Preparation And Performance Of Highly Adhesive HZSM-5Zeolite Coatings For Catalytic Cracking Of N-dodecane

The development of advanced cooling technologies could provide heat sink for the thermal managements of the hypersonic aircrafts. Catalytic cracking of hydrocarbon fuels over zeolite coating is considered as a practical cooling technique to improve the heat sink. Well adhered coatings are firmly attached onto the substrates, which is necessary for the catalytic cracking of model fuel n-dodecane when subjected to operational stresses and temperature in the reation process. Through combined the washcoating and dry-gel convertion, binderless ZSM-5zeolite coatings with high adhesion strength were successfully prepared. And the catalytic cracking activity of n-dodecane over the prepared coatings were studied.Binderless nano-HZSM-5zeolite coatings were successfully prepared through a two-step process: washcoating zeolites on the surface of the substrates with controllable thickness, and then converting SiO2binders 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 SiO2binders into MFI structure around the nano-HZSM-5zeolite crystals was confirmed by characterizations of XRD,29Si and27Al nuclear magnetic resonance and TEM. 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-5crystals into the framework of ZSM-5through 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. The low catalytic cracking activity of n-dodecane over the prepared coating with a high amount of weak Lewis acid sites is a feature of the diffution limitation.Binderless microsized HZSM-5zeolite coatings also were successfully obtained through combining washcoating and dry-gel conversion (DGC) method. It was found that the SiO2binder were converted into MFI structure between the zeolite particles, which provides the higher interlocking between the crystals and the aggregates, which was confirmed by characterization of XRD, TEM and MIP. The adhesion strength of the prepared coatings was significantly improved. The high catalytic cracking activity of n-dodecane over the prepared coating is attributed to the high amount of weak Lewis acid sites as well as the increase of the mesopore volume amount.By decreasing the amount of the SiO2binder in the coating, the binderless microsized HZSM-5zeolite coatings with high adhesion strength as well as high catalytic activity also were successfully prepared through combining washcoating and dry-gel conversion. It was found that the coating with low amount of SiO2binder possess high relative crystallinity. With the decrease of the amount of the SiO2binder in the coating, the prepared coating have the higher amount of mesopore volume and weak Lewis acid sites. The coating with low amount of binder obtained through washcoating and dry-gel conversion have well adhesion strength. Due to the high amount of weak Lewis acid sites and mesopore volume amount as well as well adhesion strengh, the coating with low amount of binder have high catalytic cracking activity of n-dodecane.