Cationic Microemulsion-mediated Synthesis Of MFI Zeolite

Zeolite, with good water thermostability and special pore structure, has been widely used in catalysis, adsorption, separation and other fields. The particle size and morphology of zeolite play a very important role in its performance. This is particularly acute in catalytic applications where the particle size can have a dramatic effect on the product distribution due to differences in rates of transport/diffusion and reaction. There have been numerous studies of how one can control the particle size of zeolites through a variation of synthesis conditions. By contrast, manipulating the morphology of zeolite crystals is poorly understood.An effective approach is to use microemulsions as confined spaces or nanoreactors for zeolite growth, as has been shown to be very successful in the synthesis of metal, metal oxide, and metal sulfide nanoparticles. There are relatively few reports in the literature that have studied the formation and growth of zeolites in the presence of a microemulsion. On one hand, the microemulsion constitutes a confined space that will potentially modulate nucleation and growth (nanoreactor). On the other hand, the surfactant will coordinate to the crystallographic faces of the growing crystal and affect the growth rates depending on the crystallographic orientation of the surface and the strength of the organic-inorganic interactions. The latter effect should be tunable in a rational manner by changing the chemical nature of the surfactant.The synthesis of MFI zeolite in cationic microemulsion has been investigated in this paper using tetrapropylammonium hydroxide (TPAOH) as template at 160℃. Since the interaction between the surfactant and silicate ions generates possible effects on the growth of zeolite, We use CTAB as a surfactant, and the effects of synthesis conditions of synthesis conditions such as silica sources, content of surfacecant and composition of the microemulsion system on the crystallinity and morphology of MFI zeolite were studied. The results showed that the ratio of CTAB/TPAOH, composition of microemulsions system, oil content and the silica sources had great influence on the crystallization of obtained zeolites and the final morphology. With the decrease in content of surfactant and n-heptane, the crystallinity of zeolite appears to be increased? and morphology is more uniform. These results will be helpful for the study of other types of zeolites on the controlling of morphology.