INFRARED SPECTROSCOPIC STUDY OF OXYGEN SPECIES IN VANADIUM PENTOXIDE WITH REFERENCE TO ITS ACTIVITY IN CATALYTIC OXIDATION

To clarify the nature of the exchangeable oxygen in vanadium pentoxide catalyst during the oxidation reaction, an infrared technique combined with the 18O tracer technique was applied to the samples isotopically substituted by treatment with carbon dioxide-18O. The bonds appearing at 1019 and 818 cm-1 can be identified to be the V=O and V-O-V groups, respectively, because the corresponding shift of both bonds appeared by isotopic substitution. Exchange experiments between gaseous carbon dioxide and vanadium pentoxide were carried out at 290, 370, 410, and 450°, and the 18O balance was investigated, taking the intensity of the above infrared bands into account. Thus, the behavior of the oxygen species at the surface and in the bulk could be determined; (a) Direct exchange of the oxygen on the surface V=O groups with gaseous oxygen is very rapid at the initial stage of reaction. (b) Oxygen exchange between V=O and V-O-V groups may occur rapidly near the lattice dislocations on the (010) surface as well as on other surfaces. (c) The exchange within the V-O-V net plane is the easiest of all the processes, so that it becomes predominant in the reaction even at the intermediate stage. (d) The exchange between the V=O and V-O-V groups on the surfaces is important from the standpoint of catalytic oxidation.