Can. J. Chem. 56.3078 ( 1978). The oxygen exchange reaction between 0, C"0, and the surfaces of vanadium pentoxide and promoted vanadium pentoxide catalysts has been studied in a circulation system using a quartz differential reactor. Isotopic compositions here analysed lvith an in-line mass spectrometer. Alkali metal sulphates, Li to Cs, were added to the pentoxide as individual promoters a t a concentration level of 9 n i o l z and the effect of variation of promoter concentration n a s examined with melts containing potassiurn sulphate at additional levels of 1, 2, and 5 n~o l z . The structures of the solids were studied by X-ray diffraction and by A T R and transniission infrared spectroscopy. The latter results have been used to explain the two activity series for the exchange rates: (i) V 2 0 , < Na i Li < K < R b < Cs (melts) and ( O n a etudie la structure des solides en utilisant la diffraction des rayons X, ainsi que la spectroxopie infrarouge par trans~nission et par RTA. Les vitesses d'echange ont conduit au classement dc l'activite des systemes selon les series suivantes: (i) V 2 0 s < N a < Li < K < R b < Cs et iii) V Z O~ < I m o l z < 2 n i o l z < 5 nmolz < 9 i n o l z (K). Les resultats des methodes enumerees ci-dessus ont permis de relier ces deus series aux effets conjugues de l'abondance et de la force relatives des liens vanadium oxygene se trouvant sur la surface des catalyseurs.[Traduit par le journal]