PREPARATION OF COLLOIDAL SUSPENSIONS OF DISCRETE TS-1 CRYSTALS

Stable colloidal suspensions containing discrete TS-1 crystals with av erage crystal sizes less than 100 nm and with a narrow particle size d istribution have been synthesized from clear homogeneous solutions. Th e products were characterized with respect to crystallinity, crystal s ize and size distribution, Ti incorporation, specific surface areas, t he nature of the Ti species in the products, and the colloidal crystal s surface electric charge. The influence of several parameters includi ng synthesis mixture composition and crystallization temperature on cr ystal size and Ti incorporation were investigated. The synthesis of co lloidal crystals with an average size less than 100 nm is favored by l ow crystallization temperatures (100 degrees C), a highly basic enviro nment, concentrated mixtures, and low Ti contents in the synthesis sol utions. The maximum incorporation of tetrahedrally coordinated Ti was 0.84 mol %. High crystallization temperatures (> 100 degrees 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 precurso r solution and its freeze-dried amorphous equivalent showed that: smal l 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 i n the precursor particles.