SYNTHESIS AND CHARACTERIZATION OF A CRYSTALLINE VANADIUM SILICATE WITH MEL STRUCTURE

Synthesis of a novel crystalline vanadium silicate having the MEL structure (silicalite-2) is reported. Tetraethyl orthosilicate and vanadyl sulfate were the raw materials and tetrabutylammonium hydroxide was the additive. The influence of various synthesis para meters such as the Si/V molar ratio, concentration of the organic base, and dilution levels on the crystallization of vanadium silicate has been investigated. The kinetics of crystallization has been followed using X-ray powder diffraction, SEM, framework i.r., and e.s.r. spectroscopic techniques. Under optimum conditions of synthesis, vanadium is incorporated as C4+ in a progressive manner in the MEL framework during the crystallization process. After calcination in air at 773 K, most of the vanadium (as V5+) is still intact within the silicalite structure.