Dry-Gel Synthesis Of Mesoporous MFI Zeolite

Compared with traditional hydrothermal synthesis (HTS), dry gel conversion (DGC) synthesis of zeolites has the advantages of high yield, less waste, less usage of template and others. During the process of DGC, the dry gel can't keep in intact with the liquid directly, but can become the form of vapor to assist the growth of zeolite. Thus, it is believed that the DGC has the unique advantages in synthesizing the mesoporous zeolite and zeolite monolith. The mesoporous zeolite combines the advantages of zeolites and mesoporous materials, and is very desirable in catalysis and adsorption, especially in bulk molecule process. The zeolite monolith can bridge the gap between laboratory research and factory production. In this master thesis, based on the recently development in mesoporous zeolite and growth mechanism of DGC, we compared the DGC and HTS in synthesizing mesoporous TS-1in terms of many perspectives. Additionally, we investigate the factors to determine the properties of zeolite monolith during DGC.There are mainly three experimental parts in this thesis. Firstly, the TS-1catalyst with combined mesoporous/microporous structures has been synthesized from the carbonized Titania-Silica cogel/citric acid (CA) composites, where CA, a common green biomolecule, actually plays versatile roles during crystallization. Particularly, it is embedded in the titania-silica cogel, and therefore serves as in situ carbon template to preserve mesoporous structure, which can greatly eliminate the diffusion limitation. The samples synthesized by this route exhibit much higher activities in the epoxidation of alkenes than those traditional microporous TS-1. Due to less limitation of mass transportation, the dry gel reacts with liquid (including water, structure directing agent and so on) more fully in the HTS than that in the DGC. Therefore the crystallinity of zeolite synthesized by HTS is better than that of DGC. Secondly, TS-1monolith is successfully synthesized by DGC from titania-silica cogel/carbon composite. During the process of growth, we use TS-1seeds to accelerate the transformation of dry gel. Because of the abundant pore structure of the carbon scaffold, the seeds can be easily absorbed, and thus the final TS-1monolith exhibits both good crystallinity and mechanic strength. Thirdly, shaped binderless ZSM-5zeolites are prepared via (DGC) technique from aluminosilicate extrudate, where the addition of seed gels not only provides crystal nuclei for rapid crystallization of zeolite but also controls the size of ZSM-5crystal. In addition, the excellent mechanical strength of shaped ZSM-5makes it potential use as industrial catalyst.