Structured zeolite/silicon carbide composites were succesfully synthesized by ZSM-5 coatings deposited on macroscopic â-SiC foams with medium surface area. A homogeneous coverage of the support (30 wt % zeolite) by ZSM-5 crystals, having 1 ím average size, was reached after a double-coating procedure. The ZSM-5/â-SiC composite materials were characterized by BET, XRD, SEM, and H/D exchange methods. 27Al MAS NMR analysis revealed that all aluminum was present in a tetrahedral coordination, thus sitting in the zeolite framework. The existence of a nanoscopic layer of silica and silicon oxycarbide on the surface of the support ensures the strong anchoring of the zeolite crystals on the â-SiC substrate. The lack of secondary chemical reaction between the synthesis solution and the support allows a precise control of the Si/Al ratio in the final zeolite. The use of ZSM-5 coated â-SiC foam packings in the methanol-to-olefins reaction presents substantial activity/selectivity improvements compared to conventional zeolite packings. Moreover, the structured composites exhibit a higher stability toward deactivation by coking, compared to the powdered form of the zeolite.
- aluminum,
- chemical reactions,
- coatings,
- composite materials,
- foams,
- nuclear magnetic resonance spectroscopy
Available at: http://works.bepress.com/jean-philippe_tessonnier/13/