CHARACTERIZATION OF CU-2+ SITES IN ZEOLITES NAX AND KX BY AL-27 ELECTRON-SPIN ECHO ENVELOPE MODULATION

The 27Al FT-ESEEM spectra of Cu2+-doped NaX, KX and KA zeolites were measured as functions of dehydration temperature and correlated with the observed ESR spectra and the Cu2+ locations within the zeolite structure. Partial dehydration of CuNaX at 25-300°C produced species B which was assigned of site I in the hexagonal prism, characterized by an 27Al FT-ESEEM spectrum of a single line at the 27Al Larmor frequency (3.5 MHz), indicating that the interaction between the unpaired electron and the 27Al nuclei is governed by weak dipolar interactions. Species A, on the other hand, observed in fully dehydrated CuNaX and in CuKX dehydrated above 100°C is characterized by an FT-ESEEM spectrum showing a doublet at 2.6 and 5.3 MHz which is a result of a rather large isotropic hyperfine coupling of ≈ 2.7 MHz. The large coupling is indicative of stronger binding of the Cu2+ to framework oxygens in sites III of III′ in the supercage. © 1990.