Role of defects in the adsorption of aliphatic alcohols on the TiO2(110) surface

The role of defects in the adsorption of aliphatic alcohols on TiO2(110) was studied by means of TPRS and XPS. Point defects (oxygen vacancies) were created by electron bombardment in order to minimize the structural damage inflicted to the surface. Ethanol, n-propanol, and 2-propanol adsorbed dissociatively on the TiO2(110) surfaces at room temperature, forming alkoxide and hydroxide groups. Adsorbed alkoxides evolved from the surface in two different reaction channels. About half of the alkoxide species recombined at 345 K with hydroxyl groups and desorbed as the parent alcohols. The rest of the alkoxide groups underwent reactions to produce the corresponding aldehydes, alkenes, and alcohols at temperatures above 550 K. The creation of point defects increased the alkoxide coverage and shifted the product distribution toward the high-temperature channel, favoring alkoxide decomposition over recombination. Within the decomposition products, formation of the dehydration product (alkene) was promoted at the expense of dehydrogenation and recombination processes when defects were present on the surface. The activation energy for alkene desorption decreased with increasing number of oxygen vacancies. Different binding sites for the alkoxide species are proposed to be responsible for the two distinct reaction channels.