Study On The Controllable Synthesis And Adsorption?Catalytic Properties Of Well-ordered Mesoporous Materials With Short Channels

Well-ordered mesoporous materials have been found great applications in the fields of catalysis, adsorption, separation and biomedicine because of their highly ordered pore structure, uniform pore size, large pore volume, high special surface area, the presence of voids of controllable dimensions at 2-50 nanometer scales, and easily modified surface characteristics. The morphology of conventional SBA-15 are usually bar or fiber aggregates. The slow transfer and diffusion of reactants in the relatively long channels has been the main problem for dynamic reaction when SBA-15 was used as catalyst, sorption and separation media. For solving such problem, a new one-step hydrothermal routine was used to synthesis highly ordered SBA-15 mesoporous material with hexagonal platelet morphology and short channels. The controlling factors for the synthesis of the new mesoporous material were systematically studied and the optimized condition was obtained. Amino-functionalized H2N-Zr-Ce-SBA-15 (H2N-ZCS) catalyst and Cu-Mn/ZCS catalyst were prepared based on the newly formed hexagonal platelet SBA-15. The catalytic and adsorption property of the catalysts based on ZCS were superior to the conventional SBA-15. The main research work and results are summarized as follows.(1) The mesoporous Zr-Ce-SBA-15 (ZCS) materials with various morphologies were synthesized by a one step hydrothermal route using tetraethyl orthosilicate as a silica source, Pluronic P123 as a template, zirconyl chloride and cerous nitrate as a precursor under a moderate self-generated acidic condition produced by the hydrolysis of the precursor, without the addition of mineral acids. The effects of the controlling factors on the morphologies and structures of ZCS, including molar ratios of nZr(Ce)/nSi and nZr/nCe, hydrothermal temperature and crystallization temperature, were systematically studied. Scanning electron microscope (SEM) and small angel X-ray diffraction (SXRD) were used to characterize the morphology and order of the arrangement of the mesopores. The relationship between synthetic parameters and the morphology and structure of mesopores was established.(2) With such a one step hydrothermal method, highly ordered mesoporous ZCS with hexagonal-platelet morphology was synthesized by controlling the reaction temperature at 35?and molar ratios of nZr(Ce)/nSi and nZr/nCe at 0.05 and 1, respectively. Inductively coupled plasma atomic emission spectrometry (ICP-AES), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N? adsorption/desorption were used to characterize the elemental and phase composition, morphology and microstructure of the as synthesized ZCS. Characterization reveals that the ZCS possesses a 2D hexagonal mesoporous structure similar to SBA-15. The average pore size, pore volume and specific surface area of the materials are 6.4nm,0.96 cm3/g and 776 m2/g, respectively.(3) Amino-functionalized H2N-Zr-Ce-SBA-15(H2N-ZCS) and thiol-functionalization HS-Zr-Ce-SBA-15(HS-ZCS) mesoporous materials with unique hexagonal platelet morphologies and short channels were respectively synthesized by post-grafting and co-condensation methods using [1-(2-amino-ethyl)-3-aminopropyl] trimethoxysilane (AAPTS), and 3-mercaptopropyltrimethoxysilane (MPTMS) as organic modifiers. The physical and chemical analysis indicates that AAPTS and MPTMS were successfully grafted to the host mesopores and the functionalized mesoporous materials have unique hexagonal platelet morphologies with short channels and they possess a highly ordered two-dimensional hexagonal mesoporous structure similar to conventional SBA-15. The study on the sorption of organic dye indicates that functionalized mesoporous materials have higher adsorption rates and adsorption capacities compared with conventional SBA-15. The improved performance is attributed to the short channels in the functionalized ZCS materials which facilitate molecular diffusion and quickly achieve the balance of adsorption/desorption.(4) Cu-Mn/ZCS catalyst was prepared by impregnation method. The catalytic activity of the catalyst was evaluated in the model reaction of toluene combustion. The synthetic condition was optimized and the mechanism was discussed. Results indicate that Cu-Mn/ZCS possesses a superior catalytic activity when it was prepared at such conditions as Cu/Mn mass ratio of 1 and 20 wt.% of Cu-Mn, being sintered at 500?for 4hrs. With such a catalyst, the ignition temperature and total combustion temperature of the toluene combustion was 247?and 270?, respectively. The improved catalytic activity was due to the highly distribution of Cu-Mn reactants in the short channels in ZCS and relatively low crystallization degree of Cu-Mn oxides. These results provide a theoretic and experimental foundation for the application of the short channels mesoporous materials in the catalyst field.