Adsorption of small molecules in zeolites: A local hard-soft acid-base approach

The interaction of small probe molecules with clusters chosen to represent Bronsted acid sites in zeolites has been investigated using a local hard-soft acid-base approach. Condensed Fukui functions and local softness values of all the atoms of the probe molecules, namely, CH4, CO, and NH3, have been calculated, and these values are compared with that of the acidic hydrogen atoms of zeolite clusters to find out the most favorable adsorption sites. We calculated the interaction energy of the molecules using local HSAB principle, and the interaction energy values are in good agreement with the experimental results. Density functional and Hartree-Fock methods are used for the calculation of reactivity descriptors. We observed that the intermolecular interaction takes place via the atoms comparable softness values rather than via atoms of equal Fukui functions.