Structural study of VO x doped aluminium fluoride and aluminium oxide catalysts

The structural properties of vanadium doped aluminium oxyfluorides and aluminium oxides, prepared by a modified sol-gel synthesis route, were thoroughly investigated. The influence of the preparation technique and the calcination temperature on the coordination of vanadium, aluminium and fluorine was analysed by different spectroscopic methods such as Raman, MAS NMR and ESR spectroscopy. In all samples calcined at low temperatures (350 deg. C), vanadium coexists in two oxidation states VIV and VV, with VIV as dominating species in the vanadium doped aluminium oxyfluorides. In the fluoride containing solids aluminium as well as vanadium are coordinated by fluorine and oxygen. Thermal annealing of 800 deg. C leads to an extensive reorganisation of the original matrices and to the oxidation of VIV to VV in both systems. - Graphical abstract: Structure model for VO x doped aluminium oxide