Deposition of zeolitic coatings onto Fecralloy microchannels: Washcoating vs. in situ growing

As an approach to deposition of zeolites on microreactors, MFI type zeolite was deposited over Fecralloy monoliths containing micron size channels by two different methods: washcoating from a stabilized slurry and in situ growing of the zeolite on the metallic surface introduced in the synthesis medium. Repeated washcoating or synthesis over the same support has been proved as a good and efficient method to cover the entire surface of the support with a zeolite layer. The support surface was totally covered with a very adherent layer in both cases but the final textural properties were different. Due to the presence of different additives in the formulation of the slurry, the washcoating method produced a coating with additional mesoporosity to the microporosity of the starting zeolite powder. Deposition by in situ synthesis produced pure microporous zeolite coating on the support surface but required longer times than washcoating method. Washcoating produced a layer with zeolite crystals randomly oriented while deposition by synthesis directed the crystal growing to a preferential orientation.