Cluster molecular models of VOx/TiO2 catalytic system based on embedding process of V-ion in the anatase support were considered. Cluster structures of (00 1) anatase surface, containing one- and two-layer were constructed and isomorphous substitution of two Ti-ions on two V-ions were calculated. Comparison of the Bronsted acidic properties of V-OH group on the surface Of V2O5 and supported VOx/TiO2 Species showed that embedding procedure increases their acidic power and the influence of the second layer of the support is essentially important. Formation of ammonium ion under the adsorption of NH3 on supported and unsupported vanadium oxide catalyst was considered and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.