Microwave-assisted hydrothermal synthesis of zeolite Beta coatings on ALD-modified borosilicate glass for application in microstructured reactors

Stable zeolite Beta coatings with a thickness of 1–2 (mu)m were synthesized on a borosilicate glass substrate by microwave-assisted hydrothermal synthesis. Prior to the synthesis, surface roughness of the substrate was increased to 1.0 _m. Then, two thin films of zirconia and titania were successively deposited at 300^ ◦C on the glass substrate by atomic layer deposition using ZrCl4 as metal precursors for zirconia and TiCl4 for titania, respectively. Oxygen and H2O were used as oxygen precursors in the ALD process. The internal zirconia film protects the glass substrate from dissolution in a highly alkaline synthesis solution. The outer titania film was made superhydrophilic (>15 OH/nm^2) by an UV irradiation, which enhances the nucleation and crystallization processes on the substrate. The duration of the zeolite nucleation period was decreased by using the additive effect between fluoride ions and the zeolite seed solution under microwave irradiation. A uniform zeolite Beta coating was obtained already after 8 h at 150^ ◦C in a microwave from a precursor gel with SiO2/Al2O3 = 25, TEAOH/Al2O3 = 8.75, H2O/SiO2 = 11.6, NH4F/SiO2 = 0.2. This is almost six times faster comparing to conventional hydrothermal synthesis.