The Properties of Cu Ions in Zeolites CuY Studied by IR Spectroscopy

The properties of both Cu2+ and Cu+ ions in zeolite CuY were followed with NO and CO as probe molecules. Cu2+ was found to be located in S-II, S-II*, and S-III sites, whereas Cu+ was found in S-II and S-II* sites. The fine analysis of the spectra of Cu2+-NO and Cu+-CO adducts suggests that both in S-II and in S-II* sites two kinds of Cu cations exist. They differ in the positive charge, which may be related to the varying numbers of AlO4- in close proximity. The experiments of NO and CO adsorption and desorption evidenced that both Cu2+ and Cu+ sites of highest positive charge bind probe molecules most strongly but activate them to a lesser extent than the Cu sites of lowest positive charge. The experiments of reduction with hydrogen evidenced that the Cu ions of higher positive charge are first reduced by hydrogen. On the other hand, Cu sites of the lowest positive charge are first oxidized by oxygen. The experiments with CuNaY zeolites of various Cu contents suggest that the first introduced Cu (at low Cu contents) created Cu+, which was the most neutralized by framework oxygens. Such Cu cations are the most stabilized by framework oxygens.

Automated summary

The study found that in zeolite CuY, both Cu2+ and Cu+ ions are distributed in different locations, with two kinds of Cu cations existing in S-II and S-II* sites. Experimental results suggest that Cu2+ and Cu+ sites of highest positive charge bind probe molecules most strongly, and reduction with hydrogen and oxidation with oxygen affect different Cu ions differently.