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Hierarchical TS-1Synthesized by Using Dry Gel Conversion Method and Its Catalytic Performance

Author: WangWeiHai
Tutor: LiGang
School: Dalian University of Technology
Course: Industrial Catalysis
Keywords: Titanium silicate zeolite Hierarchical TS-1 hard template Dry gel conversion O×idation of Sulfur compounds
CLC: TQ426
Type: PhD thesis
Year: 2012
Downloads: 33
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Abstract


The discovery of TS-1is a milestone in zeolite and heterogeneous catalysis research fields. But the pore size of TS-1is small, which limites its application in the area of petrochemical industry and fine chemicals. Hence, it is important to synthesize the hierarchical TS-1with meso/macropores. Currently, the templating method for the preparation of hierarchical zeolites is always used in the system of conventional hydrothermal crystallization. However, the preparation processes of many templates are complicated, and some other templates are costly. Moreover, the titanium and silicalite species are often separated with the meso/macroporous templates during the hydrothermal crystallization. To solve the problems mentioned above, we adopted the dry gel conversion method to synthesize hierarchical TS-1with the carbohydrates as the meso/macropore templates. The main contents of this paper are as follows.With TPABr as the microporous template, the TS-1is prepared by dry gel conversion method. The synthetic conditions and catalytic performance of TS-1samples are investigated in details.With the decrease of the n(EDA)/n(H2O) molar ratio at the bottom of autoclave, TS-1samples present the trend of increase for the crystallinity, Ti content in framework and the catalytic activities in Th oxidation. The content of TPABr has no obvious effect on the crystallinity and the framework Ti content of TS-1as the n(TPABr)/n(H2O) molar ratio exceeds0.12.The hierarchical TS-1has been prepared following the route of silicalite-carbon complex, and the meso/macropores size of the sample is mainly in the range of the5-200nm. As the crystallization time is7d, the crystallinity of the obtained hierarchical TS-1sample is high. With the carbonization temperature of dry gel decreasing, the hydrophilicity of hierarchical TS-1is strengthened and the meso/macropore size increases. The hierarchical TS-1exhibits better catalytic performance than TS-1in Th oxidation and could catalyze the oxidation of bulky molecule sulfur compounds BT. The catalytic activity of hierarchical TS-1with weak hydrophilicity is high in the oxidation of BT with the H2O2as oxidant.The hierarchical TS-1is synthesized with the meso/macroporous template caramel that could be obtained through the heat-treatment of aqueous solution of glucose and ammonia at145℃for0.5h. The caramel could spontaneously convert to hard template due to partial carbonization during dryness of gel, which avoids high-temperature carbonization in inert atmosphere. With the n(ammonia)/n(glucose) molar ratio increasing, fhe Zeta potential of caramel changes from positive to negative. But the camarel with positive or negative Zeta potential could be used as meso/macroporous templates to synthesize the hierarchical TS-1. Both N2physical adsorption-desorption and mercury porosimetry are adopted to characterize the hierarchical TS-1, and the results show that the obtained samples possess the well connected network of meso/macropores that could be fully accessible from the external surface. Compared with TS-1, hierarchical TS-1exhibits improved catalytic performance in the oxidation of sulfur compounds Th, BT and4,6-DMDBT.The hierarchical TS-1could be also synthesized by directly using agricultural product sucrose (finished product) as meso/macroporous templates. The characterization results of N2physical adsorption-desorption and mercury porosimetry indicate that these meso/macropores are not closed. The crystallinity of the hierarchical TS-1samples change little with the n(sucrose)/n(SiO2) molar ratio in the range of0.25～0.52, but the content of the extra-framework Ti increases as the amount of sucrose increasing. Moreover, the purely natural sugar juice directly squeezed from the sugarcane (the first procedure for sucrose pruduction) is also applied in the preparation of the hierarchical TS-1. The hierarchical TS-1shows better catalytic activities than TS-1in the oxidation of Th, BT and4,6-DMDBT.

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