In situ Raman spectroscopy of supported transition metal oxide catalysts:: 18O2-16O2 isotopic labeling studies

The isothermal isotopic exchange reaction of O-18(2) With O-16 Of CrO3, MoO3, Nb2O5, WO3, V2O5, and Re2O7 supported on ZrO2 has been investigated with in situ laser Raman spectroscopy. Isotopic exchange of the oxygen atoms of the supported transition metal oxides with O-18(2) is difficult and requires several successive reduction-O-18(2) reoxidation cycles at relatively high temperatures. The Raman spectroscopy data reveal that all the supported transition metal oxides an present as a monooxo species on ZrO2. This finding is consistent with the shifts calculated from the isotopic ratios for a simple diatomic oscillator, with the corresponding infrared spectra of the same catalysts and with the vibrational frequencies of several monooxo reference compounds. On this basis, coordination models of the molecular structures are proposed for CrO3/ZrO2, MoO3/ZrO2, Nb2O5/ZrO2, WO3/ZrO2, V2O5/ZrO2, and Re2O7/ZrO2 catalysts under dehydrated conditions.