Coordination and Siting of Cu+ Ion Adsorbed into Silicalite-2 Porous Structure: A Density Functional Theory Study

Coordination of Cu+ ions adsorbed on plausible sites of a silicalite-2 lattice has been investigated computationally via hybrid density functional theory method at the B3LYP/6-311+G* and B3LYP/Def2-TZVP levels of theory using molecular models of the active site. The symmetrical coordination of Cu+ ions to almost five oxygen atoms of the all-silica framework in six-membered ring (6MR) sites of the main channels was the most stable configuration of Cu-silicalite-2 clusters. On the contrary, the metal cation was found to be most weakly bound in sites at the intersections where the metal ion was twofold coordinated. Implications on the catalytic chemistry for adsorption or activation of different molecules on the exchanged sites are discussed. The average binding energy was calculated to be ~46 kcal/mol for Cu/silicalite-2. Although chemisorbed, the relatively weak bindings of Cu+ supported some unusual reactivity of high-silica Cu-doped ZSM-11 catalysts in previous studies and evinced that this adsorbent can offer substantial capacities with respect to the guest molecules, e.g., in pollution abatement.