Studies of the defect chemistry of TiO2 surfaces
- Pacific Northwest National Lab., Richland, WA (United States)
Defects are believed to play an important role in chemical reactivity of oxide surfaces. The interactions of water, formic acid and methanol with defective TiO2 surfaces have been investigated using XPS, UPS, and electronic structure calculations. The increased adsorption as increasing exposed Ti sites created by electron-beam exposure of Ar+ bombardment is corroborated by the electronic structure calculations which found a strong adsorptive interaction for formate onto both stoichiometric and defective TiO2 surfaces. The excess adsorption promoted by surface defects quantitatively corresponds to the number of newly exposed sites created by electron-beam exposure. Water heats (defect healing means an observation of the reducing of defect state intensity in both XPS and UPS spectra) defects at much higher exposure than methanol. In contrast, formic acid produces little healing at saturation exposure. As the chlorofluorocarbons (CFC`s) are being phased out, their most promising replacements are the hydrofluorocarbons (HFC`s). In particular, CFC-12 (CF{sub 2}Cl{sub 2}), widely used as a refrigerant, for example, is being replaced by HFC-1 34a (CF{sub 3}-CFH{sub 2}). One possible route to HFC-134a is the hydrodechlorination of CFC-114a (CF{sub 3}-CFCl{sub 2}) over palladium catalysts. We report results using single crystal palladium catalysts and compare the reactivity of the low Miller index planes and a polycrystalline foil. We correlate these results with parallel UHV surface science experiments. Deuterium isotope studies (D{sub 2} rather than H{sub 2}) will also be presented and discussed. Of particular interest is an observed sample history-dependent inverse isotope effect.
- OSTI ID:
- 559948
- Report Number(s):
- CONF-970443--
- Country of Publication:
- United States
- Language:
- English
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