Binderless nano-HZSM-5 zeolite coatings prepared through combining washcoating and dry-gel conversion (DGC) methods

Binderless nano-HZSM-5 zeolite coatings were successfully prepared through a two-step process: washcoating zeolites on the surface of the substrates with controllable thickness, and then converting SiO2 binders into the crystal structure by dry-gel conversion (DGC) method to remarkably improve the adhesion strength. Ethylene diamine, tetrapropylammonium hydroxide and triethylamine were used as organic amines in DGC. The conversion of SiO2 binders into MFI structure around the nano-HZSM-5 zeolite crystals was confirmed by characterizations of X-ray diffraction, 29Si and 27Al nuclear magnetic resonance and transmission electron microscopy. As a result, the adhesion strength of the prepared coatings was significantly improved by ca. one order, which is ascribed to the higher interlocking between the crystals and the aggregates after DGC treatment. NH3-Temperature programmed desorption characterization showed that the total amount of acid sites of the coatings were improved by ca. 30% due to the incorporation of extra-framework Al species of nano-HZSM-5 crystals into the framework of ZSM-5 through DGC treatment. Slight differences in DGC mechanism and thus the acidities as well as adherences of the obtained coatings were also observed depending on the amines used in DGC.

Figure optionsDownload as PowerPoint slideHighlights
► Binderless nano-HZSM-5 zeolite coatings were prepared by combining the washcoating and dry-gel conversion.
► The seeds of HZSM-5 accelerated the nucleation of ZSM-5 by assistant growth of organic amine.
► The conversion of SiO2 to ZSM-5 significantly improved the adhesion strength of coatings.
► The incorporation of extra-framework Al species increased total acid amount of the coatings.