Measurement of Bronsted Acidity of Silica-Alumina Solid Catalyst by Base Exchange Method
Silica-Alumina catalysts having three different Si/Al ratios were prepared. Surface acidity of these catalyst samples was measured by the base exchange method using aqueous ammonium acetate, CH3COONH4 solution and the results were compared with those measured by the base exchange method using KOH and NH4OH as adsorbates from aqueous solution. The amount of K4 and NH4+ adsorbed was determined titrimetrically and spectrophotometrically, respectively for measuring the concentration of K+ and NH4+ in the solution before and after adsorption. It was found that the surface acidity was more pronounced when ammonium acetate solution was used as an adsorbate. With the use of NH4OH and KOH as bases considerable dealumination takes place with a consequent decrease of surface acidity of the catalyst samples. In all cases, the surface acidity increased with decrease of sample size. It is seen that surface acidity measured with NH4OH becomes closer to that measured with KOH at the same(?) Si/Al ratio, but contrary to this, surface acidity measured with NH4OH becomes closer to that measured with CH3COONH4 at high Si/Al ratio. This phenomenon is attributed to dealumination of silica-alumina catalyst samples by the strong base.
Surface Acidity, Silica-Alumina Catalysts, Bronsted Acidity, Base Exchange.
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