Coordination and siting of Cu+ ions in ZSM-5: A combined quantum mechanics/interatomic potential function study
Siting and coordination of Cu+ ions in zeolite ZSM-5 have been studied by a combined quantum mechanics/interatomic potential function technique. A new Cu(I)–O interaction potential has been parameterized based on abinitio data which is compatible with abinitio-parametrized shell model potentials for zeolites. Several different sites of Cu+ inside ZSM-5 have been found. The structure of the site and the coordination of the Cu+ ion depend on the T-site where the Si atom is replaced by an Al atom. If Al is at the edge of the main and sinusoidal channels the Cu+ ion prefers to occupy thc open space in the channel intersection and it is coordinated to two oxygen atoms of the AlO4 tetrahedron. The largest binding energy of Cu+ with ZSM-5 was found for Cu+ located inside a six-membered ring on the wall of the sinusoidal channel, where it can coordinate to three or four oxygen atoms of the zeolite framework. The Cu+ sites predicted are in accord with available experimental results.