(695f) Effect of Heating Sources and Template-Free Secondary Growth Synthesis on Mfi-Type Zeolite Microstructure

MFI-type zeolite membranes have great potential application in the separations of gas and liquids that are difficult to achieve by traditional techniques [1]. Thus, research on high-quality MFI zeolite membrane and zeolite microstructure is increasing rapidly. In general, MFI-type zeolite membranes are synthesized by conventional heating (CH), which needs a long crystallization time ranging from several hours to a few days and usually results in the formation of impure materials because of the low heating rate and the inhomogeneous heating [2]. In addition, MFI-type zeolite membranes are usually synthesized in the presence of organic templates. However, the organic agent needs to be removed by calcination in order to open up the zeolite channels; then intercrystalline gaps tend to enlarge in the membranes, which affect the separation performance of the membranes [3]. It was found that in order to obtain a high quality MFI-type zeolite membrane, a homogeneous heating source and template removal are important factors. Therefore, it is very important to examine the influence of heating sources and template-free synthesis on zeolite microstructure.

This paper reports synthesis of MFI-type zeolite powders by a template-free method using microwave heating (MH). The influence of heat sources, the amount of seed suspension, treatment with an NaOH solution, etc., on the formation of MFI zeolite microstructure were studied by BET, XRD and SEM. Compared with CH, MH synthesis drastically reduced the crystallization time of zeolites whereas the BET surface area of MFI zeolites by MH (410m2/g) was similar to that of the samples by CH (421m2/g), which resulted from the fast and homogeneous heating by microwave. MFI zeolite powders prepared by template-free growth method exhibited a decreased BET surface area, indicating that zeolite growth was limited to silicalite seed crystals. However, XRD patterns indicated that MFI zeolite crystal could grow without an organic template on the silicalite nanoparticle seeds. To further investigate the zeolite microstructure, the amount of seed suspension was increased, which enhanced the crystal growth of the zeolite powders. BET surface area increased from 106m2/g to 435m2/g after the suspension amount increased. Additionally, the NaOH-treatment of MFI zeolite brought about the increase in BET surface area, suggesting that when an NaOH solution was used, the amorphous phases at the boundary of the crystallinties were dissolved.

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*Corresponding author: Junhang Dong

Phone:(513)556-3992; email: dongj@UCMAIL.UC.EDU

Reference

[1] J. Dong, Y. S. Lin, M. Z.C. Hu, R. A. Peascoe, E. A. Payzant, Micropor. Mesopor. Mat. 34 (2000) 241-253

[2] X.C. Xu, Y. Bao, C.S. Song, W.S. Yang, J. Liu, L.W. Lin, Micropor. Mesopor. Mat. 75 (2004) 173-181

[3] M. Masakoto, J. O'Brien, Y.S. Lin, J. Membr. Sci. 286 (2006) 213-222