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The surface acidic strength distribution in a series of silica-alumina catalysts prepared by coprecipitation and stepwise precipitation techniques has been measured by the butylamine adsorption method. The amount of silica in the finished catalysts ranged from 86.0 to 96.9 %. A linear relationship between the pH of the final gel (i.e. pH values of the solution in equilibrium with the gel material before washing) and X[=A1~03/ (SiOz+Alz03)] was observed up to a certain level of pH; for coprecipitated catalysts it was 6.0 whereas for those precipitated stepwise the limit of pH was 7.0. Coprecipitated silica-aluminas were more enriched with weak acid sites or Bronsted sites (pKa = +6.8) and their concentration reached a maximum at about 87% silica.Stepwise precipitated silica-aluminas, on the other hand, have a greater population of strong acid sites, thus making them useful for cracking reactions.

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