Type of Document Dissertation Author Moisii, Cristina URN etd-11082006-134504 Title Vibrational Spectroscopy of Silica Supported Vanadium and Chromium Catalyst Systems Degree Doctor of Philosophy Department Chemistry and Biochemistry, Department of Advisory Committee
Advisor Name Title A. E. Stiegman Committee Member E. A. Plant Committee Member John G. Dorsey Committee Member Kenneth A. Goldsby Committee Member Keywords
- Chromium Oxide
- Vanadium Oxide
- Amorphous Silica
- Resonance Raman
Date of Defense 2006-11-01 Availability unrestricted AbstractABSTRACT
In the present work, Raman, resonance Raman and IR spectroscopy were used to investigate isolated vanadium and chromium sites homogeneously dispersed in a transparent silica xerogel matrix. The use of optical monolithic glasses permits vibrational characterization with a signal-to-noise that was vastly superior to what can be obtained from powders. The use of these materials allows resolution of vibrational modes associated with the V and Cr ions even at low concentration. In addition, these materials are isotropic and non-scattering thereby allowing accurate polarization ratio analyses that were used in spectroscopic assignments.
The well-resolved Raman spectra allowed explicit assignments of the symmetric interfacial (Si-O-V) mode at 930cm-1. At high concentrations of vanadium the formation of oligomeric (V-O-V) modes was observed at 686cm-1. A transition associated with a perturbed silica mode that arises from vanadium incorporation was assigned at 1070cm-1.
Isotopic labeling and polarization studies of chromium silica xerogels confirmed that the strong 986cm-1 band is the totally symmetric terminal dioxo stretch. There was a peak observed at 1001cm-1 on the high-energy side of the symmetric mode; however, the isotopic shift and strong polarization of this mode precluded it from being the antisymmetric component of the Cr(=O)2 mode.
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