We investigated methanol adsorption and dissociation on bridge-bonded oxygen vacancies of the TiO2(110)-(1x1) surface using in situ scanning tunneling microscopy. We provide the first direct evidence that methanol dissociates on oxygen vacancies via O-H bond scission rather than C-O scission. For CH3OH coverages lower than the oxygen vacancy concentration, stationary methoxy-hydroxyl pairs form. At CH3OH coverages close to the oxygen vacancy concentration undissociated mobile CH3OH interacts with methoxy-hydroxyl pairs and facilitates the movement of hydroxyl away from the methoxy group.
Product yields and selectivities, based on ultrahigh vacuum temperature-programmed desorption, are compared for 10 C 2 to C 8 aliphatic alcohols dosed at 100 K on highly ordered TiO 2 (110) with a 3.5% concentration of surface oxygen vacancies. Dehydration to form an alkene and water typically dominates, while two other channels, dehydrogenation to form an aldehyde and re-formation of alcohol, make detectable contributions for primary alcohols. Depending on the alcohol, there are two distinct dehydration pathways: one operative at low temperature (LT, 300-425 K) and the other at high temperature (HT, 480-650 K). The HT dehydration pathway is common to all, while the LT channel is not observed for tertiary butanol and 3-and 4-octanol. The observed trends are accounted for in terms of the inductive and steric effects of the alkyl substituents.
smaller than the uncertainties related to ACP and to some of the parameters in Table I. Since AC" was, in a sense, adjusted to optimize the fit with the hign-density data of Quist, the refinement of fugacity coefficients seemed inappropriate. Debye-Hückel effects were considered and found to be negligible for the very small ionic strengths involved. Also Kw is strictly defined in terms of activity rather than molality. Thus, the effect of an activity (or fugacity) coefficient less than unity for all ions would be to increase the concentration of ions but to leave the activity product and Kv unchanged.
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