| This thesis contains two parts. The first part is focused on the interaction of several types of siliceous zeolites with some small organic molecules, which was investigated by molecular simulation. The second part is related the synthesis and the transformation of several low-silica zeolites .The interaction of tetrahydrofuran (THF), a template, with siliceous FER, MFI, MOR, MTN type zeolite was studied by molecular simulation and 13C high-power decoupling (HPDEC) magic angle spinning (MAS) NMR. Molecular dynamics (MD) together with energy minimization (EM) methods were used. According to the calculated binding energy, the favorable positions for THF in these zeolites were discussed. In FER type zeolite, THF molecule prefers FER-cage to 10 member ring (MR) channel. The variation of the potential energy calculated indicates a high-energy barrier of 256.3 kJ·mol–1 for the moving of THF molecule to 10-MR channel from FER cage. Then it is impossible for THF molecule to cross through the 8-MR window under normal conditions. The experiments of 13C HPDEC MAS NMR and adsorption were used to investigate the molecules of THF in the as-synthesized FER zeolite, and the molecules of THF adsorbed in the Na-FER and H-FER zeolite. The results demonstrate that the template molecules of THF are located in FER cages, and the adsorbed molecules of THF are in 10-MR channels of the zeolite. For FER type zeolite, the interaction of framework with other two templates of pyrrolidine and pyridine was calculated for comparison. The preferred binding site for each template investigated is the FER cage site. THF molecule can only occupy the [51264] cage in MTN structure, and the [512] cage is too small for THF to reside. The interaction of THF with MOR framework in 12-MR channel is stronger than that in the side-pocket. The preferred binding site in MFI zeolite is in 10-MR zigzag channel. Relatively, the interaction of the molecule with FER or MTN framework is stronger than that with MOR or MFI framework. The distances between the atoms of THF molecule and oxygen atoms of the zeolite framework, d H-O and d O-O, were calculated. Then the space fitting situation of THF molecule in the cavities or channels of these zeolites was investigated. When THF molecule are located in the favorable positions in these ziolites, such as FER-cage, MTN [51264] cage, it has the favorable values for d H-O and d O-O. The interaction of another template molecule, tetramethylethylenediamine (TMEDA), with FER, MFI, MOR, MTN and NON(CF-3)type zeolites was investigated by the same simulation method as well. The size of TMEDA molecule is much larger than that of THF. The FER-cage is too small for TMEDA molecule to reside in. The favorable site for TMEDA molecule in FER type zeolite is the 10-MR channel. And the calculated energy indicates it is not advantageous for part of TMEDA to occupy the FER-cage and the other part to reside in the 10-MR channel. In MFI type zeolite, TMEDA prefers the sinuous 10-MR channel to straight channel. TMEDA molecules can only locate in 12-MR channels in MOR zeolite and the [51264] cages in MTN zeolite. The cavity of NON zeolite is large enough for TMEDA molecule. The conformation of TMEDA molecule is distorted obviously in the cage of MTN or NON zeolite. The distances between the hydrogen atoms of TMEDA molecule and the oxygen atoms of the zeolite framework, d H-O, were calculated too, showing the different situation of space fitting for TMEDA molecule in the cavities or in the channels of these zeolites.The interaction of small amines, alcohols and alkanes with siliceous BEA, FAU, FER and MFI type zeolite has been simulated by using similar method. The calculated heats of adsorption for these absorbates are lowest in FAU zeolite, and are highest in MFI and FER zeolites. For alkanes , the results about the adsorption heats were in agreement with the literature reported. In all the types of zeolites investigated, the heats of adsorption rise with the number of carbon atoms increases. The adsorption heats simul...
|
PDF Full Text Request