Location and adsorbate interactions of Cu(II) ion in Cu(II)-exchanged K-L zeolite by electron spin resonance and electron spin echo modulation spectroscopy

The interaction of Cu(II) with deuterated adsorbates in Cu(II)-exchanged K-L channel-type zeolite was studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. It was found that in the hydrated zeolite the major Cu(II) species is octahedrally coordinated to six water molecules with the complex located in the main channels. Evacuation at room temperature was sufficient to remove three of these water molecules, leaving the Cu(II) coordinated to three water molecules and anchored to the zeolite lattice by coordination to three zeolitic oxygens. A minor Cu(II) species was also detected with reverse g values characteristic of trigonal bipyramidal coordination. Dehydration at 500°C produces a Cu(II) species which is inaccessible to the main channels based on a lack of broadening of its ESR lines by oxygen. Adsorption of molecules such as water, alcohols, and ethylene causes changes in the ESR spectrum of the Cu(II), indicating migration into cation positions in the main channels where adsorbate coordination can occur. Cu(II) forms complexes with two molecules of methanol and ethanol and one molecule of ethylene based on ESEM data.