Study On Preparations And Applications Of Alumina-supported KF Nanocatalyst

In the past decade, there has been a rapid growth in research and development of nanotechnology, especially nanostructured materials. Nanostructured materials of high surface area present great promises and opportunities for a new generation of materials with improved and tailorable properties for applications in sensors, optoelectronics, energy storage, separation and catalysis. The nanomaterials and nanotechnology have been recognized as the fields with the best prospects in 21 century. The catalysis can appear characteristic features by synthesis and processing of nanoparticles , and they can also be designed systematically.KF/A12O3 is a solid superbase catalyst which was extremely desirable for many organic synthesis reactions due to its distinguished advantages and it becomes a new environment-protecting catalyst. From a practical catalysis standpoint, a large specific surface for nanocatalyst is desired. In this research, we synthesized and studied KF/Al2O3. This catalyst took advantage of high surface area of nanoparticles and the KF can be dispersed in Alumina nanoparticles uniformly and was regarded as a catalyst with strong basicity and nucleophile.First of all, nanocatalyst KF/Al2O3 whose particle size is between 20-40nm was prepared by method of impregnation of KF solution in Y -Al2O3 nanoparticles supports. The effects of various factors in preparation were studied. The results of test indicated that the best preparation conditions were : immersing solvent: ethanol; immersing temperiture:65°C; the molar radio of modifiers: PEG6000:PEG4000=l:l.We chose the Michael addition of acrylonitrile and diethyle malonate as a model system of our study. Catalytic activity of KF/Al2O3 were examined by acting as a catalyst to the reaction. The reactivity was discussed on the basis of surface properties of catalyst prepared in different conditions such as loadings of KF·2H2O, quantities of used catalysts, calcining temperature, reaction time, reactants ratios and so on. When the amount of loading was 0.03mol F", the calcining temperature was 400℃ and the molar radio of malonic ester and acrylon was 1:3, the conversion was 93.3% after 1.5hour. In addition, Alumina support could be reused at least 5 times with highactivity so as to lower the cost of catalyst. The effects of varied factors in preparation also were analyzed by orthogonal experiment and non-liner regression. The experiments were carried out according the orthogonal experiment designs, and the analyzed results by ANOVA showed that the factors that had been discussed were important roles in preparation. The empirical model building were set up to express the relationship of response and factors.The KF/AI2O3 exhibited high activity in the synthesis reaction of ?> -substitutedamino( azotic heterocycle )- propionate. These Michael addition reactions proceeded very efficiently over KF/AI2O3 at room temperature. The results showed that the activities of nanoparticles KF/AI2O3 were higher than those of ordinary ones and the sample whose loading amount was N-5 gave the best catalytic results.However, the preparation of KF/AI2O3 by impregnation often resulted in agglomerated catalyst particles in support, thus decreased the active surface area, and uniformity of the active centers. A feasible approach such as sol-gel to generating a large and accessible surface area of catalyst was tried. With nanostructuring techniques, active component KF could be incorporated or grafted on the alumina nanoparticles during synthesis. Thus not only the control in catalyst particle size, surface area and dispersion could be increased, but also the cost could be reduced and problems associated with impregnation could be resolved.After several tests, we chose ihe sol-gel technology by hydrolysis of aluminum triisopropoxide (A1(OC3H7)3) to prepare the alumina nanoparticles. Some factors which influenced the particles diameters and properties were studied. The preparation conditions was obtained as follows: methanol as solvent, formic acid as peptizer, A1(OC3H7)3 : H2O=1 : 3(molar ratio), samples dried in 60°C for 6h and 120°C for 2h subsequently. Ultrasonic technique was applied in the sol-gel process to avoid the formation of agglomeration. The results showed that the Ultrasonic cavitation process could affect the agglomeration of the precursor nanoparticles. The high purity of y -AI2O3 was formed when calcination temperature was 700 °C and a - AI2O3 was formed when temperature reached 1000°C.We developed a new approach to prepared KF/AI2O3 by adding KF directly insol-gel process. The most effective preparation conditions analyzed by uniform design were obtained. The results showed that the amount of KF ? 2H2O was relevant to the catalytic activities. The results also showed that the maximum of KF ? 2H2O was 2.0g, and if the amount of KF ? 2H2O was over 2.0g, the nanoparticles agglomerated badly.Between the KF/AI2O3 prepared by impregnation and the one prepared by sol-gel, there was little difference in the catalytic activities, but there was much difference in the amount used in reactions . The conversion of Michael addition could reach 86% and 94% in Knoevenagel condensation reaction. The catalyst had catalytic selectivity for Knoevenagel condensation, only the E isomers of the products were obtained.The surface structure and properties of KF/AI2O3 prepared both by impregnation and sol-gel were studied by IR, XRD, CO2-TPD, SEM, XPS and so on. Based on the results the basic active sites on KF/AI2O3 were confirmed, the K3AIF6 and [A1-0H--F"] species were recognized to be the main active species both in Michael addition and in Knoevenagel condensation.