Chemisorption of H2O on the surface of Ti2O3: Role of d electrons and ligand geometry

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The interaction of H2O with both nearly perfect and defect Ti2O3 surfaces has been studied by ultraviolet photoemission spectroscopy. Perfect Ti2O3 (047) surfaces, which contain fivefold O-coordinated Ti3+ cations, rapidly chemisorb molecular H2O, with an accompanying transfer of electrons from the Ti a1g band to the molecule-surface complex. Saturation coverage of adsorbed H2O is less than one-half monolayer. The extramolecular relaxation-polarization shift for molecularly adsorbed H2O is 1.0 eV, and the O-lone-pair orbital is dominant in bonding to the surface. There is no evidence for dissociative chemisorption of H2O on Ti2O3 (047). On Ti2O3 surfaces containing a high density of defects, dissociative adsorption of H2O is observed; the chemisorbed species is believed to be OH- radicals. Some molecular adsorption of H2O may also occur for larger exposures. These results indicate that the presence of Ti3+ surface ions alone is not sufficient to catalyze the dissociation of H2O, in contrast to previous interpretations of data on TiO2 and SrTiO3. Presumably other Ti valence states or the more complicated ligand structure of defect sites are required for dissociation of H2O. © 1982 The American Physical Society.

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Physical Review B

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