The Synthesis And Catalytic Performance Of Hierarchical MFI Zeolite Crystals

To enhance the accessibility of the catalytic active sites in the framework of zeolite, improve the diffusion properties of zeolite and broaden the scope of its utility, hierarchical zeolites aggregated/assemblied by the nanocrystals have been paid important attentions. In present, hierarchical zeolites can be synthesized by post-treating with mulit-steps or with additional secondary templates/additives added, which makes the synthesis complicated and cost-expensive. The dissertation reports that hierarchical zeolites assemblied by the nanocrystals can be hydrothermally synthesized one-step through controlling the supersaturation, ionic strength and other parameters of the synthesis system without the other organic auxiliaries or adding some small organic compounds, and their catalytic performances have been also studied.Firstly, hierarchical nanocrystal ZSM-5 aggregates with high crystallinity and large mesopore volume can be synthesized by adding the 'seed' gel into the synthesis mixture without any other bulky molecular additives and hard templates. The effect of SiO2/Al2O3, pH, H2O/SiO2 and the amount of the 'seed' gel on the aggregate morphology of the ZSM-5 nanocrystals were investigated. The obtained aggregates possess significant textual porosity (up to 0.6 cm3/g), which is mainly contributed to secondary meso-porosity (0.35-0.45 cm3/g). And the novely hierarchical ZSM-5 exhibits the higher activity than that of the industry-ZSM-5 and similar to that of nano-ZSM-5 in the catalytic reaction of alkylation of phenol with ter-butanol, and the aggregate of nano-ZSM-5 may curtail the filtration difficulties in the preparation to some extent. The total acid sites of mesoporous calcined ZSM-5 is little influenced after ion change, which shows that template molecule don't jam the channel of the mesoporous ZSM-5 zeolite when the template molecule used is little, which makes the synthesis environmentally benign.Hierarchical nancrystalline TS-1 can be simply synthesized using tetrapropylammonium hydroxide (TPAOH) as single template through adding a 'seed' gel into the synthesis mixture. These mesoporous voids originate from the intergrowth of small primary units. Compared with the conventional TS-1, And the hierarchical nancrystalline TS-1 leads to an obviously enhanced activities in the epoxidation of bulky molecules cyclohexene using aqueous H2O2 solution as oxidant due that the small units and the presence of mesoporous voids in our TS-1 samples could effectively reduce the diffusion limitations. Meanwhile, the realtively large aggregates may curtail the filtration difficulities in the preparation and catalytic applications to some extent.Recently, the use of organosilanes has provided new routes for the preparation of zeolitic materials with hierarchical structure. Here, we use bridged organosilane, (R'O)3Si-R-Si(OR')3, as silanization agent to make the zeolites nanoseeds aggregate into large entities. The obtained TS-1 aggregates assembled from the nanocrystalline zeolites of around 100 nm range in size from 10 to 50μm, which are about two orders of magnitudes larger than those obtained by organotrialkoxysilanes. Here, the TS-1 aggregates are robust enough to suffer continuous ultrasonication for 1 h and more without any destruction, indicating that the zeolite materials may curtail the filtration difficulties in the preparation and the recovery during the catalytic applications. Most importantly, the silanization step has no inferior influence on the activity and selectivity in the epoxidation of alkene.Finally, mesoporous zeolite pentasil microsphere/aggregate using diamines with linear carbon chain, linear polyamine or bifunctional alkanolamine containing both the amino groups and hydroxyl groups as single template was synthesized successfully. The effects of SiO2/Al2O3, pH and H2O/SiO2 on the aggregate morphology of the ZSM-5 nanocrystals were investigated. During the hydrothermal synthesis, zeolite nanocrystals were formed and spontaneously assembled into uniform microspheres/aggregates. The obtained microspheres /aggregates possess significant textual porosity, which is tuneable by careful choose linear carbon chain and the amine number of the templates and the amount of aluminum in the synthetic mixture. The zeolite microspheres/aggregates not only posses high activities in catalytic applications, but also curtail the filtration difficulities in the preparation and application to some extent...