Synthesis and characterization of V-MFI obtained in fluoride-containing medium

Abstract

Crystallization fields for the formation of V-MFI were determined from gels of composition: xNa 2O– yVO 2–7NaF– ySO 3– zSiO 2–2TPABr–260H 2O at 190 °C with 3.6≤ x≤14.4 and 2.1≤ y≤7.1 for z=12.0 and with 0.3≤ y≤4.2 and 4.0≤ z≤12.0 for x=3.6; TPA=tetrapropylammonium ions. The crystallization curves were analysed together with the various intermediate phases using XRD, pH of mother liquors, thermal analysis and SEM. The final samples were analysed, in addition, by multinuclear NMR. It is concluded, that V can be introduced into the MFI framework as V(IV) ions, accompanied by the presence of two SiOH defect groups per V atom introduced. The 51 V -NMR signal due to V(V) can only be detected when additional vanadium-containing siliceous phases are formed.