The surface structure and activity of catalytic systems based on niobium oxide supported on titania were investigated. A series of catalysts with Nb content up to 3.6 atoms/nm(2) was prepared by incipient wetness impregnation of the titania support with niobium oxalate solutions. Characterization of the system by X-ray diffraction (XRD) and Raman spectroscopy studies did not show evidence of niobium oxide formation. Surface analysis was performed by X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), Raman and infrared spectroscopy. These results were correlated with Bronsted acidity and catalytic activity determined in our previous study. A direct correlation between the catalytic activity and the abundance of Bronsted acid sites had been observed. Analysis of the surface structure by infrared spectroscopy showed a similar evolution for the intensity of the band attributed to polymerized NbOx. (c) 2006 Elsevier B.V. All rights reserved.