Dissociative adsorption of water is the rate-limiting step in the water-gas shift (WGS) reaction

H₂O + CO  →  H₂ + CO₂

which is used for large-scale production of hydrogen for fuel cells, ammonia production and methanol synthesis. Due to its industrial importance, the detailed study of this reaction is crucial for optimising the catalytic conditions. Many experimental studies and theoretical predictions have been made for this reaction on different transition metal surfaces.

Here, I will focus on water dissociation on a flat Cu(111) surface, a surface which is well-known for low reactivity for water dissociation due its high activation barrier of 1.17 eV [1]. Although a clean Cu(111) surface is not reactive towards water dissociation, adsorbates such as O reduces the activation barrier to 0.76 eV, hence making the surface much more reactive to the dissociative chemisorption of water [2]. Recently, Zhou et al. showed experimentally that water dissociation on the Cu(111) is enhanced when the surface is covered with O(ads) [3]. They also claimed that the oxygen on the surface reacts with the incoming gaseous water molecule to produce 2OH chemisorbed on the surface,

H₂O(g) + O(ads)  →  2OH(ads).

This conclusion was based on their X-ray photoelectron spectroscopy where they observed a change in the binding energy of the O(ads) when water is deposited on the surface, from 530 eV to 530.9 eV [3].

Interestingly, using Reflection Absorption Infrared Spectroscopy (RAIRS), I found contradicting evidence for the O(ads) consumption during water dissociation. In my talk, I will present a RAIRS study of water dissociation using isotopic substitution to elucidate the mechanism of water dissociation on O-Cu(111).

[1] C. T. Campbell and K. A. Daube, J. Catal, 1987, 104, 109-119.
[2] G. C. Wang, S. X. Tau and X. H. Bu, J. Catal, 2006, 244, 10-16.
[3] Q. Liu, J. Li, X. Tong and G. Zhou, J. Phys. Chem. C, 2017, 22, 12117-12126.