Electronic Structure of Zn⁺‑Modified Zeolite: A Density Functional Theory Study of Ferrierite

Density functional theory (DFT) calculations were used to study the monovalent Zn⁺ cation exchanged in an extra-framework position of zeolite ferrierite. A single Zn⁺ was found to be paramagnetic. Two Zn⁺ cations combined to form a subnano-sized dimeric species [Zn–Zn]²⁺ which fits into the eight- or ten-membered rings (8MR or 10MR, respectively) of ferrierite. Within the [Zn–Zn]²⁺ pair, two cations were bound via a covalent s–s bond. Upon the pair forming, a huge stabilization was observed, linked with a decrease in potential energy by 235–296 kJ/mol, depending on the location of Zn⁺ in the framework. The [Zn–Zn]²⁺ species is an electron paramagnetic resonance (EPR) silent insulator with a band gap of 4.82 eV. Because 8MR and 10MR are present in a majority of zeolite structures, we predict that the Zn-modified electron-rich materials can be fabricated from almost any stable aluminum-rich zeolite. Because of the strong tendency for the conversion of Zn⁺ to Zn²⁺, the Zn⁺-modified zeolites are strong solid Lewis bases with promising catalytic properties.