VO Cluster-Stabilized HO Adsorption on a TiO (110) Surface at Room Temperature.

We probe the adsorption of molecular HO on a TiO (110)-(1 × 1) surface decorated with isolated VO clusters using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) and temperature-programmed desorption (TPD). Our STM images show that preadsorbed VO clusters on the TiO (110)-(1 × 1) surface induce the adsorption of HO molecules at room temperature (RT). The adsorbed HO molecules form strings of beads of HO dimers bound to the 5-fold coordinated Ti atom (5c-Ti) rows and are anchored by VO. This RT adsorption is completely reversible and is unique to the VO-decorated TiO surface. TPD spectra reveal two new desorption states for VO stabilized HO at 395 and 445 K, which is in sharp contrast to the desorption of water due to recombination of hydroxyl groups at 490 K from clean TiO(110)-(1 × 1) surfaces. Density functional theory (DFT) calculations show that the binding energy of molecular HO to the VO clusters on the TiO (110)-(1 × 1) surface is higher than binding to the bare surface by 0.42 eV, and the resulting HO-VO-TiO (110) complex provides the anchor point for adsorption of the string of beads of HO dimers.