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Porous alumina and alumina - Preparation and characterization of zeolite composites

Author: WuQingLing
Tutor: ZhaoDongYuan
School: Fudan University
Course: Inorganic Chemistry
Keywords: mesoporous materials alumina self-assembly hierarchical porous catalysis
CLC: TB383.4
Type: Master's thesis
Year: 2011
Downloads: 311
Quote: 2
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Abstract


Porous materials with numerous nanoscale pore channels and high surface areas are attracting much attention owing to their unique applications in catalysis, electrics, magnetism, optics, biochemistry, nanotechnology, and sensors et al. After years of efforts and discussions, the porous composite materials with tunable pores, various components, different morphologies and pore channels have been synthesized. However, many challenges and difficulties need to be overcome in the large-scale production and application of ordered mesoporous materials and hierachical porous materials. The synthetic methods with simple, fast, economical and environmental-friendly properties must be developed to obtain the porous materials with high quality, i.e high thermal, hydrothermal stability and crystalline framework. Moreover, the special functionalization of porous materials should be dug for their widely application in catalyst field. This procedure is full of opportunities and challenges.Novel porous alumina materials with large surface areas, ordered structures, large pore sizes and prominent acidic center can be applied in heavy oil macromolecular FCC, heterogeneous catalysis, adsorption and separation in the petrochemical process, and carried enzyme transformation aspects. However, the fast polycondensation rate of alumina gel makes it easier to form disorder pore and amorphous skeleton owing to the lower electronegativity of aluminum comparing with silicon. In addition, the pore size and morphology of mesoporous alumina as the load have a direct effect on the activity of catalyst. It is possible to tune the composition of catalytic reaction products by proper choice of organized mesoporous alumina with different pore sizes as supports. Based on the above considerations, in this thesis, we focus on the synthesis of ordered mesoporous alumina with large pore sizes and hierarchical structure with crystalline framework. Then, we also investigate their applications in catalysis and binder.In chapter two, alumina materials with ordered mesoporosity and hierarchical porosity have been synthesized via a one-step process using aluminum iso-propoxide as an inorganic precursor, pluronic P123 as a template, hydrochloric acid and citric acid as the pH adjustors, and 1,3,5-trimethylbenzene (TMB) as a swelling agent. In addition, the weight ratios of TMB/P123 play important roles in controlling the mesostructures and pore sizes of the final alumina materials. Mesoporous alumina with highly ordered 2-D hexagonal symmetry (space group p6mm) can be synthesized with weight ratios of TMB/P123 ranging from 0 to 3. Simultaneously, the pore sizes of ordered mesoporous aluminas can be gradually enlarged with the increase of the TMB content. However, phase transformation of the mesoporous alumina from the 2-D hexagonal to hierarchical could be realized when the TMB/P123 weight ratio was increased to 5.In chapter three, highly organized macroporous-mesoporous aluminas have been synthesized using poly (methyl methacrylate) colloidal crystal as a hard template and polymer P123 as a soft template. By a combination of hard-soft double template method and evaporation induced self-assemble mathod, we have prepared highly organized hierachical gama-almina. The final materials have anti-opals structure. Then, we studied the catalytic performance of propane dehydrogenation oxidation using the macroporous-mesoporous alumina materials as a support. Furthermore, spherial mesoporous alumina nanoparticles can be produced on the presence of TMB as expansive agent and plastic agent.In chapter four, large monolith ZSM-5 with macroporous architecture by using a polyether polyol-based polyurethane (PU) foam as a sacrificial scaffold has been prepared. Then, we injected the precursors of mesoporous alumina and alumina-supported metal oxides into the ZSM-5 monolith to obtain hierachical composite materials. We analyzed the structures and compotants of these materials by kinds of characterization methods, such as XRD, TEM, SEM and so on. The above method can assemble the zeolite nanocrystals into hierarchical porous zeolite materials with controllable macroscopic maorphologies, mesoporous alumina or alumina-supported metal oxides matrials. Due to the ramified pore structure in several levels, the efficency of catalysis and separation performed on the hierarchical porous zeolite materials can be well improved.

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