide. The conversion of moiety acetals can be promoted by the Bronsted acid sites either from TS-1 zeolite or the five-membered ring hydrogen bonded structure dissociating during the process of the reaction when the protic solvent was used. While, there's no detectable phenylacetaldehyde, when non-polar solvent, such as acetone, was used in the syste...
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