Wang Zhi-Tao, Wang Yang-Gang, Mu Rentao, Yoon Yeohoon, Dahal Arjun, Schenter Gregory K, Glezakou Vassiliki-Alexandra, Rousseau Roger, Lyubinetsky Igor, Dohnálek Zdenek
Microscopy Group, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352.
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.
Proc Natl Acad Sci U S A. 2017 Feb 21;114(8):1801-1805. doi: 10.1073/pnas.1613756114. Epub 2017 Feb 6.
Understanding adsorbed water and its dissociation to surface hydroxyls on oxide surfaces is key to unraveling many physical and chemical processes, yet the barrier for its deprotonation has never been measured. In this study, we present direct evidence for water dissociation equilibrium on rutile-TiO(110) by combining supersonic molecular beam, scanning tunneling microscopy (STM), and ab initio molecular dynamics. We measure the deprotonation/protonation barriers of 0.36 eV and find that molecularly bound water is preferred over the surface-bound hydroxyls by only 0.035 eV. We demonstrate that long-range electrostatic fields emanating from the oxide lead to steering and reorientation of the molecules approaching the surface, activating the O-H bonds and inducing deprotonation. The developed methodology for studying metastable reaction intermediates prepared with a high-energy molecular beam in the STM can be readily extended to other systems to clarify a wide range of important bond activation processes.
理解氧化物表面吸附的水及其解离为表面羟基是揭示许多物理和化学过程的关键，但从未测量过其去质子化的能垒。在本研究中，我们通过结合超声分子束、扫描隧道显微镜（STM）和从头算分子动力学，给出了金红石型TiO(110)表面水离解平衡的直接证据。我们测量到去质子化/质子化能垒为0.36电子伏特，发现分子结合水比表面结合羟基仅高出0.035电子伏特。我们证明，从氧化物发出的长程静电场导致接近表面的分子发生转向和重新取向，激活O-H键并诱导去质子化。在STM中用高能分子束制备的亚稳态反应中间体的研究方法可以很容易地扩展到其他系统，以阐明广泛的重要键活化过程。
