| SO42-/MxOY type superacid, as a new type of catalyst, has some advantages such as its high acid strength and high activities in many organic reactions, it is easy to seperated from the reaction mixture, no corrosive to reactor and friendly to the environment. So it has been extensively used in many organic catalytic reactions of esterification, isomerization of n-alkanes, polymerization, acylation and so on. However, SO42-/MxOY also has some disadvantages such as small in surface area, hard to adjust its acidity and easy to deactivate, which limited its utilization in some extent. In this thesis, a naturally abundant bentonite from Ningmin County, Guangxi Zhuang Autonomous Region was used as raw material to prepare A1-pillared clay by using microwave irradiation method. The A1-pillared clay is of large surface area and good thermal stability. ST/A1-PILC (SO42-/TiO2/Al-pillared clay) solid superacid was prepared by loading active component SO42/TiO2 on Al-pillared clay. The texture structure and surface properties of ST/A1-PILC were characterized by means of modern physical and chemical techniques such a X-ray powder diffraction (XRD), nitrogen adsorption-desorption isotherms, pyridine-adsorption infra-red spectra (Py-IR), Hammett indicator method, X-ray photoelectron spectroscopy (XPS) and Fourier transformation infra-red spectra (FT-IR) technique. Catalytic activity of the catalyst was evaluated using esterification of pentanol with benzoic acid as probe reaction. In order to enhance catalytic stability of the catalyst, ST/A1-PILC was modified with rare-earth elements (La and Ce), and the effect of rare-earth elements on texture structure and surface properties of ST/A1-PILC catalyst was investigated. Several conclusions can be drawn as follows.A1-pillared clay with good properties can be prepared when microwave irradiation time is 10 min, a molar ratio OH7Al3+=2, ratio of Al/clay is 5mmol of aluminum per gram of clay. The basal spacing, specific surface area and pore volume of the Al-pillared clay are 19.8 A, 239 m2/g and 0.34 ml/g respectively. Comparing that obtained from conventional heating method, the Al-pillared clay prepared bymicrowave irradiation method has larger specific surface area, better thermal stability and its pore distribution is quite narrow. The pillared structure is still preserved well after calcination at 650C. While the conventional A1-pillared clay has lower specific surface area (only 198 m2/g) and broadening pore distribution, its pillared structure collapsed after calcination at 650C.The testing results of Hammett indicator method show that the acid strength of ST/A1-PILC catalyst can be adjusted by the loading of TiO2. The acid strength decreases with the decrease in the loading of TiO22. When the loading of TiO2 is less than 29.5 wt%, the samples have no superacidity. Py-IR spectra show that ST/A1-PILC catalyst possesses both Lewis and Bronsted acid sites, and the number of acid sites on ST/ Al-PILC is much larger than that on Al-PILC carrier. The adsorption and desorption of N2 experiment indicates that the introduction of Al-PILC carrier into ST can enhance the specific surface area of ST/A1-PILC catalyst effectively. The X-ray patterns indicate that Al-PILC carrier can inhibit the formation of anatase TiO2 and the transformation of anatase TiO2 into rutile TiO2. FT-IR spectra show that a bridged bidentate complex acid site was formed.The ability of various catalysts to promoted benzoic acid esterification shows that the Al-PILC carrier exhibits very low catalytic activity, and the conversion of benzoic acid increases significantly over the ST/A1-PILC catalyst, the catalytic activity of ST/A1-PILC is higher than that of ST. By studying the stability and deactivation of catalyst, it turns out that the introduction of Al-PILC carrier into ST can reduce the rate of catalyst deactivation, acid sites partly blockage by organics and the loss of sulfur are the main contributors for deactivation, but not the change valence state of sulfur and transition of TiO2 crystal form. The... |
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