Methanol Adsorption and Reaction on TiO<sub>2</sub>(110) at Near Ambient Pressure
Ruidan Zhang, Ting Luo, Wei-Wang Zeng, Chuanyao Zhou, Xueming Yang, Zefeng Ren
Abstract
Although methanol on rutile TiO 2 (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 TiO 2 (110) at near ambient pressure and 400 K. The SFG results indicate that the bridge-bonded methoxy (CH 3 O b ) is the dominant adsorbed species on TiO 2 (110) at an elevated pressure of methanol, and its density rises with increasing the methanol pressure. By evacuating the methanol gas, only CH 3 O b species leave behind on the TiO 2 (110) surface, which is also confirmed by ultraviolet (UV) irradiation experiments. Furthermore, by a comparative SFG study of methanol adsorption on TiO 2 (110) as a function of methanol pressure at 250 K, we concluded that the recombinative desorption of bridging hydroxyl (OH b ) groups in the form of water can facilitate the continuous dissociative adsorption of methanol on bridging oxygen vacancy (O v ) sites and the continuous generation of CH 3 O b . Our results not only shed light on the adsorption and reaction of methanol on TiO 2 (110) at near ambient pressure but also demonstrate the studies of catalytic reaction under or near real reaction conditions at the molecular level.