Probing equilibrium of molecular and deprotonated water on TiO2(110).
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-TiO2(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.
Microscopy Group, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352.|Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.
Zhi-Tao
ZT
Wang
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Yang-Gang
YG
Wang
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Rentao
R
Mu
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Yeohoon
Y
Yoon
Microscopy Group, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352.|Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.
Arjun
A
Dahal
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.|Chemical Physics & Analysis Group, Physical Sciences Division, Physical & Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Gregory K
GK
Schenter
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Vassiliki-Alexandra
VA
Glezakou
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352; roger.rousseau@pnnl.gov igor.lyubinetsky@oregonstate.edu zdenek.dohnalek@pnnl.gov.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Roger
R
Rousseau
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352; roger.rousseau@pnnl.gov igor.lyubinetsky@oregonstate.edu zdenek.dohnalek@pnnl.gov.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Igor
I
Lyubinetsky
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352; roger.rousseau@pnnl.gov igor.lyubinetsky@oregonstate.edu zdenek.dohnalek@pnnl.gov.|Catalysis Group, Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352.
Zdenek
Z
Dohnálek
adsorbate dynamics; dissociative adsorption; kinetic barriers; titanium dioxide; water