T-O-T skeletal vibration in CuZSM-5 zeolite: IR study and quantum chemicalmodeling

The location of Cu cations in CuZSM-5, properties of cationic sites and the ir interaction with guest molecules have been studied by quantum chemical ( DFT) modeling and IR spectroscopy based on the frequency shift of antisymme tric T-O-T vibration of oxygen rings. The shift has been found sensitive bo th to the framework interaction with cations and to the interaction with ad sorbed molecules. It has been measured and estimated theoretically from par ameters characterising framework distorsion by Cu+ and Cu2+, with MgZSM-5 a nd NaZSM-5 used as "reference samples". It was found that the ordering of t he cation perturbing effect was. Na+ < Cu+ < Mg2+ < Cu2+. NO interaction wi th Cu cations was much stronger than that of CO and N-2. Divalent copper sh owed polarized 2-electron covalent bonding with NO strengthening its bond w hile moderate bonding ability of monovalent copper led to NO bond activatio n, in accordance with high catalytic activity of Cu(+)ZSM-5.