Halocarbon Reactions on the Chromium (III) Oxide (1012) Surface
York, Steven C.
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A nearly stoichiometric, (1x1) Cr2O3 (1012) surface was prepared from a single crystal of alpha-Cr2O3. The five-coordinate cations exposed at the stoichiometric surface dissociatively adsorb molecular oxygen to form a (1x1), terminating chromyl (Cr=O) layer that is stable to >1100 K. TDS and AES were used to investigate the reactivity of the halo-alkanes CFCl2CH2Cl, CF2ClCH2Cl, CF3CH2Cl, and CF2CH2F, in addition to the halo-alkenes CFCl=CH2 and CF2=CH2. The halo-alkanes CFCl2CH2Cl, CF2ClCH2Cl, and CF3CH2Cl undergo 1,2-dihalo elimination similar to the Zn-catalyzed dehalogenation of vicinal dihalides to form alkenes. Some acetylene is also formed. The halo-alkenes CFCl=CH2 and CF2=CH2 decompose to yield acetylene. Halogen removed from the molecules remains bound to the surface following TDS experiments and eventually terminates the surface chemistry due to site blocking of the cations. Reactivity is directly related to the chlorine content of the molecules investigated. Only CFCl2CH2Cl was reactive on a chromyl-terminated surface.
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