Synthesis of core–shell ZSM-5 zeolite with passivated external surface acidity by b-oriented thin silicalite-1 shell using a self-assembly process

A core–shell HZSM-5@silicalite-1 zeolite coated with a relatively continuous b-oriented thin silicalite-1 shell has been synthesized by a self-assembly method of reversing the negative surface charge of ZSM-5 crystals before the secondary hydrothermal crystallization. The growth orientation of shell crystals is confirmed by electron microscopy technology. N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscope with energy-dispersive X-ray spectrometry (STEM-EDS) measurements reveal that the core ZSM-5 crystals are coated with a relatively continuous monocrystal-thick silicalite-1 shell. The surface acidity analysis (Pyridine-FTIR and 2,4,6-collidine-FTIR) combined with the two probe chemical reactions using molecules that are either too large or adequately sized to access MFI pores has confirmed the passivation of external surface acid sites without hindering the intrinsic activity of the parent HZSM-5, which is consistent with the results from the electron microscopy and textural analysis.