Potential for fixation of N₂ at room temperature utilizing a copper-ion-exchanged MFI-type zeolite as an adsorbent: Evaluation of the bond dissociation energy of adsorbed N≡N and the bond strength of the Cu ⁺-N(≡N) species

A peculiar N₂ adsorption was found on a copper-ion-exchanged MFI-type zeolite (CuMFI); the N₂ adsorption was established within 20 s at 300 K. Related to this fact, the bond dissociation energy of N≡N in a stable Cu⁺-N≡N species in CuMFI was, for the first time, evaluated to be 9.11 eV from the characteristic bands at 2295, 2654, and 4553 cm^-1, which correspond to the fundamental, combination, and overtone vibrations of N≡N adsorbed on Cu⁺ of CuMFI, respectively. The vibrational frequency of Cu⁺-N in the Cu⁺-N≡N formed in CuMFI was also determined to be ∼ 360 cm^-1, together with the energy for the formation of a Cu⁺-N bond; the Cu⁺- N≡N species is stable enough to maintain a N₂ molecule on MFI at 300 K. DFT calculations reasonably explain the experimental data and also the N₂ adsorption model based on the three-coordinate Cu⁺ site in CuMFI.