X-RAY-ABSORPTION SPECTROSCOPIC STUDIES ON COPPER-CONTAINING HYDROTALCITE

EXAFS and XANES spectra have been recorded at the copper K-absorption edge on hydrotalcite samples, which contain 10 mol% copper, in order t o determine the local environment of the copper ions. The vanishingly small magnitude of the pre-edge peak in the XANES region of the spectr a indicates a centrosymmetric coordination of copper. The analysis of the EXAFS region results in a set of four oxygen ligands, 1.98 Angstro m apart from copper as well as two oxygen ligands, which are 0.26 Angs trom further apart. This is consistent with an octahedron, elongated b y Jahn-Teller effects. The best fit of the third coordination shell is obtained with 4.6 aluminium or magnesium ions at a distance of 3.05 A ngstrom from the copper.