High-valent early transition metal oxides such as V(V) and Cr(VI) dispersed on amorphous silica represent an important class of heterogeneous catalysts. The detailed spectroscopic characterization of these sites, which is required to understand fundamental physical properties such the electronic structure and the normal modes of vibration, is often difficult due to the low concentration of the metal sites present and the optical scattering of the catalyst materials. Our development of supported catalyst as monolithic sol-gel derived optical monoliths, greatly improve the quality of the spectroscopic determinations can be made. Through the use these materials we have been able to elucidate many spectroscopic details of these sites. We report the electronic structure and the assignment of the electronic transitions in the four coordinate chromyl and vanadyl sites on silica. In addition, Raman spectroscopy, both resonant and non-resonant, was carried out. The observed resonant enhancement of specific modes is explained in terms of the electronic transitions being excited. In addition, a complete normal coordinate analysis of vibrational modes has been conducted. Notably, the assignments of the normal modes differ from many of the existing assignments.

Spectroscopy of single site metal oxide catalyst on silica

251st National Meeting (2016)

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