Silicalite-1 macrostructures - preparation and structural features

Zeolite macrostructures in the form of silicalite-1 spheres were prepared u sing anion exchange resin beads as shape directing macrotemplates. The resi n was removed after the synthesis by combustion leaving solid spherical par ticles identical in shape and size to the original resin beads. The formati on of the silicalite-1 spheres was studied by Raman spectroscopy, X-ray dif fraction,, scanning electron microscopy and nitrogen adsorption measurement s. Samples prepared for different times of treatment and at two different t emperatures, 100 degrees C and 165 degrees C, were investigated. The sphere s obtained for short treatment times consist of amorphous silica, which aft er longer hydrothermal treatment in the presence of TPA cations is partiall y or entirely transformed into an MFI structure. A single treatment at 100 degrees C resulted in hard silicalite-1 spheres of low crystallinity, where as fully crystalline spheres could be obtained by a treatment at the higher temperature, However, the spheres prepared at 165 degrees C have inferior mechanical properties and can even loose their shape at certain conditions. A better control of both hardness and crystallinity was achieved by using a two-step synthesis procedure, where a treatment at 100 degrees C was foll owed by a treatment at 165 degrees C. (C) 2000 Elsevier Science B.V. All ri ghts reserved.