Acidity of silica-alumina catalysts by amine titration using Hammett indicators and FT-IR study of pyridine adsorption

In this study, characterization and surface acidity of Siral (SiO2-Al2O3) c ompounds were investigated with Hammett acidity functions, the n-butylamine titration method and FTIR analysis of the spectra of pyridine adsorption. All the samples had an acid strength of H-0 less than or equal to +2.8. The calculated total amount of acid of the samples increased with the increase in SiO2 content up to Siral 40 and then decreased sharply in the case of S iral 80. Maximum amount of acidity was observed in the case of Siral 40 as 1.37mmole/g. No evidence was found for a band at 1540 cm(-1) on Pural indic ating that there were no Bronsted sites on the surface strong enough to rea ct with pyridine. As a result, we can say that the Lewis sites predominate in all the silica-aluminas.