Adsorption of Alkenes on Acidic Zeolites. Theoretical Study Based on the Electron Charge Density

In the present work, experiments oil electron density changes in the adsorption process of alkenes on acidic zeolites, in the framework of atoms in molecules theory (AIM), were carried out. Electron densities were obtained at MP2 and B3LYP levels using it 6-31++G(d,p) basis set. This study explores the energetic and the electron density redistributions associated with O-H center dot center dot center dot pi interactions. The main purpose of this work is to provide an answer to the following questions: (a) Which and how large are the changes induced on the molecular electron distribution by the formation of adsorbed alkenes? (b) Can a reasonable estimate of the adsorption energy of alkenes on the active site of zeolite be solely calculated from an analysis of the electron densities? We have used topological parameters to determine the strength and nature of the interactions in the active site of the zeolite. All the results derived front the electron density analysis show that the stabilization of the adsorbed alkenes follows the order isobutene > trans-2-buteric congruent to 1-butene congruent to propene > ethene, reflecting the order of basicity of C=C bonds, i.e., (C-ter=C-prim) > (C-sec=C-sec) congruent to (C-prim=C-sec) > (C-prim=C-prim). In addition, we have found a useful set of topological parameters that are good for estimating the adsorption energy in adsorbed alkenes.