Determination of the surface acidities of various catalysts

The surface acidities of various Silica-Alumina, Sepiolite and Bentonite catalysts were determined by way of n-butyl amine titration technique with Hammett indicators in nonaqueous solvents such as benzene, back titration with sodium bicarbonate, sodium carbonate and sodium hydroxide bases in aqueous solution. Surface functional groups of various Silica-Alumina, Sepiolite and Bentonite catalysts were also investigated by Boehm?s titration technique. The points of zero charges were determined as neutral and acidic pH. Furthermore, the Brønsted and Lewis acid sites of the catalysts were investigated after the adsorption of pyridine in gas phase by FTIR spectroscopic method of analysis. The calculated total amount of acid of Silica-Alumina samples increased with the increase in silicon dioxide content up to Siral 40 and then decreased sharply in the case of Siral 80. FTIR spectroscopy was used successfully with pyridine as a basic probe, to determine the Brønsted and Lewis acid sites on the surface of various Silica-Alumina, Sepiolite and Bentonite catalysts. All samples have both Lewis and Brønsted acidity. The Lewis sites predominate in all the silica-aluminas.Keywords: surface acidity, Hammett acidity function, n-butyl amine titration, pyridine adsorption, FTIR spectroscopy