Characterization of surface species on iron synthesis catalysts by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have been used to characterize the surfaces of clean and oxidized iron foils, bulk iron oxide powders, and reduced and carbided iron foils and powders. Metallic, divalent, trivalent, and carbidic iron species were identified by their characteristic Fe(2p) XPS spectra, and spectra for mixed-valence surfaces were approximated by linear combinations of the spectra of the individual iron species. Results for iron carbides prepared from metallic iron indicated that surface carbides can also be identified by their characteristic iron Auger line shape. The results of this investigation show that the combination of XPS and AES can be used effectively for identification of the chemical states of iron on synthesis catalyst surfaces.