Influence of synthesis parameters on vanadium-silicalite-1 crystal growth prepared with fluoride-containing media

Abstract

Vanadium-silicalite-1 samples are readily prepared at 170 °C from fluoride-containing gels. The amounts of vanadium and fluoride salts were varied in gels of initial composition 10SiO 2: xVO 2:1.25TPABr: yMF:330H 2O with the vanadium source=VOSO 4, V 2O 5, VO(acac) 2 and 0.0 5 ⩽ x ⩾ 3.0 ; M=NH 4, Na, K and y = 1 , 3, 5, 7, 10 and TPABr=tetrapropylammonium bromide. The influence of synthesis parameters (Na/Si, MF/Si, Si/V, the vanadium source) on the preparation of well-formed crystals was systematically investigated. Sodium and potassium cations show different behaviours with respect to ammonium ions on the crystallization rates and crystal aspect ratios. Crystal morphologies are strongly influenced by the nature of the fluoride salt added to the reaction mixture. The vanadium incorporation in zeolite crystals increases regularly with the initial transition metal and fluoride content in the reaction batch. Moreover, the vanadium incorporation is similar for the various salts used. The kinetic data show that the vanadium fluoride amount not only influences the reaction rates, but also the induction periods.