Synthesis, Morphology Control, And Characterization Of Highly Stabilized Mesoporous Alumina

Mesoporous alumina is superior to silica due to resistance toward oxidation and corrosion, high mechanical strength, favorable combination of surface and textural properties, and convenience to be loaded with different metal species. These features make it highly desirable in catalysis and adsorption, especially in bulk molecule processes. However, the applications going beyond laboratory tests are at present out of reach. Aluminum alkoxides are susceptible to hydrolysis and phase transitions accompanied by thermal breakdown of the structural integrity, which make them difficult to create mesoporous alumina. Moreover, the structure in mesopore scale and morphology control need further improve. In the dissertation, with the recently development in nanotechnology and mesoporous materials formation mechanism, we hope to overcome the above motioned question, develop cost effective mesoporous alumina synthesis method, and improve the thermal stability and morphology control of mesoporous alumina. XRD, FT-IR, TG-DTG, TEM, and N₂ adsorption were used to characterize the mesoporous alumina. The results are listed below:A combination of octanol and acetonitrile is optimal for the synthesis of mesoporous alumina with high thermal stability. In the mixed solution, the aluminum alkoxide dissolved into octanol and not into acetonitrile, but water dissolved into acetonitrile. Hence, alkoxide hydrolysis is inhibited by the two phase interface. Mesoporous alumina with wormhole like mesopore channel can be synthesized with surfactant as template in sol-gel method. And mesopore diameters can be easily modified by the aging temperature. The nonionic PEO surfactant acts as a structure-directing agent to direct the formation of alumina mesostructure with excellent thermal stability through hydrogen bond inducing the arrangement of rigid boehmite particulates in the sonochemical method. Another advantage in the application of ultrasound radiation is the drastic reduction in the fabrication time from days to 3-6 h.Mesoporousγ-Al₂O₃ has been successfully synthesized by using the cheap and environmental-friendly urea. It has demonstrated that urea not only acts as a structure-directing agent via the hydrogen bonds, but also effectively preserves the sintering behavior of nanocrystals during calcination. The structural properties and thermal stability of the products can be effectively controlled through adjusting the morphologies and crystalline phases. The mesoporousγ-Al₂O₃ obtained 372 m²/g surface area and 0.84 cm³/g pore volume after calcination at 600℃. Mesoporous aluminas with high thermal stability have been prepared by hydrolysis of Al(OC₃H₇)₃ using sol-gel technique combining instant calcination without the aid of template. The results show that the organic compounds of acetoacetic ester (EAA) and acetic acid (AcOH) not only control the rate of hydrolysis and condensation but also determine the particle size and the morphology of alumina. And the instant calcination can inhibit the formation ofα-Al₂O₃ "dendrites" and improve the thermal stability.Based on the layer-structured A100H, a rolling mechanism has been introduced to explain the formation of the mesopores and the growth of one-dimensional nanostructures under solvothermal conditions at 190℃. The structural properties and morphologies of the products can be effectively controlled by manipulating the composition of the solvent and the reaction temperature.Solvent is a key factor for the formation of mesostructured alumina with high thermal stability. The thermal stability of the mesoporous alumina can be enhanced by the combination of octanol and acetonitrile. The structure and composition of pore wall can be modified by synthesis through different methods. Mesoporous aluminas prepared by ultrasound radiation obtain high specific surface areas, large porosities, and excellent thermal stabilities, which should be attributed to their crystalline and thicker framework walls. The obtained mesoporous alumina had still mesoporous structure after calcination at 900℃for 3 h and obtained 258 m²/g surface area. The growth of particle is related to the crystalline structure. The mesoporous framework is composed of fibrous nanoparticles of boehmite. The thermal stability of mesoporous alumina was affected by the heating rate.The dibenzothiophene conversions and durability superior to that of a commercial catalyst have been achieved over the mesoporous alumina catalysts. Compared with the commercial catalyst, the dibenzothiophene conversion reached 98.8% and increased 31.5% at 260℃. Inks in the form of alumina suspension have been prepared by high-shear dispersing emulsifier firstly. Compared with ball milling methodology,α-Al₂O₃ ceramic inks have shown excellent dispersiveness, stability, and high solid content (10 vol%) obtained by high-shear dispersing emulsifier which satisfy the requirements of ink-jet printer based on the print test. Another advantage of high-shear dispersing emulsifier is the drastic reduction in the fabrication time from days to 4 h.