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.