IN-SITU RAMAN-SPECTROSCOPY OF SUPPORTED CHROMIUM-OXIDE CATALYSTS - O-18(2)-O-16(2) ISOTOPIC LABELING STUDIES

The isothermal isotopic exchange reaction of O-18(2) with O-16 of chro mium(VI) oxide supported on zirconia, alumina, and titania has been in vestigated with in situ laser Raman spectroscopy. The isotopic exchang e reaction is dependent on the support type, the Cr loading, and the r eaction temperature. Complete isotopic exchange of chromium(VI) oxide with O-18(2) is difficult to achieve and requires several successive b utane reduction-O-18(2) oxidation cycles at relatively high temperatur es. The efficiency of the isothermal isotopic exchange reaction increa ses from alumina over titania to zirconia and with increasing Cr loadi ng and reduction temperature. The observed Raman shifts upon isotopic labeling are consistent with a mono-ore surface chromium oxide(VI) spe cies.