Preparation And Catalytic Performance Of Titanium-containing Hierarchical Zeolite Y

Currently, oxidative desulfurization(ODS) of fue l oil was regarded as a new alternative method to traditional hydrodesulfurization(HDS). Because this process may be operated at mild conditions such as room temperature and ambient pressure, energy consumption and processing cost could be greatly lowered. Generally, this technology needs the addition of catalysts and oxidants. In this catalytic system, usually hydrogen peroxides or organic hydroperoxides were used as oxidants and heterogeneous catalysts were favorable to facilitate the separation and recovery of catalysts. Among these catalysts, Ti-containing zeolites such as Ti-containing ZSM-5(TS-1) as one kind of important ODS catalysts have been widely investigated. This kind of catalysts showed excellent catalytic performance in ODS of small molecules such as thiophene(TH). However, they almost have no catalytic activity in the removal of large sulfur-containing molecules such as dibenzothiophene(DBT). The reason can be mainly attributed to the limitation of microspore systems where the bulky substrates cannot contact with the active titanium sites in the zeolite framework. Consequently, there has been of great interests to introduce mesopores or/and macrospores into microporous zeolites and develop titanium-containing hierarchical zeolites. In this article, firstly hierarchical zeolite Y was prepared by treating parent zeolite Y using post-treatment method. Then, titanium-containing hierarchical zeolite Y was synthesized by wetness impregnation technique, and characterized by several methods. Further, their ODS catalytic performance were systematically evaluated.First, two hierarchical zeolite Y(MY1 and MY2) with different mesoporosity were obtained by post-treatment method and active Ti species were introduced into the two supports to obtain two titanium-containing hierarchical zeolite Y. The obtained samples were characterized by X-ray powder diffraction, N2 adsorption-desorption, UV- visible spectroscopy, FT-IR spectroscopy, scanning electron microscopy and X-Ray Fluorescence spectroscopy. Then, their catalytic performance was evaluated by ODS of DBT in the catalytic system of CH3CN/H2O2 in order to screen a better catalyst support. The results indicated that MY2 was a better catalyst support than that MY1 for the introduction of active Ti species.Finally, based on the support MY2, a series of Ti-containing hierarchical zeolite Y catalysts were prepared by changing Ti content and structurally characterized. The catalytic performance of the obtained catalysts was evaluated by ODS of DBT using oil-soluble CHP as oxidants. The results indicated that Ti-containing hierarchical zeolite Y with 30wt%Ti(30%Ti-MY2) exhibited best catalytic ODS activity. Further, the catalytic performance of 30%Ti- MY2 was systematically investigated by changing reaction conditions including temperature, oxidant/sulfur, catalysts dosage and S concentrations to optimize catalytic reaction system. Besides, recycling ability of 30%Ti-MY2 was also evaluated at an optimized reaction conditions. The results showed that the catalyst could be reusable and maintain good catalytic activity. Additionally, the catalytic performance of 30%Ti-MY2 was tested in the ODS reaction of 4,6-dimethyl-dibenzothiophene(DMDBT) with relatively large molecular size and the results turned out that it still had activity in some extent.