The number of electron paramagnetic resonance (EPR) parameters for copper(II) ions held in lattice positions in dehydrated low exchanged sodium Y zeolites, as well as the relative intensity of each set of g values observed in the spectrum, was found to vary as a function of evacuation time at ambient temperature prior to activation. The usual procedure of evacuating the sample for 15-60 min before beginning the thermal treatment in hourly increments resulted in the following parameters for low Cu(II) exchanged Y zeolites: gj1 = 2.38(110), gLl = 2.06(20), gf = 2.30(175), g±2 = 2.03, and in some cases g||3 = 2.36(125), where the numbers in parentheses are the observed hyperfine splittings (in Gauss). Prolonged evacuation of the low Cu(II) ion exchanged Y zeolites yielded gj1 = 2.37(125), g^1 = 2.06(20), gf = 2.32(160), and g±2 = 2.03 following dehydration to 400-500 °C.Parameters similar to the latter values were obtained for highly ion exchanged Cu-Y zeolites following partial reduction with hydrogen or carbon monoxide, as well as upon partial reoxidation of the latter samples with oxygen or nitric oxide. The second set of EPR parameters is attributed to copper(II) ions located in sites in the small cages, while the g1 and g1 subsets of the first group are due to copper(II) ions localized in the zeolite supercages. Most, of these sites provide a distorted trigonal environment for the divalent copper ions. By correlating the zeolite treatments reported in the literature to the present results, the disparity among previously given EPR parameters for Cu(II)-Y zeolites can be explained in most cases.
Publication costs assisted by the National Science Foundation (USA) and the National Fonds voor Wetenschappeli)k Onderzook (Belgium) The changes in the epr and ir spectra of copper(Il)-ammine complexes in a Y-type zeolite have been studied as a function of the amount of ammonia adsorbed. The intensity of the epr spectrum increased linearly until the ratio of the number of ammonia molecules to the number of cupric ions was 4:1, at which point the addition of excess ammonia failed to change the spectrum. The same behavior was noted in the ir spectrum for the symmetric deformation band of ammonia coordinated to cupric ions. Adsorption of deuterated ammonia on a low-exchanged sample produced an epr spectrum which revealed the superhyperfine splitting of four equivalent nitrogen nuclei in the parallel as well as the perpendicular region of the spectrum. These data provide additional evidence that the [Cu(NH3)4]2+ complex is formed within the zeolite structure. This complex may be detected in the presence of excess ammonia and oxygen at temperatures up to 180°. The change in the epr spectrum of a moderately exchanged sample upon adsorption of ammonia indicates that the copper ions move out of the small cavities, and most of the complexes are formed in the large cavities of the zeolite.
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