Core−Shell Composite of Ti-/Cr-AFI Molecular Sieve via Solvothermal Epitaxial Growth

Abstract

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 presynthesized tabletlike Cr-AFI crystals were dispersed in the reaction system of Al(OPri)3-H3PO4-TEA-(C4H9O)4Ti-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 N2 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-...