Alcohol chemistry on rutile TiO2(110):: The influence of alkyl substituents on reactivity and selectivity

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 TiO2(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.