STRUCTURE OF A NANOPHASE IRON-OXIDE CATALYST

Iron K-edge X-ray absorption fine structure (XAFS) studies have been carried out to determine the bulk and surface structures of a nanophase iron oxide catalyst with average particle size of 30 Å. Both the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near-edge structure (XANES) spectra indicate that the structure of the catalyst is similar to iron oxyhydroxide. The intensity of the 1s → 3d transition peak in the XANES of the 30-Å catalyst is increased by a factor of 1.7 compared with that for iron oxide and iron oxyhydroxide model compounds, in which iron ions are coordinated by six oxygens or oxygen/hydroxyl groups. The increase of the 1s → 3d transition intensity is attributed to coordination unsaturated (CUS) sites on the particle surface produced by dehydroxylation. The absorption edge position of the 30-Å catalyst indicates that the valence state of the iron ions remains +3. © 1993 Academic Press, Inc.