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.