Preparation of MFI zeolite coatings within capillary microchannels

A method is described to incorporate a zeolite ZSM-5 layer as a potential catalytic coating or membrane into tubular supports by the in situ crystallization of a previously deposited silica layer. The silica layer simultaneously provides nucleation sites and functions as a nutrient source giving coatings with excellent uniformity and controllable coating thickness. The ability to control the simultaneous dissolution of the silica layer in conjunction with nucleation and growth processes was found important in controlling the morphology of the zeolite crystals contained in the final zeolite coating. The formation of a ±4 µm coating containing ±300 nm crystals was obtained at high silica dissolution and nucleation rates. A continuous intergrown zeolite layer of ±7.6 µm was obtainable at high silica dissolution rates in the presence of sodium.