Local Spin Density Functional Theory Study of Copper Ion-Exchanged ZSM-5

Abstract

We have used local spin density functional theory to investigate the electronic and structural properties of Cu species (Cu+, Cu2+O-, and Cu2+OH-) interacting with isolated ⋮Al−O-−Si⋮ sites CuZSM-5. We have also evaluated the thermodynamic stability of these species and the thermodynamics of a proposed scheme for the autoreduction of Cu2+ to Cu+. We have found all of the species studied to be thermodynamically stable and the proposed autoreduction process to be thermodynamically feasible at temperatures normally encountered in the pretreatment of as-exchanged CuZSM-5. In addition, we have investigated the interactions of Cu2+ cations with both 6-T site and 5-T site ring structures containing two Al atoms. We have found that Cu2+ in a 6-T site ring structure is thermodynamically unstable, while that in a 5-T site ring structure is thermodynamically stable.