In this paper, we report a method for preparing mono-dispersed silicalite-1 nanocrystals via hydrothermal synthesis in a water-surfactant-organic solvent consisting of a polyoxyethylene (15) oleyl-ether/cyclohexane system. Mono-dispersed silicalite-1 nanocrystals of approximately 60 nm diameter were successfully prepared. It was found that the crystal size depended on both the surfactant concentration and the amount of water solution added to the surfactant-organic solvent. The effects of the surfactant concentration and the amount of water solution on crystal morphology and size were investigated to clarify the mechanism underlying the formation of silicalite-1 nanocrystals in water-surfactant-organic solvent. Since the surfactant coexisted in the synthetic solvent, it was considered that the micellar structure and/or surfactants affected the rates of nucleation and crystal growth of silicalite-1, thus affecting crystal size. Crystal size was controllable within the range of 60 to 1000 nm by changing the W/S values.

Recently, the synthesis of nanometer-sized zeolite crystals has attracted considerable attention from many researchers. In this study, the preparation of Mordenite (MOR zeolite) nanocrystals via hydrothermal synthesis in water/surfactant/organic solvent was carried out. Polyoxyethylene-(15)-oleylether (O-15, non-ionic surfactant) and cyclohexane were employed as a surfactant and organic solvent, respectively. Interestingly, it was found that the crystal sizes and morphology of MOR zeolites depended on the surfactant concentration regardless of the same concentrations of Si and Al sources and template in the water solution. The MOR zeolite nanocrystals with average sizes of approximately 80 nm could be obtained. Moreover, the column-like morphology of MOR zeolite was also observed at a high surfactant concentration (0.75 mol/L). Accordingly, the crystal size and morphology of MOR zeolite can be controlled by the surfactant concentration. This result appears to be due to the difference in the nucleation and growth rates of MOR in the solution.

The preparation of nano-crystalline MFI zeolites (Silicalite-1 and ZSM-5) was carried out by hydrothermal synthesis in a water/surfactant/organic solvent using fumed silica and aluminum sulfate as the Si and Al source, respectively. It was confirmed that the surfactant in the solution affected the nucleation rate of the MFI zeolite. Moreover, the crystal size of the MFI zeolite decreased with increasing surfactant concentration, and nanometer-sized MFI zeolites was obtained at a surfactant concentration of 0.25 ~ 0.5 mol/L. The successful preparation of MFI zeolite nanocrystals was ascribed to the stabilization of the MFI zeolite precursors and/or crystals by the adsorbed surfactant on their surface. This method was applied to the preparation of nano-crystalline ZSM-5 zeolite. ZSM-5 zeolite with a crystal size of approximately 50 nm was obtained. The nano-crystalline ZSM-5 zeolite was well-crystallized without octahedral Al atoms in the external framework, and exhibited almost the same acidity as a reference ZSM-5 zeolite.

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Selective de-activation of acid sites located near the outer surface of zeolite was examined using the catalytic cracking of silane (CCS) method. From FT-IR analysis, adsorption species of silane compounds on the acid sites of zeolite during calcination were investigated. Moreover, the effects of types of silane compounds on the changes in zeolite properties, including the amounts of adsorbed ammonia and benzene within zeolite, prior to and after CCS treatment, were examined. The CCS method using diphenylmethylsilane (DPM-silane) was effective in de-activating the acid sites located near the outer surface of ZSM-5 zeolite. Olefin synthesis from acetone was carried out using ZSM-5 zeolite catalysts. The ZSM-5 zeolite after the CCS treatment using DPMsilane exhibited high olefin selectivity as well as low aromatic selectivity.