A philicity based analysis of adsorption of small molecules in zeolites

Abstract. Adsorption of small molecules like CH4, CO and NH3 into the acid sites of zeolites is ana-lysed as an interaction between an electrophile and a nucleophile. Global reactivity descriptors like soft-ness and electrophilicity, and local reactivity descriptors like the Fukui function, local softness and local philicity are calculated within density functional as well as Hartree–Fock frameworks using both Mul-liken and Hirshfeld population analysis schemes. The HSAB principle and the best electrophile-nucleophile combination suggest that the reaction between the NH3 and Brönsted acid site of the zeolite is the strongest. Interaction between the zeolite and a small probe molecule takes place through the most electrophilic atom of one with the most nucleophilic atom of the other. This result is in conformity with those provided by the frontier orbital theory and the local HSAB princi le