Vibrational Spectroscopy of Silica Supported Vanadium and Chromium Catalyst Systems

• Other Authors: Moisii, Cristina (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Chemistry; Biochemistry
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-7048

ABSTRACT 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. === A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Fall Semester, 2006. === November 1, 2006. === Includes bibliographical references. === Albert E. Stiegman, Professor Directing Dissertation; Ashby Plant, Outside Committee Member; Kenneth A. Goldsby, Committee Member; John G. Dorsey, Committee Member.