Zeolite (MFI) Crystal Morphology Control Using Organic Structure-Directing Agents

The effect of structure-directing agents (SDAs) on zeolite particle morphology and crystal structure was studied. Dimers and trimers of tetrapropylammonium hydroxide-the SDA of siliceous ZSM-5 (silicalite-1, structure type MFI)-lead to direct growth of the same framework but with drastically different crystal morphologies. Control over relative crystal growth rates along the three main crystallographic axes is demonstrated by obtaining crystals with their longest dimension along any of these axes. Unit cell dimensions and crystal structure were determined by refinement based on powder X-ray diffraction data and electron microscopy, respectively. The importance of the new morphologies in thin film molecular sieve technology along with possible crystal growth mechanisms is discussed.