The oxygen isotopic exchange reaction on vanadium oxide catalysts

The reactivity of lattice oxygen of vanadium oxide catalysts was studied wi th the oxygen isotopic exchange reaction. The reactivity of pure V2O5 is co mpared with the reactivity of Li0.33V2O5, V2O5/TiO2, V2O5/Al2O3, V2O5/SiO2, delta-VOPO4, and (VO)(2)P2O7. According to their behaviour in the oxygen e xchange reaction, two types of vanadium oxide catalysts could be distinguis hed. The first type of catalysts only showed exchange activity in the R-2 e xchange mechanism and the second type showed activity in both the R-1 and R -2 exchange mechanisms (mechanisms in which, respectively, one or two oxyge n atoms of the gas phase molecule are exchanged with oxygen atoms of the me tal oxide). The catalysts which belong to the first group are bulk V2O5 and delta-VOPO4 and the catalysts which belong to the second group are Li0.33V 2O5, V2O5/TiO2, V2O5/Al2O3, V2O5/SiO2, and (VO)(2)P2O7. If only the R-2 mec hanism is observed then diffusion of lattice oxygen is probably faster than when both the R-1 and R-2 mechanisms are observed. The activity of the sup ported vanadium oxide catalysts in the oxygen exchange reaction is dependen t on the support. The reactivity order is V2O5/TiO2 > V2O5/Al2O3 similar to V2O5/SiO2. (C) 1999 Academic Press.