VO Cluster-Stabilized H₂O Adsorption on a TiO₂ (110) Surface at Room Temperature

Abstract

We probe the adsorption of molecular H 2 O on a TiO 2 (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 2 (110)-(1 × 1) surface induce the adsorption of H 2 O molecules at room temperature (RT). The adsorbed H 2 O molecules form strings of beads of H 2 O 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 VOdecorated TiO 2 surface. TPD spectra reveal two new desorption states for VO stabilized H 2 O 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 2 (110)-(1 × 1) surfaces. Density functional theory (DFT) calculations show that the binding energy of molecular H 2 O to the VO clusters on the TiO 2 (110)-(1 × 1) surface is higher than binding to the bare surface by 0.42 eV, and the resulting H 2 O−VO−TiO 2 (110) complex provides the anchor point for adsorption of the string of beads of H 2 O dimers.

Understanding the prototype catalyst TiO2 surface with the help of density functional theory calculation

“…A lower overpotential of 0.48 V is found on a metastable (110) surface is stronger than that on the bare surface by 0.42 eV. 158 This makes it possible for H 2 O molecules to absorb at room temperature onto the VO/rutile (110) surface. On a MnO x -modified TiO 2 surface, as x decreases, H 2 O exhibits a decreased adsorption energy and spontaneous dissociation.…”

“…The adsorption energies on stoichiometric, defective, Ni‐doped, and defective Ni‐doped rutile (110) surfaces are −0.72, −0.82, −0.89, and −1.17 eV in the molecular form, and −0.62, −1.51, −0.96, and −1.73 eV in the dissociated forms, respectively. Tong et al's calculations show that the binding of H 2 O molecules on the vanadium oxide(VO) clusters doping rutile TiO 2 (110) surface is stronger than that on the bare surface by 0.42 eV 158 . This makes it possible for H 2 O molecules to absorb at room temperature onto the VO/rutile (110) surface.…”