DFT quantum chemical modeling of the interaction of alkenes with Cu+ sites in zeolites

In this work charge transfer phenomenon between the admolecule and the active site and its consequences for the bond weakening/strengthening in the adsorbed molecule are discussed on the example of unsaturated hydrocarbons (early alkenes) interacting with Cu+ cation embedded in a model of ZSM-5 zeolitic site. Detailed comparison of ethene interaction with various metallic sites based on this work and comparative analysis of other related studies helps to formulate working rules of charge transfer decomposition and interpretation. All studied alkenes form strongly bonded π complexes and become strongly activated on Cu+ sites in ZSM-5 by both processes: π donation and π* back-donation, what clarifies the mechanism by which the activation of the CC bond in alkenes adsorbed on Cu+ZSM-5 takes place. Calculated shifts in CC stretching frequencies qualitatively follow the experiment and are a good measure of the activation.