Alumina-supported vanadyl phosphates were investigated by X-ray photoelectron spectroscopy (XPS) and compared with respect to thermal treatments and catalytic runs in the oxidative dehydrogenation of ethane. The surface chemical composition of the samples and the modifications induced by different temperatures of calcination and catalysis were determined. XPS characterization was done after calcination in air at T = 550 and 650degreesC and after catalytic activity tests at T = 450 and 550degreesC. The oxidation state, surface distribution and evolution of vanadium species were analyzed by the V 2p(3/2) peak-fitting procedure. The surface concentration of different vanadium species was determined by XPS quantitative analysis. UV-Vis diffuse reflectance (UV-Vis DRS) and electron spin resonance (ESR) spectroscopies, which are very sensitive to the oxidation state and environment symmetry of vanadium, were also used for a detailed characterization of the samples. (C) 2003 Elsevier Science B.V. All rights reserved.