Monolayer catalysts were prepared by supporting transition metal ionic (t.m.i.)-oxo species (VOx, CrOx, MoOx and WOx) on the TiO2 (anatase) surface using the equilibrium-deposition-filtration (EDF) technique. The prepared samples were characterized by N-2 adsorption, UV/Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and tested for the selective catalytic reduction of NO by NH3 (NH3-SCR) in the temperature range 250-450 degreesC. Using the EDF method the transition metal ion (V, Cr, Mo or W) loading of the supported Titania catalysts achieved at monolayer coverage follows the order V > Mo > W > Cr. It is mainly determined by the deposition of polymeric t.m.i.-oxo species on the surface of titania in the impregnation step. The activity of the corresponding monolayers follows the order V > Cr > Mo > W. It was also demonstrated that the activity of the above catalysts correlates well with the intensity of a DRS absorption band appearing at ca. 400 nm. The intensity of this absorption band, which is considered as a measure of the extent of interactions exerted between the active phase and the support surface, depends on the kind and the amount of the transition metal. (C) 2004 Elsevier B.V. All rights reserved.