Core-shell composite of Ti-/Cr-AFI molecular sieve via solvothermal epitaxial growth

The core-shell molecular sieve composite comprised of Cr³⁺ substituted AlPO₄-5 (Cr-AFI) as core and Ti⁴⁺ substituted AlPO₄-5 (Ti-AFI) as shell was prepared via solvothermal epitaxial growth. The presynfhesized tabletlike Cr-AFI crystals were dispersed in the reaction system of Al(OPr)₃H₃PO_4-TEA-(C ₄H₉OTi-H₂O-pEG (polyethylene glycol) followed by solvothermal treatment at 170 °C. The sheetlike Ti-AFI microcrystals were epitaxially grown on the surface of the presynthesized tabletlike Cr-AFI core crystals. The growth process of the Ti-AFI microcrystals on the surface of core of Cr-AFI crystal was studied in detail by scanning electron microscopy characterization. The results demonstrate that the Ti-AFI microcrystals nucleate preferentially on the (100) basal face of the Cr-AFI core crystals. The N ₂ adsorption analysis shows that the channel systems of the core and shell have good communication, which may provide a good mass transport pathway for the catalytic reaction. The core-shell composite of Ti-/Cr-AFI makes it possible to combine two catalytic sites in one catalyst, which may benefit some special catalysis reactions.