Effect of the support on the surface composition of vanadium phosphate catalysts in the oxidative dehydrogenation of ethane

Vanadyl phosphate catalysts supported on different oxides (γ‐Al 2 O 3 , TiO 2 , SiO 2 ) have been investigated by x‐ray photoelectron spectroscopy (XPS). The surface chemical composition has been studied as a function of the thermal treatment under oxidizing (calcination) or reaction conditions in the oxidative dehydrogenation of ethane. Dispersion of vanadyl phosphates on γ‐Al 2 O 3 and TiO 2 results in the formation of vanadium species in different oxidation states, i.e. V 5+ phosphate, V 5+ and V 4+ oxide species, whose relative fraction depends both on the support and on the reaction temperature. A progressive reduction of vanadium species occurs in the samples as an effect of the temperature. Vanadyl phosphates exhibit a stronger interaction with the titania support, which undergoes surface modifications after impregnation, thermal treatments and catalysis runs. A noticeable interaction of the alumina support and a poor dispersion of the active phase on silica are also revealed by XPS.