DETERMINATION OF THE SURFACE HETEROGENEITY OF MGO-SIO2 SOL-GEL MIXED OXIDES BY MEANS OF CO2 AND AMMONIA THERMODESORPTION

Magnesia-silica mixed oxides were prepared by the sol-gel method. Simu ltaneous hydrolysis of magnesium diethoxide and tetraethoxysilane was made at pH 3 and 9. The solids obtained in acid medium show large surf ace areas between 441 and 522 m(2)/g, and those prepared in basic medi um show surface areas between 132 and 174 m(2)/g. The solids show acid ity and basicity, and they are able to retain ammonia and CO2 at 200 d egrees C. They can develop basicity by contact with a sulfuric acid so lution. Sulfation of the solids notably increases the basicity. The ba sicity of sulfated oxides is explained in terms of a magnesia segregat ion. Sulfation segregates magnesium oxide, and hence well-dispersed ma gnesia on silica is obtained.