High resolution HAADF characterization of Ir/TiO₂ catalyst reduced at 500 °c: Intensity profile analysis

A comparison is presented between experimental and simulated high resolution-high angle annular dark field images (HR-HAADF) of Ir/TiO₂ catalyst reduced at 500 °C where classical strong metal-support interaction develops. The analysis is based on integrated intensity profiles of the atomic columns of iridium nanoparticles on the TiO₂ support. The results were as expected, that when Ir/TiO₂ catalyst is reduced at high temperature, partially reduced species from the support (TiO_x) migrate to the surface of iridium nanoparticles. Two very important facts can be highlighted: one is that the Ti atoms sited on atomic columns in the [11¯0] direction preserve the atomic ordering of the metallic particle (epitaxial growth), while those located in atomic columns at perpendicular directions to the observation axis are disordered, and as a consequence, they appear as an amorphous thin film. Finally, changes in the (111) interplanar spacing of TiO₂-rutile structure could be due to an enrichment of Ti³⁺ species at the rutile surface.