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 SII, SII*, and SIII sites, whereas Cu+ was found in SII and SII* sites. The fine analysis of the spectra of Cu2+-NO and Cu+-CO adducts suggests that both in SII and in SII* 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.

STRUCTURAL STUDIES OF MOLECULAR ADSORPTION AT SURFACES USING SCANNED-ENERGY MODE PHOTOELECTRON DIFFRACTION

A short review is presented of the use of scanned-energy mode photoelectron diffraction for the quantitative determination of the local adsorption structure of molecular species on wellcharacterised metal surfaces. Some of the results [notably for NO and CO adsorption on Ni(111)] highlight the importance of such true quantitative methods relative to "fingerprinting" via vibrational spectroscopy which is shown to have led to incorrect local adsorption site assignments. The use of direct methods for approximate site identification, and chemical-shift photoelectron diffraction for studies of more complex coadsorption structures is described with the aid of specific applications to molecular fragmentation and geometrical reaction path determination. The prognosis for further development and application is discussed.