THERMAL-DECOMPOSITION OF AMMONIUM VANADYL OXALATE SUPPORTED ON VARIOUS OXIDES

The thermal decomposition of ammonium vanadyl oxalate supported on La2 O3, MgO, SiO2, Al2O3, ZrO2, TiO2, SAPO-5, and ZSM-5 oxides in a dynami c atmosphere of dry air was compared by thermal gravimetric analysis ( TG) and differential thermal analysis (DTA). The calcined catalysts we re characterized by X-ray diffractometry (XRD). The TG and DTA results demonstrate that the surface acid-base properties of the oxides play a significant role in the decomposition behaviour of the supported amm onium vanadyl oxalate, i.e. the basic oxides exhibit an endothermic ef fect and the acidic oxides show an exothermic effect. Two mechanisms a re suggested for thermal decomposition of ammonium vanadyl oxalate on basic and acidic oxides, respectively. After transformation of the amm onium vanadyl oxalate to vanadia, subsequent rearrangement of the vana dia on the surface of the supports was also observed. During the therm al treatment or calcination in air, solid state reactions of vanadia w ith the surface of oxides such as La2O3, ZrO, and TiO2 took place to f orm new phases.