| Microporous structure (pore diameteKlnm) limits the applications of microporous Molecular sieves on catalysis. Therefore, synthesis, modification and application have become the most active fields of zeolite molecular sieve, lately. Compared to traditional micropororous molecular sieves, mesoporous molecular sieves are worse in structure order and hydrothermal stability. In this dissertation, we focus on the synthesis of hexagonal mesoporous silica MCM-41 in base medium, the surface anchoring of basic functional groups and the application of functionalized mesoporous silica in the catalysis of Knoevenagel condensation.I. Pure siliceous MCM-41 were synthesized in different basic media (sodium hydroxide, ethylenediamine and hexahydropyridine) by using cetyltrimethylammonium bromide as template and tetraethyl orthosilicate as silica source. Effects of basic media and their contents on the quality of products were investigated, and the nature of the effects was discussed. It was shown that MCM-41 can be obtained in organic weak base with higher quality than that synthesized in NaOH medium. This results not only from the unity of polymerization and charge density but also from the increase in charge density on the surface of micelles caused by conjugated acid cations of organic base. Moreover, the different pH ranges suitable to synthesis are required when MCM-41 is prepared in different basic media. This range is controlled by the intensity of base, the bulk of conjugated acid cations and if the conjugate acid cations increase the charges on the surface of micelles. The polymerization of silica was hindered by the big bulk of conjugated acid cations, thus we could not get solid product in the high concentration of hexahydropyridine system. On the other hand, small conjugated acid cations could not resist the excess polymerization of silicon species, so that only morphous silica was gained in the low concentration of sodium hydroxide. The size of bulk conjugated acid cations of ethylenediamine was so proper that it could resist the over polymerization of silica in low base concentration and favor the polymerization in high base concentration. Weaker base, bulky conjugate acid cations and the penetration into the micelles of the conjugate acid cations are favorable to the synthesis of mesoporous materials in a broad pH range. Employing organic weak base, such as ethylenediamine, as basic medium can not only prepare the sample with higher structure order, crystallinity and stability, but also acquire broad pH range which makes it easier to synthesize MCM-41 with high quality.II.Furthermore, the effects of reaction temperature, addition of sodium chloride and postsynthesis hydrothermal treatment on the quality and the hydrothermal stability of the samples were investigated. It was shown that the elevated reaction temperature and the postsynthesis hydrothermal treatment are favorable to the increase of hydrothermal stability of samples, while the addition of a small amount of sodium chloride can prevent silicon species from excess condensation that may occur during postsynthesis hydrothermal treatment.III.Amino-functionlized MCM-41 was synthesized by co-condensation, the effect of adding salt, high temperature crystallinity and postsynthesis hydrothfcrmal treatment were discussed, these treatments reduced the structure order of functionalized MCM-41. ethyldiamino was imported into MCM-41 by co-condensation method, but the structure of ethyldiamino -functionalized MCM-41 declined severely than amino-functionalized MCM-41. The adding order of TEOS and silicoupling agents affect the structure order of the synthesized functionalized samples, the structure order of MCM-41 synthesized in the sequence of first adding silicoupling then adding TEOS was the best, however, first adding TEOS then adding silicoupling or adding the mixture of TEOS and silicoupling agents, the structure of the synthesized amino-functionalized MCM-41 was worse.Investigation of functionalization condition demonstrated that increase of... |
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