HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF VANADIUM SILICATE MOLECULAR SIEVES WITH ANALCIME, MAGEDIITE AND ZSM-11 STRUCTURE

Abstract

Vanadium silicates such as V-Al-analcime, V-analcime, V-magediite and V-ZSM-11 were synthesized using vanadium pentoxide or vanadyl sulfates. Vanadium silicates with analcime structure with and without aluminum (V-Al-analcime, V-analcime) were prepared as pure phase by hydrothermal crystallization from a gel with molar composition of (1 SiO2; 0.2 V2O5; 1 Na2O; 0.034 Al2O3; 35.7 H2O) and (1 SiO2; 1 Na2O; 5.3×10?3 V2O5; 34.7 H2O) at 130°C in 72 h respectively. XRD and SEM results showed that, although these two have similar XRD patterns, their morphologies were completely different. The new magediite with and without aluminum was also prepared as pure phase by hydrothermal crystallization. Vanadium silicate with ZSM-11 structure was synthesized by sodium silicate, tetrabutylammonium hydroxide (TBAOH) and V2O5 or VOSO4.nH2O. The structures obtained are stable up to 700°C. The role of tetrabutylammonium hydroxide (TBAOH), tetrabutylammonium bromide (TBABr), tetraethylammonium chloride (TEACl) and triethanolamine (TENA) were studied. The results showed that although TBAOH and TBABr had essential role on V-ZSM-11 formation, TEACl led to the formation of a mixture of V-ZSM-11 and V-magediite. Effect of time and temperature were also studied.