TiO2 supported vanadyl phosphate as catalyst for oxidative dehydrogenationof ethane to ethylene

Bulk and TiO2 supported VOPO4 has been investigated for the oxidative dehyd rogenation of ethane. XRD, SEM, TG analyses and BET surface area measuremen ts indicated that vanadyl phosphate is highly dispersed on the support up t o mono-layer coverage. A fraction of vanadium is present as V(TV) in the ca lcined samples as evaluated by EPR and TPR techniques. Both reducibility an d acidity of vanadium phosphate is strongly enhanced by deposition on TiO2 with respect to the bulk phase, as shown by TPR and NH3 TPD technique, resp ectively. The supported catalysts are active and selective in the oxidative dehydrogenation of ethane to ethylene in the temperature range 450-550 deg rees C, the mono-layer catalyst giving the best performances. Ethylene sele ctivity decreases with the contact time but increases with the temperature. The former effect indicates that ethylene is further oxidized to CO, at hi gh contact times. The effect of the temperature was attributed to the forma tion of V(IV), favoured at increasing temperature. This hypothesis was supp orted by TPR experiments carried out after catalytic tests at 550 degrees C that indicated a significant increase of the fraction of V(IV) after the r eaction. (C) 2000 Elsevier Science B.V. All rights reserved.