Carbon−Carbon Bond Formation on Model Titanium Oxide Surfaces: Identification of Surface Reaction Intermediates by High-Resolution Electron Energy Loss Spectroscopy

The interaction of CH 2 O with perfect and defective TiO 2 (110) surfaces (produced by overannealing and Ar ion sputtering methods) was studied by thermal desorption spectroscopy, high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations. Exposing the perfect TiO 2 (110) surface to CH 2 O at 100 K leads to the formation of physisorbed CH 2 O and to polymerization of CH 2 O, yielding paraformaldehyde. The latter is bound to the 5-fold coordinated surface Ti atoms and is found to decompose and release CH 2 O at about 270 K. On the defective TiO 2 (110) surface, CH 2 O adsorbs more strongly on oxygen vacancy sites, ultimately forming a diolate (−OCH 2 CH 2 O−) species, as demonstrated by HREELS. The assignment of the vibrational frequencies was aided by theoretical calculations on the DFT-B3LYP level. Upon heating to higher temperatures, this species undergoes deoxygenation, resulting in ethylene formation.