STUDY OF THE CHEMICAL-STATE OF IR IN IR AL2O3 CATALYSTS BY XPS, LOW-ANGLE X-RAY-SCATTERING, AND ELECTRON-MICROSCOPY TECHNIQUES/

A study of interaction of iridium with Al2O3 support in Ir/Al2O3 catal ysts by x-ray phase analysis, electron microscopy (EM), low-angle x-ra y scattering (LAXS), and XPS techniques has shown that various iridium species occur on the surface of the support. A portion of iridium(no more than 3-5%) occurs as Ir-n+ and forms a spinel-like Ir-2(Al2O4)(n) structure with the support. Another portion (Ir-O) is polarized, due to contacts with the first portion, and transforms into Ir-q+. The ext ernal surface of iridium crystallite is oxidized by atmospheric oxygen into Ir-m+. Such properties of iridium particles as dispersity and th e area contacting with the support are mainly influenced by pore struc ture of the latter. Any admixtures present in the support may signific antly affect the proportions of various iridium species in catalysts.