Resonance Raman Spectroscopic Study of Alumina-Supported Vanadium Oxide Catalysts with 220 and 287 nm Excitation

We present detailed resonance Raman spectroscopic results excited at 220 and 287 nm for alumina-supported VO(x) catalysts. The anharmonic constant, harmonic wavenumber, anharmonic force constant, bond dissociation energy, and bond length change in the excited state for double bonded VO and single bonded V-O were obtained from fundamental and overtone frequencies. Totally symmetric and nontotally symmetric modes could be discerned and assigned on the basis of the overtone and combination progressions found in the resonance Raman spectra. Selective resonance enhancement of two different vibrational modes with two different excitation wavelengths was observed. This allowed us to establish a linear relationship between charge transfer energy and VO bond length and, consequently, to assign the higher-energy charge transfer band centered around 210-250 nm in the UV-vis spectra to the VO transition.