The fresh catalyst V2O5-WO3/TiO2 and catalyst used in SCR for 9000 h have been studied by the solid state V-51 NMR spectroscopy in static and MAS conditions. According to V-51 NMR in both samples the majority of vanadium sites are in a distorted octahedral environment similar to that in V2O5. There is a strong interaction between vanadium oxide and the support, but the concentration of vanadium atoms strongly bound to the surface is very small and can be detected only in MAS NMR experiments or after removing the excess of V2O5 There is no influence of WO3 additives on the structure of the particles of V2O5. whereas the influence on the structure of strongly bounded V cannot be excluded. Combination of static (wide line) and MAS NMR techniques permit the characterization of not only the structure of the vanadium species but also small changes in their local environment. Hence these experiments show that there are some distortions of the local environment of vanadium sites of the vanadium oxide particles compared with the polycrystalline V2O5; treatment by SCR increases these distortions. (C) 2000 Elsevier Science B.V. All rights reserved.