Method for the in situ preparation of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications

Abstract

A method for the hydrothermal synthesis of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications has been developed. Before the hydrothermal synthesis, the surface of the substrate was modified by an etching procedure that increases the roughness at the nanoscale level without completely eliminating the surface lay structure. Then, thin films of Al 2O 3 (170 nm) and TiO 2 (50 nm) were successively deposited by atomic layer deposition (ALD) on the substrate. The internal Al 2O 3 film protects the Mo substrate from oxidation up to 550 °C in an oxidative environment. The high wettability of the external TiO 2 film after UV irradiation increases zeolite nucleation on its surface. The role of the metal precursor (TiCl 4 vs TiI 4), deposition temperature (300 vs 500 °C), and film thickness (50 vs 100 nm) was investigated to obtain titania films with the slowest decay in the superhydrophilic behavior after UV irradiation. Zeolite Beta coatings with a Si/Al ratio of 23 were grown at 140 °C for 48 h. After ion exchange with a 10 −4 M cobalt acetate solution, the activity of the coatings was determined in the ammoxidation of ethylene to acetonitrile in a microstructured reactor. A maximum reaction rate of 220 μmol C 2H 3N g −1 s −1 was obtained at 500 °C, with 42% carbon selectivity to acetonitrile.