First unseeded hydrothermal synthesis of microporous vanadosilicate AM-6

Microporous vanadosilicate AM-6 has been hydrothermally synthesized for the first time in the absence of titanosilicate ETS-10 seeds. High purity (95-100% AM-6) products were crystallized under static conditions at 430-503 K using tetramethylammonium hydroxide (TMAOH) or tetramethylammonium bromide (TMABr) as a structure-directing agent in mixtures with molar compositions xNa(2)O: 1.3K(2)O:ySiO(2):0.5V(2)O(5):wTMA:zH(2)O, where x = 4.5 or 5.6, y = 4.3-5.5, w = 2.0-3.0, and z = 206-214. The size (similar to 250 nm to similar to 9 mu m range), truncated square bipyramidal morphology (varied from square cuboid to thin (thickness <100-200 nm) tetragonal platy), and surface irregularities/faulting of AM-6 crystals (Si/V = 5.0 +/- 0.5) can be controlled by varying the molar composition or initial pH of synthesis mixture, and crystallization temperature. Structure-directing agent can be removed from the pores with little or no adverse effects on crystallinity of AM-6 by treatment with gaseous ammonia at elevated temperatures. UV-vis and FTIR analyses suggest two (V4+, V5+) oxidation states of vanadium in the AM-6 framework. (C) 2009 Elsevier Inc. All rights reserved.