This thesis describes the detailed application of uv-visible diffuse reflectance spectroscopy to several important aspects of oxide surface chemistry. The first part of the thesis concerns the high surface area synthetic aluminosilicate Zeolite Y. The dehydration of nickel-exchanged synthetic Y-type faujasite has been studied in detail. During the dehydration the divalent nickel ions become localised on the zeolite walls. The majority of the Ni2+ ions eventually entered the hexagonal prisms where they possessed Oh symmetry. The remainder of the nickel ions in the dehydrated zeolite were situated in the sodalite cages, and were partially reduced to the monovalent nickel ion in C3v symmetry. Adsorption experiments conducted with various adsorbates are discussed on the basis of this model. The second part of this thesis concerns the high surface area NiO-MgO and CoO-MgO solid solutions. The surface symmetries of the transition metal ions in the vacuum outgassed solid solutions have been determined and these were found to be C4v and possibly Td (Ni2+); Td and C3v (Co2+). As a result of the interaction with various adsorbates the surface Ni2+ and Co2+ symmetries, and in some cases valencies, changed and these are discussed. The surface Co2+ Td species was extremely resistant towards adsorbates incapable of chemically attacking the MgO matrix, indicating that the Co2+ Td species was located in a subsurface region. The subsurface ion, however, was distinguished from the bulk transition metal ion which was found to be six fold coordinated in Oh symmetry in both solid solutions. A third section of the thesis relates to pure alkaline earth oxides. The nature of the electronic transitions occurring on the surfaces of the alkaline earth oxides are fully discussed and found to be excitonic. The fluorescence properties of SrO were found to be greatly dependent on the outgassing temperature used. A series of spectra of chemi-sorbed carbanions are discussed. Finally, a short preliminary investigation into the surface exciton spectrum and chemistry of the CaO-SrO solid solution was undertaken.
|Date of Award||1977|