First unseeded hydrothermal synthesis of microporous vanadosilicate AM-6

Abstract

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 2O:1.3K 2O: ySiO 2:0.5V 2O 5: wTMA: zH 2O, where x = 4.5 or 5.6, y = 4.3–5.5, w = 2.0–3.0, and z = 206–214. The size (∼250 nm to ∼9 μm 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 (V 4+, V 5+) oxidation states of vanadium in the AM-6 framework.