Science and Mathematics Faculty Publications

Electron Paramagnetic Resonance Parameters of Copper(ll) Y Zeolites

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Journal of Physical Chemistry





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The number of electron paramagnetic resonance (EPR) parameters for copper(I1) 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(I1) exchanged Y zeolites: gill = 2.38(110), g,l = 2.06(20), g1I2 = 2.30(175), gL2 = 2.03, and in some cases g1l3 = 2.36(125), where the numbers in parentheses are the observed hyperfine splittings (in Gauss). Prolonged evacuation of the low Cu(I1) ion exchanged Y zeolites yielded gill = 2.37(125), g,l = 2.06(20), g1I2 = 2.32(160), and gL2 = 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(I1) ions located in sites in the small cages, while the gl and g2 subsets of the first group are due to copper(I1) 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(I1)-Y zeolites can be explained in most cases.