Characterization of zeolite acidity by n-butylamine titration. A comparative study using Hammett indicators and calorimetry

Abstract

The acidity of three H-zeolites, a mordenite (HM), a dealuminated mordenite (DHM) and a HY zeolite, has been determined both by calorimetric titration and titration with non-aqueous n-butylamine solution using coloured Hammett indicators in the range H₀=–3.0–6.8. Neither method is satisfactory for the mordenite (HM), and it is considered that the n-butylamine molecule blocks the entrance to the pores of this zeolite, preventing an accurate estimation of its acidity. The results for HY are in satisfactory agreement with published work. There is some uncertainty as to the acidity of DHM, as dealumination may have enlarged the opening of the channel system with pore blockage occurring further down from the entrance to the pore, or on the other hand it may have caused the formation of strong acid sites on the exterior surface.