| KF/Al2O3 as a kind of solid base catalyst is superior to the liquid alkali in many aspects, such as: easier separation from the final products, better reutilization, high stereoselectivity, environmental protection and et al. In recent years, KF/Al2O3 has been employed in many organic reactions, especially in Michael addition ,Knoevenagel condensation,Witting reactions and so on, which all play a key role in various compounds'synthesis. So it is very import to develop an efficient KF/Al2O3 solid base catalyst. The classical KF/Al2O3 was prepared by immersing Al2O3 powder into KF hydrous solution. The disadvantages of this catalyst are: the uneven distribution of the KF on Al2O3, the lower surface area of the catalyst, which all lead to the worse catalytic performance. It has also been obscure of KF/Al2O3's surface morphology, catalytic mechanisms. In this paper the study on increasing the catalyst'surface area and improving the uniformity of KF on Al2O3 surface have been done. Meanwhile, the substance which has the catalytic capacity and mechanism of the catalyst have also been discussed. With the development of the nanometer technologies, the literatures about its application in the preparation of catalysts are more and more. The Sol-gel method is particularly attractive for its advantages such as: lower processing temperature, the control of the catalyst at the initial time, high homogeneity and purity of the final materials. Enlightened by above ideas, firstly 50nm Al2O3 has been prepared by the organic Sol-gel method with organic acid catalyst. The effects of way of adding water,quantity of water,time of gelation,different species of catalyst,quantity of catalyst and ultrasonic technology on particles size were studied. A series of techniques of characterization, e.g. scanning electron microscope (SEM), powder X-ray diffraction (XRD), temperature weight and differential scanning calorimetry were used to characterize the intermediate and final products. In the second part, 80nm Al2O3 has been synthesized by Sol-gel method with KF catalyst. Then, 50nm KF/Al2O3 has been synthesized by Sol-gel method. In the process, KF acted with the surface Al2O3 in some way to form the active base center while as a catalyst in the synthesis of nano-Al2O3. Knoevenagel condensation and Michael addition reactions have been selected to test the catalyst's performance and "Even Design"software are also used to optimize the preparation process. As for the Knoevenagel condensation reaction, the optimal conditions of preparation of KF/Al2O3 were: KF·2H2O: 1.9g, reaction time: 5h, reaction temperature: 80℃; calcinations temperation, 400℃and the α-cyanocinnamic acid ethyl ester yield is 94.5%. For Michael addition reaction, the optimal conditions were: KF·2H2O: 2.9g, reaction time: 5h and the(2-cyanoethyl)malonic acid diethyl ester yield is 88.0%. In addition , nano-KF/Al2O3 also has high stereoselectivity for the Knoevenagel condensation reaction and excellent reutilization performance. In the third part, the catalyst was been characterized by several technologies of characterization including scanning electron microscope (SEM), powder X-ray diffraction (XRD) , temperature programmer desorption (CO2-TPD) and X-ray photoelection spectrometry(XPS). From the analysis, it can be concluded that nano-KF/Al2O3 catalyst has three basic sites, [Al-OH…F] species may be response to Knoevenagel reactions and K3AlF6 may be response to Michael addition reaction. |
