CHARACTERIZATION OF SURFACE SPECIES OF SUPPORTED V2O5-AL2O3 CATALYSTS BY V-51 NMR

V-51 NMR spectra were used for the study of the interaction between vanadium oxocomplexes in solution and the Al2O3 surface, and for the identification of surface vanadium species formed over Al2O3 surface for different preparation conditions (pH, concentration of supported V, treatment temperature). At low vanadium concentration, mainly isolated tetrahedral surface complexes are formed over the Al2O3 surface, bound with one or two bonds. The increase in vanadium concentration results in the formation of surface clusters with a part of the V in a distorted octahedral environment. After treatment at 500-degrees-C and at a V concentration of approximately 10 wt.%, the formation of AlVO4 and V2O5 crystals over the Al2O3 surface takes place.