Preparation And Catalytic Performance Of Zirconium Silicates With MFI Structure And Its Sulfated Solid Superacid

Microporous molecular sieve with MFI structure contains regular three- dimensional channel and its basic structural unit consists of eight five-membered ring, forming a molecular sieve having a good hydrothermal stability of the skeleton structure and high surface area properties, which exhibit a good shape-selective catalytic function, but it own weak acidity; SO42-/Zr O2 solid super acid catalyst has high acid strength, high catalytic activity, relatively low temperature catalytic performance, renewable and reusable, and no corrosion and pollution, etc., but its relatively small surface area, irregular pore structure make its catalytic selectivity poor, which limit their applications in industry. This paper aims to combine the super acid features of strong acidic solid and advantages of the microporous structure of MFI zeolite, developing a promising molecular sieve catalyst with super acid performance and environmentally friendly features.In this thesis, hydrothermal method(DHT) and template ion exchange method(TIE) were used for the synthesis of the zirconium silicon molecular sieve with MFI structure. The effects of synthesis method and synthesis conditions on its structure were investigated.Firstly, zirconium silicon zeolite was synthesized by hydrothermal method(DHT). The effect of synthesis conditions including zirconium source, solvent type, the molar ratio of zirconium silicon, template dosage, crystallization time, crystallization temperature, calcination time and calcination temperature on the molecular sieve structure were investigated by the technique of XRD, FT-IR, ICP, N2 physical adsorption-desorption and SEM. Results showed that zirconium nitrate pentahydrate as zirconium source, anhydrous ethanol as solvent source were the best choice; with mole ratio of(Zr)/(Si) increasing in the range of 0.005 to 0.03, the zirconium content of the molecular sieve did not increase to some extent; external skeleton Zr O2 was absence; increasing the mole ratio of(TPAOH)/(TEOS) increased the content of zirconium in the molecular sieve framework; accelerating the crystallization rate made the particle size of molecular sieve smaller; crystallization process basically completed after 12 h crystallization time; long crystallization time and higher crystallization temperature is favor of the incorporation of zirconium atom into the zeolite framework; roasting time more than 4 h had little effect on the structure of zirconium silicon MFI structure; calcination temperature below 550℃ made the roasting incomplete, but the skeletal structure of molecular sieves was destroyed under the higher calcination temperature above 550℃.Secondly, zirconium silicon zeolite with MFI structure was synthesized from the ion-exchange method(TIE). The effect of synthesis conditions including zirconium source type, switching temperature, switching time and the molar ratio of zirconium/silicon on the structure of the zeolite were investigated by the means of XRD, FT-IR, UV-Vis, ICP, N2 adsorption-desorption and other physical characterization methods. The results showed that zirconium oxychloride was the proper zirconium source; higher temperature is beneficial to distribution of more zirconium species into the molecular sieve; longer the exchange time favored the zirconium atom incorporating into the zeolite framework, while the total zirconium content of molecular sieve decreased simultaneously; increasing the mole ratio of(Zr)/(Si), tetragonal zirconia reunited outside the zirconium species was appeared, which also resulted in the increase of total zirconium content.Finally, SO42-/Zr-MFI as super acid catalyst with MFI zeolite structure were synthesized. Their structural features were analyzed by a variety of means. Esterification reaction of cyclohexyl ester from cyclohexene and formic acid was used as the probe reaction to evaluate the catalytic performance. The results showed that the obtained SO42-/Zr-MFI catalysts from two methods both have good MFI topology structure and super-acidic sites. SO42-/Zr-MFI(TIE) had the stronger acid sites than SO42-/Zr-MFI(DHT) significantly. Two kinds of super acid catalyst SO42-/Zr-MFI exhibited the better performance of acid catalyst in the reaction of cyclohexene-formic acid esterification reactions. Relatively, the catalytic activity of SO42-/Zr-MFI(TIE) was higher than that of SO42-/Zr-MFI(DHT).