Formation of CuI—N2 adducts at 298 and 77 K in CuI-ZSM-5: an FTIR investigation

Abstract

Cu^I-exchanged ZSM-5 contacted with N₂ at room temperature or at 77 K exhibits a narrow IR band at 2295 cm^–1. On the basis of ¹⁴N₂/¹⁴N₂ and ¹⁴N₂/¹⁴N¹⁵N/¹⁵N₂ isotopic substitution experiments this peak is assigned to the N—N stretching vibration of Cu^I—N₂ end-on dinitrogen complexes formed on isolated Cu^I sites inside the zeolite channels. The problem of the location of the Cu^I ions and the role of surface heterogeneity in determining the FWHM (ca. 9 cm^–1 at N₂ coverage θ= 1) of the 2295 cm^–1 band are discussed. Some hypotheses concerning the bonding structure are made by comparison with the spectra of the purely electrostatic M⁺–N₂ and M⁺–CO adducts (where M⁺ is an alkali-metal ion) and of the Cu^I—CO complex formed on the same support.