Thermal decomposition of ammonium metavanadate supported on Al 2O 3

Abstract

The thermal decomposition of ammonium metavanadate supported on aluminium oxide was investigated using DTA, TG and X-ray diffraction techniques. The results obtained revealed that ammonium vanadate decomposed at 225–250°C giving an intermediate compound ((NH 4) 2V 6O 16) which decomposed readily at 335–360°C producing V 2O 5. Alumina was found to chance the formation of the intermediate compound and retard its decomposition. Some of the V 5+ ions of V 2O 5 lattice seemed to be reduced into V 4+ and V 3+ ions by heating in air at 450°C in the presence of Al 2O 3. Such a reaction was attributed to dissolution of some Al 3+ ions in the V 2O 5 lattice via location in interstitial positions and/or in cationic vacancies. Al 2O 3 was found to interact with V 2O 5 at 650° C giving well-crystalline A1VO 4 which decomposed at about 750°C forming well-crystalline δ-Al 2O 3 and V 2O 5,. Pure Al 2O 3, heated in air at 1000°C, existed in the form of the κ-phase which, on mixing with V 2O 5 (0.5 V 2O 5:1 Al 2O 3) and heating in air at 1000°C, was converted entirely to the well-crystalline α-Al 2O 3 phase.