摘要
Dehydroxylated, hydroxylated and hydrated anatase TiO 2 samples have been exposed to acetylene at room temperature. The interaction leads to the formation of polycyclic aromatic hydrocarbons (PAHs) and is accompanied by the appearance of Ti 3+ ions, as shown by electron paramagnetic resonance (EPR) spectra. Fully or partly dehydroxylated samples show higher reactivity, whereas the hydrated samples are chemically inert. The experimental results point towards a crucial role of the more reactive (001) facets of anatase nanoparticles. Density functional theory calculations show that acetylene physisorbs on the anatase (101) surface without activation of the C-H bond. The reduced (101) surface (O vacancies) leads to acetylene activation but not to dissociative adsorption. In contrast, the dehydroxylated (001) anatase surface is very active and leads to the spontaneous splitting of the C-H bond with formation of Ti-C 2 H and OH groups. This is followed by subsequent additions of C 2 H 2 molecules with formation of PAHs. During the dissociation of C 2 H 2 , radical species do not form and electrons are not transferred to the surface because direct Ti-C covalent bonds form on the surface. However, the ring closure in the formation of the aromatic compounds leaves behind hydrogen atoms that donate their valence electrons to the oxide. This results in the appearance of EPR-active Ti 3+ centres. On the surface of things: Acetylene oligomerisation occurs on the surface of anatase TiO 2 leading to the formation of polycyclic aromatic hydrocarbons and a reduced titania surface. The mechanism of the reaction has been elucidated by EPR measurements and DFT calculations (see figure).