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 ( s x +), local softness for electrophilic attack ( s x −) and their ratio, which is called `relative electrophilicity' ( s x +/ s x −), 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 (Δ ν) and interaction energy of CO molecule with alkali cation-exchanged zeolite clusters vary linearly with s x +/ s x − values.