Characterization by solid state V-51 NMR spectroscopy

The fresh catalyst V2O5-WO3/TiO2 and catalyst used in SCR for 9000 h have b een studied by the solid state V-51 NMR spectroscopy in static and MAS cond itions. According to V-51 NMR in both samples the majority of vanadium site s are in a distorted octahedral environment similar to that in V2O5. There is a strong interaction between vanadium oxide and the support, but the con centration of vanadium atoms strongly bound to the surface is very small an d 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 part icles of V2O5. whereas the influence on the structure of strongly bounded V cannot be excluded. Combination of static (wide line) and MAS NMR techniqu es permit the characterization of not only the structure of the vanadium sp ecies but also small changes in their local environment. Hence these experi ments show that there are some distortions of the local environment of vana dium sites of the vanadium oxide particles compared with the polycrystallin e V2O5; treatment by SCR increases these distortions. (C) 2000 Elsevier Sci ence B.V. All rights reserved.