Thermochimica Acta, Vol.420, No.1-2, 145-154, 2004
Synthesis and characterization of V-MFI obtained in fluoride-containing medium
Crystallization fields for the formation of V-MFI were determined from gels of composition: xNa(2)O-yVO(2)-7NaF-ySO(3)-zSiO(2)-2TPABr-260H(2)O at 190degreesC with 3.6 less than or equal to x < 14.4 and 2.1 less than or equal to y less than or equal to 7.1 for z = 12.0 and with 0.3 less than or equal to y less than or equal to 4.2 and 4.0 less than or equal to z less than or equal to 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 V-51-NMR signal due to V(V) can only be detected when additional vanadium-containing siliceous phases are formed. (C) 2004 Elsevier B.V. All rights reserved.