The formation of CaO-SrO solid solutions and investigations of their surface properties.

Abstract

The present work is concerned with the preparation, the phase characterization, the surface characterization and the catalytic properties of CaO-SrO solid solutions. Double carbonates of calcium and strontium were prepared and examined by X-ray diffraction analysis. A miscibility gap was found in the range 20-45% Sr content. CaO-SrO solid solutions have been prepared by thermal decomposition of the double carbonates at 145O K. The lattice parameter variation with Sr content has been evaluated and complete miscibility has been proved to exist in the full range of composition. UV-Vis diffuse reflectance spectroscopy has been used to study the adsorption of CO and butene on the solid solutions. CO produced dimeric and polymeric anion species. Butene produced carbanionic species and there was evidence of polymerization. Butene does not interact chemically with the pre-formed CO anionic species nor is there interaction of CO with chemisorbed butene. Both CO and butene polymeric species remained on the surface even after prolonged outgassing. Nitrobenzene and oxygen adsorption on CaO-SrO produced anion radical species which were studied by ESR spectroscopy. The surface concentration of the nitrobenzene anion radical, as determined from the integrated ESR spectrum, has been used as a measure of the electron-donor character of the solids. Isomerization of trans-but-2-ene was chosen as a model reaction for the comparison of the catalytic activity through the solid solution series. The mild conditions under which the reaction can be carried out indicated high basicity and electron-donor character for these solids. The change in these properties with composition has been interpreted in terms of structural, ionic and electronic factors. The structural factor consists of the change in lattice dimensions, in cation size and in surface area. The ionic and electronic factors consist of the ionicity of the metal-oxygen bond, the cation polarizing effect and the influence of the cation field. OS.60 which is the solid solution with 60% Sr content has shown the greatest basicity and the highest catalytic activity for the isomerization of trans-but-2-ene.

Date of Award	1980
Original language	English
Awarding Institution	University of Bath