Delaminated vanadoaluminosilicate with [V,Al]-ITQ-18 structure

Abstract

This paper reports on the delamination of the layered [V,Al]-Nu-6(1) to originate the [V,Al]-ITQ-18, where vanadium and aluminum were inserted in the structure by direct synthesis. The delaminated solids were obtained directly from the basic medium used for swelling, after sonication and after acid addition. Vanadium and aluminum atoms are part of the lattice sites as confirmed by Al-27-MAS-NMR,V-51-MAS-NMR and UV-Vis spectroscopy. The extent of delamination was monitored by X-ray diffraction, N-2 adsorption-desorption isotherms and Si-29-MAS-NMR. The presence of FTIR bands in the double rings region indicates that the structural unit of the initial lamellar precursor is still preserved in the delaminated materials. The material obtained after acid addition contains V5+ in extraframework octahedral and in tetrahedral sites, the first ones are easily exchanged by sodium ions. On the other hand, the material prepared only under alkaline conditions presents only framework tetrahedral V5+. The presence of the V4+ was confirmed in the lamellar precursor by EPR but the vanadium oxidation state and localization change throughout the delamination procedure. (C) 2012 Elsevier Inc. All rights reserved.