A LUMINESCENCE SPECTROSCOPY STUDY ON SUPPORTED VANADIUM AND CHROMIUM-OXIDE CATALYSTS

The luminescence properties of dehydrated silica- and alumina-supported vanadium and chromium oxide catalysts at low loadings at 4.2 K are reported and discussed. It is shown that one luminescent oxo-vanadium (-chromium) species is present on silica surfaces and more than one species on alumina surfaces. The Cr/Al2O3 sample does not show luminescence. The monomeric tetrahedral species show vibrational structure in their emission spectra, and their decay times amount to 10-30 ms. These luminescence properties are different from those of similar complexes in the solid state. The discrepancy is ascribed to a different electronic structure of the surface species which localizes the excited state in a short metal-oxygen bond.