Basic sites and reducing sites of calcium oxide and their catalytic activities

The amounts of basic and reducing sites of calcium oxides prepared by heat-treating the hydroxide at various temperatures were measured, respectively, by titration with benzoic acid, using bromothymol blue, etc., as indicators and by observing ESR, spectra or visible reflectance spectra of adsorbed nitrobenzene or m-dinitrobenzene. The maximum amount of basic sites was found to be 0.57 mmole/g when the hydroxide was calcined at 500 ° in air, while that of reducing sites to be 5 × 1014 and 1016 sites/g, respectively, when calcined at 700 ° in air and at 500 ° in a vacuum. It has been found that the catalytic activity of various calcium oxides for the esterification of benzaldehyde correlates well with the basicities, whereas that for the polymerization of styrene does with the amounts of reducing sites. On the basis of the above results together with infrared spectra of adsorbed benzaldehyde, isopropyl alcohol, and chloroform, the nature of basic and reducing sites was discussed, the reducing sites being shown to be entirely different from the basic sites.