Abstract
Stable colloidal suspensions containing discrete TS-1 crystals with average crystal sizes less than 100 nm and with a narrow particle size distribution have been synthesized from clear homogeneous solutions. The products were characterized with respect to crystallinity, crystal size and size distribution, Ti incorporation, specific surface areas, the nature of the Ti species in the products, and the colloidal crystals surface electric charge. The influence of several parameters including synthesis mixture composition and crystallization temperature on crystal size and Ti incorporation were investigated. The synthesis of colloidal crystals with an average size less than 100 nm is favored by low crystallization temperatures (100 °C), a highly basic environment, concentrated mixtures, and low Ti contents in the synthesis solutions. The maximum incorporation of tetrahedrally coordinated Ti was 0.84 mol %. High crystallization temperatures (>100 °C) favor products with a low Si/Ti molar ratio, but larger crystals are formed, >100 nm, and octahedrally coordinated Ti and extra-framework Ti are detected. A preliminary investigation of the clear hydrolyzed precursor solution and its freeze-dried amorphous equivalent showed that small particles with an average size of 4.8 nm exist in the solution and a certain degree of ordering resembling the MFI structure was present in the precursor particles.
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