ACIDITY AND CATALYTIC ACTIVITY OF SILICA-ALUMINA GELS PREPARED BY COGELATION USING INSTANTANEOUS MIXING METHOD

By using the instantaneous mixing method, silica alumina co-gels with different compositions were prepared from aqueous solutions of sodium silicate and aluminium nitrate. The Al2O3 compositions of the co-gels were found to be correlated with the compositions of the solutions by a relation similar to that of a vapor-liquid equilibrium. This suggests that the escaping tendency of each chemical species in the solution influences the composition of the solid deposit as similarly observed in the case of liquid condensation from vapor phase. Although the specific surface areas and the primary particle diameters of the co-gels went through a minimum and a maximum, respectively, at an alumina content of 50 mass%, both the amounts of solid acid and the catalytic activities for the isomerization of 1-butene went through maxima at two alumina contents of 20 and 70 mass%. The two maxima in the solid acid amount can be predicted based on a surface arrangement model.