Journal of physical chemistry c vol:111 issue:12 pages:4535-4542
Two different types of zeolitic materials were structured in core-shell composites possessing a large core (BEA-type) and a thin shell (MFI-type). The core structure comprised a hierarchical porous organization where the access to the zeolite micropores was enabled by macro- and mesopores. This structure was prepared by macroporous anion exchange resin templating, that is, zeolite beta was crystallized within the pores of the resin beads. The organic macrotemplate was then removed by combustion leaving stable 300-500 mu m macrospheres of zeolite beta. Preliminary seeding of the calcined beads with silicalite-1 nanocrystals induced the formation of a well-intergrown silicalite-1 shell during the hydrothermal treatment. The shell thickness did not exceed 1.0 mu m, thus providing a material with a very high core-shell aspect ratio. The integrity of the shell layer was tested by N-2 adsorption measurements on materials comprising a calcined core and a noncalcined organic templatecontaining silicalite-1 film, thus providing information about the percentage of composite beads possessing defect-free shells. Complementary techniques, such as X-ray diffraction, thermogravimetry/differential thermal analysis, scanning electron microscopy/transmission electron microscopy, energy-dispersive spectrometry, and X-ray fluorescence analyses were employed in order to fully characterize the composites and their intermediates.