| Owing to the differences of purities, chemical compositions and crystal morphologies, Al2O3 displays many different performances, which has been used widely in many fields, such as metallurgy, astronautics, electronic, chemical processes, catalysts and supports, fireproof materials, insulation materials, filling agents, ceramics and mechanics, etc. As the catalytic materials, AI2O3 should behave a high thermal stability, big surface area, special structure and morphology. Nowadays, mesoporous Al2O3 with a high thermal stability, big surface area, special structure and morphology has attracted people's much more attention. In this thesis, some novel methods were designed to synthesize novel mesoporous Al2O3 and doped mesoporous Al2O3 and their textural and structural properties have been characterized by the recent analytic techniques. The catalytic performances of Pt catalysts supported mesoporous Al2O3 were investigated for the hydrogenation of acetophenone (or nitrobenzene). The effects of the textural and structural properties and morphologies of supports on the catalytic hydrogenation performances of Pt catalysts were studied. The main results obtained are as follows:Mesoporous Al2O3 was synthesized with the synthesis solution of "Chitosan (CS)-Al(NO3)3-NH3-H2O ". The results indicate that, the CS amount in the synthesis solution has a great influence on the macro-shapes, surface mirco-morphologies, pore structures and surface areas of prepared Al2O3. When supported Pt/Al2O3 catalyst was prepared by the "incipient wetness impregnation method" with the H2PtCl6 aqueous solution (7.72×10-2 mol/L, pH≈1), the acid eroding phenomenon of Al2O3 will occur, which results in the structure re-construction of Al2O3 and the surface area of the prepared Pt/Al2O3 catalyst is larger than that of the Al2O3 support, at the same time, its pore volume and pore size distribution will be changed. The calcination temperature of the as-synthesized catalyst has a great influence on the Pt dispersion. The appropriate calcination temperature is 550℃and is in favor of the good dispersion of Pt on the surface. For the hydrogenation of acetophenone, Pt/Al2O3 (synthesized A12O3 using CS as a template) has higher catalytic activity than Pt/y-Al2O3 (commercialγ-Al2O3). The catalytic properties of Pt active sites and Pt dispersion on the catalyst will be varied by the surface morphology and pore structure of support, resulting in the change of the catalytic efficiency of whole catalyst. A novel flower-like spherical mesoporous A12O3 was synthesized hydrothermally first at 180℃in the synthesis solution of "Al(NO3)3-Glucose-H2O". The possible evolution process of flower-like spherical mesoporous A12O3 was proposed based on the relations of the structure characteristics and the effect factors on the structure properties of Al2O3. The results show that, the mole ratio of Al(NO3)3 to glucose, pH value in the synthesis solution and so on have a great influence on the morphology of prepared Al2O3, and the different Al precursors such as Al(NO3)3, AlC13, Al(OCH(CH3)2) and Al2(SO4)3 affect also the morphology and composition of prepared Al2O3. Using this novel method, the metal doped flower-like spherical Al2O3 (such as La-Al2O3 and Ce-Al2O3) and other metal oxides (such as La2O3, Ce2O3 and Fe2O3) with special morphology can be synthesized, indicating it is an excellent approach to prepare the metal oxides with special morphology. Using the flower-like spherical Al2O3 as the support, the Pt/Al2O3 catalysts were prepared by an incipient wetness method and in-situ reduction method. The catalyst prepared by an incipient wetness method has an uneven Pt dispersion and large Pt particles. The catalyst prepared by an in-situ reduction method has a good Pt dispersion, however, during the preparing process, a quite amount of Pt will be lost, and the structure of Al2O3 support will be destroyed in a certain degree. For the hydrogenation of nitrobenzene,3.2%Pt/Al2O3 catalyst prepared by an in-situ reduction method in aqueous solution has the higher catalytic activity than that of 3.3%Pt/Al2O3 prepared by the in-situ reduction method in ethanol solution, the latter has the similar catalytic activity to 5.0%Pt/Al2O3 prepared by an incipient wetness method.In the synthesis solution of "Ethyl Acetate (EA)-NaAlO2-H20", the nanowire assembled mesoporous Al2O3 was synthesized first at room temperature. The properties (such as morphology, pore size distribution and pore volume) of the synthesized Al2O3 are affected by the reaction time, aged time under stirring before standing, NaAlO2 and EA amounts, and reaction temperature, solvent and so on. Using synthesized Al2O3 and commercialγ-Al2O3 as the supports, the Pt catalysts were prepared by an incipient wetness method. Compared with the Pt catalyst on commercialγ-Al2O3, the Pt catalyst on the nanowire assembled mesoporous Al2O3 (Pt/Al2O3), has much more positive charged adsorption centers with different strengths, or the PtOx supported on it exists as much more dispersed phase or particle phase, which makes some Pt particles supported on the synthesized Al2O3 exist as Pt nano-crystals. For the hydrogenation of nitrobenzene, Pt/Al2O3 has an excellent catalytic activity, which is higher than that of Pt/γ-Al2O3.Using cetyltrimethylammonium bromide (CTAB) as a liquid crystal template and Al(OCH(CH3)2)3 as Al source, obtained Al2O3 after washed with ethanol is of a certain ordered meso-pore structure, which will be lost after being calcined. Using sodium dodecylbenzenesulfonate (SDBS) or sodium dodecylsulfonate (SDS) as a template and the "Urea-Al(NO3)3-H2O" synthesis system, the as-synthesized sample is of the ordered meso-structure and will be destroyed after being calcined in air. The amounts of template, urea and Al(NO3)3 in the synthesis solution have a influence on the ordered pore structure of as-synthesized samples. When the as-synthesized sample is calcined at below 200℃in N2, its ordered meso-structure can be maintained, and after being calcined at above 200℃its ordered meso-structure will be lost because of the carbonization of organic compounds and the severe dehydration of the calcined sample.Spherical-like Pt-MCM-41 meso-materials (including Pt-MCM-41, Pt-Al-MCM-41 and Pt-La-MCM-41) and MCM-41 were synthesized by a "one-step" approach with orthosilicate (TEOS) as silica source and cetyltrimethylammonium bromide (CTAB) as a template in the acidic solution at 0℃. The prepared samples have high surface areas of 1151-1389 m2/g with the pores of 2-3 nm. As the metallic cations (such as Al3+ and La3+) are very stable in acidic solution and the metal-O-Si bonds can formed uneasy, they are hardly incorporated into the synthesized samples. H2PtCl2 precursor can be almost 100% incorporated in the samples, based on the strong electrostatic interaction between the negatively charged PtCl62- and the positively charged C16H31(CH3)3N+, which avoids the low utilization of precious metal in synthesizing the precious metal-containing catalyst at the basic condition. H2PtCl6 in the as-synthesized samples can be decomposed mostly into metallic Pt with part of Pt2Si and few Pt oxides, when the as-synthesized sample was calcined at 550℃to remove the template. For the catalytic hydrogenation of nitrobenzene, the calcined Pt-MCM-41 meso-material exhibits high catalytic activity with excellent selectivity to aniline, which is similar to the corresponding reduced sample.
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