The Research Of Synthesis And Catalytic Performance Of MCM-41 Mesoporous Molecular Sieves

This thesis takes the synthesis and characterization of mesoporous molecular sieves MCM-41 as the main research content, and find out the optimum synthetic conditions, methods and the application in catalytic realm as the research targets. Firstly, the thesis expounds the significance of studying inorganic mesoporous materials, reviews the research development course in this field, generalizes the characteristic, synthetic mechanism, routes and diversified characteristic data, and points out the existing problems of these materials. Thereform, the research plan of this thesis is proposed. We study systematically the influence of synthetic factors on the structure and properties of silica MCM-41 and the MCM-41 containing mixed metal atomic by Powder X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Transmission Electron Microscope (TEM) and N₂ physisorption studies.In the preceding parts of the experiments, silica MCM-41 mesoporous molecular sieves were prepared by the hydrothermal crystallizing method in basic media and microwave radiation with materials of cetyltrimethyl ammonium bromide (CTAB), as a template, and sodium silicate (Na₂SiO₃·9H₂O), as silicon sources, respectively. The experimental results indicate that MCM-41 materials can be prepared by the hydrothermal crystallizing method and microwave radiation. The suitable synthetic conditions of silica MCM-41 are that the value of PH equals to 10～11, the radio of surfactant/silica is 0.2, radio of water/silica is 70, aging time is 80 minutes, crystallizing temperature is 130℃and crystallizing time is 72 hours in hydrothermal crystallizing method, the crystallizing time is 2.5 hours and the radiation power is 280W in microwave radiation method. The all characteristic data of MCM-41 materials prepared via the two methods are almost same. Particle size distribution range in 30～50 nm, BET surface area was more than 800 m²/g, thermal stability is higher than 1000 K. The MCM-41 materials prepared by microwave radiation has a very short inducement time and very fast crystallizing speed, some of them have a surface more than 1000m²/g. But the hydrothermal stabilities of the MCM-41 materials are not good and waiting for improvement.The thermal stability of silica MCM-41 and the MCM-41 containing mixed metal atomic prepared by the two methods are better than other mesosturctured materials. The most of mesopores still exist after MCM-41 materials are calcined at 700℃. But calcining at higher temperature 900℃may make some mesopores be destroyed, surface area become small, pore distribution broaden and framework intend to amorphous silica's. The almost all organic templates can be removed by calcination in microwave radiation also while it is difficult to control calcining power and time neither more nor less than。Comparing MCM-41 modified in framework by Co, Cu and Ni with silica MCM-41, it is found that the structure of Co-MCM-41, Cu-MCM-41 and Ni-MCM-41 with M/Si=0.05～0.15 are similar to the structure of silica MCM-41. Metal atoms entering into the framework of MCM-41 instead of some Si make the regularity of the structure of MCM-41 be worse. Surface area is smaller, pore diameter is larger and pore distribution is broader than silica MCM-41's. When M/Si is more than 0.2, the framework of part of samples collapse, surface minish sharply and the diffraction apex in low angle area disappear. The phenomenon mentioned above show that there are influence when metal atoms enter into the framework of MCM-41.In the rear parts of the experiments, the H-MCM-41 is prepared via dipping in NH₄NO₃ solution, calcining, and pressing with MCM-41 synthesized by microwave radiation, and is applied in alkylation reaction of Phenol with tert-butanol to validate its catalytic performance. The result of experiment shows that H-MCM-41 synthesized by microwave radiation has remarkable catalysis to alkylation reaction of Phenol with tert-butanol, but its selectivity is obvious different with the data reported by literature. The main outcome is 4-TBP, 6-DTBP and 2, 4, 6-TTBP but not 2, 4-DTBP。The acidity of H-MCM-41 has obvious influence to alkylation reaction. The selectivity of alkylation could be controlled in a certain degree by modulating reaction temperature, airspeed and ratio of materials. H-MCM-41catalyst's life is about 50 h in alkylation reaction of phenol with tert-butanol. The transform ratio would drop obviously after 50h which shows that the acidity center of H-MCM-41 prepared by dipping into NH₄NO₃ solution is comparatively weak and is easy to be divorced from framework.