Abstract Monolayer catalysts were prepared by supporting transition metal ionic (t.m.i.)-oxo species (VO x , CrO x , MoO x and WO x ) on the TiO 2 (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 NH 3 (NH 3-SCR) in the temperature range 250–450 °C. 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.