Local reactivity descriptors to predict the strength of Lewis acid sites in alkali cation-exchanged zeolites

Abstract

Lewis acidity of alkali cation-exchanged zeolite is studied using local reactivity descriptors based on hard-soft acid–base (HSAB) concept. The local softness for nucleophilic attack (sx+), local softness for electrophilic attack (sx−) and their ratio, which is called `relative electrophilicity' (sx+/sx−), are calculated for the exchanged cations and Lewis acidity of the cations is found to decrease in the order: Li+ > Na+ > K+ > Rb+ > Cs+. Calculated blue shift of CO vibrational frequency (Δν) and interaction energy of CO molecule with alkali cation-exchanged zeolite clusters vary linearly with sx+/sx− values.