Oxidative dehydrogenation of ethane on W-Al2O3 supported vanadyl and iron vanadyl phosphates. Physico-chemical characterisation and catalytic

g-Al2O3 supported vanadyl and iron vanadyl phosphates (VOPO4 and Fe0.23(VO)0.77PO4) calcined at 550 or 650°C have been investigated as catalysts for the oxidative dehydrogenation of ethane to ethylene in the temperature range 450-650°C in a fixed bed reactor operating under atmospheric pressure. Catalysts have been characterised by XRD, BET surface area measurements, XPS spectroscopy, NH3 TPD and TPR. Good dispersion of active phase has been obtained. The presence of various species (vanadyl phosphate, V(IV) and V(III) ions, V(V) and VIV) oxides) have been detected on the catalysts surface with a significantly different distribution between supported vanadyl and iron vanadyl phosphate, V(IV) ion being the prevailing species on VOPO4/Al2O3. The different surface species show a different acidity and reducibility. Supported vanadyl phosphate catalysts are more active than iron modified samples, moreover, catalysts calcined at 650°C give better catalytic performances than those calcined at 550°C. Catalytic tests promote the formation of V(III) whose fraction increases with reaction temperature. The better catalytic properties of supported vanadyl phosphate have been attributed to the presence of surface V(IV) ion.