Methanol Adsorption and Reaction on TiO₂(110) at Near Ambient Pressure

Although methanol on rutile TiO2(110) has been widely investigated under ultrahigh vacuum (UHV) conditions as a prototypical model, the adsorption structure and reaction of this system under or near real reaction conditions are still unclear. Surface-sensitive sum frequency generation vibrational spectroscopy (SFG-VS) has been utilized to in situ study the adsorption and reaction of methanol on TiO2(110) at near ambient pressure and 400 K. The SFG results indicate that the bridge-bonded methoxy (CH3Ob) is the dominant adsorbed species on TiO2(110) at an elevated pressure of methanol, and its density rises with increasing the methanol pressure. By evacuating the methanol gas, only CH3Ob species leave behind on the TiO2(110) surface, which is also confirmed by ultraviolet (UV) irradiation experiments. Furthermore, by a comparative SFG study of methanol adsorption on TiO2(110) as a function of methanol pressure at 250 K, we concluded that the recombinative desorption of bridging hydroxyl (OHb) groups in the form of water can facilitate the continuous dissociative adsorption of methanol on bridging oxygen vacancy (Ov) sites and the continuous generation of CH3Ob. Our results not only shed light on the adsorption and reaction of methanol on TiO2(110) at near ambient pressure but also demonstrate the studies of catalytic reaction under or near real reaction conditions at the molecular level.