This paper concerns species of WO3-V2O5 solid solution and of vanadia-tungsta intermediate compound (IC) formed as a result of oxidation-induced vanadium segregation on the surface of an unsupported V-W-O catalyst. The evolution of the surface species during their interaction with ammonia (64 Torr) and nitric oxide (64 Torr) at room temperature was investigated by FT-Raman spectroscopy. The transformation of WO3-V2O5 solid solution species into ammonium methavanadate (V) ones and the reduction of intermediate compound species, followed by inward vanadium diffusion into subsurface layers, were observed as a result of the catalyst interaction with ammonia. The next catalyst interaction with NO was found to cause restoration of the WO3-V2O5 species but not of the intermediate compound ones at the surface.