The Au-TiO2 system is a promising catalyst for the synthesis of nitro-aromatic compounds. The adsorption of azobenzene (C6H5N=NH5C6) and aniline (C6H5NH2) on two single-crystalline TiO2 surfaces, anatase (101) and rutile (110), has been investigated with scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and X-ray photoemission spectroscopy (XPS). While azobenzene adsorbs as an intact molecule at low coverages, ordered overlayers of phenyl imide (C6H5N) form at saturation coverage, indicating that TiO2 surfaces cleave the N=N bond even without the presence of Au. The same superstructures, p(1 × 2) on anatase and c(2 × 2) on rutile, form upon adsorption of aniline, suggesting the formation of the same, or a very similar, reaction intermediate. These results suggest that the main role of the supported Au in catalytic aniline <-> azobenzene conversion is the activation of O2/H2 for de/hydrogenation reactions.
Reprints available from U. Diebold (diebold).
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