Synthesis and structural investigation of ordered mesoporous MFI zeolite using carbon templates

Abstract

The work presented in this dissertation addressed synthesis and structural investigation of ordered mesoporous MFI zeolites, which was synthesized by following steam-assisted dry-gel conversion method and using CMK carbon templates. Crystallization of MFI zeolite using carbon templates was studied under various conditions such as humidity, aluminum content and structure of carbon template. And structure and physical properties such as strain, mechanical stability and adsorption properties of ordered mesoporous MFI zeolite was investigated. Moreover, study of argon adsorption in ordered mesoporous MFI zeolite was performed by investigation of in situ powder X-ray diffraction data and grand canonical Monte Carlo simulation. In chapter 2, suitability of the ‘dry-gel conversion method’ was investigated for the synthesis of ordered mesoporous MFI zeolite using CMK-type mesoporous carbons as the template. Ordered mesoporous carbons with various pore diameters and topologies were infiltrated with a zeolite precursor sol, which was composed by tetrapropylammonium hydroxide, tetraethoxysilane, aluminum isopropoxide and H2O. The porous carbon with the zeolite precursor was heated inside an autoclave under a controlled humidity condition at 443 K. The resultant product indicated that the zeolite precursor migrated onto the external surface of the carbon template to form a bulk zeolite when relative humidity was too high (≥ 95%). A highly ordered mesoporous zeolite was synthesized in a carbon template with 10 nm pores when the humidity was lowered to 80 - 85%. Crystalline zeolite framework was not generated in the case of 2.5 nm pores with rigid walls. When a CMK-3 carbon with 4-nm pores was used as the template, the template walls were degraded so that the zeolite crystalline domain was several times larger than a single pore diameter. Thus, humidity, template pore diameters and framework rigidity should be taken into account for the application of the dry-gel synthesis...